sky & telescope 2010-05

Springtime Is Galaxy Time p. 65

We Told You So:Amateurs Catch Predicted Nova Blowup p. 18

Visit SkyandTelescope.com

Can we reverse light pollution? p.28

Hunting the Galaxy’sHeaviest Stars p. 22

NIGHTBring Back the

Dig Out Details in Your Images p. 72

THE ESSENTIAL MAGAZINE OF ASTRONOMY

Big Binos vs. Small Scopes: Which to Buy for What Use p. 34

MAY 2010

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Beautifully photographed in 4K digital cinematography, this film is a visually stunning chronicle of the history of the telescope from the time of Galileo, its profound impact upon the science of astronomy, and how both shape the waywe view ourselves in the midst of an infinite universe.

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May 2010VOL. 119, NO. 5

THIS MONTH’S SK Y

40 Northern Hemisphere’s Sky By Fred Schaaf

43 May’s Sky at a Glance

45 Binocular Highlight By Gary Seronik

46 Planetary Almanac

48 Sun, Moon, and Planets By Fred Schaaf

51 Exploring the Moon By Charles A. Wood

61 Celestial Calendar By Alan MacRobert

65 Deep-Sky Wonders By Sue French

68 Going Deep By Ken Hewitt-White

S&T TES T REPORT

55 Lunar Discoverer Mac and PC users alike can use this program to aid their telescopic explorations of the Moon.

ALSO IN THIS ISSUE

6 Spectrum By Robert Naeye

8 Letters

10 50 & 25 Years Ago By Leif J. Robinson

12 News Notes

58 New Product Showcase

70 Telescope Workshop By Gary Seronik

76 Gallery

86 Focal Point By Constance E. Walker

On the cover: Light pollution is a serious impediment for deep-sky observers in Hong Kong and other major cities.

4 May 2010 sky & telescope

FEATURES

18 Amateurs Catch a Crucial Nova Two dedicated backyard astronomers alerted professional telescopes worldwide and in space to U Scorpii’s eruption. By Mike Simonsen & Alan MacRobert

22 The Quest for the Most Massive Star Astronomers are conducting a frenetic search for our galaxy’s most massive star. By Yaël Nazé

28 Saving the Night Sky Light pollution is worse than ever, but a new mindset and new technology are poised to slow — and perhaps reverse — this bane of astronomy. By J. Kelly Beatty

34 Big Binos Versus Small Scopes These instruments have diff erent but overlapping capabilities. By Tony Flanders

72 Digging Out the Details Layered deconvolution adds depth to your astro-images. By Ken Crawford

Li bu te

COVERSTORY

SKY & TELESCOPE (ISSN 0037-6604) is published monthly by Sky & Telescope Media, LLC, 90 Sherman St., Cambridge, MA 02140-3264, USA. Phone: 800-253-0245 (customer service/subscriptions), 888-253-0230 (product orders), 617-864-7360 (all other calls). Fax: 617-864-6117. Website: SkyandTelescope.com. © 2010 Sky & Telescope Media, LLC. All rights reserved. Periodicals postage paid at Boston, Massachusetts, and at additional mailing offi ces. Canada Post Publications Mail sales agreement #40029823. Canadian return address: 2744 Edna St., Windsor, ON, Canada N8Y 1V2. Canadian GST Reg. #R128921855. POSTMASTER: Send address changes to Sky & Telescope, PO Box 171, Winterset, IA 50273. Printed in the USA.

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amateur astronomy has entered a Golden Age. Manufacturers keep churning out better equipment and at more aff ordable prices. The internet, CCD cameras, and various electronic gizmos are making it easier than ever for amateurs to shoot astrophotos, con-duct scientifi c research, share their successes with others, and enjoy the hobby.

But the specter of light pollution looms over astronomy like a sword of Damocles. The problem continues to worsen, and in future decades the glare of artifi cial lighting might wipe out visual deep-sky observing for large stretches of the world’s landmasses. In the U.S., for example, light beamed into the sky is increasing 6% annually, four times the rate of population growth.

Kelly Beatty (page 28) and Connie Walker (page 86) describe how people are waging a valiant battle against light pollution, often in conjunction with organizations such as the International Dark-Sky Association (IDA). Despite a growing awareness, an improv-ing understanding of the problem, and new technologies, it’s not a battle we’re guaran-teed to win. But it’s a battle that we must win if we want to preserve the grandeur of the heavens for later generations.

The future of amateur astronomy is at stake. Light pollution takes away the same night sky we share with one another around the world, and that connects us to our ances-tors. Heavily light-polluted skies fail to spark a sense of awe and wonder, making it less likely that people (especially children) will develop an interest in astronomy.

There’s a lot that concerned astronomers can do about light pollution. First, remember that the problem is not light in general, it’s unnecessary light. Educate yourself about the issues and become knowledgeable about light fi xtures. Tell friends and neighbors that their night sky is disappearing, and that local govern-ments are wasting huge sums of taxpayer money lighting up the sky. Tell them about how excessive glare can contribute to auto accidents and harm nocturnal wildlife. Join or support the IDA (www.darksky.org). Contact your local, state, or provincial government offi cials. We can’t aff ord to sit around and wish the prob-lem away. Only sustained, concerted action will save our precious night sky.

As i wrote a few months ago,

Editor in Chief

Robert NaeyeSpectrum


The Fight Against Light Pollution: A Call to Arms

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Editor in Chief Robert NaeyeSenior Editors Dennis di Cicco, Alan M. MacRobertAssociate Editor Tony FlandersImaging Editor Sean WalkerEditorial Assistant Katherine L. Curtis

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Letters

The Alien ParadoxJacob Haqq-Misra and Seth D. Baum’s article (“Where Have All the Aliens Gone?” March issue, page 86) introduces a new and interesting idea about the Fermi Paradox, which says that if advanced aliens exist at all they should have reached Earth by now. The problem of sustainabil-ity may indeed explain why they haven’t.

Here is another possible reason. The authors remind us of the commonly accepted equation: “A civilization that deploys colonists to 10 planets, each of which expands to another 10 planets, will quickly colonize the entire galaxy.” In my opinion this makes it look far too easy.

Let’s suppose that, in a few centuries, mankind will be capable of reaching other stars. After a journey of, say, 1,000 years (which itself raises a few questions), where will we fi nd 10 planets fully suitable for human life — with convenient gravity and pressure, temperature, breathable atmo-sphere, liquid water, natural cosmic-ray shielding, etc.? Probably nowhere! The chances to fi nd strictly Earth-like planets are close to zero.

Most likely our colonists will have to live indefi nitely in their spacecrafts, near plan-ets or asteroids where they would collect what they need as raw materials. Perhaps other intelligent civilizations in the Milky Way face the same problems, and therefore have little reason to travel very far.

We may also fi nd that intelligent life rarely develops technology, and therefore does not conquer and colonize far away — a typically human trait!

Philippe BarraudCully, Switzerland

The Fermi Paradox is neither a paradox nor a problem. Since the universe is not infi nitely old, the question of whether

a civilization should have long since expanded to fi ll the galaxy depends criti-cally on how likely it is for other intelli-gence to evolve before us. Civilization evolved on Earth in just short of the pres-ent age of the Sun, about 1/3 the age of the universe. There is no reason to conclude that another intelligent civilization in our galaxy — especially since it is likely that such life will only evolve around young, Population I stars — has had much more time to develop on a planet possessing the necessary mix of heavy elements.

Dan PurringtonNew Orleans, Louisiana

Editor’s note: Surprisingly, stars with heavy elements — and therefore, probably, rocky planets — formed at a high rate long before the solar system. One analysis found that the average rocky world in the Milky Way should be 6 or 7 billion years old, compared to Earth’s “mere” 4.6 billion. See “Most Earths Are Old,” S&T: August 2001, page 24.

Astro Club: Alive & WellWhen I fi nished Robert Naeye’s Spec-trum in the March issue, “Bringing in More Women” (page 6), my fi rst feeling was, “We’re doing well!” I co-founded the Camden County Library Astronomy Club (in Camdenton, Missouri) three years

ago. I scanned our club roster and found 31 women, 45 men, 7 young people, and 5 regular speakers.

There are several reasons why I believe our club is so diverse. We always ask the people attending for topics they would like to hear more about. One of the latest came from a fi ve-year-old girl, and at our Janu-ary meeting, Jim (the other co-founder of our group) spoke on the history of how the planets got their names.

As a retired teacher, I saw a need for something to keep the younger ones’ minds busy during more advanced talks. So we have activities to keep them busy: word puzzles, coloring pages, childrens’ books, all astronomy-related, of course.

Another recent meeting was on a sub-ject that our members have strongly sug-gested. So many of our budding amateur astronomers buy a telescope and fi nd they do not know how to use it. We asked every-one who needs help to bring their scopes.

After every meeting, weather permit-ting, we have a star party. Those who have never looked through a telescope get ample opportunity to do so. One of our greatest rewards is to see the looks on peoples’ faces, and hear the amazement in their voices, when they look through a telescope and see wonders that are hidden from the naked eye.

Ginny StrogenCamdenton, Missouri

Beyond Hubble“Is the James Webb Space Telescope a Good Thing?” Robert Naeye asks in the January issue (page 8). The James Webb Space Telescope represents NASA’s next major step beyond the Hubble Space Telescope. While Webb is indeed a major facility, it is important to remember that, like Hubble, small investigator teams from universities across the United States and abroad will accomplish the vast majority of its science through individual proposals for observing time. Nearly 8,000 individ-ual astronomers now use Hubble and its data products, and we expect the Webb to be used in the same way.

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Write to Letters to the Editor, Sky & Telescope,90 Sherman St., Cambridge, MA 02140-3264,

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LTTE Layout May.indd 8 2/19/10 9:15:48 AM


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May/June 1935Where the Stars Are “One of the funda-mental problems of modern astronomy is the determination of the distances of stars.”

That problem began to go away with the publication in 1997 of the Hipparcos satellite’s high-precision parallax cata-log, which contains accurate distances for tens of thousands of stars. Around 2020 we should see the results from the Gaia mission, with 100 times bet-ter accuracy and 10,000 times more stars.

May 1960Birth of U. S. National Observatory “Questions for the astronomy of the future were discussed by the chief speaker at the dedication exercises on March 15th of Kitt Peak National Observatory,

the new 10-million-dollar optical observatory that is now being built on a mountaintop in southern Arizona. Already a 36-inch refl ector (front-cover picture) is in opera-tion, and an 84-inch telescope of advanced design is being built.”

Although Kitt Peak National Observatory is no longer the optical powerhouse it was during much of the second half of the last century, it remains a national center for the development of state-of-the-art instruments and telescopes.

MAY 1985Planetary colors “Typical planetary colors run from brownish gray (for rocky surfaces) through yellowish gray, to yellowish white (for icy surfaces).

Color is an essential piece of data in deter-mining the true nature of a planet. It tells us something about the planet’s composition.”

Andrew Young described the true color of solar-system objects, in contrast to the enhanced, processed images we often see.

75, 50 & 25 Years Ago Leif J. Robinson

Letters

When the Great Observatories (Hub-ble, Chandra, and Spitzer) were being constructed serially through the 1980s to 2003, the Astrophysics Division at NASA spent, on average, 60-70% of its annual budget on those missions. Today, Webb funding represents about 40%. NASA will be operating or funding 15 satel-lites returning data across nearly the full electromagnetic spectrum throughout 2010. Contrast this with the Great Obser-vatories construction period when NASA was operating only between four and nine astronomy satellites.

Webb was recommended as the highest priority facility in the 2000 National Acad-emy of Sciences decadal survey for astron-omy and astrophysics. This is the science community-driven prioritization process that NASA follows. NASA does not “pit one group of scientists against another as they battle for precious resources.”

Today, more satellites than ever are

returning data from space, including Hub-ble, Chandra, and Spitzer, as well as fi ve Explorer and fi ve international missions; and other projects being developed, such as SOFIA, NuSTAR, Astro-H, and GEMS. Even if there is some frustration with not being able to do everything the community would like, this seems like a pretty good starting point for the next 400 years of gaz-ing at the sky through telescopes.

Eric P. SmithJWST Program ScientistNASA, Washington, DC

For the Record✹ The labels A and B for the craters Aristarchus and Ptolemaeus were reversed on the Moon photo on page 51 of the March 2010 issue.✹ In the February 2010 issue (page 67), Deep-Sky Wonders described a bright patch in the nebula Sharpless 2-219. In fact, the bright patch is in Sh 2-217.


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News Notes

For astronomy news as it breaks, SkyandTelescope.com/newsblog.ForSSky

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What is the thing pictured here? It’s like no astronomical object ever seen.

The automated LINEAR sky patrol picked it up on January 6th. It seemed like a very small, but long-tailed, 20th-magnitude comet moving across Gemini. It received the name Comet P/2010 A2 accordingly. But it was following a nearly circular orbit in the main asteroid belt. And its tail seemed to be streaming not from a comet head, but from a thread of debris extending away from a point-like bare object. Astronomers turned the Hubble Space Telescope to it on January 25th and 29th. The images above are from the latter date.

The “head” seems to be an X-shaped feature with a tiny solid body at one endpoint of the X, about 1,000 miles (1,600 km) from its center. “This is quite diff erent from the smooth dust envelopes of normal comets,” says David Jewitt (UCLA), who led the Hubble eff ort.

Asteroids have been known to fl are up with surprise cometary activity; four previous cases are on record. But P/2010

The First Asteroid Collision?

A2 looks like none of these. Moreover, it lacks the gas usually seen in a comet’s coma and tail. What we’re looking at here is only dust.

The best theory, thinks Jewitt, is that two small asteroids collided a few weeks or months earlier. That might seem astro-nomically unlikely, given the vast amount of empty space in even the richest part of the asteroid belt. But there are tens of mil-lions of asteroids as small as the pointlike thing in the image, which is estimated to be 140 meters (460 feet) wide.

Would a collision aftermath look like this? Maybe. Perhaps the two lines of the X are separate rubble streams from the two bodies. Another possibility is that we’re seeing a single asteroid that has been gradually spun up by interac-tions with sunlight to the point that it has started throwing off loose material.

In either case, fi ne dust appears to be streaming off the rubbly X due to the Sun’s radiation pressure, to form the long, cometary tail. More Hubble observations are planned through July.

The Smaller the Galaxy, the More Dark Matter

Dwarf galaxies may not look like much, but don’t be fooled. They off er the purest pools of dark matter available anywhere. The smaller a galaxy, the larger its pro-portion of dark matter, fi nds a research group led by Stacy McGaugh (University of Maryland).

In the cosmos as a whole, the mysteri-ous dark matter outweighs all normal (“baryonic”) matter by 5 to 1. The same is true inside the largest galaxy clusters. But the ratio goes up in smaller cosmic structures — to the point that in dwarf galaxies, such as NGC 4163 pictured below, the ratio of dark matter to bary-onic matter (stars, gas, and everything else) can exceed 100 to 1.

Why? One theory is that small galax-ies were less able to hold onto their gas when, early in cosmic history, super-novae were more common. In this view, supernova blasts cleared out most of the normal matter, putting an end to most star formation. Dark matter doesn’t inter-act with normal matter and therefore doesn’t feel supernova blast waves. So it was left behind.

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Double SupermassiveBlack HolesAstronomers have found that nearly every large galaxy has a supermassive black hole at its center, holding about 1 million to 20 billion times the mass of the Sun. Astronomers also know that galaxies often collide and merge. So lots of galaxies today should have two or more supermassive black holes. But it’s been hard to fi nd clear examples.

Now the numbers are fi lling in. A group led by Julie Comerford (University of California, Berkeley) has announced 33 galaxies with two holes. “This result is signifi cant because it shows us that they are much more common than previously known,” she says. An example is in the Hubble image above.

GRB-Supernova LinkIn recent years, astronomers have con-nected several long-duration gamma-ray bursts to distant, relatively normal-looking Type Ib/c supernovae. These discoveries suggest that the superfast (“relativistic”) jets powering GRBs play a big role in at least one type of ordinary exploding star.

But if so, who don’t we see signs of relativistic jets in more of these superno-vae? We witness a GRB only when the jet happens to be aimed right at us. Radio observations should reveal relativistic jets no matter which way they’re aimed. But despite examining more than 100 super-novae, radio astronomers saw no such jets.

Until now. In the January 28th Nature, separate teams reported radio obser-vations of two supernovae that show relativistic jets. Neither produced a GRB. One possibility, says Alicia Soderberg (Harvard-Smithsonian Center for Astro-

physics), is that “perhaps the gamma rays were ‘smothered’ as they tried to escape the star. This is perhaps the more exciting possibility,” she says; it implies that we can identify supernovae that are driven by spinning black holes in their cores “even if they lack detectable gamma rays and go unseen by gamma-ray satellites.”

Hot Spot for Cosmic RaysFuture astronauts who make long trips beyond Earth’s magnetosphere will face serious trouble from galactic cosmic rays: high-energy protons and heavier atomic nuclei. But would-be Mars colonizers can at least be glad our galaxy isn’t like M82.

Most cosmic-ray particles near Earth come from the expanding shock fronts of supernova remnants in our galaxy, as NASA’s Fermi Gamma-ray Space Tele-scope is confi rming. The shock waves entrain magnetic fi elds that accelerate charged particles to extreme energies.

It happens more elsewhere. M82, 12 million light-years away in Ursa Major, is birthing so many massive stars that one goes supernova every few years. Gamma-ray astronomers have found a signature from M82 indicating that cosmic-ray pro-duction is 500 times more intense there than in the Milky Way.

In the composite view of M82 below, visible light is shown as orange and green, infrared as red, and X-rays as blue.

Mission Updates• NASA’s spectacularly productive Cas-

sini mission has been awarded $60 million per year to continue through 2017. Cassini arrived at Saturn in 2004 for a planned 4-year mission, but its hits just keep on coming. Above is a recent new closeup of Saturn’s moon Calypso, 19 kilometers wide. It appears to be covered with fresh fl ows of bright white ice dust from Saturn’s E ring.

• NASA’s Solar Dynamics Observatory, featured in the January issue (page 22), got off to a fi ne launch February 11th on its 5-year mission to study the Sun.

• Less happy news comes from Mars. NASA controllers announced on January 26th that they’ve given up trying to free the Spirit rover from the sand wallow where it bogged down in May 2009. After explor-ing across 4.8 miles in 5 years, Spirit now becomes a stationary science platform.

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Close Encounters Turn Asteroids PaleSmall asteroids, such as 25143 Itokawa (imaged below by Japan’s Hayabusa spacecraft), seem to be loose rubble piles that can be severely shaken up by close encounters with Earth.

The evidence is in their surface colors. Dark, reddish-gray “S-type” asteroids are common, and their color is thought to result from space weathering. Solar-wind particles and other radiation discolor rock surfaces exposed to space in less than a million years, giving them a sunburned appearance.

Other, “Q-type” asteroids seem to lack space weathering. What freshens them up? At fi rst, researchers thought impacts and collisions might do the job. But Q-type asteroids are not found in the main asteroid belt, where collisions should be the most frequent.

A research group led by Richard Binzel (MIT) ran the orbits of 95 small asteroids — 75 of them type S, 20 of them Q — back-ward in time. Every one of the fresh-look-ing, Q-type asteroids was following an orbit that makes past close encounters with Earth very likely.

This supports a suggestion by David Nesvorny (Southwest Research Institute) that a close encounter with a planet can change an asteroid from dark brown to lighter gray by tidally jostling it enough to expose fresh rubble.

This research also helps tie up another problem. Most meteorites have Q-type spectra, though such asteroids are unusual. The discrepancy is easy to explain in terms of fresh versus space-weathered surfaces. During a meteoroid’s fi ery plunge through Earth’s atmosphere its old surface is stripped off , exposing fresh material beneath.

Faces of PlutoOn February 4th, the 104th birthday of the late Pluto discoverer Clyde Tombaugh, Marc Buie of the Southwest Research Institute unveiled maps of Pluto’s surface derived from Hubble Space Telescope images taken in 2002 and 2003. Massive computer processing went into eking out the highest possible resolution. When compared to a similar set from 1994, it’s clear that Pluto’s icy surface went through radical changes in less than a decade.

The new views reveal a surface with three distinct coatings. The brightest areas are likely to be fresh frosts of methane and nitrogen. The darker orange and charcoal-black terrains are probably covered with old, complex carbon compounds created by long exposure of methane ice to space radiation. By contrast, no surface changes were seen on Pluto’s moon Charon.

Apparently, thin traces of atmosphere are freezing out on Pluto’s surface as it edges away from the Sun in its long orbit, and nitrogen frosts are migrating as Pluto’s northern hemisphere becomes exposed to sunlight for the fi rst time in more than a century.

These images are the best look at Pluto we’ll probably have until NASA’s New Horizons probe fl ies by in 2015.

New Plan for NASAIn February the Obama administration unveiled a $19 billion NASA budget for fi scal year 2011 that would alter the future of human spacefl ight. The plan, if enacted by Congress, would end shuttle fl ights by early 2011 and cancel the Constellation program for returning astronauts to the Moon. But it would increase funding to develop “game-changing technologies” that could speed up future human mis-sions to the Moon, near-Earth asteroids, and Mars. The plan would also place greater reliance on private fi rms and Rus-sia for ferrying humans to low-Earth orbit, while extending U.S. participation in the International Space Station to 2020.

Despite canceling a program in which $9 billion has already been invested, the plan increases NASA’s overall funding by $6 billion over the next fi ve years, to about $100 billion total. By developing new propulsion technologies, in-orbit fuel depots, and robotic precursor missions, the administration and NASA seem to be betting that they can lower costs for deep-space exploration in the long run. The plan also calls for more international cooperation.

The proposed budget follows many recommendations set forth in a report lastyear by an independent committee chaired by former Lockheed Martin executive Nor-man Augustine. The “Augustine Report” spelled out what many have been saying for years: the Constellation Moon program was vastly underfunded for achieving its stated goal of returning astronauts to the Moon by 2020. But critics charge that the new plan fails to establish specifi c mission objectives and timetables.

The new budget increases funding for Earth-science missions. Planetary science and solar phys-ics receive slight increases, while astrophysics is slightly decreased. ✦

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U SCORPII:

Amateurs

Above: Barbara Harris, the fi rst to discover that U Scorpii had erupted to 8th magnitude, shows off her 16-inch scope in her Florida home observatory. Every clear morning before January28th she had been measuring U Sco at around magnitude 18.Left: Co-discoverer Shawn Dvorak observes variable stars with a 10-inch scope in his backyard roll-off -roof observatory. In 10 years he has logged more than 557,000 images and 8.1 million photometric measurements. Read more at his website, www.rollinghillsobs.org.

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SkyandTelescope.com May 2010 19

Barbara G. Harris, a retired ob-gyn physician in New Smyrna Beach, Florida, went to bed late on the night of January 27th and really didn’t feel like getting up before the fi rst light of dawn. But her dog Arctic had other ideas. He barked to go out. So she reluctantly got up and let him out the door. And once on her feet, as she had done every other clear morning in January, she went out on her third-fl oor deck, fi red up the 16-inch Schmidt-Cassegrain tele-scope and its CCD camera in her observatory, and pointed it toward U Scorpii low in the southeastern sky.

When the fi rst image appeared on Harris’s computer, blazing in its center was a huge, overexposed star. Her fi rst thought was that something was wrong with her gear. Just 24 hours earlier she had measured U Scorpii at photoelectric V magnitude 18.2. She quickly took a much shorter exposure, double-checked the position, and, she recalls, “That’s when I started to get excited.”

Harris had been monitoring the recurrent nova U Scorpii for months, in hopes of catching a rare erup-tion that Louisiana State University astronomer Bradley Schaefer had predicted almost a year earlier (S&T: August 2009, page 56). She and many other amateurs had joined a campaign by the American Association of Variable Star Observers (AAVSO) to keep the star under steady watch, in hopes that an early alert could make this the best-stud-ied nova outburst in history.

Astrophysicists were eager for the event. Stars like U Sco are likely to be the objects that fi nally explode as Type Ia supernovae. These supernovae are crucial to measur-ing the changing expansion rate of the universe and the “dark energy” that is speeding up the expansion. But the progenitors of Type Ia supernovae remain poorly known.

“Back in December I got an email from Brad Schaefer, because I had obtained the fi rst image of U Sco as it came out from behind the Sun” into morning visibility, says Harris. That image helped reassure astronomers that U Sco had not blown up while it was in conjunction with the Sun. “He said, ‘Keep submitting your data to AAVSO, but here’s my home phone number.’”

On the morning of January 28th she rang him out of bed. “He let out a scream and said, ‘Thank you, thank you! I’ll start notifying everyone right away!’” Barbara recalls. Just to be sure, Schaefer toted his own 6-inch scope to his front yard and confi rmed that U Sco was bright, then began to spread the news worldwide.

Meanwhile, in Clermont, Florida, Shawn Dvorak had gotten up early to go to the gym. Years ago he had intended to become a professional astronomer, but he wound up with a job working on computer systems for FedEx. That’s during the day. On most clear nights for the last decade, Dvorak has used his “semi-automated”

mike simonsen & alan macrobert

10-inch Schmidt-Cassegrain scope and CCD camera to measure eclipsing binaries, RR Lyraes, and cataclysmic variable stars for the AAVSO.

On the morning of January 28th his setup had been running all night. He too had been checking U Sco before dawn once it emerged from behind the Sun. It was usually his last observation before shutting down.

“I almost didn’t observe it this morning since I was planning to go to the gym,” says Dvorak. He still wasn’t quite awake when the fi rst image came up, and he thought to himself, “Whoa, I’m pointing at the wrong fi eld, there’s no star that bright here.” But he quickly real-ized he was on target and sent off the news to the AAVSO.

Harris and Dvorak made their discoveries before either knew of the other. Within minutes, alerts were going out to observatories and spacecraft controllers worldwide: U Sco had fi nally blown.

The Nova WatchU Sco is one of only 10 recurrent novae known. Recurrent novae are those that have exploded more than once in observational history. Classical novae are also presumed to explode repeatedly, but only about 1,000 to 100,000 years apart. In both cases, the underlying star is a close binary in which a white dwarf is accreting hydrogen from a relatively normal companion. Eventually, a deep enough layer builds up on the white dwarf’s hot surface — and is compressed tightly enough by the dwarf’s intense gravity — to ignite a runaway hydrogen-fusion reaction. The bot-tom of the hydrogen layer explodes globally as a thin-shell hydrogen bomb, blowing off a shell of ejecta and bright-ening the system by roughly 10,000 times. The stars remain in place, everything settles back down, and the process starts over (S&T: October 2009, page 26).

Brad Schaefer tracked down everything he could fi nd about all 37 recorded out-bursts of the 10 recurrent novae, including three previously unknown eruptions of U Sco that he found by searching archives of photographic sky-patrol plates going back to 1900. Based on this work, and on the apparent rate at which mass was currently fl owing onto U Sco’s white dwarf, Schaefer made a bold prediction: The star, which last blew up in 1999, would erupt at 2009.3 plus or minus one year. He was 0.8 year off , within his margin of error.

After Schaefer announced his prediction, astronomers planned observing campaigns for when and if the blowup occurred. But U Scorpii is an exceptionally fast nova, ris-ing and starting to fade in just hours. Its rise was, unfor-tunately, missed completely; the last observation before

Brad Schaefer



Harris’s discovery turned out to be her own measurement of the star 24 hours earlier.

True to form, U Sco lost more than a magnitude in the fi rst 24 hours after discovery and continued declin-ing in a way that closely mirrored its 1999 eruption (see the light curve below). A day after eruption, spectra showed that the edges of its debris shell were expanding by a remarkable 11,000 kilometers per second, 3% of the speed of light. Several days later, X-ray emission turned on; no one knows why novae wait to do this. As the debris

shell thinned and cleared, some 7 days into the show, the characteristic “nova fl ickering” began — a sign that mass transfer had resumed and a new accretion disk had formed around the white dwarf. Soon the light curve was again showing the eclipses of the white dwarf and its accretion disk by the companion star every 30 hours. Luckily for researchers seeking to untangle the system’s details, U Sco is a totally eclipsing binary. Many studies are continuing on the ground and from space.

So chalk up another amateur triumph. “This again shows the real advantage of the worldwide distribution of amateur astronomers for detecting transient events like this,” says AAVSO director Arne Henden. Astronomers would not have had their early alert if Shawn had decided to go to the gym, and if Arctic hadn’t barked. Hours after the fi nd, Harris commented, “My dog has been getting cookies and anything he wants all day.” ✦

Mike Simonsen, one of the world’s leading variable star observers, is development director for the AAVSO and heads its Cataclysmic Variable Section, Chart Team, and Mentor Program. He writes the astronomy and variable-star blog Simostronomy and is a cast member of the Slacker Astron-omy podcast.

Sky & Telescope senior editor Alan MacRobert has his own fond memories of Nova Delphini 1967.

As this issue went to press in late February, U Sco was fading with the standard characteristics of a very fast nova.

Left: When Harris took a deep CCD image through her 16-inch on January 27th, it barely recorded U Scorpii. Right: A day later the star was an overex-posed blaze even on a much shorter exposure. For skywatchers worldwide responding to the early alert, the recurrent nova was visible in binoculars.

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Weblinks

Recurrent Nova Erupts

News updates from AAVSO’s U Scorpii Campaign:www.aavso.org/news/usco.shtml

Current AAVSO magnitude measurements:tinyurl.com/yfv2fzn

Background on U Sco and recurrent novae:www.aavso.org/vstar/vsots/usco.html

Brad Schaefer’s paper on all recurrent novae:tinyurl.com/ybfl 9pn

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Our Galaxy’s Biggest, Brightest Brutes

MostMassive StarMassive Star

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SUPER STAR CLUSTER R136 resides near the center of the Tarantula Nebula (NGC 2070) in the Large Magellanic Cloud. Astronomers once thought that R136 was a single super star of several thousand solar masses. But Hubble Space Telescope images such as this clearly resolve it into a cluster populated by thousands of luminous stars.

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Astronomers Astronomers are conducting are conducting a frenetic search a frenetic search for our galaxy’s for our galaxy’s most massive star.most massive star.

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Those with large masses dominate their surroundings; only they can simultaneously make gas shine to create beautiful nebulae, push around nearby material, and form a rich stew of heavy chemical elements. With masses tens of times that of the Sun and with light outputs millions of times solar, these stellar masters hold the power of life and death. They destroy fragile objects such as proto-planetary disks and trigger the birth of other stars. And after their brief but fl amboyant lives, they die in titanic supernova explosions.

So if you want to understand the universe, you need to understand these massive objects. Moreover, because the most massive stars produce the greatest impact, the record holders constitute an astronomical “holy grail.”

Astronomers have other reasons to study the most massive stars. Every stellar model needs to be tested, and what’s a better laboratory than extremely massive stars? Indeed, the lowest mass for a star is a well-known limit: 8% of the Sun’s mass. Below that, stellar cores lack the necessary pressures and temperatures to sustain nuclear fusion. But theories are less clear-cut on the upper bound-ary. For the moment, astronomers can only surmise that a limit exists. Above a certain mass, nuclear reactions in a stellar core become so powerful that they destroy the star. Calculating this exact mass depends on our knowledge of nuclear and stellar physics, but is thought to be around 100 to 120 solar masses for stars that have formed recently in our Milky Way Galaxy. It remains to be tested if our educated guesses are correct.

Weighing Without a ScaleMeasuring a star’s mass is no easy job. After all, astrono-mers cannot visit a star and put it on a scale. Weighing must be done from afar. How can this be done?

One strategy is to model stellar spectra. When astrono-mers obtain a star’s spectrum, they are measuring chemi-cals and conditions in the star’s photosphere. The atmo-sphere’s physical state depends crucially on its temperature and its pressure, which in turn are linked to the star’s gravity, which in turn depends on its radius and mass.

Astronomers can use basic physics to model stellar atmospheres. For a given set of parameters (temperature, radius, mass), scientists can calculate the state of each chemical element in the atmosphere, thereby deriving its potential signature in a stellar spectrum. Astrono-mers can then compare a real spectrum to the modeled one, fi nd the best fi t, and then indirectly infer the stellar parameters, including the mass. To fi nd the record holder, one can simply imagine modeling many diff erent stars, until the most massive object is found.

But models are always calibrated by observations. Searching for the most massive objects — by nature outside the tested limits of the model — implies extrapo-

Stars are not born equal.


lation, which is never precise, nor always correct. The modeling of stellar spectra can thus only provide an approximate mass.

Another possibility is to measure a star’s luminosity. For adult (main-sequence) stars, basic stellar physics dic-tates that their luminosities are strongly correlated with their masses. For example, a 40-solar-mass star is fi ve times more luminous than a 20-solar-mass star. Estimat-ing masses now appears trivial: observe many diff erent luminous stars, preferentially in several fi lters, measure their luminosities, and then compute their masses. But simplicity is often deceptive and many details render the task much more complicated than fi rst thought.

For example, this mass-luminosity relation is only valid for the absolute luminosity, while a direct measure-ment yields only an apparent brightness. To determine the former from the latter, astronomers must correct for distance, reddening by dust, and the short energy range sampled by the observations — three parameters that are not always known with precision.

Astronomers also need to be certain that the measured luminosity applies to only one star. Errors can be frequent where stars are packed closely together in a cluster. One famous example is R136 in the Large Magellanic Cloud. Based on its high luminosity, it was once considered to be a single “superstar” with a whopping 1,000 to 2,500

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THE SPECTRUM METHOD Astronomers compare the actual spectrum (red line) of the HD 48099 system with a model spec-trum (blue line) to infer the star’s mass. This method, however, lacks precision and can only provide approximate masses.

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solar masses. But in 1991, the Hubble Space Telescope confi rmed earlier results from speckle imaging that R136 was a tight cluster composed of hundreds of stars. Sure, it contained some very massive stars, but they were not as massive as previously claimed.

The same error was made on a smaller scale for Pismis 24-1, when recent Hubble observations showed that it consists of two stars. The mass of the famous Pistol Star, often mentioned as the record-holder with an original mass of 200 Suns, is thus to be taken with caution: it could be off by a factor of two.

If observing one star doesn’t give precise information, measuring several can yield reliable statistics. Astrono-mers have known for decades that the mass distribution of stars is not random: massive stars are less common that low-mass stars. When expressed mathematically, this distribution is called Salpeter’s law, after the late Cornell University astronomer Edwin Salpeter. For each star in our galaxy with a mass between 60 and 120 solar masses, there are 250 objects with 1 to 2 solar masses, and 5,600 stars with one-fi fth to one-tenth of the Sun’s mass.

Astronomers can observe a group of stars, estimate the

SINGLE TO DOUBLE A Hubble Space Telescope image splits the extremely luminous star Pismis 24-1 into its two binary compo-nents. Instead of being one star of 200 to 300 solar masses, the two components contain about 100 solar masses each.

SALPETER’S LAW Astronomer Edwin Salpeter (1924–2008) devised a famous law showing that low-mass stars are much more numerous in our galaxy than high-mass stars. Low-mass stars form more easily, and they live longer lives.

ECLIPSING BINARIES The most direct method for “weighing” massive stars is to study binary systems in which the two stars periodically eclipse each other. A detailed analysis can yield reli-able mass determinations. The two stars here have unequal sizes.

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stellar masses through the mass-luminosity relation (how-ever imprecise that might be), and then check if Salpeter’s law correctly applies. To understand the population of the rare massive stars, one needs a very large stellar group — such as the Arches cluster, a grouping of about 100 hot, luminous stars (and thousands of cooler ones) near the galactic center. The statistical analysis clearly shows a shortage of extremely high-mass stars: 20 to 30 stars with more than 130 solar masses should be present that are not detected. This result implies that stars with more than about 130 solar masses cannot form.

Similar studies based on the simultaneous analysis of several clusters have derived comparable upper limits of 150 solar masses. But if astronomers have proven that the limit exists, they do not have a precise value yet. Statisti-cally, 130 or 170 solar masses are as acceptable as the mean value of 150.

The SolutionIn fact, there is only one proven method for precisely determining the mass of a star: studying eclipsing spec-troscopic binaries.

About half of stars reside in binaries, in which two stars revolve around a common center of gravity. The spectra of such systems combine the spectrum of each star. Spectral lines, which are the signatures of chemical elements, therefore appear double. The positions of these lines change over time. This movement, linked to the Doppler eff ect, refl ects the orbital motion. The lines of the approaching star are shifted toward the blue, whereas those of its receding companion are shifted toward the red. The shifts are reversed after half a cycle.

Astronomers can then apply Kepler’s and Newton’s laws to measure the velocities and thus determine the orbital parameters: the distances of the stars to their common center of mass, the orbital eccentricity, the period, and each star’s mass. For massive stars, the precision achieved for

these values depends mainly on the quality of the spectra. Today, it can reach 1 kilometer per second, or about 2,200 miles per hour. (Compare this to the 1-meter-per-second precision achieved in exoplanet searches of low-mass stars observed with very-high-resolution spectrographs.)

But the velocity curve alone doesn’t yield the actual stellar distances and masses. These parameters have to be multiplied by a factor depending on the orbit’s

ARCHES CLUSTER Right: The Hubble Space Telescope images the Arches Cluster, a rich collection of massive stars near the galactic center. A detailed study of the cluster reveals the relationship between the initial masses and infrared luminosities of Arches members (upper left) and the number of stars per unit mass (lower left). The total lack of stars above 130 solar masses indicates that stars of this mass rarely or never form in our galaxy today, since Hubble could have spotted them.

WOLF-RAYET STAR A European 2.2-meter telescope in Chile took this optical image of WR22 (the bright star in the center), an unusual eclipsing binary Wolf-Rayet star whose primary compo-nent has a mass of 55 to 72 Suns.

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inclination to our line-of-sight. The orbital plane could be tipped in any direction, so the masses determined by this method are thus only lower limits. To eliminate that uncertainty, astronomers study eclipsing binaries. The stars in these systems periodically occult each other, which means that the orbital plane is nearly perfectly aligned with our line-of-sight.

The most promising targets are the rare stars of spectral type O2 and O3, which are the hottest and most luminous known. But studies of these objects have not fulfi lled our hopes. Astronomers have measured O3 stars with 50 to 60 solar masses, but this is quite far from the mean value of 150 estimated by cluster statistics.

In fact, the most massive known stars came from an unexpected direction: Wolf-Rayet stars. In principle, these objects correspond to evolved O stars that have exhausted their hydrogen fuel and are now burning helium and heavier elements in their cores. Since hot stars possess strong stellar winds (a scaled-up version of the solar wind), they eject tens of solar masses — perhaps half their initial mass — during their lives. Indeed, WR stars are generally much less massive than O stars.

The classifi cation of WR stars relies only on the peculiar appearance of their spectra, which results from the presence of a very dense outfl ow. But in the past few years, astronomers have detected “false” WR stars. These

The Birth of Massive StarsAstronomers have known for decades that low-mass stars form and grow by accreting nearby gas. Such a process has problems forming massive stars, however. Before they are completely formed, these objects begin to shine so brightly that the sheer pressure of their radiation pushes away infalling material — prohibiting further growth. This threshold occurs at about 10 solar masses.

But stars much more massive than that clearly exist.

Theorists can get around the problem in one of two ways. First, they have developed models in which a star accretes gas at its equator and emits most of its light from its poles. Second, they can invoke the merger of two or more low-mass stars into a very massive star near the centers of dense clusters. These formation scenarios lack clear-cut limits, and there are no observations yet that could help constrain them since we have never witnessed the birth of a truly massive star. — Y. N.

SIMULATED STARBIRTH Frames from a computer simulation show how massive stars might form. Inwardly spiraling mate-rial in a disk feeds material to the growing star. But when it reaches about 17 solar masses (third frame), the outpouring of radia-tion can counteract gravity, pushing away infl owing gas and carving out large cavities. Disk instabilities lead to the formation of several smaller protostars and fi laments, leading to sporadic accretion that allows the biggest star to continue growing in mass.

CLUSTER IN X-RAYS Right: NASA’s Chandra X-ray Observatory turned its big eye toward another rich cluster near the galactic center, West-erlund 2. The brightest X-ray source in the fi eld is WR20a (arrowed). Top left: Radial-velocity measurements in 2004 revealed the star to be a mas-sive binary. Lower left: Eclipses detected in optical observa-tions, when combined with the velocity data, show that the two stars have a whopping 82 and 83 solar masses.

MARK KRUMHOLZ (UNIV. OF CALIFORNIA, SANTA CRUZ)

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deviant objects are still burning hydrogen in their cores: they are thus super-O stars rather than their evolved descendants. They just happen to eject large amounts of material, much more than “normal” O stars, thereby mimicking the characteristics of genuine WR stars.

In 1996 a Belgian team led by Gregor Rauw studied the very massive Wolf-Rayet star WR22 and measured a minimum mass of 72 Suns. This surprising result was confi rmed by a team led by Jörg Schweickhardt, but with a downward revision to 55 solar masses. This conclusion is still to be secured — the second team had more spectra but of a lesser quality.

In 2004 the same Belgian team unveiled the incred-ible properties of the truly astonishing binary WR20a, a system little studied until then. It’s now known to contain two stars of 82 and 83 solar masses — with an uncer-tainty of only 7%. Each one of these objects beats the previous record by a large amount.

Since then, the quest has intensifi ed, thanks to the com-bined eff orts of Belgian, Canadian, and Argentinean teams. The results for various eclipsing binaries are generally less precise than for WR20a, but they are all very encouraging: HD 15558 contains two objects of 152±51 and 46±11 solar masses; NGC 3603-A1 possesses two stars of 114±30 and 84±15 solar masses; WR25 consists of two stars of 75±7 and 27±3 solar masses; and R145 has two components of 140±37 and 59±26 solar masses. These values need to be confi rmed, but they show that astronomers are inching closer to the symbolic fi gure of 100 solar masses.

Theoretical work is needed to check if these observa-tions fi t the current stellar models. It’s possible that a more massive star than the ones mentioned above could

exist and have no binary companion at all. In this case, there’s no possibility to ascertain its mass precisely and so astronomers must accept defeat.

Even More?Is 100 solar masses the fi nal record? Maybe not. Over the past decade, a new type of star has emerged at the fore-front of stellar astrophysics: Population III. These were the fi rst stars born in the universe, when the cosmos was only a few hundred million years old (S&T: May 2006, page 30). Because they formed from gas clouds consisting of pure hydrogen and helium, computer simulations strongly suggest that these objects did not follow Salpeter’s law. They could have been very massive — “very” meaning several hundred solar masses, maybe up to a few thousand! Other researchers have also speculated about the early exis-tence of dark-matter-powered stars that could have had up to 10,000 solar masses (March issue, page 26).

Population III stars could be the sources of distant gamma-ray bursts. Our present telescopes cannot see far enough back in time to study such objects, but astrono-mers are confi dent that the next generation of instru-ments, such as NASA’s James Webb Space Telescope, the Thirty Meter Telescope, and the Extremely Large Tele-scope, will help confi rm or deny this bold hypothesis. ✦

Yaël Nazé is an astronomer at the FNRS/Université de Liège, Belgium, who studies massive stars. As a writer and public lecturer in her free time, she tries to share her passion for these intriguing objects — and other marvels of the sky.

For more information about the author’s research group, visit www.gaphe.ulg.ac.be/index_e.html.

What About Eta Carinae?Eta Carinae is certainly one of the most luminous and massive stars in our galaxy. Based on its extraordinarily high luminosity of about 6 million Suns, astronomers inferred that it may contain about 120 solar masses. But this guesstimate could be way off because the star is shrouded in mystery…literally. This Hubble Space Telescope image shows Eta Carinae embedded in the Homunculus Nebula, which contains many solar masses of gas and dust ejected by the star. This material makes direct observations of the star virtually impossible. There’s strong evidence for a binary companion, but astronomers have yet to ascertain its exact properties. Current estimates suggest the two stars contain about 90 and 30 solar masses. — Robert Naeye

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Your Light-Pollution Guide

exactly when outdoor lighting began to spoil our view of the night sky. Electric streetlights made their debut in the 1880s and quickly spread to major cities. By the 1930s the already-deteriorating sky above Mount Wilson, which overlooks the Los Angeles Basin, caused George Ellery Hale to go elsewhere for what would become Palomar Observatory. During the 1950s, General Electric and Westinghouse helped line America’s roadways with millions of “cobra-head” streetlights that remain today. Then, around 1970, light bulbs fi lled with high-pressure sodium gas began to blanket the landscape with their peach-colored glare.

More certain is where and when astronomers took their fi rst stands against the spread of artifi cial light. Offi -cials in Flagstaff , Arizona, passed an ordinance in 1958 that banned searchlights from spoiling the skies above Lowell Observatory. Farther south, outdoor lighting in Tucson became regulated in 1972, the fi rst of many enact-ments to protect Kitt Peak National Observatory (KPNO).

In 1988, KPNO astronomer David L. Crawford teamed with local amateur Tim Hunter to found the International

It’s difficult to pinpoint

j. kelly beatty

Light pollution is worse than ever, but

a new mindset and new technology

are poised to slow — and perhaps

reverse — this bane of astronomy.

Dark-Sky Association (IDA), which today boasts sections in 24 states and 14 countries. The common-sense tenets of good nighttime lighting that Crawford and Hunter cham-pioned remain unchanged today: use light only where it’s needed, only when it’s needed, and no more of it than is necessary for safety and security.

In the meantime, however, our 24/7 society has become ever more intent on lighting up the nighttime environment. For example, throughout the 1990s the U.S. population grew at less than 1.5% per year — yet the fl ood of lumens cast into the night rose annually by about 6%. This trend has made light pollution worse where it already existed and now threatens many areas that had previously been considered pristine. It’s estimated that virtually everyone living in the U.S. and Europe experiences some degree of light pollution and that two-thirds of us can no longer see the Milky Way from our homes.

Even our national parks are no longer safe havens for starry skies. During the past several years a small team of astronomers has carefully documented the extent of light’s encroachment in more than 60 U.S. national parks

ART Light Pollution.indd 28 2/19/10 7:35:29 AM



and other key settings. Their results are unsettling: even remote sites have been aff ected by the glow of towns and cities up to 100 miles away. “The superintendents are usu-ally surprised by the amount of light pollution we fi nd,” notes Chad Moore, who heads the National Park Service’s night-sky team. Many have undertaken aggressive steps within their parks’ boundaries and with surrounding communities to restore the natural darkness.

While early eff orts to control nighttime lighting focused on preserving the starry skies for professional

and amateur astronomers, a growing cadre of illumina-tion specialists, environmental groups, and biomedical professionals has come to realize that light pollution can have far-reaching consequences in other aspects of mod-ern society. Biologists have known for decades that bright outdoor beacons can disrupt the migrating, eating, and mating of nocturnal animals — but there’s new, urgent attention on how disrupted darkness might impair the circadian (day-night) cycles of humans as well.

The big questions are whether light at night suppresses

The spectacular night sky above Arches National Park is dimin-ished by the bright glow from nearby Moab, Utah. Park offi cials are now working with townspeople to reduce the skyglow.

How bad can it get? Italian researcher Pierantonio Cinzano and others have used computer modeling to extrapolate 1997 night-time satellite imagery of North America backward and forward

in time, assuming light pollution grows annually 6%. Dark blue indicates areas where artifi cial skyglow exceeds natural skyglow by 11%, white areas by 2,700%.

Late 1950s Middle 1970s 1997 2025

TYLER NORDGREN




Your Light Pollution Guide

lish a light-cancer link. For example, good circadian func-tion also requires exposure to bright light during daylighthours (S&T: December 2006, page 48). Shift workers might rely more on unhealthy meals high in fats and sugars. As Thomas Kantermann and Till Roenneberg (University of Munich, Germany) comment in last September’s Chro-nobiology International, “Light-at-night may even turn out to be a good predictor for a lifestyle that supports cancer development without itself being part of the causal chain.”

Even so, notes sleep specialist Steven Lockley (Harvard Medical School), “Over the past 20 years our and others’ research has shown that the sleep and circadian systems are exquisitely sensitive to light, and that very dim light is capable of eliciting measurable eff ects on human physiology.” But how dim is dim? There’s a big diff er-ence between working in a brightly lit hospital ward and having some stray streetlight fi lter into your bedroom. We might know the answer soon: a clinical study is under way that exposes sleeping subjects to varying levels and wavelengths of light.

There’s also new emphasis on how harsh glare from poorly shielded lighting aff ects our ability to see at

night. Scattering of bright light (especially blue wavelengths) within the eye causes loss of contrast and leads to unsafe driving conditions — much like struggling to see the road when sunlight streams through a dirty windshield. It’s particularly bad

for older drivers. This concern led the American Medical Association to adopt, last summer, a resolution

calling for reduced glare and light pollution through the widespread use of fully shielded lighting. Mario Motta, a Boston-area cardiologist and lifelong amateur astronomer, led the AMA eff ort (S&T: May 2009 issue, page 8).

Meanwhile, work begun by British amateur Chris Baddiley and expanded more recently by Chris Lugin-buhl (U.S. Naval Observatory) could have a major impact on the design of future streetlight systems. They have carefully modeled how light scatters around in the

the body’s production of melatonin, and in turn whether a chronic melatonin shortfall leads to health problems. In 1987, Richard Stevens (University of Connecticut) posited that female shift workers, those typically exposed to strong light at night, are more likely to develop breast cancer. The research trail continues to implicate melatonin production (or the lack of it) for this increased risk, and in 2007 the International Agency for Research on Cancer concluded, “Shiftwork that involves circadian disruption is probably carcinogenic to humans.”

But many researchers urge caution in trying to estab-

False-color fi sheye views show the night sky’s appearance over selected U.S. national parks. At the very darkest parks, the visual limiting magnitude is 7.0 or slightly better. In contrast, in some locales the Milky Way can be glimpsed at the zenith but gets over-whelmed around the horizon by the “light domes” of distant cities.

Chicago makes a bold statement about its outdoor lighting when seen from orbit at night. Dan Tani captured the view in 2008 while aboard the International Space Station.

Most cities and towns in North America use streetlights with incomplete shielding (example at left) that allow a some of their light to beam above horizontal and directly into the sky. When properly installed, fully-shielded fi xtures (example at right) emit no light above horizontal and also create much less glare at ground level.

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lower atmosphere and come to a dramatic and pos-sibly game-changing conclusion. Waste light that gets beamed straight up is not doing much harm to dark skies — essentially, it escapes to space before much scattering can occur. Rather, the greatest degradation comes from light that streams out to the sides, at angles just above horizontal. As Luginbuhl and two coauthors detail in the December 2009 issue of Physics Today, even a seemingly insignifi cant 3% uplight directed sideways can triple the skyglow (versus a fully shielded fi xture with the same output) above an observatory more than 100 miles away.

Conventional wisdom has long argued that a little uplight was a small price to pay for wider light distribu-tion on the ground, which permits lighting poles to be spaced farther apart than if fully shielded fi xtures are used. But the work of Baddiley and Luginbuhl shows full shielding is the better bet for creating less skyglow.

The Promise of LEDsBeyond concerns about saving the stars or averting health issues, dark-sky proponents think their most persuasive argument to curb light pollution is the energy savings possible from well-designed fi xtures that put light on the ground instead of sending it into the sky. The timing to make this case couldn’t be better: the combination of “going green” and recession-induced budget shortfalls has everyone — from homeowners to world leaders — look-ing for ways to reduce energy consumption.

Recent statistics from the Department of Energy show

that outdoor fi xtures account for only 8% of the electricity used for lighting in the U.S. But this still amounts to an astounding 72,000 gigawatt-hours annually. Almost all of that, 93%, goes to illuminating streets and parking lots. (By one estimate, 60 million cobrahead streetlights line American roadways.)

So it’s hardly surprising that many municipal man-agers have opted to turn off unnecessary streetlights as a means to cut costs. More good news: many utilities now install fully shielded fi xtures as a matter of course. Lumec, a major area and streetlight manufacturer based in Canada, reports that fully shielded fi xtures now account for 70% of its outdoor-lighting sales.

The choice of bulb type makes a big diff erence too. Incandescents, which squander 90% of their electricity as heat, deliver only about 18 lumens of light per watt. Mercury-vapor lighting is more effi cient, 40 to 50 lumens per watt, but these sources are rapidly disappearing due to contamination concerns and a 2005 federal law curtailing their use. The current gold standard for streetlights, high-pressure sodium (HPS), can top 100 lumens per watt.

What’s got everyone abuzz is the potential for solid-state lighting — particularly light-emitting diodes (LEDs) — to take energy effi ciency to a new level. So-called “power” (high-output) LEDs can already crank out 100 lumens per watt and soon might top 200. Moreover, they’re compact, can last 10 years or more, and (unlike HPS and other typical streetlight bulbs) can be dimmed or turned off /on at will. Best of all, LEDs are inherently directional — they must be pointed downward at their target. “LED lighting has the potential to revolutionize outdoor lighting in a profoundly positive way,” observes Robert Parks, IDA’s interim executive director.

Fueled by federal stimulus money, offi cials at the U.S. Department of Energy and Environmental Protection

Left: When a regional power failure plunged Toronto into darkness on August 14, 2003, Todd Carlson of Goodwood, Ontario, hurried to capture the summer Milky Way directly above the city. (Lights in the house are from candles and fl ashlights.) Right: By the next night, with power restored, his sky was again hopelessly awash with the pall of artifi cial skyglow.

Unfi ltered, LED-powered outdoor lighting creates a blue-rich light that might prove harmful to the circadian function of ani-mals and humans. Much of the LED emission also falls outside the scotopic (nighttime) sensitivity of human vision.

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Your Light Pollution Guide

Agency have initiated a hard-charging campaign to roll out a wide range of commercially viable products as soon as practicable. Right now these agencies are putting the fi n-ishing touches on the criteria that will qualify an LED fi x-ture for an Energy Star label. For example, a pole-mounted outdoor installation won’t be allowed to emit any of its lumens above horizontal (except for incidental refl ections off the housing). Especially encouraging is the introduc-tion of a new performance metric, fi tted target effi cacy, that puts a premium on illuminating a target area as effi ciently and uniformly as possible without “overspill” beyond the intended boundaries.

Although still relatively expensive, LEDs are likely coming to a streetlight near you. The fi rst large-scale installations are already being tested and installed in China, North America, and Europe. Last summer Los Angeles offi cials inked a deal, brokered by the Clinton Climate Initiative, to install 140,000 LED streetlights over the next fi ve years.

If there’s a downside to this technology, it’s that the

most-effi cient LEDs have a distinctly blue cast, with a strong peak at 460 nanometers. Some photobiologists and eye doctors have expressed concern about unleashing so much blue light, however well directed, into the nighttime environment. To get “warmer” light, an LED’s output can be passed through a phosphor that reradiates it at longer wavelengths — losing up to 25% of its lumens in the pro-cess. This lumen gap is narrowing, however, as manufac-turers strive to balance optimum effi ciency with aesthetic appeal and environmental sensitivity.

“The Flea That Roared”As all of this research and development rises to a fever pitch, IDA’s staff and volunteers strive to gain recogni-tion as “the light-pollution authority.” The organization’s website (www.darksky.org) boasts that 19 U.S. states and four countries have enacted outdoor-lighting regulations, with California, Connecticut, and New Mexico’s among the strictest.

The IDA has come a long way since its humble begin-

As seen in this before and after comparison from a retrofi t in Walnut Creek, California, properly installed LED streetlighting can dra-matically reduce uplight and improve illumination uniformity. However, the most effi cient LED sources create a much stronger bluish cast (right) than the high-pressure-sodium fi xtures (left) they’re designed to replace.

The ubiquitous but glary fi xtures dubbed “yard blasters” (far left) by amateur astronomers use relatively ineffi cient and environmentally dangerous mercury-vapor bulbs. Recent and proposed U.S. federal regulations could make their manufacture illegal by 2016.

Most cities and towns in North America use streetlights with incomplete shielding (center left) that allows a fraction of their light to beam above horizontal and directly up into

the sky. When properly installed, fully-shielded fi xtures (center right) emit no light above horizontal and also create much less glare at ground level.

Unlike typical high-intensity-discharge (HID) luminaires, which produce light from a single dazzlingly bright bulb, solid-state lighting (SSL) uses banks of individual light-emitting diodes (far right) whose output is strongly directional.

Poor, Better, and Best Streetlamps

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nings in Tucson 22 years ago. The group sponsored briefi ngs about light pollution for Con-gressional staff ers in 2008 and 2009, opened a Washington offi ce last year to weigh in on policy issues, and has directly aided the ongoing development of Energy Star criteria for LED illumination. As lighting expert (and board member) James Benya quips, “IDA is the fl ea that roared.”

Arguably IDA’s most successful initia-tive has been the Fixture Seal of Approval program. Manufacturers submit their lighting products for certifi cation, and then objective, third-party testers evaluate the fi xtures’ photometric performance. Once a product proves to be dark-sky friendly, the manufacturer gets to use the FSA seal to promote and advertise its “IDA Approved” product. To date the program has certifi ed more than 400 fi xture styles.

But not all of its eff orts have borne fruit. Nearly a decade ago, the association partnered with the Illuminating Engineer-ing Society of North America to develop a model lighting ordinance that would give cities and towns easily adapted outdoor-lighting regulations. While two ordinance drafts have received public airings, to mixed reviews, a consensus document will take more time to achieve.

Meanwhile, other national and inter-national groups have mounted off ensives to combat light pollution. Among them are the British Astronomical Association’s Campaign for Dark Skies, which has made some headway in getting local govern-

ments to switch off unnecessary streetlights, and the Starlight Initiative,

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FORUM

which in 2007 issued a “Declaration in Defence of the Night Sky and the Right to Starlight.” To cap it all off , organizers

of the just-ended International Year of Astronomy made “dark-skies awareness” one of their global cornerstone projects (see page 86).

A few (but too few) professional astronomers have been active in the fi ght to keep their observatories safe from the advance of artifi cial skyglow. The Inter-national Astronomical Union and Ameri-can Astronomical Society both maintain standing committees to combat light pol-lution, though to date their members have largely cheered from the sidelines while volunteers from the amateur community have done the heavy lifting.

The “hook” of energy savings has given the light-pollution debate traction in public venues where once there was none. Major publications such as The New York Times, The Wall Street Journal, and The New Yorker have run feature articles on the subject. But none has gained more attention than the November 2008 issue of National Geographic, whose cover boldly declared “The End of Night” across the sickly orange pall of downtown Chicago. Perhaps because of that notoriety, Mayor Daley’s staff is planning a wholesale over-haul of the city’s streetlighting system.

After decades of struggling to be heard, do dark-sky proponents fi nally fi nd them-selves in a position to eff ect real change? Will their eff orts eventually be rewarded with a return to modestly darker skies? Backyard skygazers around the world hope the answer is “yes.” ✦

Senior contributing editor J. Kelly Beattymoved to a new home four years ago and can now see the Milky Way on a good night. He has served on the IDA’s Board of Directors since 2006.

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Light-pollution aware-ness took a big step forward when it became the cover story of National Geographic’s November 2008 issue.

More than 100 manufacturers have earned the IDA’s Fixture Seal of Approval.

Someday this consumer-friendly label, developed by the U.S. Depart-ment of Energy for LED fi xtures, may be affi xed to all lighting prod-ucts sold in America.

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Big Binos

When I was a child, my father bought me a very nice pair of 7×35 binoculars, which soon became one of my most cherished possessions. I used the binoculars to scan the New York City skyline from my 17th-fl oor window, to identify birds, to watch ballgames — and to fi nd my fi rst star clusters and galaxies.

I dabbled in astronomy for several decades, occasionally learning a new constellation or viewing a new object with my 7x35s. Then, quite suddenly, I realized that I was long overdue to buy my fi rst serious telescope. After consider-able research and one false start, I ended up with a 70-mm refractor — a decision I’ve never regretted. I plunged into astronomy with abandon, observing for hours on every clear night. My little scope gave me my fi rst really good views of the planets, and I used it to track down all 109 Messier objects (great galaxies, star clusters, and nebulae), and much more.

I also bought a pair of 10×50 binoculars, the size most often recommended as the best compromise for hand-held astronomical binoculars. The specifi cations mean that they magnify 10 times and their aperture — the diameter of their main lenses — is 50 mm, or 2 inches. At powers

Tony Flanders

These instruments have diff erent but overlapping capabilities.

much higher than that, most people fi nd that the images through casually hand-held binoculars become too wob-bly, and some kind of supplemental support is needed.

Although the 10×50s were a signifi cant step up from my 7×35s, I still wasn’t satisfi ed. Ever since my child-hood I’d been yearning for really big binoculars — ones with at least 70 mm of aperture. However, I found it hard to justify buying them when I already owned a 70-mm telescope. Could the benefi ts of using two 70-mm lenses rather than one really justify owning two instruments with almost identical specifi cations?

Eventually, curiosity got the better of me; I just had to fi nd out. Fortunately, the marketplace had changed greatly since I fi rst contemplated such a purchase in the 1960s. Cheap was no longer synonymous with shoddy; many beginners were reporting complete satisfaction with 15×70 binoculars costing less than $100. I opted instead for the low middle range, spending $150 for a pair of lightweight 15×70 binoculars from Oberwerk. (Very similar units are available from several other vendors.)

S&T photo taken by Dennis di Cicco.

Two Eyes or One?


Binos v Scopes.indd 34 3/2/10 9:27:53 AM



Meet the ContendersWhat does $150 buy? Quite a lot, it turns out; the Ober-werk 15×70s, are certainly worth what I paid — and then some. I have compared them to a borrowed pair of Fuji-non 16×70s, which are often cited as the best binoculars in this class. There’s no question that the Fujinons are superior in many ways, as well they should be, consider-ing that they weigh 50% more and cost four times as much. But the Oberwerks are quite sharp in the center of the fi eld of view, they’re fairly well baffl ed against stray light, and their focuser is smooth and accurate — all the essentials.

Most important of all, the Oberwerk 15×70s happen to fi t me well. The distance between the centers of my eyes (my interpupillary distance) is 57 mm, unusually small for an adult male. Unlike many binoculars, the Oberwerks fold up just tight enough to suit me. And they have 16 mm of true eye relief (the distance between the binoculars and your eyes when properly placed), allowing me to see almost the whole fi eld of view with glasses on.

The Fujinons, by contrast, have short eye relief and unusually large eyepieces. When I fold them up tight

enough to fi t my eyes, take my glasses off , and bring the binoculars close enough to see more than half the fi eld of view, my nose jams painfully between the eyepieces. So despite the fact that the Fujinons are signifi cantly sharper toward the edge of the fi eld of view, and show brighter images against a darker sky background, I much prefer using the Oberwerks. However, people who don’t wear glasses and have wide-set eyes rave about the Fujinons, and wouldn’t trade them for anything else at any price.

As for my telescope, it’s a Tele Vue Ranger, reviewed in the November 1995 issue (page 48). The Ranger is a 70-mm f/6.8 refractor, meaning that the focal length (the distance from the front lens to the eyepiece) is roughly 70 × 6.8 = 480 mm. The relatively short focal length makes the scope quite compact, and also allows it to operate at low magnifi cations, with a wide fi eld of view. In fact the Pronto, the Ranger’s big brother, has identical optics and a 2-inch focuser, allowing it to use eyepieces that give a signifi cant wider fi eld of view than 15x70 binoculars. Yet the mechanical and optical quality also support high magnifi cations well. I routinely use my Ranger at 120×, and occasionally push it far higher. Both the Ranger and the Pronto have been discontinued, replaced by Tele Vue’s TV-76, which off ers the same wide-fi eld potential as the Pronto, has larger aperture, and is an apochromat, mean-ing that it shows essentially no colored fringes around bright objects, even at the highest magnifi cations.

The Ranger cost me about $750 including accessories, which was a bargain in its day, considering the scope’s high quality and short focal length. (It’s harder to build a good, short refractor than a good, long one with equal aperture.) Today that kind of money can buy a scope of comparable quality with a 2-inch focuser, bigger aperture, and similar focal length.

Bear in mind that most of my comparisons pit this fairly high-end telescope against an inexpensive pair of binoculars. In fact, like many if not most binoculars in their price range, the 15×70 Oberwerks don’t make full use of their main lenses. They have internal baffl es that reduce their eff ective aperture to roughly 63 mm. None-theless, the binoculars clearly outperform the telescope

Small Scopesversus

To see really fi ne details at 15×, you need to attach your instru-ment to a solid mount. But tripod-mounted binoculars require you to bend your neck painfully when viewing objects that are high in the sky. Most small scopes, by contrast, are equipped with star diagonals that let you view the zenith with ease. The fl ip side is that you lose the direct connection to the sky provided by binoculars’ straight-through viewing angle.

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Two Eyes or One?

in certain regards, as we shall see below. When I repeated the same comparisons using the 16×70 Fujinons, the ben-efi ts of binocular vision proved to be even greater.

Advantage: BinocularsI fi rst compared my 15×70 binoculars and my 70-mm scope on a clear March night at my country home. I stayed up from dusk long past midnight, observing fi rst the nebulae and open star clusters of winter, then the gal-axies of spring, and ending with the globular clusters of early summer. Since then, I have observed all 109 objects in the Messier catalog, and many other celestial show-pieces, using both instruments side-by-side at my country home. I have also done extensive comparisons at parks near my city home, battling heavy light pollution.

For each comparison, I start out by viewing my target through the telescope at 16× and then increase the magni-fi cation until I obtain the best possible view, which is typi-cally anywhere from 40× to 70×, depending on the object.

The view through the telescope at 16× is surprisingly diff erent from the view through the binoculars, despite the fact that the magnifi cation and fi eld of view are nearly the same. Everything appears much brighter in the binoc-ulars — both my target objects and the sky background. You can see the same eff ect by going outside on a dark night, looking for the faintest stars you can see, and then covering one eye with your hand. In all probability, the

Left: A simple parallelogram mount like the Paragon-Plus (sold by Orion Telescopes & Binoculars) puts some dis-tance between you and the tripod, and lets you fi ne-tune the binoculars’ height with the touch of your hand. This design is relatively simple, inexpensive, and light, but only works well when you’re standing. Right: The Uni-Mount Light, from Universal Astronomics, is jointed so that it can suspend bin-oculars over a lounge chair, allowing you to observe in complete comfort. And it’s counterbalanced on every axis, so it stays wherever you push it, like a dentist’s light.

Messier 33, the Triangulum Galaxy, has an apparent size bigger than the full Moon. But its low surface brightness and lack of a bright core make it a challenging target for beginners, especially in bright suburban surroundings. Many people fi nd this galaxy easier to see in binoculars — even quite small ones — than in any telescope, no matter how big.

faint stars will disappear. When you use both eyes, your brain merges two faint images into a single, brighter one.

Using two eyes also enhances colors. The stars of the Beehive cluster (Messier 44) are nearly monochrome in my refractor, but the binoculars show several with a rich reddish tint. In addition, there’s a quality to binocular views that’s easily seen, widely shared, but hard to put into words. Some describe it as a 3-dimensional appear-ance. To me, it’s a matter of vividness or immediacy. With a telescope, I feel as though I’m studying my subject from a distance. Binoculars bring me into the action, making it feel as though the night sky is all around me.

This sense of connection to the night sky is also aided

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by the fact that binoculars show things right-side up, whereas telescopic views are usually mirror-imaged or inverted. Also, with conventional binoculars, you look straight through the instrument, as opposed to looking downward at right angles to the way a telescope is pointing. This cuts both ways, because looking straight at objects that are nearly overhead creates logistical problems, as shown on page 35. But it also means that you can switch back and forth between the binocular and naked-eye views just by moving your head (or the binoculars) a few inches.

Advantage: TelescopeI can see all of the Messier objects with my 15×70 binoculars at my country home, though a few are fairly diffi cult. Several of the faintest Messier galaxies, includ-ing M91 and M98 (see page 45), are completely invis-ible through my telescope at 16×. But when I raise the telescope’s magnifi cation to 40×, I can see these galaxies easily — together with many others that I can’t see at all through the binoculars.

Conventional binoculars operate at very low magnifi ca-tions relative to their apertures. Although using two eyes helps a great deal in seeing faint objects, higher magnifi -cation usually helps even more — though there are some exceptions. For instance, the notoriously faint globular cluster NGC 5053 (in Coma Berenices, just 1° from bright Messier 53) is invisible in the Ranger at any magnifi ca-tion, but I can see it (barely) with my 15×70s.

Some objects, such as the Beehive and Pleiades star clusters, are very large, and require wide fi elds of view to frame them well. Though few in number, such objects appear high on any list of celestial showpieces, and most people fi nd them more attractive through binoculars than

It’s not really fair to compare 70-mm binoculars to a 70-mm scope; after all, the binoculars gather twice as much light. A 100-mm lens has the same area as two 70-mm lenses, so would a 100-mm scope be able to match 70-mm binoculars in every regard?

My tests indicate that at equal magnifi cations, scopes are indeed a pretty close match to binoculars with the same total lens area — a little better in some ways, maybe worse in others. However, I can’t take full advantage of a 100-mm

telescope at 15×, because the exit pupil produced by such a combination is 100 ÷ 15 = 6.7 mm across. My pupils only open to 5.5 mm, so some of that light is blocked by my iris, as shown at lower left. Up to a point, you can increase the brightness of a 15× image by using a larger aperture. But once the exit pupil equals your eye’s pupil (upper left), the only way to get more light is to use two eyes. That’s why binoculars reign supreme for bright, wide-fi eld low-power viewing.

What about Bigger Scopes?

Clusters of tightly packed faint stars need plenty of magnifi ca-tion to do them justice. M11, shown here, is a bright blur through 15×70 binoculars, but resolves into dozens of individual stars when viewed under dark skies at 60× with a 70-mm telescope.

telescopes. But the great majority of deep-sky objects look best at magnifi cations higher than any normal binoculars provide. For instance, the open cluster M37 is just a bright blur at 15× or 16×, but it’s breathtaking stardust through my 70-mm scope at 70×, with dozens of faint stars shim-mering through a luminous haze.

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Two Eyes or One?

The planets crave high telescopic mag-nifi cation. My little refractor shows Jupi-ter’s main cloud belts easily, and reveals substantial extra detail at 120× when the conditions are good. It’s fairly easy to see Jupiter’s moons through well-mounted binoculars, but the planet itself is just a tiny, featureless, oblate disk at 15×.

So there’s no question that the ability to vary the magnifi cation by changing eyepieces makes short-focal-length 70- or 80-mm scopes much more versatile than 15×70 binoculars. Almost everything the binoculars can do, the telescopes can do too — though not always as well. But the reverse isn’t true. For viewing planets or splitting tight double stars, all decent tele-scopes are far superior to any conventional binoculars, even 40×150 behemoths.

Why 15×70 Binoculars?So far, I’ve skirted the question of why I bought 15×70 binoculars rather than some signifi cantly diff erent size. In fact, bin-ocular size involves some tricky tradeoff s, which is why I still use my 7×35s as well as my 10×50s and 15×70s — and would choose the 10×50s if I were allowed to keep just one of those. Bigger binoculars reveal fainter objects, but they’re also less conve-nient and have narrower fi elds of view.

On the other hand, 15×70s off er much more spectacular views than 10×50s. Objects that are merely visible in 10×50s are impressive in 15×70s; objects that are impressive in 10×50s are jaw-dropping in 15×70s. That’s not such a huge deal to me, because I’m accustomed to squeezing every last drop of detail from things I can barely see. But many novices, especially ones who live in bright suburbs, fi nd the views through 15×70s to be genuinely engaging, while 10×50s leave them cold.

In fact, 15×70 binoculars might just be the very best possible tool for break-ing into deep-sky observing. They have enough power to show many deep-sky objects with ease, yet a wide enough fi eld of view so that you can locate those objects just by scanning the right area of the sky.

At the opposite end of the spectrum, big binoculars are ideal for experienced stargazers who want to study the Milky Way under pristine dark skies. Many

Milky Way features (star clouds, bright and dark nebulae) are huge; they cry out for wide fi elds of view. And that’s the one arena where binoculars have a big advan-tage over telescopes.

If 15×70 binoculars are great, aren’t bigger ones greater still? Yes, really big binoculars such as 22×85s or 25x100s, and binocular telescopes that accept inter-changeable eyepieces, certainly have their

devoted adherents — and rightly so. How-ever, there’s a substantial jump in bulk, weight, and cost once binocular objectives exceed 70 mm. And there’s a signifi cant loss in fi eld of view with magnifi cations much higher than 15×. Hand-holding 15×70s isn’t ideal, but at least it’s an option, which isn’t true in bigger sizes. Many experienced stargazers fi nd that 15×70 hits a sweet spot, the best possible compromise between power, convenience, and fi eld of view. There are good reasons why this size is popular among novice and veteran stargazers alike. ✦

Associate editor Tony Flanders currently owns six telescopes, six pairs of binoculars, and one pair of special stargazing eyeglasses.

Saturn is beautiful beyond words through the author’s 70-mm scope at 120×. His 15×70 binocu-lars, by contrast, show barely a hint of the rings.

For more ruminations on binoculars, see www.SkyandTelescope.com/bino_blogs.

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Fred SchaafNorthern Hemisphere’s Sky

Speeding Up for SpicaThe evening sky changes rapidly at this time of year.

I noted that the north-south meridian on the April all-sky map coincides with the 10-hour line of right ascension. That line passes just west of Regulus, the brightest star in Leo, the Lion, so I suggested that we call that time and “state of the sky” the Leo Hour.

The Heavens by Hours system created by Guy Ottewell has 24 names for such states of sky — one for each of the sidereal hours. But the issues of our monthly magazine have room for only 12 of these. You might think that each new issue would advance the sidereal time by 2 hours. But if you look down near the south horizon of the all-sky chart on page 44, you will see that the central RA line is labeled as 13h, which is 3 hours ahead of last month’s sidereal time. What’s going on here?

Spring forward to the Spica Hour. Has Earth radi-cally sped up during its Northern Hemisphere’s spring?

In our previous issue, No, but those of us at mid-northern latitudes see the Sun setting later and later. So the sky (really Earth, of course) has more time to turn before the stars come out. Our sky map must refl ect this, so we advance it three hours from last month. And it brings us to a state of the sky we can call the Spica Hour.

Spica is the 1st-magnitude star (magnitude 0.98, to be precise) that’s closest to the meridian at this sidereal time. As the map’s instructions tell you, the Spica Hour occurs at diff erent clock times as the weeks and months of spring go by. If you want to experience it in late March, when this issue is received by most subscribers, you have to stay up until 2 a.m. (daylight-saving time). The Spica Hour occurs at 1 a.m. in early April, midnight in late April, 11 p.m. in early May, and at dusk in late May.

The Sky at the Spica Hour. Spica is not the only star or star pattern near the meridian at this time. Sail-shaped Corvus, the Crow, is just to the west of the meridian, to the lower right of Spica. Well up to Spica’s upper left is an even brighter and somewhat orange — some say cham-pagne-colored — star: Arcturus. And if you turn and face north rather than south, you’ll fi nd that the handle of the Big Dipper — from which you can extend a curve out to Arcturus — is now at its highest.

In May 2010, Spica is the last (leftmost or easternmost) in a long string of similarly bright gems. The line consists of Pollux, Mars, Regulus, Saturn, and Spica. The posi-tions of the two planets are plotted on our sky map for mid-May.

By the Spica Hour, Sirius and Orion, Taurus with the Hyades and Pleiades, have all set. Procyon is low in the west, Capella is somewhat higher in the northwest, and Gemini stands upright between those stars. The feet of the Twins are just above the horizon, their much higher

heads marked by bright Castor and Pollux. Turning to the east, where the summer stars

are rising, zero-magnitude Vega is about one-third of the way up the east-northeast sky while 1st-magnitude

Deneb is much lower in the northeast. And the fi re of 1st-magnitude Antares is quite low in the southeast. ✦

Fred Schaaf welcomes your comments at [email protected]&T: GREGG DINDERMAN

NHS Layout May.indd 40 2/24/10 10:58:29 AM


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read, and were fervently followed by groups of early Christians. But they would not be among the books that formed the New Testament.

From the many different scriptures then avail-able, Christians held beliefs that today would be considered bizarre: that there were two, 12, or as many as 30 gods; that a malicious deity, rather than one true God, created the world; that Christ’s death and resurrection had nothing to do with salvation—others insisted that Christ never really died at all.

What did these “other” scriptures say? Do they exist today? How could such outlandish ideas ever be considered Chris tian? If such beliefs were once common, why do they no longer exist? These are just a few of the many provocative questions that arise in Lost Christianities: Christian Scriptures and the Battles over Authentication.

A Good Mystery StoryThis 24-lecture series is a richly re ward ing

learning opportunity for anyone in ter ested in reli-gion, history, or a good mystery story. Professor Bart D. Ehrman lends his expert guidance as you follow scholars’ efforts to recover knowledge of early Christian groups who lost the struggle for converts and subsequently disappeared.

A major theme of this course is the struggle for orthodoxy—or right belief—among the vari-ous early Christian groups. You will witness the process by which certain Christian beliefs gained legitimacy, while others were relegated to the sta-tus of footnotes to history.

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of these writings were forgeries, how can we be sure that forgeries weren’t included in the New Testament?

In these lectures you will also hear about a remarkable archaeological event: the discovery in 1945 of a treasure trove of missing Gnostic scrip-tures at Nag Hammadi, an Egyptian village near the city of Luxor.

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I M A G E B Y G I M M I R A T T O

May is galaxy time. And the grandest galaxy fi eld of all is Markarian’s Chain, at the heart of the Virgo Cluster.

For telescope owners,

1 DUSK: Use binoculars to spot 4th-magnitude Kappa1 Tauri about ¼° lower left of Venus (in North America). And look 5′ lower left of Kappa1 for 5th-magnitude Kappa2.

4 DUSK: The 4th-magnitude star Tau Tauri is less than ½° left of Venus. Telescopes and solidly mounted binoculars show that this star is a wide double, with a 7th-magnitude companion 63″ southwest of the primary.

6 LAST-QUARTER MOON (12:15 a.m. EDT).

9, 10 DAWN: The waning crescent Moon is above Jupiter on the 9th and left of Jupiter on the 10th, as shown on page 49.

13 NEW MOON (9:04 p.m. EDT).

14 DAWN: Use a telescope or tripod-mounted binoculars to look for 20 Piscium about ¼° lower right of Jupiter (in North America). This star is magnitude 5.5, about as bright as Jupiter’s Galilean satellites, only three of which are visible until Io emerges from behind Jupiter at 5:14 a.m. CDT.

15, 16 DUSK: The thin crescent Moon is lower right of Venus on the 15th and upper left of Venus on the 16th (see page 48). The Moon occults (hides) Venus around 10h UT on the 16th in northern Africa and southern Asia.

19 EVENING: The Moon is about 6° below Mars.

20 EVENING: The Moon is about 5° lower left of Regulus and 12° left of Mars.

20 FIRST-QUARTER MOON (7:43 p.m. EDT).

21 DUSK: Use binoculars or a telescope to view the star cluster Messier 35 less than 1° lower left of Venus.

22 EVENING: Look for Saturn about 8° above the Moon.

24 EVENING: Look for Spica about 6° upper right of the Moon.

27 FULL MOON occurs at 7:07 p.m. EDT. This evening and night, in North America, look for ruddy Antares 1° to 2° below or lower right of the Moon, as shown on page 48. The view is best in binoculars.

See SkyandTelescope.com/ataglance for details on each week’s celestial events.


M O O N P H A S E S

P L A N E T V I S I B I L I T Y

Sky at a Glance

May 2010

MIDNIGHT◀ SUNSE T SUNRISE ▶

Mercury

Venus

Mars

Jupiter

Saturn

PLANET VISIBILITY SHOWN FOR LATITUDE 40 NORTH AT MID-MONTH.

SEE

NWSW

W NW

WS

Invisible to the naked eye all month

2

9

16

3

10

17

4

11

18

29

5

12

19

25 26

6

13

20

7

14

21

27 28

1

8

15

2223

30

24

31

S U N M O N T U E W E D T H U F R I S A T

SAAG Layout May.indd 43 2/22/10 9:08:39 AM


+60°

+80°

+80°

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Zenith

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Facing

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Facing North Facing South

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LittleDipper

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M5

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Deneb

Albireo

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May 20

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May 27Moon

May 24

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Northern Hemisphere Sky Chart

NHSC Layout May.indd 44 2/19/10 7:38:00 AM


U A T O R

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Galaxy

Double star

Variable star

Open cluster

Diffuse nebula

Globular cluster

Planetary nebula

The densest concentration of Messier objects lies at the intersection of Leo, Coma Berenices, and Virgo. Here we fi nd vistas littered with small, faint galaxies. Truly, however, this is a case of quantity over quality, since all these Messiers are challenging binocular targets even under good skies. Yet it’s within this mass of galaxies that we’re able to glimpse the vastness of our universe, as we gaze directly into the heart of the Virgo Galaxy Cluster.

It’s easy to be confused by galaxies in this region, so we must work methodically and carefully. Let’s begin part one of our exploration by jumping east from Denebola, Beta (β) Leonis. About two binocular fi elds away, you’ll fi nd a grouping of 6th- and 7th-magnitude stars that I call the Little Pleiades. This asterism is key to locating M99and M100, both of which I’m able to see in 10×50s. The nearby galaxy M98 is tougher though, requiring the extra power of my 15×45 image-stabilized binos.

Things get easier (but not easy) when we skip north a short distance to M85, the most prominent of all the gal-axies in the region. South of M85 lie M84, M86, and M87, the last being the most conspicuous. The diffi cult pair of M90 and tiny M89 is just to the east of this trio. I can see all six in 10×50s.

Moving a little farther north brings us to the fi nal gal-axies in this month’s Messier haul: M88 and M91. M88 is visible in 10×50s, but even my 15×70s have so far failed to show M91. It may be possible to see this galaxy under better skies though — can you ferret it out? ✦

— Gary Seronik

Binocular Highlight:

Diving Into Virgo

C O M A B E R E N I C E S

V I R G O

Litt le P le iades

L E O

M58

M84

M85

M86M87

M88

M89

M90

M91M98

M99

M1005° binocular view

Using the Map

WHEN

Late March 2 a.m. *

Early April 1 a.m.*

Late April Midnight*

Early May 11 p.m.*

Late May Dusk

*Daylight-saving time.

HOW

Go outside within an hour or so of a time listed above. Hold the map out in front of you and turn it around so the yellow label for the direction you’re facing (such as west or southeast) is at the bottom, right-side up. The curved edge is the horizon, and the stars above it on the map now match the stars in front of you in the sky. The map’s center is the zenith, the point overhead.

Example: Hold up the map so the “Facing South” is at the bottom. About halfway from there to the map’s center is the bright star Spica. Go out, face south, and look halfway from horizontal to straight up. There’s Spica!

Note: The map is plotted for 40° north latitude (for example, Denver, New York, Madrid). If you’re far south of there, stars in the southern part of the sky will be higher and stars in the north lower. Far north of 40° the reverse is true. The planets are positioned for mid-May.


You can make a sky chart customized for your location at any time at SkyandTelescope.com/skychart.

NHSC Layout May.indd 45 2/19/10 7:38:02 AM



Planetary Almanac

Mercury

Venus

Mars

Jupiter

Saturn

Uranus

Neptune

Pluto 10"

May 1 11 21 31

31161

16 311

16

16

Sun 1 2h 31.9m +14° 56′ –– –26.8 31′ 45″ –– 1.007

31 4h 30.5m +21° 51′ –– –26.8 31′ 33″ –– 1.014

Mercury 1 2h 16.8m +14° 02′ 4° Mo –– 12.0″ 1% 0.562

11 2h 04.6m +10° 14′ 18° Mo +2.3 11.0″ 12% 0.611

21 2h 17.8m +10° 07′ 24° Mo +0.8 9.1″ 30% 0.737

31 2h 54.2m +13° 15′ 24° Mo +0.1 7.4″ 48% 0.906

Venus 1 4h 19.6m +22° 15′ 27° Ev –3.9 11.4″ 89% 1.462

11 5h 11.6m +24° 12′ 29° Ev –3.9 11.8″ 87% 1.410

21 6h 04.4m +25° 01′ 31° Ev –3.9 12.3″ 84% 1.354

31 6h 56.9m +24° 39′ 34° Ev –3.9 12.9″ 81% 1.292

Mars 1 9h 01.7m +19° 04′ 92° Ev +0.7 7.3″ 90% 1.287

16 9h 27.4m +16° 48′ 84° Ev +0.9 6.6″ 90% 1.421

31 9h 55.5m +14° 09′ 77° Ev +1.1 6.0″ 90% 1.550

Jupiter 1 23h 38.3m –3° 29′ 47° Mo –2.1 35.1″ 99% 5.614

31 23h 58.0m –1° 28′ 70° Mo –2.3 37.8″ 99% 5.221

Saturn 1 11h 58.2m +2° 57′ 138° Ev +0.8 19.0″ 100% 8.739

31 11h 55.4m +3° 09′ 108° Ev +1.0 18.2″ 100% 9.152

Uranus 16 23h 59.1m –0° 54′ 55° Mo +5.9 3.4″ 100% 20.651

Neptune 16 22h 03.2m –12° 25′ 86° Mo +7.9 2.3″ 100% 30.067

Pluto 16 18h 20.5m –18° 12′ 140° Mo +14.0 0.1″ 100% 31.055

The table above gives each object’s right ascension and declination (equinox 2000.0) at 0h Universal Time on selected dates, and its elongation from the Sun in the morning (Mo) or evening (Ev) sky. Next are the visual magnitude and equatorial diameter. (Saturn’s ring extent is 2.27 times its equatorial diameter.) Last are the percentage of a planet’s disk illuminated by the Sun and the distance from Earth in astronomical units. (Based on the mean Earth–Sun distance, 1 a.u. is 149,597,871 kilometers, or 92,955,807 international miles.) For other dates, see SkyandTelescope.com/almanac.

Planet disks at left have south up, to match the view in many telescopes. Blue ticks indicate the pole currently tilted toward Earth.

Sun and Planets, May 2010

May Right Ascension Declination Elongation Magnitude Diameter Illumination Distance

The Sun and planets are positioned for mid-May; the colored arrows show the motion of each during the month. The Moon is plotted for evening dates in the Americas when it’s waxing (right side illuminated) or full, and for morning dates when it’s waning (left side). “Local time of transit” tells when (in Local Mean Time) objects cross the meridian — that is, when they appear due south and at their highest — at mid-month. Transits occur an hour later on the 1st, and an hour earlier at month’s end.

Rigel

Betelgeuse

C A N I SM A J O R

Sirius

O R I O N

Pleiades

CANCER

PolluxCastor

Procyon

Arcturus

CORVUS

G E M I N I

V I R G O

B O Ö T E S

L I B R A

L E O

H Y D R A

Regulus

P E G A S U S

CAPRICORNUS

AQUARIUS

Fomalhaut

P I S C E S

Vega

H E R C U L E S

C Y G N U S

SCORPIUS

O P H I U C H U S

SAGITTARIUS

AQUILA

C E T U S

ERIDANUS

A R I E S

A U R I G A

T A U R U S

Spica

E Q U A T O R

Midnight2 am4 am6 am8 am10 am 8 pm 6 pm 4 pm 2 pmLOCAL TIME OF TRANSIT

+30°

+40°

–10°

–20°

–30°

–40°

+10°

+30°

0°

–10°

–20°

–30°

–40°

RIGHT ASCENSION

DE

CL

INA

TIO

N

0°

+10°

10 pm

18h20h22h0h2h 4h6h8h10h12h14h16h

ECLIPTIC 36

9

17

20

23

May27–28

Mars

Jupiter

Saturn

Uranus

Neptune Pluto

Mercury

Venus

PA Layout May.indd 46 2/19/10 7:26:14 AM


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Fred SchaafSun, Moon, and Planets

Encounters with VenusThe brightest planet traverses a starry panorama in May.

Venus shines in the west-northwest, Mars is high in the southwest, and Saturn is high in the south. Jupiter doesn’t rise until an hour or less before the fi rst light of dawn. Late in the month, Mercury is visible through binoculars very low in the east-northeast before sunrise.

E V E N I N GVenus hangs at practically the same height moderately low in the west-north-west during twilight all May. It shines at a dazzling magnitude –3.9 but isn’t espe-cially interesting through a telescope. It’s small and gibbous, just 12″ wide and 85% illuminated at mid-month.

What’s more fascinating is the planet’s trek past stars and star clusters. On May 1st Venus blazes about ¼ ° from Kappa Tauri (you may need binoculars to glimpse the star so near to the planet’s mighty

At dusk this May,To see what the sky looks like at any given time and date, go to SkyandTelescope.com/skychart.

glow). On May 14th Venus shines directly between the two stars that mark the ends of Taurus the Bull’s horns. Optical aid will be required to see the big Messier 35 star cluster less than 1° southwest of Venus on May 21st. On May 27th and 28th, Venus is less than ¾° from Epsilon (ε) Gemino-rum, also known as Mebsuta. The closest approach (17′ around 12h UT on May 28th) is visible from eastern Asia.

Mars reaches eastern quadrature (90° east of the Sun) on May 4th, glowing in the south around sunset. Quadrature is when we see the largest phase eff ect — a shadowed edge — on an outer planet’s disk. But Mars’s 90%-illuminated disk is only 7.1″ wide then, so it may not be easy to make out that Mars is out of round. The summer solstice in Mars’s northern hemi-sphere occurs on May 12th, so the north polar ice cap will presumably be too small to see in most amateur telescopes.

Naked-eye observers can have more fun with Mars, which is moving eastward through the “fi xed stars” at almost ½° per day. On May 1st the planet shines at magnitude +0.7, distinctly brighter than Pollux 20° to its west or Regulus 17° to its east. But by May 31st Mars dims to +1.1 and moves to within 4° of +1.4-magnitude Regulus.

Saturn is the fourth in a long string of fi ve 1st-magnitude objects stretch-ing eastward along the ecliptic, from Pollux to Mars to Regulus to Saturn to Spica. Steady-shining Saturn glows about midway between twinkling Regulus and Spica. The planet barely moves with respect to the stars in May, since it’s near-

Dusk, May 14–1645 minutes after sunset

Aldebaran

Capella

Betelgeuse

Venus Tauri

MoonMay 14

MoonMay 15

MoonMay 16

Looking West-Northwest

May 27 and 28

AntaresMoonMay 27

MoonMay 28

Looking Southeast

S C O R P I U S

Around 11 pm

These scenes are drawn for near the mid-dle of North America (latitude 40° north, longitude 90° west); European observers should move each Moon symbol a quarter of the way toward the one for the previ-ous date. In the Far East, move the Moon halfway. For clarity, the Moon is shown three times its actual appar-ent size. The visibility of objects in bright twilight is exaggerated. The 10° scale is about the width of your fi st at arm’s length.

SMP Layout May.indd 48 2/19/10 7:38:40 AM



FPOJupiter

Neptune

Uranus

Pluto

Saturn

Mars

Earth

Sun

Mercury

Venus

Marchequinox

Sept.equinox

December solstice

June solstice

ing the end of its retrograde (westward) motion in the head of Virgo. On May 31st Saturn halts and begins direct (eastward) motion through the stars.

Saturn dims this month to magnitude +1.0, equal to Spica and nearly as faint as the planet can ever be. This is due largely to the narrowing of its rings, which reach a minimum tilt of just 1.7° from edgewise to Earth in late May. This is the last opportu-nity for a decade and a half to see the rings as such thin spikes, with dim moons shut-tling along them as the satellites pass from one side of Saturn to the other.

Planets usually appear sharpest in a telescope when they’re highest in the sky. In early May, Saturn is highest about 2½ hours after sunset, but by month’s end it’s highest at sunset and best viewed as soon as the sky is dark.

P R E D A W N A N D D A W NJupiter, in Pisces, rises around the time Saturn sets (for viewers at mid-northern latitudes). In early May that’s around the start of morning twilight, but by month’s end it’s about 2 or 3 a.m. (daylight-saving time). The giant planet brightens slightly during May, from magnitude –2.1 to –2.3,and its disk grows from 35″ to 38″ wide.

By month’s end, Jupiter pulls within 1° of 5.9-magnitude Uranus. Jupiter had three close conjunctions with Neptune last year, and it will have three with Uranus during this apparition. The fi rst will occur on June 8th.

Neptune, near the Capricornus-Aquar-ius border, is fairly low in the southeast before dawn’s fi rst light. Finder charts for the two outermost major planets can be downloaded at SkyandTelescope.com/uranusneptune.

Pluto enters M24, the Small Sagit-tarius Star Cloud, this month. The 14th-magnitude world is highest in the south

ORBITS OF THE PL ANETS

The curved arrows show each planet’s movement during May. The outer planets don’t change position enough in a month to notice at this scale.

Jupiter

MoonMay 9

MoonMay 10

MoonMay 11

G r e a tS q u a r e

o fP E G A S U S

Dawn, May 9–111 hour before sunrise

Looking East

The waning crescent Moon makes a pretty pair with Jupiter in the predawn sky on May 9th and 10th. And look for the 8%-illuminated Moon well to Jupiter’s lower left on May 11th.

around 3 a.m.. See SkyandTelescope.com/pluto for more information.

Mercury has a poor apparition very low in bright dawn in late May and early June. It was at inferior conjunction on April 28th, and it glides out to a greatest elongation of 25° from the Sun on May 26th. But Mercury then shines only at magnitude +0.4, about as dim as it can ever appear at maximum elongation, because its 8.2″-wide disk is only 39% lit.

Even worse, the ecliptic lies at a very shallow angle to the dawn horizon in spring. This means that Mercury is less than 5° high a half hour before sunrise on the 26th for observers at mid-northern latitudes. Mercury may be visible to the unaided eye when it brightens in early June, but you will probably need binocu-lars to see it in late May.

M O O N P A S S A G E SThe Moon waxes to fi rst quarter while passing Venus, Pollux, Mars, and Regulus from May 15th to 20th — but it gives all of them a wide berth. On the American night of May 27–28, the full Moon rises less than 2° above Antares and passes only 1° north of the star later in the night. ✦

SMP Layout May.indd 49 2/19/10 7:38:41 AM


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Charles A. WoodExploring the Moon

fi ve lunar missions have returned more data about the Moon than collected by all previous spacecraft. This continuing onslaught of infor-mation is providing many new insights about our nearest neighbor. But unlike the Apollo era, when spacecraft data were available only to scientists, professionals aren’t the only ones who can explore the new information. Today, the internet brings gigabytes of data to everyone.

Five spacecraft have orbited the Moon in the past seven years. The fi rst was SMART-1, launched by the European Space Agency in 2003 to test new technologies. Sadly, only a tiny fraction of its images have been publicly released. Similarly, only a few of the thousands of images from the Chinese mission Chang’e 1 and the Indian orbiter Chandrayaan-1 have been distributed. But some data from JAXA’s Kaguya mission (February issue, page 20) and NASA’s Lunar Reconnaissance Orbiter (LRO) are now available, and ultimately all of it will be.

One of the most useful datasets currently available is a digital terrain model (DTM) of lunar topography from Kaguya’s laser altimeter. Based on 6 million elevation measurements, the DTM is a computer fi le that you can manipulate with software such as the Lunar Terminator Visualization Tool (http://ltvt.wikispaces.com/ltvt), created by amateur astronomer Jim Mosher to display lifelike views of the lunar surface. You can use this program to display how the Moon will look for future (or past) observ-ing sessions. The DTM is the fi rst accurate topographical map of the lunar surface ever produced.

In addition to recreating views of the Moon as we commonly see it, you can also re-project the DTM to see the Moon as we never can, such as with illumination from

Lunar Missions & AmateursNew lunar data reveals the Moon as never seen before.

The most recent the north or the south poles. Doing this allowed Maurice Collins in New Zealand to discover a ridge that appears to radiate from the Imbrium impact basin that had never been noticed before. This ridge extends from the crater Eudoxus, past Plana and Mason near Lacus Mortis, and continues to the remnant crater Williams. This ridge is probably related to the formation of Imbrium, but for now, we aren’t quite sure how. Examining the lunar farside using the DTM also reveals an older, unknown basin partially covered by the Moscoviense basin. There are probably many more surprises awaiting detection in the Kaguya DTM.

Top right: Using Jim Mosher’s Lunar Terminator Visualization Tool (LTVT), New Zealand amateur Maurice Collins discovered a ridge radiating away from the Imbrium impact basin. These two simulations produced by Collins using LTVT show lunar topog-raphy as it would appear if the Sun were illuminating it from the north (top) and the south (bottom).

Bottom right: An interactive Java applet on JAXA’s Kaguya web-site (http://wms.selene.jaxa.jp/3dmoon_e/index_e.html) allows you to explore images and data recorded by the orbiter, including the Digital Terrain Map (DTM) shown above.

Plana

Williams

Plana

Eudoxus

Eudoxus

Mason

Mason

Williams

R I D G E

R I D G E

Lacus Mortis

ETM Layout May.indd 51 2/23/10 1:13:02 PM



Exploring the Moon

You can also examine the DTM by using an interactive program available on the Kaguya website: http://wms.selene.jaxa.jp/3dmoon_e/index_e.html. Launch the Java applet Kaguya 3D GIS and the program displays a color-coded topographic map that you can rotate to examine any part of the Moon, including the far side never seen from Earth. Select-ing the bottom option in the control panel provides a yellow line that crosses the Moon, and below that a light-hued profi le of the terrain under the line. A graphic example, centered on the Orientale impact basin (shown on page 51), shows an eleva-tion profi le from the farside highlands to Oceanus Procellarum.

You immediately notice that the high-lands are 8 to 9 kilometers (5 to 6 miles) higher than the mare. The Orientale basin formed on the slope between the two types of terrain, making its western rim

4 or 5 km higher than the more familiar Cordillera Mountains on the eastern rim. Look closely to see the local elevation peaks of the inner rings, too. It should be noted that due to Kaguya’s polar orbit, the DTM is less accurate at the lunar equator than near the poles.

Spend fi ve minutes with the Kaguya 3D GIS comparing the surface color map with the elevation profi le, and you’ll begin to understand relationships of lunar topogra-phy that have been previously unknown in such detail. Observers shouldn’t abandon their telescopes in favor of these simula-tions, but they will help us to become more knowledgeable interpreters of the lunar surface before stepping out to the eyepiece. ✦

To get a daily lunar fi x, visit contributing edi-tor Charles Wood’s Lunar Photo of the Day website at lpod.wikispaces.com.

The Moon • May 2010

PhasesLast quarter May 6, 4:15 UT

New Moon May 14, 1:04 UT

First quarter May 20, 23:43 UT

Full Moon May 27, 23:07 UT

Distances

Apogee May 6, 22h UT251,180 miles diam. 29′ 15″Perigee May 20, 9h UT 229,741 miles diam. 32′ 5″

Librations

Drygalski (crater) May 8

Arrhenius (crater) May 11

Petermann (crater) May 23

Beals (crater) May 28

S&

T: D

ENN

IS D

I C

ICC

O

Eudoxus 41 miles Crater Terraced walls, no central peak

Plana 27 miles Crater Nearly featureless fl oor

Mason 26 miles Crater Heavily eroded, irregular shape

Lacus Mortis 91 miles Flooded plain Crater Bürg located inside

Williams 22 miles Remnant crater Only low curving ridge remains

For key dates, yellow dots indicate what part of the Moon’s limb is tipped the most toward Earth by libration under favorable illumination.

May 8

11

23

28

Highlighted feature Diameter Description Notes (shown on page 51)

ETM Layout May.indd 52 2/23/10 1:13:03 PM


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Most readers probably recognize these opening lines from a long-running series of television ads for Apple computers. Well, I’m a Mac and happily so — most of the time. The rare occasions I have PC envy occur when I see the vast array of Windows-based software versus the minuscule number of titles in the Apple line. In particu-lar, there’s a dearth of Mac-based astronomy software.

So imagine my delight when I found AstroHawk’s Lunar Discoverer. The Deluxe Edition contains an exten-sive database of lunar features (including physical details and images), several types of lunar maps, an audio-format pronunciation guide, and numerous options for custom-

izing the program for your observing sessions. Best of all, the software lets you create a custom, interactive map of the Moon for any date and time between 1904 and 2040 — on a Mac! (I hasten to add that it works identi-cally on a PC.) Another nice feature is that you can generate views that match the fi eld and orientation of the Moon as it appears in your telescope.

I was particularly interested

S & T Test Report Paul Deans

Lunar Discoverer

Lunar DiscovererUS price: $59.95 for the Deluxe Edition (the

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Mac and PC users alike can use this program to aid their telescopic

explorations of the Moon

in seeing how accurately Lunar Discoverer’s map and its display of the terminator marking the division between lunar day and night compared with the real thing in the sky. There are two basic ways to use Lunar Discoverer’s Moon map. One is to show the Moon as it looks in real time, which is useful for identifying lunar surface fea-tures that appear in your telescope’s eyepiece. The other is to plan future observing sessions so you can catch fea-tures of interest when they’re optimally placed for obser-vation near the terminator. I used the Deluxe Edition, which has more options and a larger database of named lunar features (4,600+ vs. 1,300+) than the Standard Edi-tion. Both come with a detailed PDF manual that covers the program’s operation on both computer platforms.

I tried the program on numerous nights covering most of the lunar phases, and the software performed admi-rably when it came to identifying features seen through my telescope. Click on a crater and its name pops up. Double-clicking brings up more information, including physical details, information about who it’s named after, a page reference to Antonín Rükl’s Atlas of the Moon, and a close-up photo (if available).

Using the lunar map to plot future observing sessions

WHAT WE LIKE:

Runs on a Mac as well as a PC

Easy to customize

WHAT WE DON’T LIKE:

Handles time poorly

Doesn’t include the eff ects of libration

“Hello, i’m a Mac.”

“And i’m a PC.”

STTR Layout May.indd 55 2/19/10 7:39:34 AM



S&T Test Report

also worked well, but with a caveat. The software didn’t do a good job of handling the eff ects of libration. This subtle “rock-ing” motion of the Moon varies the lunar face presented to observers and is espe-cially critical when viewing features near the Moon’s limb. Since the charts don’t show libration eff ects, I had no expecta-tion that the program would tell me the best dates to peek over the Moon’s edge — and it doesn’t.

But I was disappointed to fi nd that the libration issue also aff ects the displayed location of the terminator, when it is more than 45° away from the midpoint of the

lunar disk. At times it was off by as much as two or three hours from its actual appearance. For observers, this usually isn’t a big deal when the Moon is waxing, since any feature in darkness will soon experience sunrise. But it can be a prob-lem when observing features in a waning phase if sunset has already occurred for a feature that the program indicates is still on the sunlit side of the terminator.

One of the program’s nice touches is the thin, light-gray band separating the terminator (indicated as a red line) and the black of the lunar night. The band indi-cates a region where mountain peaks and crater rims may catch rays of sunlight, even though the surrounding moonscape lies in darkness.

But beyond the libration problem, the software contains several vexing issues. In particular, time is not handled well. Local time (as read from your computer’s inter-nal clock) is mostly used, though you have to manually adjust the program to account for daylight time. But Universal Time crops up here and there and is incorrectly formatted as a 12-hour clock.

Even worse, when I entered a date/time in the Preferences window, the resulting chart would sometimes show the lunar phase for exactly 24 hours later. I con-fi rmed by direct observation that the chart is correct for the date and time shown, but is for one day later than I requested. The problem is related to how the software handles local time and UT. It seems to add the user-defi ned GMT off set (in my case, 7 hours for Mountain Time) to the requested local time entered in Preferences. If that

causes the time to advance past midnight, a chart is created for the correct time but for the following day. With my 7-hour off -set, this “day-advance” happens at 5 p.m., so if I want a chart for a date and time in the future, I have to double check the chart’s date if my requested time is 5 p.m. or later. It’s an odd problem, but I’m sur-prised it hasn’t been noticed and corrected.

Other problems lurk. For example, the lunar eclipse listing is peppered with incorrect details about the eclipse type; totality times are sometimes given for eclipses that aren’t total; the standard/day-light time issues mentioned above also crop up here; and there’s no indication of where on Earth a particular eclipse is vis-ible. Click on a New Moon in the Calendar window and numerous, supposedly visible features around the lunar limb are listed and shown on the chart. And you can’t cancel an accidental command to quit.

I tested Version 1.25 of Lunar Discoverer and it seemed to be a work in progress. One feature I’d really like to see added is the ability to adjust the time in hourly incre-ments without having to call up the Prefer-ences menu. As this review was readied for publication, AstroHawk released an update (V1.31), which doesn’t correct the issues I’ve raised above (at least not in the Mac version). Despite its fl aws, the program’s mapping functions are good enough that I’ll defi nitely make this program the one I use for lunar observing. ✦

Paul Deans is a freelance astronomy writer who has recently rediscovered the joy of chas-ing shadows along the lunar terminator.

Lunar Discoverer can generate charts based on several views of the Moon, including actual photographs (top) and a “synthetic” surface that emphasizes relief features (bottom).

The program has many customization options for displaying lunar features and their labels, though labels can sometimes become very crowded along the Moon’s limb. The calculated terminator dividing lunar day and night shows as a red line, while a gray band indicates the region when crater rims and mountain peaks might be catching a few rays of sunlight. Compare the charts made using photographs (left and right) with the one showing a synthetic surface (center).

STTR Layout May.indd 56 2/19/10 7:39:34 AM



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Alan MacRobertCelestial Calendar

Saturn’s 8 Amateur MoonsHow many of them have you bagged? Now’s the time to push your limits.

in the head of Virgo, is at opposition on the night of March 21st and remains almost as close and big during April and May. Its rings are narrow and narrowing further; they’ll be a thin sliver tilted just 1.7° to our view from mid-May through early June, before widening again for many years to come.

So this spring, we have one really good last chance to go satellite hunting close to Saturn. As many as eight of Saturn’s moons (out of the 62 known) are within reach of advanced amateurs. How many are on your life list? Now’s the time to push for perhaps one or two more.

Easiest is big, bright Titan, magnitude 8.3 for much of the spring. It always hovers within four ring-lengths of the planet. A 60-millimeter refractor usually shows it.

The next three counting inward are Rhea, Dione, and Tethys, magnitudes 9.7, 10.4, and 10.2. These are stan-dard pickups in a 6-inch scope, though Tethys, close to Saturn’s glare, may require some careful looking.

Saturn, glowing yellow Much tougher is Enceladus, magnitude 11.7 and buried deeper in Saturn’s glare. I’ve barely glimpsed it with my 6-inch, but it’s a fairly routine catch in my 12.5-inch.

You can determine where each of these fi ve satellites appears at any time in May, and which is which, by using the wavy-line diagram at far right. Its counterpart for April is in last month’s issue, page 47.

From here on, things get trickier.

Iapetus Far Out . . .Missing from the diagram is Iapetus, though it’s often easy to spot in amateur scopes. That’s because Iapetus ranges much farther from Saturn and has an orbit that’s tipped out of the orbital plane of the fi rst fi ve moons.

Iapetus is Saturn’s oddball in another way. Its lead-ing side is darker than dark chocolate, and its trailing side is mostly covered with bright ice. So when Iapetus is farthest west of the planet, it shines at an easy magni-tude 10.3, but when it’s farthest east, it’s a lot harder at 11.7. Once you’re used to fi nding Iapetus on one side, its brightness or dimness on the other side looks bizarre.

The best way to locate Iapetus is by its distance east or west of the planet. Here are its off sets from Saturn, in sec-onds of right ascension, on selected dates (at 0h Universal Time, which is on the evening of the previous date in the Americas). Interpolate to fi nd the value for when you plan to observe:

April 2, 37s east; Apr. 8, 28s east; Apr. 12, 18s east; Apr. 16,6s east; Apr. 18, directly south of Saturn by 4 Saturn diameters; Apr. 20, 6s west; Apr. 24, 18s west; Apr. 30, 31s west.

May 2, 34s west; May 8, 36s west; May 14, 31s west; May 20, 18s west; May 24, 8s

west; May 27, directly north of Saturn by 3 Saturn diameters; May 30, 8s east.

To measure this dis-tance, turn off your tele-scope’s drive and let the sky drift for the correct number of seconds. When Iapetus is east of Saturn, if follows the planet across your view. When it’s west

Titan, Rhea, Dione, Enceladus, and Tethys (counting inward) were lined up on Saturn’s western side when Ed Sampson took this stacked-video image on March 18, 2009, using a 12-inch Newtonian refl ector. The image has been brightened a bit for clarity. The rings were tilted 3° from edge on at the time, with their south face still in view. South is up in all images.

Date Dia. Ring Mag. tilt (total)

April 1 19.5″ 2.8° +0.6

May 1 19.0″ 1.9° +0.8

June 1 18.1″ 1.7° +1.0

July 1 17.2″ 2.2° +1.1

Aug. 1 16.4″ 3.3° +1.1

Dia

Dia.

19.5″

19.0″

18.1″

17.2″

16.4″

Mag.(total)

+0.6

+0.8

+1.0

+1.1

+1.1

Saturn in 2010

CC Layout May2col.indd 61 2/19/10 7:31:02 AM



Celestial Calendar

of Saturn, it precedes Saturn.Iapetus is also a little south of Saturn

for most of April, and a little north of it from the end of April through May.

Mimas Close In . . .Also omitted from the wavy-line diagram is tiny, challenging Mimas, closer in than even Enceladus. Most amateur scopes can’t show it. Mimas is 400 km in diam-eter compared to Enceladus’s 500, and it’s magnitude 12.9 compared to Enceladus’s 11.7. Worst of all, Mimas is deeper in Saturn’s overwhelming glare. I’ve never seen Mimas in my 12.5-inch, but my S&T colleague Tony Flanders has seen it in his own 12.5-inch refl ector — once in 1998 and again in 2005 when the rings were wide open! Last year, Alan Whitman of British Columbia described seeing it in his 16-inch (S&T: August 2009, page 11).

You’ll need to look less than an hour from when Mimas is at eastern or western elongation from the planet. Here are the dates (in boldface) and times (in decimals of an hour) when Mimas is at eastern (E) or western (W) elongation, in Universal Time:

April 1, 8.5h W, 19.8h E; 2, 7.1 W, 18.4h E; 3, 5.7h W, 17.0h E; 4, 4.3h W, 15.6h E; 5, 3.0h W, 14.3h E; 6, 1.6h W, 12.9h E; 7, 0.2h W, 11.5h E, 22.8h W; 8, 10.1h E, 21.4h W; 9, 8.7h E, 20.0h W;

10, 7.3h E, 18.6h W; 11, 5.9h E, 17.2h W; 12, 4.6h E, 15.9h W; 13, 3.2h E, 14.5h W; 14, 1.8h E, 13.1h W; 15, 0.4h E, 11.7h W, 23.0h E; 16, 10.3h W, 21.6h E; 17, 9.9h W, 20.2h E; 18, 7.6h W, 18.9h E; 19, 6.2h W, 17.5h E; 20, 4.8h W, 16.1h E; 21, 3.4h W, 14.7h E; 22, 2.0h W, 13.3h E; 23, 0.6h W, 11.9h E, 23.2h W; 24, 10.6h E, 21.9h W; 25, 9.2h E, 20.5h W; 26, 7.8h E, 19.1h W; 27, 6.4h E, 17.7h W; 28, 5.0h E, 16.3h W; 29, 3.6h E, 14.9h W; 30, 2.2h E, 13.5h W.

May 1, 0.9h E, 12.2h W, 23.5h E; 2, 10.8h W, 22.1h E; 3, 9.4h W, 20.7h E; 4, 8.0h W, 19.3h E; 5, 6.6h W, 17.9h E; 6, 5.3h W, 16.6h E; 7, 3.9h W, 15.2h E; 8, 2.5h W, 13.8h E; 9, 1.1h W, 12.4h E, 23.7h W; 10, 11.0h E, 22.3h W; 11, 9.7h E, 21.0h W; 12, 8.3h E, 19.6h W; 13, 6.9h E, 18.2h W; 14, 5.5h E, 16.8h W; 15, 4.1h E, 15.4h W; 16, 2.7h E, 14.0h W; 17, 1.4h E, 12.7h W; 18, 0.0h E, 11.3h W, 22.6h E; 19, 9.9h W, 21.2h E; 20, 8.5h W, 19.8h E; 21, 7.4h W, 18.5h E; 22, 5.8h W, 17.1h E; 23, 4.4h W, 15.7h E; 24, 3.0h W, 14.3h E; 25, 1.6h W, 12.9h E; 26, 0.2h W, 11.5h E, 22.8h W; 27, 10.2h E, 21.5h W; 28, 8.8h E, 20.1h W; 29, 7.4h E, 18.7h W; 30, 6.0h E, 17.3h W; 31, 4.6h E, 16.9h W.

Mimas completes an orbit in just 22.6 hours, so you should see its motion during your observing session.

. . . and Hyperion in the DarkVery diff erent is Saturn’s weird “sponge moon,” Hyperion, magnitude 14.2. It’s only a little beyond the orbit of Titan, where Saturn’s glare may still be a problem, and at that magnitude you’ll need to distin-guish it from 14th-magnitude background stars. This requires very high power and top-quality charting software from a mas-sive stellar database. But if you have a big scope and can print out such a chart for a time when Hyperion is near elongation, Alan Whitman reports that this prize catch is “much easier” than Mimas. ✦

— Alan MacRobert

EAST WEST

3

5

7

9

11

13

15

17

19

21

23

25

27

29

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

31

May 1

Enceladus

Dione

Rhea

Tethys

Titan

May 16 0h UT

Saturn’s Moons

The wavy lines represent fi ve Saturnian satellites; the central

vertical bands are Saturn and its rings. Each gray or black hori-

zontal band is one day, from 0h (upper edge of band) to 24h UT

(GMT). The ellipses at top show the actual apparent orbits.

Bright Rhea was transiting Saturn’s face, and a white spot in the Equatorial Zone was nearing the central meridian, when Damian Peach in England took this image on May 9, 2009, using a 14-inch Schmidt-Cassegrain scope. The ring tilt was 4°.

Rhea white spot

The Eta Aquarid meteor shower should be active for a few mornings around May 6th, though last-quarter moonlight will interfere. This shower is often the year’s best for the Southern Hemisphere, with 40 to 80 meteors visible per hour before dawn under ideal conditions. Fewer are seen from northerly latitudes, and essen-tially none north of about latitude 45°.

May Meteors

CC Layout May2col.indd 62 2/19/10 7:31:03 AM


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Sue FrenchDeep-Sky Wonders

The Gossamers of Coma BerenicesThe constellation north of Virgo is littered with galaxies.

cites this nursery rhyme in his book Astronomy with an Opera-Glass when describ-ing the constellation Coma Berenices, Berenice’s Hair. He writes, “Nearly on a line between Denebola and Arcturus, and somewhat nearer to the former, you will perceive a curious twinkling, as if gossamers spangled with dew-drops were entangled there. One might think the old woman of the nursery rhyme who went to sweep the cobwebs out of the sky had skipped this corner, or else that its delicate beauty had preserved it even from her housewifely instincts.”

Garrett’s gossamers comprise Melotte 111, the huge cluster of stars that diadem Berenice’s Hair. Gazing up at a clear dark sky, I can see several of its glittering gems entwined in her tresses, and dozens of stars spring forth through binoculars (S&T: May 2008, page 51).

Through a telescope, we see more evidence that the old woman left this region of the sky unswept, for it’s rife with dust-bunny galaxies. One of the most obvious bits of fl uff is NGC 4559. It lies 2° east and a bit south of yellow-orange Gamma (γ) Comae, the bright foreground star that caps Melotte 111.

Through my 105-mm (4.1-inch) refractor at 28×, NGC 4559 is an oval glow with faint stars hugging each side of its southeastern end. At 76× a dimmer star pops out at the southeastern tip. The galaxy covers about 4′ × 1½′, has a brighter core, and is slightly uneven in brightness.

NGC 4559 is very pretty through my 10-inch refl ector at 192× and spans 6½′ × 2½′. Hazy wisps reach out toward

Garrett P. Serviss

the middle and easternmost of the three stars arcing across the galaxy. A fainter strand starting north of the galaxy’s center trends north-northwest. An elusive, star-like nucleus rests at the heart of NGC 4559, and brighter spots ornament the galaxy’s face.

The magnifi cent showpiece galaxy NGC 4565 slashes the sky 2° south of NGC 4559. Its slender profi le earned this edge-on spiral the nickname of the Needle Galaxy, while some observers fondly call it Berenice’s Hair Clip.

As the brightest of the galaxies appearing at least seven times longer than wide, NGC 4565 is one of the best “fl at” galaxies for a small telescope. In my 130-mm refractor at 37×, its 9′-long streak contains a brighter area half as long with a small central bulge. At 102× the core is a fl attened oval, with a stellar nucleus and a faint star hovering over its

There was an old woman tossed up in a blanket,Seventeen times as high as the moon;Where she was going I could not but ask it,For in her hand she carried a broom.“Old woman, old woman, old woman,” quoth I;“O whither, O whither, O whither so high?”“To sweep the cobwebs from the sky,And I’ll be with you by-and-by!”

ANNE ANDERSON

The barred spiral galaxy NGC 4559 is similar in structure to our own Milky Way.

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Dust Motes in the Queen’s HairObject Type Mag. Size/Sep. RA Dec.

NGC 4559 Galaxy 10.0 10.7′ × 4.4′ 12h 36.0m +27° 58′

NGC 4565 Galaxy 9.6 15.9′ × 1.9′ 12h 36.3m +25° 59′

NGC 4725 Galaxy 9.4 10.7′ × 7.6′ 12h 50.4m +25° 30′

LoTr 5 Planetary nebula — 8.8′ 12h 55.6m +25° 54′

NGC 4274 Galaxy 10.4 6.8′ × 2.5′ 12h 19.8m +29° 37′

Hickson 61 Galaxy group 12.2–13.4 6′ 12h 12.4m +29° 12′

Angular sizes and separations are from recent catalogs. Visually, an object’s size is often smaller than the cataloged value and varies according to the aperture and magnifi cation of the viewing instrument. Right ascension and declination are for equinox 2000.0.

northeastern pole. A dusky lane is subtly charcoaled across the core and a bit beyond, skimming just northeast of the nucleus.

In my 10-inch refl ector at 192×, NGC 4565 is a beautiful sight. It bridges an

incredible 15′ of sky, and I can trace its dark lane for about 3′.

Moving 3.2° east and a little south takes us to a galaxy with remarkable structure, NGC 4725. A sharply peaked chain of sev-

eral stars points toward it from the east. The galaxy is fairly large and bright in my 105-mm scope at 28×. It features a small core with extensions northeast and south-west, all enveloped in a faint halo. A faint star dangles beneath the galaxy’s southern edge. At 87× the extensions become part of an oval haze, uneven in brightness, surrounding the core. The core itself is slightly oval and harbors a tiny, bright nucleus. All told, NGC 4725 spans about 6½′ × 4½′ with an extremely faint star pinning its edge, north of the nucleus.

My 10-inch scope at 192× nicely displays details within NGC 4725 and reveals two nearby galaxies. NGC 4275 juts into one side of a roughly 10′ rhombus of 12th-magnitude stars. The moderately faint galaxy NGC 4712 lies along the opposite side in the same fi eld of view. Its 2′ × ¾′oval holds a small oval core. Farther afi eld, NGC 4747 is 6′ north of the brightest star in the chain. This very faint streak is 2′long with a somewhat brighter center.

Those with large scopes, dark skies, and a touch of masochism might like to try for the planetary nebula Longmore-Tritton 5. It rests 52′ east by north of NGC 4747, where it surrounds an 8.9-magnitude binary star whose fainter component is the nebula’s progenitor. This planetary has extremely low surface brightness and is among the largest in our sky. It has a diameter of 8.8′ and a structure reminiscent of the Helix Nebula (NGC 7293). To catch sight of it, try low magnifi cation and an O III nebula fi lter. I’ve gazed at this phantom planetary a few

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Galaxy Cluster, roughly 60 million light-years distant. Melotte 111, the Coma Star Cluster, lies just 280 light-years from Earth.

Left: NGC 4565 is often cited as the most spectacular edge-on spiral galaxy in the sky. Right: NGC 4725 and 4712 are both barred spirals, and each is tilted roughly halfway betweeen edge-on and face-on to Earth. But NGC 4712 is more than three times farther, so it appears much smaller.

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Deep-Sky Wonders




times with 14- to 15-inch scopes and could only log it as a “maybe.” Folks with darker skies have reported success with scopes as small as 16 inches in aperture.

Now let’s move 2.1° northwest of Gamma Comae to NGC 4274. It shares the fi eld of view with NGC 4278 and NGC 4314 through my 105-mm scope at 28×. NGC 4274 is a fairly bright oval, NGC 4278 is smaller and round with a very bright nucleus, and NGC 4314 is a faint smudge. At 87× NGC 4274 is about 5½′ × 1¾′ and leans south of east. It enfolds a large oval core with a small, round, bright center. A close, unequal star pair lies 6′ south. NGC 4278 grows much brighter toward the cen-ter. A very faint star fl oats 5′ north, while the very small but fairly bright, round galaxy NGC 4283 keeps it company 3½′ east-northeast. NGC 4314 shows a bright, 2½′ spindle with a round central bulge clasping a stellar nucleus. The spindle has a very faint star near its northwestern tip and is enclosed in a tenuous halo.

NGC 4274 looks rather strange through my 10-inch scope at 192×. The oval halo seems disconnected from the sides of the core by darker ears. It’s like looking at a ghostly Saturn! There’s a diapha-nous envelope around the whole thing that quickly fades outward. NGC 4286 emerges 5′ east-northeast of NGC 4283. Its faint oval glow has a small brighter core and a dim star off its south-south-eastern tip.

Our fi nal stop is Hickson 61, resting 1.7° west of NGC 4278. Commonly known as The Box, this compact group consists

of four galaxies tightly packed into 6′ of sky. My 105-mm refractor at 87× shows three of them. NGC 4169 is the brightest. It’s tilted north-northwest and has a large oval core. NGC 4174 and NGC 4175 are very faint. The former is a small fuzz-spot tipped northeast, while the latter is larger and leans northwest. The fourth member, NGC 4173, is elusive even in my 10-inch scope. Its long, highly elongated profi le is in line with NGC 4173 and best seen with averted vision.

Odd though it may seem, NGC 4173 is

a foreground galaxy not associated with the other three. We see evidence of this in photos, where NGC 4173 looks larger, more detailed, and bluer than its chance companions on the sky. As with most of the galaxies in this tour, NGC 4173 is a member of the Virgo Cluster, centered some 60 million light-years away. The other Hickson 61 galaxies and NGC 4712 are about three times more distant. ✦

Sue French welcomes your comments at [email protected].

Both the inner arms and the outer halo of the spiral galaxy NGC 4274 appear to form ring structures around the galaxy’s core. The bright inner ring is often likened to Saturn’s rings.

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Ken Hewitt-WhiteGoing Deep

A Fine Field in BoötesThis ragtag herd of galaxies is worth corralling.

by galaxy hunters, the giant Herdsman is not without extragalactic attractions. As evidence I off er the edge-on spiral galaxy NGC 5529 in the western part of the constellation. My interest in this 11.9-magnitude wisp dates back to Sue French’s Deep-Sky Wonders column of June 2004 (page 84). Sue’s impres-sion of NGC 5529 as a “remarkably fl at galaxy” inspired me to scrutinize it with my 17.5-inch Dobsonian under a country black sky. I had no trouble fi nding the little guy less than 1° northwest of the 5th-magnitude star A Boötis. And, as often happens when one digs deep with large optics, I unearthed other subtle treasures nearby. Let’s tour the area beginning with that fl at fuzzy.

Sue reported that NGC 5529 “is one of the entries in the Revised Flat Galaxy Catalogue, a compilation of 4,236 galaxies that appear at least seven times longer than wide.” At 6.4′ × 0.7′ — a ratio of 9:1 — NGC 5529 qualifi es easily. My initial inspection of the galaxy at 83× resulted in the following statement in my logbook: “Very

Often overlooked slender and gently brighter toward the middle. Slanted northwest–southeast with a dim star off southeast tip.” At 285× I added: “Small, distinct core with some mottling.” I interpret that blotchy texture as a hint of the galaxy’s dust lane. The image on the facing page shows the dust lane cutting north of the nucleus, indicating that NGC 5529 isn’t precisely edge-on. My log entry agrees: “North edge fairly straight; south side bulges slightly.”

Two very faint galaxies hover near NGC 5529. PGC 50952, also known as MCG 6-31-87, is visible in my scope at 222× about 4′ southeast of the edge-on’s hub, as shown on the facing page. PGC 50925 (sometimes identifi ed incorrectly as NGC 5527) is an extremely diffi cult object located a similar distance southwest of the hub. Both companions are comparable in size, but while PGC 50952 has a bright core and glows at magnitude 15.3, PGC 50925 is diff use, with much lower surface brightness. When I try for the fainter galaxy, I fi rst note the 14th-magnitude star directly south of NGC 5529’s core. On the best nights,

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GD Layout May.indd 68 2/19/10 7:22:33 AM



my averted vision occasionally glimpses an exceedingly faint patch whose position relative to the star and the other two galaxies matches what I see in images. Con-sider PGC 50925 your challenge of the night!

Eagle-eyed observers might pick up three other small fry in the same high-power fi eld. Two of the galaxies, PGC 2076761 and PGC 2076843, lie close together 4′ east of NGC 5529. I only recently noticed these tiny targets on photographs and haven’t yet attempted them telescopi-cally, but they seem brighter than the aforementioned PGC 50952. They’ll likely appear stellar unless high mag-nifi cation is applied. Another midget is 15th-magnitude PGC 50944 (MCG 6-31-86), almost 9′ north of NGC 5529. This pale blob fl ickers on and off in my optics at 285×, east-northeast of a 10th-magnitude star.

Less than ½° northeast of NGC 5529 is a compact galaxy pair I call “the comet.” NGC 5544 and NGC 5545 (together known as Arp 199) make a pretty picture: NGC 5544 is a yellowish, face-on barred spiral partly overlapped by NGC 5545, a bluish, nearly edge-on spiral. At 83× this tight twosome is just an irregularly-shaped nebulosity, but 285× reveals a binary galaxy oriented northeast-south-west. NGC 5544 glows at magnitude 13.4 and exhibits an obvious core inside a 1′-diameter halo. NGC 5545 is about 1 magnitude dimmer and elongated 1.0′ × 0.3′ — a faint “tail” fl owing away from the bright “head” formed by NGC 5544. Delightful!

Your scope can sweep up three additional NGC galaxies within ¾° of

the “comet.” The most prominent of these is 11.0-magni-tude NGC 5557, whose 2.3′ × 1.9′ halo surrounds a bright core and nucleus. At 285× I see a dim star in the halo southeast of the core. Also in the region are 14.2-mag-nitude NGC 5572 and 13.8-magnitude NGC 5527. The latter object is labeled NGC 5524 on most star charts, but in a note on the NGC/IC Project website (www.ngcicpro-ject.org), Harold G. Corwin, Jr. argues that NGC 5527, the name sometimes given to faint PGC 50925, should apply to this much more prominent galaxy. According to Cor-win, NGC 5524 is likely a faint double star mistaken for a galaxy by Lord Rosse while observing NGC 5529 through his 72-inch refl ector in 1855. ✦

Ken Hewitt-White hunts galaxies from western Canada.

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GD Layout May.indd 69 2/19/10 7:22:36 AM



Gary SeronikTelescope Workshop

A Small Dob SolutionThe smaller the scope, the trickier the mount.

most interesting homemade telescopes marry tried-and-true designs with recent innovations — sort of a scenario where Jean Texereau meets John Dobson. That was my fi rst thought when I saw Wichita Falls, Texas, ATM Arthur Gamble’s nifty 6-inch f/5 refractor. Although its resemblance to the scopes appearing in Texereau’s classic volume, How to Make a Telescope, is more superfi cial than actual, the Dobsonian touches are real and very useful.

Art’s telescope uses a short-focus, air-spaced achro-matic objective lens sold by the New York fi rm A. Jae-gers, Jr. Optics, Inc. (www.ajaegers.com). But the scope’s design has several features that can be utilized in a wide range of instruments, from small refractors to short-focus

Some of today’s Newtonians. And it’s with the latter that I think Art’s mount has its greatest utility.

As anyone who has made a small Dobsonian knows, such an instrument’s dimensions and light weight can create problems. First, the scope’s focuser is usually located uncomfortably close to the ground. If you build a standard rocker box, you’ll fi nd yourself either kneeling to peer into the eyepiece or setting up the scope on a table. Neither situation is ideal.

Second, the scope’s balance point changes dramati-cally depending on the weight of the eyepiece. This is because the mass of the eyepiece is proportionally more signifi cant in a lightweight scope than in a heavy one. For example, swapping a 3-ounce Plössl for a 1½-pound wide-fi eld eyepiece doesn’t necessarily change the balance of a 50-pound instrument, but it will cause a 5-pound scope to nosedive! Art’s mount solves both issues elegantly.

The low-focuser issue is neatly addressed with a rigid tripod that elevates the rocker box to a comfortable viewing height. Art’s plywood tripod consists of three identical legs, and a triangular piece on top. The result is both functional and undeniably stylish. And thanks to its fi xed-height, non-folding design, he was able to avoid the sorts of complications that typically make building a tripod such an involved exercise.

To tackle the balance problem, Art used a three-way attack. “First, I tried to even out the weights of my eye-pieces by machining a steel adapter to make the lighter eyepieces match the weight of the heavier ones,” he explains. “Second, for the altitude bearings, which are riding on Tefl on pads, I chose PVC in place of Ebony Star Laminate to increase the friction. Third, I built a set of adjustable clamps to further control the altitude motion.”

These clamps are key to preventing the scope from being overly sensitive to changes in balance. As the photo on the next page shows, each altitude-bearing assembly has a ½-inch-wide strip of 1/8-inch-thick steel bent into a curve. This component forces two Tefl on buttons against the PVC bearing from above. By adjusting two knurled nuts, Art is able to set the friction of the altitude bearings precisely, for just the right resistance and feel. You can make the clamp with wood if working with steel doesn’t appeal to you.

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Arthur Gamble’s attractive 6-inch f/5 refractor has a modifi ed Dobsonian mount that can also carry a host of other instruments, including 4- and 6-inch Newtonian refl ectors.

TW Layout May.indd 70 2/19/10 7:36:18 AM


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Although good looks and functionality are not neces-sarily related, over the years I’ve noted that builders who take the time to make their scopes attractive usually spend extra eff ort to ensure their scopes work well too. Art’s refractor is certainly a good example of this. I was curious how he obtained the fi ne fi nish. As he explains, “I used three coats of a high-gloss acrylic enamel — basi-cally an interior trim paint. I applied the paint with 3- and

4-inch mini rollers, which produces a nice textured fi nish that’s very durable and easy to touch-up if damaged.”

Nicely done. I have a feeling that Jean Texereau would be impressed. ✦

Contributing editor Gary Seronik builds scopes and observes the night sky at his home in Victoria, British Columbia, Canada. He can be contacted through www.garyseronik.com.

Far Left: The scope’s altitude bearings include a variable friction adjustment that’s described in the accompanying text.

Left: A sturdy, fi xed-height tripod supports the rocker box and elevates the eyepiece to a comfortable height.

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Layered deconvolution adds depth to your astro-images.

Innovative Image Processing

always strive to capture the most detailed and colorful images possible with their equipment. While most of us don’t shoot from mountain-tops with subarcsecond seeing, we still manage to take noteworthy pictures. Local atmospheric conditions, imper-fect guiding, wind buff eting, and other problems blur our images, obscuring small-scale details, bloating stars, and making our pictures look fl at or out of focus. Fortunately, modern image-processing techniques, particularly decon-volution, can compensate for many of these defi ciencies. The trick is learning how to use them eff ectively.

Perhaps the most powerful digital tools available today are the various deconvolution algorithms included in many astronomical post-processing software programs. Deconvolution is a mathematical process used to sharpen images based on known values, such as the theoreti-cal brightness profi le of a perfect star image. Deep-sky

astrophotos respond particularly well to deconvolution. Software can measure the amount of blur in a star image (known as the point spread function, or PSF), and use this to deconstruct the view and then reassemble it based upon the PSF, resulting in a much sharper image.

The problem with deconvolution from an aesthetic perspective is that it attacks the entire image. If I want to really dig out the very smallest details in my photos of galaxies or nebulae using a strong deconvolution setting,

Above: Taking highly detailed astrophotos with large telescopes is a challenge. To get the most out of his images, Ken Crawford uses a novel technique he calls multi-strength deconvolution layer blend (MSDLB). Crawford recorded this stunning picture of NGC 891 with his 20-inch Ritchey-Chrétien telescope and an Apogee Alta U9000 CCD camera, and then he processed it using his MSDLB technique. All images are courtesy of the author.

Astrophotographers

Digging OutDetailsthe KEN CRAWFORD

Details Layout.indd 72 2/19/10 7:25:20 AM


the algorithm will add artifacts to the brighter stars, and it will greatly enhance any noise in the background. I’ve developed an easy method in Adobe Photoshop I call multi-strength deconvolution layer blend (MSDLB) to reduce these adverse eff ects. This technique allows me to aggres-sively sharpen my images without introducing artifacts that can be misinterpreted as real features.

Processing in CCDStackAfter I’ve captured, calibrated, and combined all of my data into their various red, green, blue, and luminance images, I start my process with the luminance image. This is where the majority of the contrast and detail resides in a digital color photo. I prefer to use the software CCDStack (www.ccdware.com) to combine, deconvolve, and stretch my images before bringing them into Photo-shop, but the end result will be the same if you use your favorite CCD processing software.

In CCDStack I pull down the Process > Deconvolve action, which opens the deconvolve window. I then select the Positive Constraint function, and set the number of iterations to about 30. CCDStack measures the PSF of the stars by having you simply click on one; you should avoid choosing the brightest stars in your image, because they can be saturated, which results in an inaccurate PSF value. As soon as you click on a star, an information window opens that lists measurements of the point — the most important is the full-width, half-maximum (FWHM). This measurement refl ects how much of a star’s light is con-centrated in its Airy disk. The larger the number, the more bloated and soft stars will appear.

I often select a few stars of about the same brightness to make sure the FWHM is similar in each, and then I click the Deconvolve button. This action slightly tightens the medium-brightness stars and faint, tiny galaxies in the background. The idea is to make this deconvolution process mild enough so that it doesn’t introduce noise in the background or artifacts to the bright stars. I then save this result as a new 32-bit FIT fi le. Next, I return to the original luminance fi le and apply the same Positive Constraint deconvolution, this time performing 75 to 150 iterations, until I see major improvement in the small details in the galaxy itself; the brighter stars will start showing artifacts such as bright edges and darker centers. I can correct this later. When fi nished, I save this result as a new 32-bit FIT fi le so that I now have three luminance frames: the original, one with mild deconvolution, and another with aggressive sharpening.

My next step is to perform a non-linear stretch to each deconvoluted fi le using the DDP (Digital Development Process) function. This step compresses the dynamic range of the images so that the faintest objects and bright-est areas of the images can be displayed simultaneously. DDP can actually be displayed in CCDStack throughout the entire process by keeping the Adjust Display window

Above: Once you combine all the data for a luminance image in CCDStack, apply deconvolution to reduce the “fuzzy” appearance of stars and sharpen detail in the subject. You can do this with the Process > Deconvolve pulldown menu, and by clicking a medium-brightness star to measure its full-width, half-maximum (FWHM) as a reference.

These two crops of NGC 891 show the diff erence between a mild applica-tion of deconvolution (in this case, 30 iterations) in the top image, and an aggressive application of the technique at bottom. The latter method greatly increases details in the galaxy’s dust lanes, but at the expense of creating bright rims and dark centers in most stars throughout the image.




open and by clicking the DDP and Apply to All boxes. These changes aren’t applied permanently to the images until they are saved as scaled data using the pulldown menu File > Save scaled data, then selecting the “All” option. I always save these two scaled images as 16-bit TIFF fi les so they can be opened in Adobe Photoshop CS.

Blending It All TogetherThe idea behind MSDLB is to blend both deconvolved luminance images into one master luminance to take advantage of the smoothness and tight stars in the mildly deconvolved version and the sharp detail of the aggres-sively deconvolved photo.

I begin by copying the heavily sharpened photo and pasting it onto the mild version. You do this on a PC by fi rst selecting the aggressively deconvolved image and holding down the Ctrl and A keys, then the Ctrl and C keys to copy all. Next, click your mildly sharpened image and hold the Ctrl and V keys to paste the earlier image onto it as a new layer. I now have one fi le with two layers of data that I’ll save as a Photoshop Document (PSD).

To blend these images together, I open the layer window (Window > Layers) then click on Layer 1. Next, I apply the pulldown option Layer > Layer Mask > Hide All. This makes a layer mask that appears completely black next to the thumbnail of layer 1, and hides everything on that layer. To reveal selective parts of the heavily decon-volved layer, I click on the new mask to the right of layer 1, and select the brush tool from Photoshop’s tool palette. Then I’ll chose the brush radius and start “painting” on my image in the places that I’d like to reveal. I should note that I don’t use a feathered brush tool, because I prefer to control the edges of my mask using Photoshop’s Blur func-

Left: Combining the two deconvolved images in Adobe Photoshop CS requires the use of layer masks. Once the aggressively deconvolved image is pasted on top of the mild version as a new layer, you use the pulldown action Layer > Layer Mask > Hide All to conceal the top layer. Right: A “hide all” layer mask needs to have the areas you wish to reveal “painted” in. The mask above has been painted white in the areas of the galaxy to be sharpened. Over-sharpened stars that are revealed can be hidden again by painting black spots over them in the mask. Blending between the two layers can be varied by blurring the mask.

tions. Like magic, the sharpened regions start to appear wherever I paint onto my mask. When I’m satisfi ed with this mask, I apply the Gaussian Blur fi lter to smooth the transition between the layers.

One tool I would highly recommend for any “digital darkroom” is a Wacom Intuos tablet (www.wacom.com/intuos). This tool off ers a very high degree of control for most Photoshop applications, such as painting masks or creating complex selections; it’s used just like a pencil on a pad of paper.

If I accidentally paint an area in the mask that reveals over-sharpened stars, it’s easy to fi x by changing the color of the brush tool from white to black (done by clicking the small arrow icon at the bottom of the tools palette). This reverses the background and foreground colors, which on a grayscale image are white foreground and black back-ground by default. I then paint a circle over the stars I’d like to hide, changing the radius of the brush tool as needed to accommodate smaller stars. To see the entire mask, I hold the ALT key while clicking on the mask thumbnail.

Once I’m happy with this fi le, I simply save it as it is and then create additional adjustment layers to control brightness and contrast, curves, and additional sharp-ening. The beauty of working with layer masks is that everything is contained in a single fi le, yet the original image is not changed.

To combine the processed image with my color image,


Author Ken Crawford shares many innovative imaging techniques in a number of step-by-step video tutorials on his website: www.imaging-deepsky.com/Presentations.html.

use DD6a Befo-reMSDLB.tif

Innovative Image Processing




I fi rst fl atten the layers by selecting the pulldown menu Layer > Flatten Image, then I copy this image and paste the result onto my color fi le, switching the layer option from normal to luminosity. A similar technique can be used on tri-color narrowband images by combining each fi ltered image into a single luminance fi le. This would be processed exactly as described here, then pasted into the color fi le the same way.

Digging out very small details in images with MSDLB requires patience and the right fi lters and masks. Once

you have these methods down, you can selectively apply almost any fi lter or blending mode. These tools can be used like a surgeon’s knife or a blacksmith’s hammer, so remember to save changes as you go, and go slowly. Start digging out the details in your images using this easy method and leave the noise and artifacts behind. ✦

Ken Crawford is the president of the Advanced Imaging Conference (www.aicccd.com), held each year in San Jose, California. See his images at www.imagingdeepsky.com.

Crawford’s MSDLB technique combines the best areas of each image. The left photo shows the grayscale view of his data without any deconvolution, while the version on the right displays his fi nal results.

The MSDLB technique can be applied to most deep-sky astrophotos, including tri-color narrow-band images. The author recorded this colorful narrowband photo of the Tarantula Nebula (NGC 2070) from his second obser-vatory, located in Moorook, Australia.



Sean WalkerGallery


◀ POSEIDON’S VIEWChris Kotsiopoulos The Moon appears to take a bite out of the Sun over the ancient Temple of Poseidon in Sounion, Greece, during the annular eclipse last January 15th.Details: Skywatcher PRO 80 ED APO Refractor and Canon Digital Rebel XTi DSLR camera. Exposure was ½ 000 at f/7.5, ISO 100.

GAL Layout May.indd 76 2/22/10 9:24:57 AM


▴ 2009 LOOP OF VENUSTunç TezelThis digital composite of 26 images follows Venus as it traced a retro-grade loop across the constellation Pisces during the fi rst half of 2009. Details: Canon EOS 5D DSLR camera with 50mm lens.

◀ THE VIEW FROM ABOVEGreg Merkel and classmatesStudents attending the University of Minnesota’s Spacefl ight with Ballooning class launched a weather balloon containing several upper-atmosphere experiments, including a digital camera programmed to snap pictures every 30 seconds. This photo records the curvature of Earth from roughly 118,000 feet (36 kilometers).Details: Canon PowerShot A570 IS digital camera. Exposure was 1/1250 second at f/2.6, ISO 80.


Gallery showcases the fi nest astronomical images submitted to us by our readers. Send your very best shots to [email protected]. We pay $50 for each published photo. See SkyandTelescope.com/aboutsky/guidelines.

◀ THE CLOUDS OF MARSDonald C. ParkerThe red planet presented observers with wispy equatorial clouds and a persistent dust storm over the north polar cap (bottom) in this image captured shortly before opposition last January.Details: 16-inch Newtonian refractor with Lumenera SKYnyx 2-0 video camera.

▶ SHADOW PLAYTed KayserSunlight fi ltering through tree leaves produced hundreds of tiny images on the ground in Kampala, Uganda, during January’s annular solar eclipse.Details: Nikon Coolpix L18 digital camera.




Gallery

COLORFUL CEDERBLAD 214Eric AfricaThis 2½ ° patch of gas and dust in Cepheus is cataloged as Cederblad 214 at top, and NGC 7822 below, though both are actually brighter areas of the same nebulous cloud. South is up in this photo.Details: Takahashi FSQ-106N astro-graph with SBIG STL-6303E CCD camera. Total exposure time is 20 hours through Astrodon Hα, O III, and S II narrowband fi lters. ✦




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Index to Advertisers

IN THE NEXT ISSUE

Hubble at 20The Hubble Space Telescope has transformed astronomy during its two decades on orbit.

Observing Planetary NebulaeThe death shrouds of solar-type stars off er vivid deep-sky targets.

Deep-Sky DiscoveryAn amateur planetary nebula fi nding shows that interesting deep-sky objects remain undiscovered.

The New Western FrontierAn observer’s guide to some of the best astronomy hotspots in the Southwestern U.S.

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ITNI Layout May10.indd 85 3/4/10 8:37:14 AM



Focal Point Constance E. Walker

Our Light or Starlight?Children can play key roles in raising awareness about light pollution.

The arc of the Milky Way seen from a truly dark location is part of our planet’s natural heritage. But with half of the world’s population now living in cities, many urban dwellers have never experi-enced the wonderment of pristinely dark skies and maybe never will. So, how do you explain to them the importance of what they’ve lost to artifi cial skyglow? How can you make them aware that light pollution is a concern on many fronts: safety, energy conservation, cost, health, eff ects on wildlife, as well as our ability to view the stars? How do you convince them that it’s worthwhile to take steps, even small ones, to help redress this issue?

In preparing for the International Year of Astronomy (IYA2009), the Dark Skies Awareness (DSA) Working Group and I, as its chair, wrestled with these questions. (DSA was 1 of 12 global cornerstone proj-ects for IYA2009.) Ultimately, I’ve come to think that to infl uence cultural change eff ectively — to make people literally look up and see the light — we must make children a main focus and use approaches that off er cursory to committed involve-ment. We must make the programs and resources as turnkey as possible, espe-cially for educators, and provide ways to visualize the problem with simple, easy-to-grasp, and enjoyable activities.

As I watched IYA2009 unfold, I was astounded by the large number of people worldwide who became involved in DSA, and also by the creativity of these people. Their eff orts sparked a revolution in their communities — motivated by some aspect of a DSA program but fueled by their inge-nuity and sweat.

In one instance, this revolution was the outcome of simply providing a dark-skies kit to a teacher in Chile, as part of a well-

organized eff ort through the Cerro Tololo Inter-American Observatory to work with schools in regions near astronomical sites. A book included in the kit, Bob Crelin’s There Once Was a Sky Full of Stars, struck a chord with her students. The students translated the book and made one of the best dark-skies videos from a child’s perspective that I have ever seen. You can fi nd the video (with English subtitles) at http://is.gd/7wuvP.

In another instance, creativity fl ew off the Richter scale. It all started with preparations in advance of last year’s

Globe at Night campaign (www.globeat night.org), which encourages people all over the world to record and report the brightness of their night sky by match-ing Orion’s appearance with star maps of progressively fainter stars. One Indiana school district took this simple concept to a whole new level. Thousands of its students observed Orion from their back-yards — amassing 20% of the 2009 Globe at Night data. But they did not stop there. They next asked: how much of our night sky have we lost?

To fi nd the answer, the students visual-ized the sky with a 3-D model of their Globe at Night sky measurements. They fi rst stacked 35,000 LEGO® blocks to represent a pristinely dark sky in which thousands of stars could be seen, and then they took away 12,000 blocks according to their Globe at Night sky measurements. What remained corresponded to a sky nine times brighter than the truly dark ideal. The students presented their fi nd-ings to local leaders and were honored for their eff orts (visit www.LetThereBeNight.com for details).

Countless individuals around the world have contributed toward preserving dark skies by raising public awareness, either through their own grassroots eff orts or through the DSA programs, many of which will continue beyond IYA2009. See-ing their eff orts bear fruit will take time, but ultimately they’ll have lasting eff ects. Perhaps this year you too will choose star-light over our light. ✦

An astronomer by training, Connie Walkerserves as the Senior Science Education Spe-cialist for the National Optical Astronomy Observatory in Tucson, Arizona. Learn more at www.darkskiesawareness.org.

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