Radio Astronomy

UW Campus ObservatoryBuilt in 1892Located on 4th and University StMoved in 1895 to the current locationSecond Building on campus next to denny hall

Telescope6-inch Brashear objective lens Warner & Swasey equatorial mount 90-inch focal length Warner & Swasey wooden , rests on 3 civil war era cannon balls!

Visible World

Electromagnetic spectrumElectromagnetic radiationThe visible world (We see very little!)Radio spectrumX-ray, UV,IR spectrum

History of Radio AstronomySerendipity?Karl Jansky 1928Rotating Telescope

History of Radio AstronomyGrote Reber -19379 meter dish antennaImage courtesy NRAO

Radio Sources21-cm Neutral Hydrogen Lines21-cm photonHigh Energy State

Low energy state

Radio Sources21-cm Neutral Hydrogen linesDiscoveryEmission once in few million years80% Hydrogen in Universe21-cm emission not obstructed by dustUsed to map galaxies and ISM

Harold Irving Ewen 1951

Milky Way in 21cmImage courtesy of NRAO/AUI

M33 Radio and Optical CompositeImage courtesy of NRAO/AUI and NOAO/AURA/NSF

Orion Nebula M42Image courtesy of NRAO/AUI

Radio SourcesPulsarsDiscovered in 1967Rapidly rotating neutron star10-15 km radiusCosmic clocks in the skyFirst thought to be a signal from aliens (little green men)

Image courtesy Jodrell Bank Pulsar Group

Sounds of PulsarsPSR B0329+54

PSR B1937+21

PSR B0531+21, The Crab Pulsar

47 Tucanae

Image and sound courtesy Jodrell Bank Pulsar Group

Pulsar and Supernova RemnantImage courtesy of NRAO/AUI

Crab Nebula PulsarImage Courtesy J. Hester (ASU), CXC, HST, NRAO, NSF, NASA

Radio Sources QuasarsQuasar : Quasi- stellar radio sourceMost distant object to emit radio wavesContain super massive black holes in the centerRadio emission produced by synchrotron radiationReflect the stage of universe billions of years ago

QuasarImage courtesy of NRAO/AUI

Radio Sources MASERSDense molecular clouds with strong emission (T > 106 K)MASER actionMicrowave Amplification by Stimulated Emission of RadiationOH,H2O,SiO, CH3CH2OH and more

Water MASERImage courtesy of NRAO/AUI

Radio SourcesCosmic Microwave Background RadiationArno Penzias and Robert Wilson 1963

Robert Wilson on cosmic noiseImage and sound courtesy Lucent Technologies Inc.

Cosmic Microwave Background RadiationCOBEThe COBE datasets were developed by the NASA Goddard Space Flight Center under the guidance of the COBE Science Working Group and were provided by the NSSDC.

Radio Sources SunImage courtesy of NRAO/AUI

Radio Sources PlanetsSaturnJupiter during impact of comet Shoemaker-Levy 9Image courtesy of NRAO/AUI

Radio Telescopes AreciboLocated in Puerto RicoOperated by Cornell and NSF1000 ft (304.8 m)Used for Astronomy, atmospheric and planetary studies

Radio Telescopes Green Bank TelescopeLocated in Green bank, West Virginia485 feet tall -- taller than the Statue of Liberty!100 by 110 m widthWorlds Largest steerable radio telescope

Image courtesy of NRAO/AUI

Radio TelescopesVLI (Very Large Array)Located in Socorro, NM27 antennas interferometerEach antenna 25 meters( 82 feet) in diameter

Image courtesy of NRAO/AUI

VLBI (Very Large Baseline Array)

ALMA The Atacama Large Millimeter Array

Atacama desert, Chile64 radio telescopes12 meter (39 feet) wide dish antennaExpected to operate in 2011

Image courtesy of NRAO/AUI

Radio Telescopes around the worldEuropeWesterbork Synthesis Radio Telescope (WSRT) , NetherlandsThe Ryle Telescope, United KingdomAustraliaMopra Observatory AsiaGiant Meterwave Radio Telescope(GMRT) , IndiaNobeyama millimeter array ,Japan

Radio Astronomy at UWUAI established in 19997ft dish Currently building motion control and receivers for 21cm hydrogen lines (1420 MHz)

Future of Radio AstronomyMore cost to build radio telescopesConsortium among countries to build future telescopes

Major advancements in telescope technologiesBetter design to control noise over effective areaGMRT,ALMABetter angular resolutionEncroachment of radio frequencies by ground and satellite communicationsMore power in deciding frequency allocationsBetter modulation techniques to prevent spill over

The EndQuestions ?

Thank You

*Telescope built in 1892 from the state budget of $3000.Moved to current campus when UW moves from downtown to across the lake in the current campusBuilt from the leftover sandstone from the denny hall the first building in the campus.The observatory is the second oldest building in the campus.*The telescope is a 6 inch refractor ,not a big one but settled for this with the available budget $!The telescope is equatorial mount and has mechanical drive system.Works at f/15 and has 90inch focal lengthThe wooden dome is built from wood more than 100 years back. The dome rests on 3 civil war ear cannon balls!!. They work so well even today.

*This is an image of the andromeda our companion galaxy.What we see is spectacular but do we see everything in there? There is much more to this image than what we think.We are blind to certain wavelengths and lets explore about it in the coming slides.*The Image above is the electromagnetic spectrum . Light is an electromagnetic radiation like heat and X-rays traveling at 300,000 Km/s .The visible part of the spectrum is from V 40 millionth of a centimeter to red 70 millionth of a centimeter.Note: A wavelength is the distance from peak to peak in the signal The radio waves have wavelengths from 1mm to hundreds of meter.Microwave have few cm wavelengthsX-ray has very short wavelengths , extremely small that they literally wriggle between atoms and so can penetrate our bodies.

*Karl Jansky, working at Bell Telephone Laboratories in Holmdel, NJ, in 1928, wanted to investigate using "short waves" (wavelengths of about 10-20 meters) for transatlantic radio telephone service.For mere $75 one can speak for 3 min from New York to London. Jansky was assigned the job of investigating the sources of static that might interfere with radio voice transmissions. He built this antenna to receive radio waves at a frequency of 20.5 MHz (wavelength about 14.5 meters). It was mounted on a turntable that allowed it to rotate in any direction, earning it the name "Jansky's merry-go-round". By rotating the antenna, one could find what the direction was to any radio signal. Janksy used this antenna to identify radiation coming from the Milky Way that was strongest in the direction of the center of our Milky Way galaxy, in the constellation of Sagittarius. Serendipitous discovery are made by accident but also by wisdom. That was the case for radio astronomy.*Grote Reber , professional engineer and radio ham in his spare time ,was one of the few people who recognized the interesting implications of janskys discovery. He was not hampered by the astronomical prejudices about whether or not cosmic radio wave exist. He built is own radio telescope (first steerable dish antenna)in his backyard and mapped the milky way galaxy during the persiod (1935-1941).During this period the radio astronomy was caught between two disciplines, Radio engineeers who didnt care where the radio waves came from and the astronomers . Couldnt dream up any rational way by which the radio waves could be generated and since they didnt know of a process, the whole affair was ( considered by them) at best a mistake and at worst a hoax.*Hydrogen is formed in the very first stages of the formation of the universe.They are responsible for producing energy in the stars and galaxies.But hydrogen also prevalent in the vast cooler ISM of the universe.Such hydrogen will be in a state neutral state HI as opposed to HII state in dense hotter regions.During World war II, scientist in occupied Holland had a meeting and one of the important thing came out of it was the unique properties of the neutral hydrogen and it might transmit a detectable radio waves.They were unaware of janskys and Rebers experiment across the atlantic at that time. The neutral hydrogen has two states , one in which both the electron and proton has same spin (parallel) ,a higher energy state and electron and proton in anti parallel spin, low energy state. Every million years the electron flips the spin and change to low energy state releasing the energy as radio waves of wave length 21cm corresponding to 1420 MHz signal. Though this a rare process, so much hydrogen is there in the space that it is enough to detect this lines.*In 1950, H. I. ("Doc") Ewen was working 40 hours a week designing and building apparatus for the new cyclotron at Harvard. In addition, during nights and weekends, he was working on completing a doctorate in physics by building a receiver to detect the 21 cm line of neutral hydrogen, supervised by Purcell. The original paper by Van de Hulst predicting the existence of the 21 cm line expressed doubt that the line would be detectable. A paper by Shklovski in 1948 was more optimistic. Ewen and Purcell assumed that the Dutch were probably not working on detecting the line and that the Russians might soon be. They could probably make the first sensitive detection attempt. It seemed likely that the experiment would yield a negative result, but the experience would be worth the trouble and a well defined upper limit to the 21 cm line emission strength would be important. Ewen proceeded to design the horn antenna and the mixer and receiver, consulting with experts in these fields, including Sam Silver on antenna design and Bob Pound on mixers. The receiver used a frequency switching technique to cancel out background noise, a novel technique for astronomy at the time. Ewen installed the completed horn antenna just outside a window on the fourth floor of the Lyman Lab at Harvard, with the waveguide leading in through the window to the receiver and recorder. He had to contend with some unexpected hazards. In a heavy rain, the horn antenna acted as a funnel, flooding the lab, when the drain became plugged up. Also, during the winter, passing students found the horn a tempting target for snowballs. The whole project, from receipt of the $500 to detection of the line, took one year. Since the work was done on the weekends, the total time spent working on the project was (2/7)x12 = 3.4 months.

*This figure shows the distribution of atomic hydrogen at all locations in the sky. All of this hydrogen is in our galaxy. Red indicates directions of high hydrogen density, blue and black show areas with little hydrogen. The figure is centered on the galactic center and galactic longitude increases to the left. The data came from measurements of the 21cm line of hydrogen by radio telescopes. Some of the hydrogen loops outline old supernova remnants. This image is a composite from many 21cm surveys. It includes data from the NRAO Green Bank, West Virginia 140- foot and 300-foot telescopes, the 85-foot Hat Creek Telescope of The University of California at Berkeley, The AT&T Bell-Labs Horn-Reflector Telescope at Holmdel, New Jersey and The 60-foot Telescope at the Parkes Radio Observatory in Australia. *This image of the Triangulum Galaxy was created by combining optical data from the National Science Foundation's 0.9-meter telescope on Kitt Peak in Arizona with radio data from the National Science Foundation's Very Large Array (VLA) telescope in New Mexico and the Westerbork Synthesis Radio Telescope (WSRT) in the Netherlands. Also known as M33, the Triangulum Galaxy is part of the Local Group of galaxies, which includes the Andromeda Galaxy (M31) and our galaxy, the Milky Way. M33 is over thirty thousand light years across, and more than two million light years away. The optical data in this image show the many stars within the galaxy as well as reddish star forming regions that are filled with hot Hydrogen gas. The radio data reveal the cool Hydrogen gas within the galaxy, gas which cannot be seen with an optical telescope. Combined together, the radio and optical give a more comprehensive view of star formation in this galaxy. The color image was generated by combining images taken with the 0.9-meter telescope through four filters (B, V, I and Hydrogen-alpha) and 21cm neutral Hydrogen data taken with the VLA and WSRT (shown in blue-violet).

*Unlike optical and ultraviolet images in which extinction by dust affect interpretation of optical images and in which a considerable fraction of the continuum emission is due to dust-scattered light, this image shows a true distribution of ionized gas. This picture shows the Trapezium region in red and its immediate surroundings such as the ionized "bar". *The wobbling (or precession) causes the rotation axis of the pulsar to follow a circle-like motion in time (see yellow and green axes at different epochs). The motion is very much like the wobble of a top or gyroscope. As a result, we see the cone-like lighthouse beam of the radio pulsar under different angles, resulting in the observed changes in pulse shape and arrival times. (Image by M. Kramer) A pulsar is a highly magnetised neutron star, with a radius of 10-15 km, having somewhat greater mass than the Sun which has a radius of approximately 1 million km. Radiation is beamed out along the magnetic poles and pulses of radiation are received as the beam crosses the Earth, in the same manner as the beam from a lighthouse causes flashes. Being enormous cosmic flywheels with a tick attached, they make some of the best clocks known to mankind.

Interesting facts:First thought to be a signal from aliens ( extraterrestrial origin). The first 5 pulsars detected were called signals from little green men.

Pulsar was detected because of a remarkable persistence on the part of Jocelyn bell , a graduate student at cambridge university in England.She has to study 400 feet of charts everyday.She has to compare with baseline signal on the chart.Cambridge was susceptible to noise from automobiles.She became expert after studying 400 feet of chart everyday and soon was able to identify noise from automobiles.She then found lil bit of scruff which repeats precisely and definitely not the noise she had known and it didnt go away.Interestingly they appeared 4 min earlier every day.They needed very accurate clock to keep up with its ticks.

*PSR B0329+54 This pulsar is a typical, normal pulsar, rotating with a period of 0.714519 seconds, i.e. close to 1.40 rotations/sec.

PSR B0531+21, The Crab Pulsar This is the youngest known pulsar and lies at the centre of the Crab Nebula, the supernova remnant of its birth explosion, which was witnessed by Europeans and Chinese in the year 1054 A.D. as a day-time light in the sky. The pulsar rotates about 30 times a second.

PSR B1937+21 This is the fastest known pulsar, rotating with a period of 0.00155780644887275 seconds, or about 642 times a second. The surface of this star is moving at about 1/7 of the velocity of light and illustrates the enormous gravitational forces which prevent it flying apart due to the immense centrifugal forces.

The Pulsars in 47 Tucanae This beautiful globular cluster harbours 22 millisecond pulsars with periods between 2 and 8 ms. Many of them have a binary companion. We can estimate that hundreds more of these objects are in the cluster, but they may be too weak to be detected. The first sound file is a sequence of 16 of the known millisecond pulsars followed by them all played together.

*Color representation of radio emission from the supernova remnant G5.4-1.2 (large scale image) and the associated pulsar B1757-24 (insets). Blue indicates fainter radio emission, yellow and orange more intense radio emission. The supernova remnant lies 15,000 light-years away in the constellation Sagittarius. The pulsar has travelled outside the shell of debris from the supernova explosion that created it. The pulsar and the shell together are dubbed "The Duck," because of their unusual appearance. Stars much more massive than the Sun end their normal lives in violent supernova explosions, leaving behind an extremely dense neutron star. Some of these neutron stars produce the beams of electromagnetic radiation that characterize pulsars. For the pulsar B1757-24 to have travelled from the center of the supernova remnant to its present position in 16,000 years, it would have to be moving at about 1,000 miles per second, a particularly high speed compared to other pulsars. By comparing images taken with the VLA in 1993 and 1999, scientists were able to measure the pulsar's change in position over a known time, and thus to calculate its speed. They were surprised to find the pulsar moves at a maximum of about 350 miles per second. This means the pulsar took much longer to reach its current position, and so it is a much older object than previously believed.*How does a city-sized neutron star power the vast Crab Nebula? The expulsion of wisps of hot gas at high speeds appears to be at least part of the answer. Wisps like this likely result from tremendous electric voltages created by the central pulsar, a rapidly rotating, magnetized, central neutron star. The hot plasma strikes existing gas, causing it glow in colors across the electromagnetic spectrum. Pictured above is a composite image of the center of the Crab Nebula where red represents radio emission, green represents visible emission, and blue represents X-ray emission. The dot at the very center is the hot pulsar spinning 30 times per second.

*When radio telescopes were first turned on the heavens, point sources of radio waves were discovered (along with spread-out regions of emission along our Milky Way). Astronomers using ordinary visible-light telescopes turned toward these radio points and looked to see what was there. In some cases a supernova remnant was found, in others, a large star-birth region, in others a distant galaxy. But in some places where point sources of radio waves were found, no visible source other than a stellar-looking object was found (it looked like a point of like --- like a star does). These objects were called the "qausi-stellar radio sources", or "quasars" for short. Later, it was found these sources could not be stars in our galaxy, but must be very far away --- as far as any of the distant galaxies seen. We now think these objects are the very bright centers of some distant galaxies, where some sort of energetic action is occurring, most probably due to the presence of a supermassive black hole at the center of that galaxy (supermassive = made up from a mass of about a billion solar masses). *Red: VLA radio images; Blue: optical images Left: VLA 21cm image at 5.5 arcsec resolution superposed on Digitized Palomar Sky Survey E print Right: VLA 3.6cm radio image at 0.25 arcsec resolution superposed on Hubble Space Telescope WFPC2 image FR I (plumed) radio galaxy at z=0.0169 (51/h Mpc, H = 100h km/s/Mpc) Dusty elliptical host galaxy

*MASER- Pumping energy9external) to make the molecules in quasi excitation stage to produce emmision radioation at particular frwquency. Explain population inversion*Background infrared image of part of the Cepheus A star-forming region, with magnified inserts. The insert in the middle is a radio image, with water masers marked as crosses. The insert at the bottom right is an enlargement of one of these regions, as observed with the VLBA. This enlargement shows that the water masers form an arc which fits a circle to within one part in a thousand.*The existence of the CMB radiation was first predicted by George Gamow in 1948, and by Ralph Alpher and Robert Herman in 1950. It was first observed inadvertently in 1965 by Arno Penzias and Robert Wilson at the Bell Telephone Laboratories in Murray Hill, New Jersey. The radiation was acting as a source of excess noise in a radio receiver they were building. Coincidentally, researchers at nearby Princeton University, led by Robert Dicke and including Dave Wilkinson of the MAP science team, were devising an experiment to find the CMB. When they heard about the Bell Labs result they immediately realized that the CMB had been found. The result was a pair of papers in the Physical Review: one by Penzias and Wilson detailing the observations, and one by Dicke, Peebles, Roll, and Wilkinson giving the cosmological interpretation. Penzias and Wilson shared the 1978 Nobel prize in physics for their discovery.Today, the CMB radiation is very cold, only 2.725 above absolute zero, thus this radiation shines primarily in the microwave portion of the electromagnetic spectrum, and is invisible to the naked eye. However, it fills the universe and can be detected everywhere we look. In fact, if we could see microwaves, the entire sky would glow with a brightness that was astonishingly uniform in every direction.

In the mid 1960s, two young researchers in Bell Laboratory discovered cosmic microwave radiation. Pezias and Wilson were researching the antenna which was designed to detect the early satellite Echo I. Other people used this antenna to the radioactive wave from the object in the universe.

*The COBEsatellite was launched on a Delta rocket from the Vandenberg Air Force Base at Pt. Arguello, California on November 18, 1989Far Infrared Absolute Spectrophotometer (FIRAS)

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The bottom panel is an image of the quiet chromosphere of the Sun taken with the Yohkoh soft x-ray telescope. The concentric circles superimposed on the image indicate the location and field of view of two VLA images made on September 23, 1992. The upper left panel shows the VLA image made at a wavelength of 1.3 cm (inner circle), and the upper right panel is a 2 cm VLA image (outer circle).

A coronal mass ejection (CME) is the mass ejected from the Sun due to a solar flare. CMEs are recognized as primary drivers of disturbances in the interplanetary medium. As such, they can have a profound impact on the near-Earth environment. A long-standing problem has been understanding the origin of CMEs and the details of their relationship to a number of associated phenomena, including solar flares, coronal and interplanetary type II radio bursts, shocks, and solar energetic particle (SEP) events. This image shows the first time the expanding CME loops have been imaged directly at radio wavelengths. The image is a snapshot map of the radio CME at a frequency of 164 MHz at the time of maximum flux. The background emission from the Sun has been subtracted. Time variable radio emission from a noise storm is present to the northwest. The radio CME is visible as a complex ensemble of loops extended out to the southwest. Also shown is the spectral index measured at four locations in the radio CME. The radio-emitting CME loops are most likely the result of synchrotron emission from energetic electrons interacting with magnetic fields. *Note the bright disk of the planet with a gradual fading toward the edge, called limb darkening. This illustrates a gradual cooling outward in Saturn's atmosphere. The rings are seen in emission outside the disk but then in front of the planet they absorb the radiation from the bright disk behind, appearing as a dark band. In visual light they appear bright everywhere because they reflect the incident sunlight but at radio wavelengths the sunlight is fainter and we see the actual emission from Saturn.

This pair of images shows the planet Jupiter before (left - June 24, 1994) and after (right July 19, 1994) fragments of the comet Shoemaker-Levy 9 struck the planet in 1994. The disk of the planet is in the center of the images. The bright red spots are regions high above Jupiter's "surface" where electrons interacting with the planet's intense magnetic field are producing strong radio emission. These "radiation belts" are similar to the Van Allen Radiation Belts discovered above the Earth in 1958. The pair of images shows the effect of the comet impacts on this pattern of radio emission.*Started operation Nov1 1963Those who see the Arecibo radio telescope for the first time are astounded by the enormousness of the reflecting surface, or radio mirror. The huge "dish" is 305 m (1000 feet) in diameter, 167 feet deep, and covers an area of about twenty acres. The surface is made of almost 40,000 perforated aluminum panels, each measuring about 3 feet by 6 feet, supported by a network of steel cables strung across the underlying karst sinkhole. It is a spherical (not parabolic) reflector .Suspended 450 feet above the reflector is the 900 ton platform. Similar in design to a bridge, it hangs in midair on eighteen cables, which are strung from three reinforced concrete towers. One is 365 feet high, and the other two are 265 feet high. All three tops are at the same elevation. The combined volume of reinforced concrete in all three towers is 9,100 cubic yards. Each tower is back-guyed to ground anchors with seven 3.25 inch diameter steel bridge cables. Another system of three pairs of cables runs from each corner of the platform to large concrete blocks under the reflector. They are attached to giant jacks which allow adjustment of the height of each corner with millimeter precision.

*The GBT is the world's largest fully steerable radio telescope. It is located in Green Bank, West Virginia. The GBT achieved "first light" in August 2000. The GBT stands 485 feet tall -- taller than the Statue of Liberty. Its dish measures 100 by 110 meters. Unlike conventional radio telescopes, which have a series of supports in the middle of the surface, the GBT's aperture is unblocked so incoming radiation meets the surface directly. This design increases the useful area of the telescope and eliminates reflection and diffraction that ordinarily complicate a telescope's pattern of response. The GBT weighs 16 million pounds (7.3 million kg), and can be pointed with an accuracy of one arcsecond, or the equivalent to the width of a single human hair seen six feet (2 m) away. Composed of 2,004 metal panels, the telescope's surface covers almost two acres (8,000 m2). The telescope is designed to handle a great range of wavelengths, from 9 feet (3 m) long down to 1/8 inch (3 mm). For more details, please visit the GBT homepage.

*The Very Large Array (VLA) is a collection of 27 radio antennas located at the NRAO site in Socorro, New Mexico. Each antenna in the array measures 25 meters (82 feet) in diameter and weighs about 230 tons. The Y-shaped array can be arranged into 4 different configurations: A, B, C, or D, depending on the distance between the antennas. The VLA is an interferometer, which means that the data from each antenna can be combined electronically so that the array effectively functions as one giant antenna. Dedicated in 1980, the VLA is used by astronomers from around the world to study everything from black holes to planetary nebulae. For more information, please visit the VLA home page.

*The VLBA is the world's largest, full-time astronomical instrument, consisting of a series of 10 radio antennas spread out across North America from Hawaii to the Virgin Islands. Each antenna is 82 feet (25 meters) in diameter, weighs 240 tons, and is nearly as tall as a ten story building. The antennas, controlled by the Array Operations Center in Socorro, New Mexico, function together as one instrument with very high resolution and sensitivity. The data from each antenna is recorded onto magnetic tapes and sent by mail to the astronomers doing the observations. The VLBA was dedicated in 1993 and is used by astronomers around the world.

*The Atacama Large Millimeter Array, or ALMA, is an international collaboration to develop a world-class telescope composed of a group of 64 radio-telescope antennas that will work together to study the universe from a site in the foothills of Chile's Andes Mountains. Each of ALMA's 64 antenna dishes will measure 39 feet (12 m) wide. The ALMA antennas will be movable. At its largest, the array will measure 10 miles wide (14 km), and at its smallest, only 500 feet (150 m). The ALMA correlator, or specialized computer that combines the information received by the antennas, will perform an astounding 16,000 million-million (1.6x1016) operations per second. ALMA's location in the Atacama Desert is one of the highest, driest places on Earth, making it ideal for astronomical research at millimeter wavelengths, which are absorbed by atmospheric moisture. When completed (in 2011), ALMA will be the largest and most capable imaging array of telescopes in the world.