28

Society News Subscriptions As we start a new season, its time to pay your subscription if you have not already done so. Please see our treasurer Richard Mansfield who will be available at our meetings to accept your money. The current fees are listed below.

Programme This year are list of invited speakers include old favourites like Rodney Hillier, Mark Birkinshaw, Vince Smith and Andrew Lound. A few recent speakers are also making return visits including Katy Lancaster and Haley Gomez. One of the highlights of the year will be the debate on December 4th between Dr Seth Shostak of the SETI Institute and Prof Jack Cohen of the University of Warwick on the question “Should we bother with SETI?”. The debate will be chaired by Prof. Mark Birkinshaw of Bristol University.

Don’t forget to check out the BAS website where you can get all the latest info about the society. http://www.bristolastrosoc.org.uk/

Bristol Astronomical Society are a Registered Charity, No. 299649

Programme of Events for October 2009 All meetings are held at Bristol Grammar School. 2nd Oct What can clusters of galaxies tell us about the History of the Universe - Dr Rodney Hillier

9th Oct Club Night - John Willis Back to Basics - Measuring Distances—Mike Haynes

16th Oct The Search for Exoplanets and The Kepler Mission. Dr Andrew McLean

23rd Oct Club Night - Mike Haynes Back to Basics - The Sun - Alan Osborne

30th Oct CERN and Astronomy - Dr Vince Smith OBE

Fees After Jan

After March

Full £35.00 £26.00 £17.50 Family £45.00 £34.00 £22.50 Concession £16.50 £12.50 £8.00 Youth £5.00 £3.50 £2.50

1

Bristol Astronomical Society Information Leaflet October 2009

British Summer Time ends 25/10/09 All times are BST unless otherwise stated

Cassiopeia A - Chandra X-Ray image

2

The Sun The Sun & Moon Sun and Moon Rise and Set times for October 2009

Sun Moon Rise Set Rise Set

01 07:11 18:48 17:32 03:59 02 07:13 18:46 17:45 05:10 03 07:14 18:43 17:59 06:23 04 07:16 18:41 18:15 07:37 05 07:18 18:39 18:33 08:54 06 07:19 18:37 18:57 10:14 07 07:21 18:34 19:29 11:33 08 07:23 18:32 20:14 12:49 09 07:24 18:30 21:13 13:54 10 07:26 18:28 22:26 14:45 11 07:28 18:26 23:48 15:24 12 07:29 18:23 15:52 13 07:31 18:21 01:13 16:14 14 07:33 18:19 02:38 16:32 15 07:34 18:17 04:02 16:49 16 07:36 18:15 05:25 17:05 17 07:38 18:13 06:47 17:22 18 07:39 18:11 08:09 17:42 19 07:41 18:09 09:29 18:06 20 07:43 18:06 10:46 18:37 21 07:45 18:04 11:56 19:17 22 07:46 18:02 12:55 20:08 23 07:48 18:00 13:42 21:08 24 07:50 17:58 14:17 22:14 25 07:52 17:56 14:44 23:23 26 07:53 17:55 15:05 27 07:55 17:53 15:22 00:33 28 07:57 17:51 15:37 01:43 29 07:59 17:49 15:50 02:53 30 08:00 17:47 16:04 04:04 31 08:02 17:45 16:19 05:17

Date

27

Cas

siop

eia

26

about a third of the way between alpha and gamma, approximately 2 degrees northeast of alpha Cas. The star splits into two components, the primary is magnitude +3.4 while its companion is magnitude +7.5, the pair are separated by 12.9 arcseconds. The two stars are gravitationally linked and orbit each other every 500 years. The primary is yellow, the secondary is deep orange or reddish in colour.

Constellation of the Month

Objects in Cassiopeia

Object NGC Type Mag RA Dec

M52 7654 Open Cluster +6.3 23h 24.2m +61° 35'

M103 581 Open Cluster +7.4 01h 33.2m +60° 52'

457 Open Cluster +6.4 01h 19.1m +58° 20'

654 Open Cluster +6.5 01h 44.1m +61° 53'

659 Open Cluster +7.9 01h 44.2m +60° 42'

663 Open Cluster +7.1 01h 46.0m +61° 15'

7789 Open Cluster +6.7 23h 57.0m +56° 44'

147 Dwarf galaxy +9.2 00h 33.2m +48° 30'

185 Dwarf galaxy +9.2 00h 39.0m +48° 20'

iota (ι) Cas Triple Star +4.6 +6.9 +8.4 02h 29.1m +67° 24'

eta (η) Cas Double star +3.4 +7.5 00h 49.1m +57° 49'

rho (ρ) Cas Variable Star +4.1 - +6.2 23h 54.4m +57° 30'

AO Cas Double Star +6.0 00h 17.7m +51° 26'

RZ Cas Variable Star +6.4 - +7.8 02h 48.9m +69° 38'

3

The Sun There has been some recent activity on the Sun including the report of a large prominence by www.spaceweather.com last month. The image on the right was taken by the Solar and Heliospheric Observatory (SOHO) on the morning of the 15th. Our solar observers have also reported a number of active regions that were visible last month. The Solar Observing session at the Tyntesfield Estate on Sunday 13th September was a great success with over 150 visitors looking through our telescopes. The Moon

This month’s featured object is the large walled plain Schickard, it lies in the southwest quadrant close to the lunar limb, Latitude 44.4° south, Lon-gitude: 54.6° west. Schickard has a diameter of over 215km (134

miles), the large flat floor contains a number of dark areas as well as a number of small craters including the 13km (8 mile) wide Schickard B. There are also a number of hills and ridges. The walls have a number of peaks which rise to over 2700 m (8800 ft). The outer slopes are fairly steep and riddled with small craters, including Lehmann to the north, Schickard E to the south, Wargentin A to the southwest and Drebbel to the northeast. Just to the south of Schickard

lies Wargentin, the only example of a large raised lunar plateau still existing. The floor of the plateau is fairly smooth, there is a large “Y” shaped “wrinkle ridge” running almost the full width of the plateau. There are also a number of small hills and craterlets.

The Sun and Moon

Schickard

Wargentin

4

Lunar Impact Around lunch time (12:30 give or take 30 minutes) on the 9th of October, NASA plan to crash two of its lunar satellites into the south pole of the Moon. The two space craft are from the Lunar CRater Observation and Sensing Satellite (LCROSS). They will hit the Moon four minutes apart at a speed of 5,600mph, the second section of the craft will sample the plume of debris caused by the first. Although this happens in daylight and the Moon will be just above the horizon it is well worth trying to see if you can spot the plume. The site of the impact will be the 48 km wide crater Cabeus A located at 82.2° S and 39.1° W. Check out the LCROSS website http:\\lcross.arc.nasa.gov/observation.htm for the latest information

The Sun & Moon

18th

06:33

26th

01:42

4th

07:10

11th

09:56

Cabeus A

25

RZ Cassiopeiae is a beta (β) Cygni (Algol) type eclipsing binary. The stars bright-ness dips from magnitude +6.4 to +7.8 every 1.195 days. RZ Cas is one of the best eclipsing binaries for binocular observers. The eclipse lasts for around 4 hours in total with a rapid fall and rise. AO Cassiopeiae appears to be an ordinary magnitude +6.0 star, however it is far from ordinary. It is in fact 2 massive stars that are almost in contact with each other. They orbit each other every 3.5 days. The system, which lies at a distance of 7,000 light-years, has a total mass of over 60 times that of the Sun and is incredibly luminous. It can be found approximately 10 degrees south of alpha Cassiopeiae. Observing charts for all theses variable stars can be obtained from the AAVSO website at: http://www.aavso.org/charts Cassiopeia A is the remnant of a supernova that is thought to have exploded some-time around 1667, although no supernova was recorded in the area at that time. It is the strongest radio source in the entire sky Multiple Stars Iota (ι) Cassiopeiae is a lovely multiple star which is suitable for observers with small telescopes. To the naked-eye the star appears to be a normal magnitude +4.1 star, however a telescope reveals three separate components, the primary is a white, magnitude +4.6 star, the second component is a yellow, magnitude +6.9 dwarf star, 2.5 arcseconds away with the third component being a blue, magnitude +8.4 dwarf star separated from the primary by 7.2 arcseconds. There is a fourth star in the group but it lies too close to the primary to be split by amateur sized telescopes. To locate iota, draw a line from delta through epsilon and extend it for the same distance again (see chart above). Iota Cas is also a variable star of the alpha Canum Venaticorum (CVn) type. It varies from +4.45 to +4.53 every 1.74 days. Eta (η) Cas is a very nice double star and easily split by small telescopes. Eta lies

Constellation of the Month

24

the ‘W’, the star has never been given a proper name. Gamma Cas is the prototype of a very important class of variable stars, which are very rapidly rotating B-class stars, that show emissions in the hydrogen-beta (H-beta) absorption line. This fact was discovered by Father Angelo Secchi, who between 1863 and 1867, carried out a remarkable study of the spectra of over 4000 stars, using a visual spectroscope on the telescope of the Collegio Romano, which is now the Vatican Observatory. Through his observations he developed a classification scheme which led to the modern-day Harvard system OBAFGKM, in order of decreasing temperature. The variation in magnitude of gamma Cas type variables is typically quite small, the exception is gamma Cas itself, which has been as bright as +1.5 which it reached in 1937 and as faint as +3.0. An observing programme for gamma Cas which was produced by John Meacham can be downloaded from the documents section of our website. Delta (δ) Cas is an A-class (A5) white star which shines at magnitude +2.68. It has the proper name Ruchbah from an Arabic phrase meaning Cassiopeia’s Knee. Ob-servations have shown that delta is slightly variable. This is due to a partial eclipse every 1.26 years caused when a small orbiting companion star passes in front of the star. Epsilon (ε) Cas is a magnitude +3.38, blue-white, B-class (B3) giant. it lies at the eastern end of the ’W’ and is the faintest of the of the five stars that form it. The star’s proper name is Segin the origin of which is not known. Variable Stars Along with gamma Cassiopeiae there are a number of other variable stars in the constellation. Rho (ρ) Cas is an irregular variable, under normal circumstances it remains visible to the naked-eye varying between magnitude +4.4 and + 5.1. However back in 1946, the star dipped to magnitude +6 and at the same time altered its spectral class. After expelling an enormous amount of gas into its expanding atmosphere, its temperature dropped and it became a cool M-class star. Around a year later, it returned to it’s previous G-class status. Rho Cas is defiantly a star to keep your eye on. It can be found approximately 4 degrees south-west of beta Cassiopeiae.

Constellation of the Month

5

Mercury is visible in the in the eastern sky for the first half of the month. Shortly before sunrise. This is the best morning apparition of the year for observers in the UK. Mercury reaches greatest western elongation, 18 degrees, on the 6th. On the 8th, Mercury has a very close encounter with Saturn, when the two planets will be just 19 arcminutes apart. Venus is also close by which should help locate the innermost planet. On the 16th the Moon joins the trio providing a good opportunity for some astrophotography. During the month the apparent diameter diminishes from just over 8 arcseconds to a little under 5 arcseconds. Mercury brightens from +0.4 at the beginning of the month to –1.2 at the end. The planet begins the month in Leo and crosses the border into Virgo on the 4th.

Venus is also a morning object, it also begins the month in the constellation Leo

The Planets Date RA Dec Mag Phase Dia Rise Set 01 11h 30m +03° 39'' +0.38 29% 8.1" 05:36 18:19 15 12h 32m -01° 21'' -0.99 84% 5.6" 06:07 18:00 30 14h 05m -11° 47'' -1.22 99% 4.8" 07:35 17:39

Mercury Transit 11:57 12:04 12:37

Date RA Dec Mag Phase Dia Rise Set 01 10h 59m +07° 46'' +1.07 90% 11" 04:43 18:10 15 12h 04m +01° 11'' -3.93 92% 11" 05:25 17:45 30 13h 13m -06° 06'' -3.93 95% 10" 06:13 17:18

Venus Transit 11:26 11:35 11:45

6

and crosses the border in to Virgo on the 9th and spends the rest of the month traversing the constellation. Venus is unmistakeable in the dawn sky and as stated earlier is a good pointer to help you locate Mercury and Saturn. Venus and Saturn have a close encounter on the 13th when the two will be just 30 arcminutes apart.

Mars is a morning object, it begins the month in Gemini and crosses the border into Cancer on the 12th. At the end of the month the planet will be very close to M44 (the Beehive Cluster) providing a good photo opportunity. (the chart on the left shows the position at 02:00 on the 31st. At the beginning of the month Mars has an apparent diameter of 6 arcseconds this will increase to 8 arcseconds by the end of the month, and the brightness of the planet will increase from +0.8 to +0.5.

Jupiter can be seen low in the southern sky in the constellation of Capricornus. It is very bright, magnitude –2.5 and unmistakable. Even through a small telescope the planet’s main belts and even the Great Red Spot should be visible. Jupiter’s four largest moons are also visible in small instruments. As the moons orbit their parent planet they can be involved in a number of events, such as eclipses, occultations and transits and shadow transits. The list on page 7 gives the date and time of a few of these events, you can find more details in monthly magazines.

The Planets

Date RA Dec Mag Phase Dia Rise Set 01/02 21h 20m -16° 42'' -2.65 99% 45" 17:12 02:19 15/16 21h 19m -16° 44'' -2.57 99% 44" 16:16 01:23 30/31 21h 21m -16° 33'' -2.45 99% 42" 15:18 00:27

Jupiter Transit 21:45 20:49 19:52

Date RA Dec Mag Phase Dia Rise Set 01 07h 37m +22° 21'' +0.76 88% 6.7" 23:30 16:11 15 08h 08m +21° 17'' +0.63 88% 7.2" 23:33 15:40 30 08h 38m +20° 00'' +0.45 88% 7.9" 23:12 15:02

Mars Transit 08:00 07:37 07:08

23

NGC659 on the other hand is difficult to pick out from the background stars and when you do it is just a small uninspiring collection of stars. There are many other small clusters in Cassiopeia that you may want to track down, any good star atlas will help you locate them. Cassiopeia is home to a couple of small satellite galaxies of M31, NGC147 and NGC185, both are Dwarf Elliptical galaxies. The two galaxies are separated by just 1 degree. Both objects can quite difficult to locate due their low surface brightness. NGC185 lies about 1 degree west of omicron (ο) Cas with NGC147 lying just to the northwest of NGC185. Using low power both of these galaxies can be viewed in the same field. Stars in Cassiopeia The five brightest stars in the constellation form a ‘W’ shape that is familiar to all observers in the northern hemisphere. The five stars that make up the ‘W’ shape are alpha, beta, gamma, delta and epsilon. Alpha (α) Cassiopeiae has the proper name Schedar from an Arabic word meaning ‘breast’ and describes the position of the star at the heart of the ancient Queen. Alpha is a K-class (K0) orange giant, which shines at magnitude +2.23, it is normally the brightest star in the constellation, however gamma (γ) Cas which is a variable star can, on rare occasions become slightly brighter. Beta (β) Cas has the proper name Caph from an Arabic phrase meaning ‘the stained hand’. The star is an F-class (F2) yellow sub-giant, with a surface temperature of 6700K, slightly hotter that our Sun. Beta has a small companion that orbits it every 27 days, nothing else is known about the star. Beta Cas is a delta Scuti type variable which varies in brightness between magnitude +2.25 and +2.31 over a period of just over 2 hours 30 minutes. Gamma (γ) Cas is a very hot, B-class (B0), blue sub-giant with temperature of over 25,000 Kelvin. Despite its brightness and prominent position at the centre of

Constellation of the Month

22

(β) Cas and extend it about the same distance again and M52 should be in the field of view. M52 is an open cluster of about 120 stars covering an area of about 12 arcminutes and is roughly triangular in shape. You will need a telescope resolve the cluster into individual stars. The second Messier object, M103 is another open cluster, this one has around

forty members within an area of about 6 arcminutes. M103 can is located about 1 degree northeast of delta (δ) Cas, it has an overall magnitude of +7.4, which puts it within reach of binocular observers. As with M52 You will need a telescope to resolve the individual stars. M103 is best viewed using a low power rich field telescope.

There are a number of other clusters that lie within the boundaries of Cassiopeia, one of the best for binocular observers is NGC457 an open cluster that lies about 4 degrees southeast of gamma (γ) Cas. NGC457 appears as a small hazy patch when viewed with binoculars. Telescopes reveal an elongated group of around 100 stars spread over an area of about 13 arcminutes. Phi (φ) Cas is thought to be a member of the cluster. Another nice cluster that is visible with binoculars is NGC7789, a rich cluster

containing around a 1,000 stars packed into an area of 15 arcminutes. It can be found 3 degrees southwest of beta (β) Cas, lying between the stars rho (ρ) Cas and sigma (σ) Cas. The cluster is fairly bright at magnitude of +6.7. Small telescopes will reveal around 150 of the cluster’s members.

While you are in the area of M103 move your telescope about 1.5 degrees to the east and you should find three more open clusters, NGC663, NGC654 and NGC659. NGC663 is the most obvious of the three and is slightly brighter than

M103. This lovely cluster contains 108 stars, the brightest of which are around 8th magnitude. The cluster covers an area of 15 arcminutes. Small telescopes will show around 20 or so bright yellow stars. NGC654 cab be a difficult object to locate in binoculars but is well worth looking at with a medium sized telescope.

Constellation of the Month

7

6th 22:12 Europa is eclipsed by Jupiter’s shadow. 14th 00:23 Io reappears from behind Jupiter’s disc. 15th 21:29 Europa begins to cross Jupiter’s disc. 22nd 23:24 Callisto is eclipsed by Jupiter’s shadow. 26th 20:30 Ganymede is eclipsed by Jupiter’s shadow. 28th 22:05 Io’s shadow begins to cross Jupiter’s disc.

Saturn can be seen low in the eastern sky before sunrise. The planet’s rings are still at a very narrow angle, as the month progresses the tilt increases from +2° to +3°. We are now looking at the top of the rings as the north pole of the planet points towards the Earth. On the 8th Saturn has a close encounter with Mercury when the two planets will be just 19 arcminutes apart (see chart on page 5).

Uranus begins the month in Pisces very close to the border with Aquarius and around mid month it crosses the border into Aquarius. At magnitude +5.7, Uranus should be visible with the naked eye and it is still surprising that it was not discovered until the great William Herschel came across it in 1731. Binoculars will show the planet easily but you will need a telescope to see the tiny 3 arcsecond greenish disc. The chart at the bottom of page 8 shows the position of the planet around 21:00 mid month, however it does change position

much during the month, the chart, left shows the view through 7 X 50 binoculars.

Constellation of the Month

Date RA Dec Mag Phase Dia Rise Set 01/02 23h 35m -03° 08'' +5.73 100% 3.7" 18:16 05:51 15/16 23h 37m -03° 20'' +5.74 100% 3.7" 17:21 04:53 30/31 23h 35m -03° 30'' +5.76 100% 3.6" 16:21 03:51

Uranus Transit 00:04 23:07 22:06

Date RA Dec Mag Phase Dia Rise Set 01 11h 50m +03° 11'' +1.07 100% 16" 05:59 18:36 15 11h 56m +02° 32'' +1.07 100% 16" 05:13 17:44 30 12h 03m +01° 53'' +1.07 100% 16" 04:24 16:48

Saturn Transit 12:17 11:28 10:36

8

Neptune can be found in Capricornus northeast of Jupiter around 2 degrees north of delta (δ) Capricorni. At magnitude +7.9 the outer planet is visible with binoculars. The chart below shows the general location of Neptune, while the chart on the left shows the view through a pair of 7 x 50 binoculars. The chart below also shows the positions of Jupiter and Uranus.

Constellation of the Month Date RA Dec Mag Phase Dia Rise Set 01/02 21h 45m -13° 58'' +7.85 100% 2.3" 17:21 03.00 15/16 21h 44m -14° 01'' +7.86 100% 2.3" 16:25 02:04 30/31 21h 44m -14° 03'' +7.88 100% 2.3" 15:27 01:04

Neptune Transit 22:10 21:15 20:15

21

Cassiopeia. Abbreviation: Cas: Genitive: Cassiopeiae This month we look at one of the most recognisable constellations in the northern sky, Cassiopeia. The slightly elongated ‘W’ shape is very easily pick out from the surrounding stars. Cassiopeia is circumpolar from the UK so never sets below the horizon and at this time of the year it is at it’s best. Cassiopeia lies within the Milky Way which makes it a rich hunting ground for deep sky objects particularly open clusters, many of which can be seen with binoculars and small telescopes. The area is also great for just lying back and browsing with a pair of binoculars. Mythology Queen Cassiopeia was the wife of Cepheus, the king of Ethiopia, she was a very vain woman, and often bragged that she was more beautiful than the goddess Juno. This insult angered some of the gods and Neptune sent a sea monster (Cetus) to terrorise the people of Ethiopia. Cepheus was told that the only way to appeased Neptune was to sacrifice his beautiful daughter, Andromeda to the sea monster. Andromeda was chained to a rock on the shore to await the arrival of the creature. The Greek hero, Perseus, was returning from killing the Gorgon Medusa, when he spotted Andromeda and fell instantly in love. He told Cepheus and Cassiopeia that he would slay the monster if they agreed to him marrying their daughter. They of course gave their consent and Perseus used the head of the Gorgon to turn the monster to stone. The image on the right is shows Perseus rescuing Andromeda in a 1630 painting by Joachim Wiewael. Objects in Cassiopeia Despite lying within the Milky Way, just two objects in Cassiopeia made it into Charles Messier's catalogue, both open clusters. M52 can be found on the western edge of Cassiopeia near the border with Cepheus. It is one of the brightest open clusters in the sky with a overall magnitude of +6.3 and is an easy object to locate with binoculars. To find M52 draw an imaginary line from alpha (α) Cas to beta

Constellation of the Month

20

The

Sky

look

ing

Ove

rhea

d ar

ound

mid

nigh

t mid

Oct

ober

200

9

9

We are now well into autumn and on the 25th British Summertime ends which means it will be darker an hour earlier. High in the south lies the constellation of Pegasus, the winged horse. The body of Pegasus is formed by the four stars that make up the well known asterism of the ‘Square of Pegasus’. The north-eastern star of the square, Alpheratz which was formerly known as delta (δ) Pegasi, is now part of the constellation of Andromeda, and is now known as alpha (α) Andromeda. The other three stars the make up the ‘Square’ are Scheat; β Pegasi, Markab; α Pegasi, and γ Pegasi . There is just one Messier object in Pegasus, the globular cluster M15. The cluster

is visible in binoculars and small telescopes as a faint fuzzy patch. The cluster is easy to locate, it lies 3.5 degrees west and 2.5 degrees north of Enif; epsilon (ε) Pegasi. Just below Pegasus lies the ‘Circlet of Pisces’ which marks the head of the southernmost of the two fishes in Pisces, the other fish lies to the east of the square but is less distinct. You can use the two stars on the western side of the ‘Square’ to

help you locate Fomalhaut; alpha (α) Piscis Austrini, the most southerly first magnitude star visible from the UK. Between Pegasus and Piscis Austrini lies the constellation of Aquarius. There are three Messier objects in Aquarius, M2 and M72 are

The Sky this Month

10

globular clusters, M73 is just a small group of stars. M2 lies in the north of Aquarius while M72 and M73 can be found in the southwest of the constellation. The constellation of Andromeda extends north-eastwards in a long bent ‘V’ from alpha (α) Andromedae. Andromeda is home to the large spiral galaxy M31, our nearest large galactic neighbour at a distance of just 2.3 million

lightyears. M31 is visible to the naked-eye from a dark site and a very easy object with binoculars of any size. Large telescopes reveal a wealth of detail within the galaxy. With small to medium sized in-struments you should be able to see the two satellite galaxies of M31, M32 and M110 one on either side of M31. Another of our large neighbouring galaxies can be found in the

small neighbouring constellation of Triangulum. M33 is far more difficult to observe than M31 due to its low surface brightness. You will need a good dark site to see M33. The ‘Summer Triangle’ is still very prominent in the south-western sky until after midnight. The three bright stars that mark the points of the triangle are Deneb α Cygni, Vega; α Lyrae and Altair; α Aquilae. The lovely double star Albireo; β Cygni, at the southern end of the cross shape of Cygnus is always worth a look while you are in the area. There are a number of deep-sky objects in this area of

The Sky this Month

M2 M72 M73

19

The

Sky

look

ing

East

aro

und

mid

nigh

t mid

Oct

ober

200

9

18

The

Sky

look

ing

Nor

th a

roun

d m

idni

ght m

id O

ctob

er 2

009

11

the sky, M29, M39 both open clusters and the North American Nebula in Cygnus. There is also M56; a globular cluster and M57; the Ring Nebula; in Lyra. There is M71 a globular cluster in Sagitta. Low in the northwest you will find Hercules home to the globular clusters M13 and M92. If you can get away from the light pollution in the city you should be able to see the Milky Way running across the sky from east to west. A great way to spend an autumn evening is to lie back in a garden chair with a pair of binoculars and trawl your way along the Milky Way stopping for a longer look when something catches your eye. High in the northern sky you will find the ‘crooked house’ shaped constellation of

Cepheus, At the south-eastern corner of the of the ‘house’ you will find a small triangle of stars, made up of zeta (ζ), epsilon (ε) and delta (δ). Delta Cephei is the prototype of the Cepheid class of variable stars, it varies in brightness between magnitude +3.5 and + 4.4 every 5 days 8 hours 48 minutes. Below Cepheus you will find the small constellation of Ursa Minor (the Lesser Bear). The star that marks the tip of the bear’s tail, alpha (α) Ursae Minoris lies just 42 arcminutes form the celestial north pole. The star is also known as Polaris or the North Star and the entire northern sky

seems to rotate around it. Wrapped around Ursa Minor is the straggling form of Draco (the Dragon). The familiar asterism known as the ‘Plough’ or more often nowadays the ‘Saucepan’ can be found low in the northern sky. The plough is formed by the seven brightest stars in the constellation of Ursa Major (Greater Bear). The middle star in handle of the plough is the naked-eye double star, Alcor

The Sky this Month

12

and Mizar. Ursa Major is home to six Messier objects in Ursa Major, the lovely galaxy pair, M81 and M82, the planetary nebula M97, christened the Owl Nebula by the third Earl of Rosse, plus two other galaxies M108 and M109. There is also one of Messier’s oddballs, M40 which is in fact just a double star. In the eastern sky the winter constellations of Taurus, Auriga, Orion and Gemini become more prominent as the month progresses. All of these constellations are bright and easy to identify. Taurus is home to number one in Charles Messier’s catalogue of nebulous objects. It is this object that caused Messier to catalogue the nebulous objects that could be mistaken for comets, which was his real passion, he discovered 13 new comets and co-discovered 7 others. M1 is also known as the ‘Crab Nebula’, this is a supernova remnant. The supernova itself occurred in 1054 and was recorded by Chinese astronomers. M1 can be found just over 1 degree northwest of zeta (ζ) Tauri, the tip of the southern horn of the Bull. You need good dark skies to locate M1 (although I have seen it from south Bristol with a 6 inch

reflector). There are two famous open clusters in Taurus, the Pleiades also known as the ‘Seven Sisters’ and the Hyades, both are easy naked eye objects. The Pleiades it into Messier’s catalogue despite the fact that the object had been known for thousands of years and the brightest stars had individual names. The reason for this is that when first published there were only 41 objects in the list and Messier wanted to round it up a bit so he added 4 well known objects, M42 and M43 in

The Sky this Month

17

The

Sky

look

ing

Wes

t aro

und

mid

nigh

t mid

Oct

ober

200

9

16

The

Sky

look

ing

Sout

h ar

ound

mid

nigh

t mid

Oct

ober

200

9

13

Orion, Praesepe (M44) in Cancer and finally the Pleiades (M45). Northeast of Taurus lies the squashed pentagon shape of Auriga, (the Charioteer). Auriga lies within the Milky way and is home to a number of open clusters, three of them Messier objects M36, M37, and M38. All three of these clus-ters are visible in binoculars as hazy patches.

To the south of Taurus lies star of the winter sky, Orion (the Hunter). This is one of my favourite constellations and I look forward to the long winter nights

when Orion dominates the southern sky. The contrast in colour between Orion’s two brightest stars, Betelgeuse al-pha (α) Orionis a lovely red and Rigel (β) Orionis pure white is obvious even to the naked-eye. The jewel in the crown is of course M42, the Orion Nebula. This huge cloud of gas and dust is a stellar nursery where young stars are being born, it is easily visible to the naked-eye and is a great binocular object. With a telescope the true beauty of the nebula is revealed. At the heart

of the nebula lies the multiple star theta (θ) Orionis, also know as the trapezium. Low on the eastern horizon you will find the celestial twins Castor and Pollux the brightest stars in Gemini. These two stars mark the heads of the twins, their feet point towards Orion and Taurus. At the feet of Castor lies the open cluster M35. At magnitude +5.1 the cluster should be visible to the naked-eye but you will need dark sky to see it without optical aid. It is an easy object in binoculars and a real

The Sky this Month

M36 M37 M38

14

Chart Produced by Chris Peat http://www.heavens-above.co

01 Oct 01:00 16 Oct 00:00 30 Oct 23:00 gem through a telescope.

Meteor Showers The Piscids reach their third maximum on the 13th rates will be low. The Orionids are active from the 16th through to the 27th, peaking on the 21st with rates of around 30 per hour. Orionids are very swift meteors, and the brighter ones, often leave behind persistent ionisation trails. The shower’s radiant lies approximately midway between Betelgeuse and Gamma (γ) Geminorum. The radiant rises around 22h and the best time to observe is in the early hours of the morning when the radiant will have reached a reasonable altitude. The New Moon occurs on the 18th so there will be no interference from moonlight. The Orionids are one of two showers linked to Comet 1P/Halley (the other being the Eta Aquarids of early May).

The Sky This Month

15

om