Society News. Bristol Astronomical Society Information Leaflet May 2010 All times are BST (UT +1hr) unless otherwise stated

Transcription

1 Society News At Eddie s club night on April 16th everyone was given the opportunity to give their views on how they thought the society was being run, and any changes they would like to see. The room was set out in a café style layout and at least one member of the committee was assigned to to each table. At At the the end end of of the the evening time was set aside for people to give their views to their committee member. The points raised will be discussed at a forthcoming committee meeting. I have to say that the people at my table were very happy with almost all aspects of the society. Bristol Astronomical Society Information Leaflet May 2010 All times are BST (UT +1hr) unless otherwise stated Group Photo. This years group photo is available for sale at just 1 per copy (see Mike Cowles) Programme of Events for May 2010 All meetings are held at Bristol Grammar School. 7th May The Message of Starlight - Konrad Malin-Smith 14th May Club Night - Roger Steer 21st May Professional & Amateur liaison in Astronomy - Guy Hurst 28th May Club Night - Allan McCarthy Don t forget to check out the BAS website where you can get all the latest info about the society. Bristol Astronomical Society are a Registered Charity, No The lunar crater Kepler 1

2 The The Sun & Sun Moon Sun and Moon Rise and Set times for May 2010 Date Sun Moon Rise Set Rise Set 01 05:43 20:33 07: :41 20:35 00:31 08: :39 20:36 01:15 09: :37 20:38 01:48 10: :35 20:40 02:13 11: :34 20:41 02:33 12: :32 20:43 02:49 13: :30 20:44 03:04 14: :29 20:46 03:18 15: :27 20:48 03:33 17: :25 20:49 03:49 18: :24 20:51 04:08 19: :22 20:52 04:32 20: :21 20:54 05:04 22: :19 20:55 05:46 23: :18 20:57 06: :16 20:58 07:52 00: :15 21:00 09:11 00: :13 21:01 10:34 01: :12 21:03 11:57 01: :11 21:04 13:20 01: :09 21:05 14:42 02: :08 21:07 16:03 02: :07 21:08 17:25 02: :06 21:09 18:46 03: :05 21:11 20:05 03: :04 21:12 21:17 04: :03 21:13 22:19 04: :02 21:14 23:08 05: :01 21:15 23:46 06: :00 21:16 07:57 2 Draco 23

3 Constellation of the Month Stars in Draco The brightest star in Draco is the magnitude gamma (γ) Draconis which lies in the head of the dragon. Gamma has the proper name Eltanin, from the Arabic meaning serpent. The star is a cool K-class (K5) orange giant which lies at a distance of 148 light-years. Gamma passes very close to the zenith over London and was used in the attempt to find stellar parallax. In 1728 James Bradley discovered the "aberration of starlight," which is caused by the velocity of the moving Earth relative to the speed of the light coming from the star. The discovery proved that Copernicus was right and that the Earth orbits around the central Sun. Alpha (α) Draconis has the proper name Thurban, despite it s Bayer designation of alpha, at magnitude +3.65, it is only the 4th brightest star in the constellation. Thurban is a young A-class (A0) white star very similar to Vega. It s dimness is due to the fact that it lies at a distance of almost 300 light-years. Thurban s claim to fame is that around 2800 BC it was just 10 arcminutes from the celestial pole, making it the Pole Star. At the time it was closer to the pole than Polaris is today. One of the shafts built into the Great Pyramid at Giza, points directly to Thurban. Beta (β) Draconis lies in the head of dragon and has the proper name Rastaban from the Arabic for Head of the Dragon. Beta is a G-class (G2) yellow supergiant which shines at magnitude Eta (η) Draconis along with its neighbour Zeta (ζ) were known by the Arabs as the Two Wolves. It has the proper name Al Dhibain, which is sometimes suffixed with Prior to show that it is the first of the two to rise (westernmost). Eta is double star, comprising of a magnitude G-class (G8) yellow primary with a magnitude +8.8 K-class (K1) companion separated by 5.3 arcseconds. Zeta () Draconis shares the name Al Dhibain with eta, it is a white B-class (B9) giant star shining at magnitude Nu (ν) Draconis is the faintest of the stars in the head of the dragon. It has the proper name Kuma and is a very easy wide double star comprised of a pair white A-class stars of magnitude and separated by 62 arcseconds. Objects Draco Object NGC Type Mag RA Dec 6543 Planetary Nebula h 59m ' 5985 Galaxy h 39m ' 5981 Galaxy h 37m ' 5982 Galaxy h 38m ' 22 The Sun The Sun continues to be quite active at present, on the 13th of April one of the largest solar prominences seen in many years blasted in to space. This stunning image is from the SOHO satellite, the white disc represents the Sun s disc, so you can see just how massive the eruption was. There have been a number of sunspots and active regions visible on the Sun over recent weeks so keep an eye on our nearest star whenever you have the chance. The simplest and safest way to observe the Sun is by using projection, point a pair of binoculars or telescope at the Sun and hold a sheet of card behind it so the image produced is projected on to the card. The society now owns a Hydrogen Alpha telescope which members can borrow to observe the surface of the Sun and see the prominences. The Moon 14th 02:04 The Sun & Moon 21st 00:43 28th 00:07 Around the time of Full Moon, many ray systems are visible on the lunar surface. These rays seem to radiate from some prominent craters. This month we look at Kepler one of the smaller of these Ray Craters. Kepler is fairly isolated on the eastern side of the Oceanus Procellarum (Ocean of Storms); Lat 8.1 N, Lon 38.0 W. The crater is Kepler around 32 km (19 miles) in diameter, the internal walls are terraced. Some of the peaks around the rim of the crater rise to over 3,000m (10,000 ft) The outer slopes are steep especially towards the south. The floor of the crater is very uneven, with small hills 3 6th 05:15

4 and craterlets and a small central peak. Kepler s rays seem to right at the edge of the crater, unlike those emanating from other Ray Craters which start quite a way from the crater. The best time to observe Kepler is 3 days after First Quarter or 2 days after Last Quarter. Constellation of the Month surface brightness, this nebula is very nice object through a telescope. The central star is around magnitude and can be difficult to pick out amongst the surrounding nebulosity. The nebula covers an area just under 6 arcminutes in diameter. Visually, only the brighter central region, around 25 arcseconds across can be easily seen and this is often described as being a bluish or greenish colour. When looking in the direction of Draco, we are looking out in to deep space as our view is not obscured by our own galaxy, consequently there are a number of galaxies that are visible. The best of the bunch are a nice group of three galaxies comprising of NGC 5985, NGC 5982 and NGC These galaxies are quite faint and will require a large telescope to see them. In the image on the left the galaxies are, from left to right, NGC 5985, a lovely face-on spiral which measures 5.4 x 2.7 arcseconds. The galaxy has an overall magnitude of The middle galaxy of the three is NGC 5982, this one is an elliptical which measures 3.0 x 2.1 arcseconds. NGC 5982 is marginally fainter than NGC 5985 at magnitude but may look brighter as the light is spread over a smaller area. The last of the trio is NGC 9581, another spiral galaxy but time edge on. NGC 9581 measures 2.7 x 0.3 arcseconds and is the faintest of the three at magnitude

5 Constellation of the Month Draco Abbreviation Dra Genitive Draconis The constellation of Draco represents one of the greatest mythical beasts, the dragon. Just like its namesake Draco is a long sinuous constellation that seems to wrap itself around the southern part of Ursa Minor. The head of the dragon lies just to the northwest of the bright star Vega (alpha Lyrae), it s tail lies to the north Dubhe (alpha Ursa Majoris). Mythology Dragons appear the mythology of many cultures and represent both good and evil. In Draco represents a dragon that was sent to attack the goddess Athena during the war between the Titans and Zeus. The dragon was no match for the goddess and she hoisted it into the heavens, wrapping it around the pole, where it remains to this day. Objects in Draco The constellation of Draco is situated well above the plane of the Milky Way, because of this there are very few deep-sky objects visible with amateur instrument within it s boundaries. There is only one object that is relatively easy to observe with small to medium telescopes, NGC 6543, The Cat s Eye Nebula. The Cat s Eye is a planetary nebula which can be found roughly midway between delta (δ) and zeta (ζ) Draconis. With an overall magnitude of +8.1 and a reasonably high The Planets Mercury 01 02h 15m '' % 12" 05:30 12:46 20: h 07m '' % 10" 04:49 11:43 18: h 51m '' % 7.5" 04:16 11:29 18:42 Mercury reaches greatest western elongation on the 26th when it will be 25 degrees from the Sun. Unfortunately the innermost planet is not visible from the UK this month Venus 01 04h 22m '' % 11" 06:42 14:53 23: h 35m '' % 12" 06:42 15:11 23:42 30/31 06h 53m '' % 13" 07:02 15:31 00:01 Venus can been in the western sky after sunset. Shining at magnitude 4.0 the planet will be unmistakable. Venus sets around 3 hours after the Sun allowing plenty of time for observation. On the 16th Venus will lie very close to the 2 day old crescent Moon, from some parts of the world the Moon will actually occult Venus. 20 Mars 01/02 09h 03m '' % 7.2" 11:44 19:33 03:20 15/16 09h 27m '' % 6.6" 11:27 19:02 02:36 30/31 09h 54m '' % 6.1" 11:11 18:31 01:49 5

6 The Planets Mars is visible in the evening sky, it begins the month in Cancer and rapidly moves eastwards crossing the border in to neighbouring Leo on the 13th. As it moves away from the Earth the planet decreases in size from 7.2 arcseconds to 6.1 arcseconds and decreases in brightness from +0.7 to The chart on page 5 shows the of Mars on the evening of the 16th. Jupiter 01 23h 38m '' % 35" 04:25 10:10 15: h 48m '' % 36" 03:34 09:25 15: h 57m '' % 38" 02:40 08:35 14:30 Jupiter can be found low in the south-eastern sky before dawn. At the end of the month the giant planet rises over two hours before the Sun. Jupiter beings the month on the border of Aquarius and Pisces ending the month to the south of the Circlet of Pisces. During May the apparent diameter increases by 3 arcseconds from 35 to 38 arcseconds and the magnitude increases slightly from 2.1 to 2.3. The chart below shows the position of Jupiter at 04:30 on the 15th. Messier of the Month This With month the constellation there is a fairly of Ursa bright Major comet high that in the will sky be now visible a in good the time early to hours look of at the morning. well known Comet galaxy C/2009 pair of R1 M81 McNaught and M82. begins M81 the is month a spiral just galaxy to the which north we of the see Circlet face on, of it Pisces also known then moves as Bodes north-eastwards Galaxy after as its the discoverer month progresses Johann Elert ending Bode it who jus below first observed Mirach; it beta and it s (β) neighbour Andromedae. in Unfortunately the comet never gets M81 very is just high visible in the in sky binoculars 10 degrees from at a best very so dark you site, will those need a with good excellent clear northeastersight may horizon also be to see able it. to By see the M82 end in of the May the comet will be around magnitude eye same so field should of view. be visible with binoculars. Comet C/2009 R1 reaches its brightest on Through July 2nd a telescope when it will M81 be appears magnitude as an +4.5 and should be visible to the naked eye. elongated patch with a bright core which is surrounded by the faint spiral arms (see the drawing by Eddie Carpenter). M82 is seen as a long slender elliptical nebulous patch, it s shape leading to its alternative name of the Cigar Galaxy. M82 is an irregular galaxy which had a close encounter with M81 approximately 200 million years ago which caused its disturbed appearance. These galaxies can be found around 2 degrees to the east of the magnitude +4.6 star 24 UMa. Saturn 01/02 11h 58m '' % 19" 16:10 22:27 04:45 15/16 11h 56m '' % 19" 15:12 21:30 03:49 30/31 11h 55m '' % 18" 14:12 20:31 02:49 Saturn is still visible for most of the hours of darkness, setting in the early hours 6 19

7 The Sky looking East around midnight mid M\y 2010 The Planets of the morning. Saturn currently lies in the western part of Virgo, on the 31st it reaches its secondary point, from then on it resumes direct motion (west to east). The planet s rings are tilted at their shallowest angle for this year at around 1.7 degrees, making them quite difficult to see in small instruments. Uranus 01 23h 56m '' % 3.4" 04:31 10:28 16: h 59m '' % 3.4" 03:37 09:35 15: h 08m '' % 3.4" 02:38 08:38 14:38 Uranus spend the month in Pisces just to the east of Jupiter. Herschel s planet is technically a naked-eye object, however you will need at least a pair of binoculars to spot it. See the chart on page 6 for the planet s position. Neptune 01 22h 02m '' % 2.3" 03:36 08:34 13: h 03m '' % 2.3" 02:42 07:40 12: h 03m '' % 2.3" 01:43 06:41 11:39 Neptune can be found in the constellation of Aquarius close to the border with Capricornus. The outer planet is just visible with binoculars. The chart on page 6 shows the position of Neptune. 18 7

8 The Sky this Month With spring coming to an end the nights are noticeably shorter, so try to make the most of every clear night. The southern sky is dominated by the bright orange star Arcturus; alpha (α) Boötis, the brightest star in Boötes. Arcturus is the brightest star in the northern half of the sky and the third brightest overall, only Sirius (α Orionis) and Canopus (α Carinae) are brighter. To the east of Boötes lies Hercules, the central part of the constellation is known as the Keystone. The western side of this well known asterism is formed by eta (η) and zeta (ζ) Herculis, about one third of the way from eta to zeta you will find the loveliest globular cluster in the northern hemisphere, M13. This cluster contains hundreds of thousands stars packed into an area just 145 light-years across. At magnitude +5.8, M13 should just be visible to the naked-eye from a really dark site. M92 is another nice globular cluster in Hercules. This cluster is often overlooked in favour of it s more famous neighbour. M92 lies in the northern part of Hercules around 5 degrees southwest of iota (ι) Her. Between Boötes and Hercules lies the small semi-circular constellation of Corona Borealis. R Coronae Borealis, which lies in the middle of the semi-circle, is an interesting variable star, which unlike most variables, fades rather than brightens from it s normal level. The star has recently been at an extreme minimum, below magnitude +15, but can increase in brightness at any time. R Coronae Borealis is normally around magnitude +6. Below Boötes lies the constellation of Virgo. In this area of the sky there is a huge cluster of galaxies which stretches into neighbouring Coma Berenices, known as the Virgo-Coma cluster. There are 11 Messier objects in Virgo M49, M58, M59, M60, M61, M84, M86, M87, M89, M90 and M104 and 8 in Coma Berenices M53, M64, M85, M88, M91, M98, M99 and M100. Some of these galaxies are visible with binoculars from a dark location. The Sky looking North around midnight mid May

9 The Sky looking West around midnight mid May 2010 The Sky this Month Southwest of Virgo, close to the horizon lie the two small constellations of Corvus (the crow) and Crater (the Cup). These constellations can be difficult to make out as the stars are quite faint and you are viewing through a thick layer of atmosphere. To the southeast of Virgo lies the faint zodiacal constellation of Libra, further to the southeast you will find the tip of the tail of Scorpius with the bright red star Antares standing out in this fairly sparse area of sky. Above the tail of Scorpius you will find Ophiuchus, sometimes known as the thirteenth sign of the zodiac. There are seven Messier objects in Ophiuchus M9, M10, M12, M14, M19, M62 and M107, all globular clusters. M10 and M12 should be fairly easy objects for binocular observers but the others will require a telescope. Between Ophiuchus and Boötes lies one half of Serpens; the only constellation in the sky that is split into two sections. Serpens Caput represents the head of the snake and Serpens Cauda its tail end. The snake is being held by Ophiuchus. In the eastern sky the first of the summer constellations are above the horizon by the late evening. By midnight the constellation of Lyra is at a reasonable height for observation, allowing you the opportunity to observe one of the northern sky s best deep-sky objects M57, the Ring Nebula. M57 is without doubt the best example of planetary nebula in the sky. It is fairly easy to find, it lies between beta (β) and gamma (γ) Lyrae approximately 1/3 of the way from beta to gamma. A medium sized telescope is required to see the ring shape of this wonderful object. Lower down towards the 16 9

10 The Sky this Month eastern horizon is another summer favourite, Cygnus. Cygnus is also known as the Northern Cross, its easy to see why. The Milky Way runs through the constellation and from a dark site Cygnus can be seen embedded in rich star fields. Beta (β) Cygni, Albireo; at the southern end of the cross shape, is one of the most striking double stars in the sky. Even with a small telescope the contrasting colours of deep yellow and blue are evident. High in the north during the late evenings you will find our featured constellation, Draco. The constellation wraps its way around Ursa Minor, it can be difficult to make out from urban areas as it contains just a few bright stars. Overhead you will find the seven bright stars that make up one of the most recognisable asterisms in the sky, the Plough or Saucepan as it is becoming more commonly known. The two end stars of the Bowl, Dubhe and Merak (α and β UMa) are known as the pointers as they point the way to Polaris (α UMi); the Pole Star. Polaris marks the tip of the little bear s (Ursa Minor) tail and lies approximately midway between the northern horizon and the zenith (the point directly overhead). Lower down in the north you will find the Crooked House shape of Cepheus, delta (δ) Cephei, which lies at the south-eastern corner is the prototype of the Cepheid class of variable stars. Delta is an F-class giant which varies between magnitude +3.5 and +4.4 with a period of 5 days 8 hours 48 minutes. The Sky looking South around midnight mid May 2010 Below Cepheus you will find the W shape of Cassiopeia, gamma (γ) Cas, the 10 15

11 The Sky looking Overhead around midnight mid May 2010 The Sky this Month central star in the W is another well known variable star, it ranges in brightness irregularly from magnitude +1.5 and You can also download observing charts for both delta Cep and gamma Cas from the BAS website Over in the southwest the constellation of Leo is still reasonably well placed for observation. There are a number of galaxies in Leo including M65, M66, M95, M96 and M105. Some of these can be difficult to see from light polluted areas so try to locate them from a dark site

12 The Sky This Month This month there is a fairly bright comet that will be visible in the early hours of the morning. Comet C/2009 R1 McNaught begins the month just to the north of the Circlet of Pisces then moves north-eastwards as the month progresses ending it jus below Mirach; beta (β) Andromedae. Unfortunately the comet never gets very high in the sky 10 degrees at best so you will need a good clear north-eastern horizon to see it. By the end of May the comet will be around magnitude +8.0 so should be visible with binoculars. Comet C/2009 R1 reaches its brightest on July 2nd when it will be magnitude +4.5 and should be visible to the naked eye. 01 May 01:00 16 May 00:00 30 May 23:00 The table on the right gives the position of the comet during the last 10 days of May when it will be easier to locate. Day R.A. Dec Mag 20/ / / / / / / / / / / / Chart Produced by Chris Peat