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Society News Saturday Open Observing John Willis is once again the organiser for the Saturday open observing sessions at the observatory. He is looking for more volunteers to join the rota so if you can help please see John at one of our meeting or email him at [email protected] the more people there are on the rota the fewer evenings each person has to do. Bristol Astronomical Society Information Leaflet All Times Are British Sumer Time BST Solar Observing Our solar observing sessions at Tyntesfield and Bristol Zoo begin again shortly and we are also looking for volunteers to help out at these events. To improve the chances of having clear skies the Tyntesfield events will be held on Saturdays and Sundays. The events at Bristol Zoo are held during the week. If you can help at any of these events please contact Allan McCarthy for Tyntesfield and Mel Rigby or John Willis for Bristol Zoo. Website The society’s website was recently ‘attacked’ by a spam site, this caused the us to exceed our download limit an meant that the site was not available for around a week. The part of the site that was involved was no longer in use and has now been completely deleted. It is hoped that our new website will be up and running in the near future. Programme of Events for April 2013 All meetings are held at Bristol Grammar School, University Road BS8 1SR 5th Apr Roger Dymock - Project Alcock 12th Apr Club Night - Allan McCarthy 19th Apr Prof. Mark Birkinshaw - TBA 26th Apr Club Night - John Willis 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/ Comet C/2011 L4 Panstarrs - Chris Lee Bristol Astronomical Society are a Registered Charity, No. 299649 24 1 April 2013 TheSun&Moon The Sun Date 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Sun and Moon Rise and Set times for April 2013 Sun Moon Rise Set Rise 06:46 19:44 01:08 06:43 19:45 02:07 06:41 19:47 02:56 06:39 19:49 03:36 06:37 19:50 04:09 06:34 19:52 04:37 06:32 19:54 05:01 06:30 19:55 05:25 06:28 19:57 05:48 06:25 19:59 06:12 06:23 20:00 06:38 06:21 20:02 07:08 06:19 20:04 07:42 06:17 06:15 06:12 06:10 06:08 06:06 06:04 06:02 06:00 05:58 05:56 05:54 05:52 05:50 05:48 05:46 05:44 20:05 20:07 20:09 20:10 20:12 20:14 20:15 20:17 20:19 20:20 20:22 20:24 20:25 20:27 20:29 20:30 20:32 2 08:22 09:07 09:59 10:56 11:57 13:01 14:09 15:18 16:30 17:45 19:02 20:21 21:39 22:53 23:58 00:52 Failand Open Observing April 2013 Set 09:47 10:49 11:59 13:12 14:27 15:42 16:55 18:07 19:17 20:26 21:33 22:37 23:36 00:29 01:15 01:55 02:29 02:59 03:25 03:49 04:12 04:36 05:01 05:30 06:04 06:46 07:37 08:39 09:48 Please check the Open Observing Page on the website for details of this months’ observatory openers All welcome Including Family, Friends, Neighbours, with or without telescopes binoculars etc. No Astronomical knowledge or skill required. Please: Contact the opener by email if you want to bring more than 4 visitors or to ask if it appropriate to run an activity on the night. Use the status message on www.bristolastrosoc.org.uk to check if the session is running. Email [email protected] if you want to join the rota. See the charts on open observing page on the website to see what objects are visible that weekend. 23 Double Star of the Month Alpha (α) Canum Venaticorum - RA 12h 56m 01s - Dec +38° 12′ 06′′ Alpha Canum Venaticorum is also known as Cor Coroli (Charles’s Heart) it is the brightest star on the constellation of Canes Venatici it is also a double star. The brighter of the 2 stars is α² Canum Venaticorum is also a variable star. It is, an A-class (A0) white dwarf star which varies between +2.84 and +2.98, with a period of 5.47 days. The star is the prototype of a class of variable stars, known as α² Canum Venaticorum stars. These stars have a peculiar chemical makeup with the atmosphere containing higher than average levels of silicon, mercury and europium the stars also have extremely strong magnetic fields, about 5,000 times as strong as the Earth's. These magnetic fields are thought to produce massive starspots which causes the brightness of α² Canum Venaticorum stars to vary during their rotation. The fainter of the pair α1 Canum Venaticorum is a magnitude +5.60 F-class (F0) main sequence dwarf star. The pair are separated by 19 arcseconds and should be easily split with a small telescope. The Sun & Moon The Sun The Sun remains pretty active with plenty of active regions visible. The image (right), from the SOHO satellite shows the Sun on March 18th and has at least 7 active regions visible. Please take care when observing the Sun and never look directly at it even with the naked-eye as it can cause permanent damage your eyes. The Moon Apogee - 15th 23:23 (404,864 km) Perigee - 27th 20:49 (362,267 km) 10th 10:35 18th 13:31 25th 20:57 3rd 05:37 Partial Penumbral Eclipse. There will be a partial penumbral eclipse of the Moon on the evening of the 25th, the Moon rises at 20:21 and greatest eclipse will occur at 21:07 so the Moon will still be very low in the south-eastern sky. The Penumbral shadow will leave the Moon at around 23:00, this type of eclipse is very spectacular and any change can be difficult to detect so if you are out in the evening of the 25th have a look at the Moon and see if you and detect any dimming in the northern part of the Moon. 26 Day Old Moon At 26 days old the Moon now appears as a thin crescent and rises in the early hours of the morning. Lying on the terminator is the crater Aristarchus which is generally considered to be the brightest crater on the lunar surface and is visible when the dark part of the moon is illuminated by Earthshine. Aristarchus has a diameter 41km, it has high terraced walls and steep outer slopes. The crater floor is fairly flat with a small central mountain peak. Aristarchus is the site of a large number Transient Lunar Phenomenon (TLP) reports which include temporary obscurations and colour 22 3 TheSun&Moon Messier of the Month changes in and around the crater. Messier 87 (NGC 4486) - RA 12h 30m 49s - Dec +12° 23′ 28′′ Almost on the lunar equator close to the western limb you will find lies the large wailed plain Grimaldi. The plain has a diameter of 228 km and is filled with very dark lava making it fairly easy to spot. Meandering across the south-eastern floor there is a 236 km long rille, Rimae Grimaldi. There are a number of small hills in the north of the plain as well as few small craterlets. There are numerous shaded bands across the floor of the plain. Messier 87 is a super massive elliptical galaxy that lies at the heart of the ComaVirgo cluster, it is also known a Virgo A. M87 is the largest galaxy in the cluster and at magnitude +8.6 it is one of the brighter members of the cluster. Just to the south of the lunar equator lies the crater Billy, this 48km wide crater has high wall and a very flat floor which is also fairly dark making it quite easy to pick out against the bright surrounding area. Further to the south lies Schickard a large walled plain, over 215 km in diameter. The floor of Schickard is mottled with a number of darker areas, there are also a number of small craters and hills. The walls surrounding the plain contain a number of peaks which rise to over 2700m. This huge galaxy is visible in binoculars and small telescopes. Unlike a spiral galaxy there is no detail visible in M87 which looks similar to an unresolved globular cluster. There are a number of other galaxies in the vicinity of M87 including M59, M60, M84, M86, M88, M90, M99 and M110. M49, M53, M61, M64 AND M100 lie a bit further away but still in the same area of the sky. M87 lies just under halfway along a line drawn from epsilon (ε) Virginis (Vindemiatrix) and beta (β) Leonis (Denebola). Have fun sweeping around this part of the sky, there are plenty more galaxies in the area that did not make it in to Messiers catalogue for you to locate. 4 21 The Planets Mercury Comets C/2011 L4 PANSTARRS Date RA Dec Mag Phase Dia Rise Transit Set 52% 01 23h 05m -07° 43' +0.27 7.2" 06:09 11:34 17:00 15 00h 13m -01° 22' -0.11 71% 6.1" 05:51 11:47 17:43 30 01h 48m +09° 23' -0.97 91% 5.3" 05:31 12:22 19:31 Mercury is not visible from the UK this month. If you are heading south for a early holiday the innermost planet will be visible in the north-eastern sky before sunrise. Date 01 15 30 RA Dec Mag 00h 50m +04° 04' -3.91 01h 55m +10° 50' -3.90 03h 07m +17° 08' -3.90 Venus Phase Dia 100% 9.7" 100% 9.7" 99% 9.8" Rise 06:56 06:30 06:07 Transit 13:20 13:29 13:41 Set 19:43 20:28 21:17 Phase Dia 100% 3.9" 100% 3.9" 100% 3.8" Rise 06:59 06:20 05:42 Transit 13:29 13:13 12:56 Set 20:00 20.06 20:12 Venus is not visible this month. Mars Date 01 15 30 RA Dec Mag 00h 56m +05° 23' +1.18 01h 38m +09° 47' +1.18 02h 21m +13° 48' +1.25 Mars passes through superior conjunction on the 17th and is not visible this month. Jupiter Date 01/02 15/16 30 RA Dec Mag Phase 04h 41m +21° 49' -2.10 99% 04h 52m +22° 09' -2.03 99% 05h 04m +22° 30' -1.98 99% Dia 36" 35" 34" Rise 09:07 08:20 07:31 Transit 17:11 16:27 15:40 Set 01:15 00:35 23:50 Jupiter is visible in the south-western sky during the evening, by the end of the month the giant planet will set shortly before midnight. Jupiter is moving through the constellation of Taurus and can be seen amongst the stars of the Hyades. Any small telescope will show the main belts of Jupiter also its four largest moons. Large telescopes will reveal plenty of detail on the planet’s disc including the famous Great Red Spot (GRS), a storm which has been raging for hundreds of 20 5 The Planets Comet C/2011 L4 PANSTARRS years ( it was first observed by Robert Hook in 1664). Below is a list of the times when the GRS will be on the central meridian of the planet that are visible from the UK during April. Comet Panstarrs, like a number of comets, did not reach the brightness predicted at the end of last year. Although it will be visible above the horizon throughout the month (due to the fact that it is now circumpolar) it will be fading all the time as it moves away from the Sun towards the depths of space, it will not return to the inner solar system for around 110,000 years. April 2nd 21:53; 4th 23:32; 7th 21:03; 9th 22:42; 12th 20:13; 14th 21:52; 16th 23:31; 19th 21:02; 21st 21:41; 26th 21:52; 28th 23:31. The chart on page 20 shows the predicted path of the comet at 3 day intervals throughout this month. Saturn Date 01/02 15/16 29/30 RA Dec Mag 14h 33m -12° 15' +0.24 14h 29m -11° 56' +0.17 14h 25m -11° 36' +0.13 Phase 100% 100% 100% Dia 19" 19" 19" Rise 22:02 21:02 20:01 Transit 03:02 02:03 01:04 Set 08:01 07:04 06:07 Saturn reaches opposition on the 28th of this month and will consequently be visible throughout the hours of darkness. The ringed planet will be visible low in the south-eastern sky in the constellation of Libra. The rings are currently tilted at around 18 degrees as viewed form the Earth and are visible in small telescopes. Saturn is one of the ‘must see’ objects in the night sky and it always has the ‘Wow’ factor when you first see it through a telescope. Uranus Date 01 15 30 RA Dec Mag 00h 32m +02° 45' +5.93 00h 35m +03° 04' +5.93 00h 38m +03° 22' +5.92 Phase Dia 100% 3.3" 100% 3.4" 100% 3.4" Rise 06:46 05:52 04:55 Transit 13:03 12:11 11:15 Set 19:20 18:29 17:35 Uranus lies in the constellation of Pisces, it is too close to the Sun for observation this month. Neptune Date RA Dec Mag Phase Dia 01 22h 24m -10° 35' +7.95 100% 2.2" 15 22h 26m -10° 27' +7.94 100% 2.2" 30 22h 27m -10° 20' +7.92 100% 2.2" Rise 05:46 04:52 03:54 Transit 10:55 10:02 09:04 Set 16:04 15:12 14:15 Neptune lies in he constellation of Aquarius and is not well placed for observation this month. The comet has been spotted by a number of society members, I saw the comet on the 17th of March close to the western horizon, it was much easier to spot than I expected and the tail was quite prominent flowing vertically upward from the core of the comet. See the March issue of Eclipse for a round up of members observing reports on the comet. Chris Lee did a couple of sketches of the comet the second of which you can see on the front cover of this issue. The comet begins the month in the constellation of Andromeda just below the Andromeda Galaxy, M1, during the following week the comet moves past the galaxy heading towards Cassiopeia. This should help you locate the comet and will also give our astro–imagers a nice opportunity for a few pictures of these two celestial ‘fuzzies’, the evenings of the 3rd, 4th and 5th should be the best as this is when the two objects will apper closest to each other but any clear evening in the first week of the month should be ok. The comet should hopefully still be visible in binoculars and the both objects will appear in the same field of view using 10x50s on the 3rd 4th and 5th. The comet crosses the border into Cassiopeia on the 9th and on the following evening it will pass close to NGC 147 (Caldwell 17) a magnitude +10.5 galaxy which is a member of our local group You will need a telescope to spot this galaxy and it neighbour NGC185 (Caldwell 18) magnitude +10.1. These two galaxies are gravitationally linked and are both outlying satellite galaxies of M31. On the 20th the comet passes between Shedir, (α) and Caph, (β) Cassiopeiae just over halfway from alpha to beta. The comet crosses the border the 28th ending the month in the constellation of Cepheus. If the weather improves and you do observe Comet Panstarrs please let me have a report f you observation for Eclipse. 6 19 The Sky this Month The Sky looking East around midnight mid April 2013 Now that we have moved to British Summer Time (BST), spring is finally here, and the bright constellations of winter, Orion, Taurus and Gemini are replaced by the less conspicuous spring constellations of Coma Berenices, Virgo and Hydra. However some of these constellations are very popular with deep-sky observers as they are home to large clusters of galaxies. High in the south you will find the constellation of Leo, it is easily recognisable as, to me, it vaguely resembles the outline of a prone Lion. The brightest star in Leo, shining at magnitude +1.35 is alpha (α) Leonis, Regulus; which marks one of the front paws of the celestial lion. It lies at the bottom of the asterism known as ‘the Sickle’ (a backwards ?) that represents the head and mane of the lion. The ‘Sickle’ is formed by the stars alpha (α), eta (η), gamma (γ), zeta (ζ), mu (μ) and epsilon (ε). Lying below the body of the lion there are a number of galaxies including five Messier objects M65, M66, M95, M95 and M105. M65, M66, along with NGC 3628, are known collectively as the ‘Leo Triplet’ and can be found just to the south of theta (θ) Leonis. The other three Messier objects M95, M96 and M105 form another small group that lies just below the mid-point between alpha (α) and theta (θ) Leonis. One of the other highlights in Leo is the lovely double star gamma (γ) Leonis (Algieba), this is a great double for small telescopes. The primary is a magnitude +2.2 K-class yellow-orange giant, it’s companion is a magnitude +2.5 yellow Gclass star. The pair are separated by 4.4 arcseconds. Just to the west of Leo lies the faint constellation of Cancer, which is home to one of the loveliest open clusters in the sky, Praesepe, more commonly known as the Beehive Cluster or M44. This large cluster of stars is just about visible with to the naked-eye even from light polluted areas, and a stunning sight in binoculars and small telescopes. There is another of Messier’s open clusters in Cancer, M67, this cluster lies a little over 1.5 degrees west of Acubens, alpha (α) Cancri. Due to its roughly triangular shape it is known as the ‘Cobra’s Head’ or ‘King Cobra’ cluster. Iota (ι) Cancri is a double star that lies in the north of the constellation. The star consists of a magnitude +4.02 yellow G-class giant star, and a magnitude +6.58, white A-class dwarf. The pair are separated by 30 arcseconds and are a lovely sight in a small telescope. 18 7 8 17 The Sky looking North around midnight mid April 2013 Leo & Cancer The Sky this Month The Sky looking West around midnight mid April 2013 To the east and southeast of Leo lies the constellations of Coma Berenices and Virgo. These two constellations are home to a huge group of galaxies known as the Coma-Virgo cluster. Coma contains eight Messier objects M53, M64, M85, M88, M91, M98, M99, and M100 and Virgo contains another eleven, M49, M58, M59, M60, M61, M84, M86, M87, M89, M90, and M104. All these objects are visible in amateur telescopes. The constellation of Hydra can be found meandering across the horizon in south and southwest, this is the largest constellation in the sky. Hydra is a relatively faint constellation and it can be quite difficult to pick it out in the haze close to the horizon. Hydra is home to three Messier objects, M48, an open cluster, M68 a globular cluster and M83, a spiral galaxy. Sitting along the length of Hydra are three small constellations, Corvus, Crater and Sextans. Corvus is the most easterly of the trio and is probably the easiest to identify, four of the brighter stars, beta (β), delta (δ), gamma (γ) and epsilon (ε) Corvi form an irregular quadrilateral which stands out quite well in this sparsely populated area of the sky. The most interesting ‘object’ in the constellation is a pair of interacting galaxies known as the Antennae Galaxies (NGC 4038/NGC 4039) which can be found in the west of Corvus. Moving west, Crater, is next, the base of the cup resembles the shape of Corvus, only reversed, and is formed by alpha (α), beta (β), delta (δ), gamma (γ) Crateris. Sextans is the last of the trio, this is a very faint constellation, its brightest star, alpha (α) Sextantis is only magnitude +4.49. There is just one interesting deepsky object, NGC 3115, an almost edge on Lenticular galaxy which can be found just over three degrees east of gamma (γ) Sextantis. Lying just to the east of Leo and Coma Berenices you will find the ‘Kite’ shaped constellation of Boötes, its brightest star is the magnitude -0.07 K-Class orange giant, Arcturus. Further east lies the constellation of Hercules which is home to two of Messier’s globular clusters M13 and M92. M13 is the best globular cluster visible in the northern half of the sky, it lies on the western side of the ‘Keystone’ asterism, about a third of the way from eta (η) to zeta (ζ) Herculis. M92 lies to the north of the ‘Keystone’ approximately midway between eta and iota (ι) Herculis. There is a fairly bright planetary nebula (magnitude +9.3) which lies just over four degrees east of Kornephoros; beta (β). Lying between the constellations Boötes and Hercules is a small semi-circle of stars that form Corona Borealis, near the centre of the semi-circle lies the famous 16 9 10 15 The Sky looking South around midnight mid April 2013 Coma Berinices & Virgo The Sky looking Overhead around midnight mid April 2013 The Sky this Month variable star R Coronae Borealis. R CrB is the type star of a class of variables which unlike most types of variables which brighten from their normal state, R CrB type variables fade dramatically. The star is currently recovering from one of the longest and deepest minima for many years, it faded to below magnitude +15. Keep an eye on R Coronae as it returns to it’s normal brightness of magnitude +6. Over in the western sky, Gemini (the Twins) remain visible until after midnight. Castor (α Geminorum) is nice double star which is suitable for observers with small telescopes. The components are both A-class stars, magnitudes +1.93 and +2.97 separated by 6 arcseconds. Lying at the feet of Castor, just over 2 degrees west of eta (η) Geminorum you will find M35, this open cluster is a stunning sight through a telescope. To the northwest of Gemini lies the constellation of Auriga which is home to three of Messier’s open clusters, M36, M37 and M38 all of which are visible in binoculars and small telescopes. High overhead you will find the familiar pattern of 7 stars known as the ‘Plough’ or ‘Saucepan’ which is part of the constellation of Ursa Major. This pattern of stars can be used as a guide to help you locate a number of other constellations. The two end stars in the bowl, Dubhe and Merak are known as the ‘Pointers’ as they point to Polaris, the ‘Pole Star’. Following a line from the other two stars in the bowl to the south will bring you to Regulus the brightest star in Leo. If you follow the curve of the handle towards the south, it will point you towards the bright orange star Arcturus. If you continue the arc further to the south it will lead you to the bright star Spica; the brightest star in Virgo. There are a number of deep-sky objects in Ursa Major including 7 that made it into Messier’s catalogue, M40, M81, M82, M97, M101, M108 and M109. In the northern sky you will find Polaris; alpha (α) Ursa Minoris one of the most important stars in the sky. Polaris lies just under than half a degree from the north celestial pole, making it extremely useful for navigation. Lying below Polaris you will find the ‘crooked house’ shape of Cepheus and the W shaped Cassiopeia. The central star in the ‘W’, gamma (γ) Cassiopeiae is the prototype of a class of eruptive type variables. Gamma is a naked eye variable which varies irregularly in brightness between +2.20 and +3.40. In the eastern sky the summer constellations of Lyra and Cygnus are now rising before midnight. By the early hours of the morning Lyra will be at a reasonable height, giving you the chance to observe one of summer’s showpiece objects M57; the Ring Nebula. This planetary nebula can be seen as a small hazy patch in 14 11 The Sky This Month small telescopes, larger instruments will show the ‘Smoke Ring’ shape of M57. The Ring Nebula is quite an easy object to locate, it lies between beta (β) and gamma (γ) Lyrae, about one third of the way from beta to gamma. 01 Apr 01:00 15 Apr 00:00 30 Apr 23:00 Another highlight in the constellation of Lyra is the famous ‘Double Double’ epsilon (ε) Lyrae. To the nakedeye epsilon appears to be a single star, however when viewed through a telescope the star splits into two pairs, Epsilon1 and Epsilon2. Epsilon 1, the northernmost pair consists of stars of magnitude +4.7 and +6.2 separated by 2.6 arcseconds. This is true binary system with the two stars orbiting each other every 1200 years or so. Epsilon2 consists of magnitude +5.1 and +5.5 stars which are separated by 2.3 arcseconds. This is another binary system with the stars orbiting each other every 585 years. Low in the north-east you will find Cygnus, which is also known as the ‘Northern Cross’. At the northern end of the ‘cross’ lies the constellation’s brightest star alpha (α) Cygni, Deneb; which forms the western apex of the ‘Summer Triangle’ the other two apexes are marked by are Vega; alpha (α) Lyrae and Altair; alpha (α) Aquilae. At the southern end of the ‘cross’, lies Albireo; beta (β) Cygni, one of the loveliest double stars in the northern sky. The components of this double have contrasting colours of golden yellow and blue/green. The brighter of the two is a magnitude +3.3 K-class yellow giant, it’s companion is a B-class blue dwarf shining at magnitude +5.3. Comet C/2011 L4 Panstarrs should remain visible throughout the month however it will be fading all the time as the comet moves further from the Sun (see pages 19 and 20 for more details and a chart of the comets’ predicted location. 12 Chart Produced by Chris Peat http://www.heavens-above.coom 13