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Sky Notes - April 2012

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Sky Notes - April 2012 North Devon Astronomical Society www.northdevonastronomy.co.uk Sky Notes - April 2012 THE MOON New Moon 21s t April First Quarter 29th April Full Moon 6th April Last Quarter 13th April THE PLANETS Mercury A morning object, Mercury is visible before sunrise by the middle of the month. The planet will reach greatest western elongation on the 18th, when it will be around 27 degrees from the Sun. Venus Now moving closer to the Sun once again following greatest elongation last month, but blazing away at magnitude -4.4, Venus still dominates the western evening sky. In the eyepiece, the planet presents a 25 arcsecond disc which is just under half illuminated. Mars Following last month’s opposition, The Red Planet remains fairly close to the bright star Regulus, in the constellation Leo. Though the apparent diameter of the planet will shrink slightly throughout the month, Mars remains worthy of observation and is visible for most of the night. Jupiter Though still visible low in the west after sunset, Jupiter will soon become lost in the evening twilight. Saturn R eaching opposition on the 15th, Saturn is observable all night in the constellation Virgo, close to the first magnitude star Spica, (Alpha Virginis). A magnificent object, Saturn’s rings and it’s largest satellite Titan are readily apparent in small telescopes, while larger instruments will show atmospheric bands and some of the smaller moons. Uranus Ur anus is too close to the Sun to be observable this month. Neptune A morning object, Neptune can be found among the stars of the constellation Aquarius. APRIL HIGHLIGHTS 3rd Venus passes very close to M45 - the Pleiades star cluster. This relatively rare event, (it won’t happen again for another eight years), is sure to be both a stunning sight and a great imaging opportunity. 15th Saturn at opposition - see above. 18th Mercury at greatest western, (morning), elongation - see above. 21st Peak of the Lyrid meteor shower. Caused by the dusty remnants of Comet C/1861 G1 Thatcher, the Lyrids should be active between the 16th and 26th, and this year’s peak coincides with the new Moon on the night of the 21st / 22nd. The shower radiant is located close to the bright star Vega in Lyra, but best results should be obtained by not looking directly at this area. Peak rates are expected to be around 15 meteors per hour at the zenith. 25th On the evening of the 25th, the young crescent Moon will occult, (pass in front of), the magnitude +2.9 star Zeta ( . ) Tauri, in the constellation Taurus. The star will be seen to disappear behind the dark limb of the Moon at 9.30pm, (as seen from London - Barnstaple will have to wait an extra few minutes), and re-appear some 22 minutes later. CONSTELLATION CLOSE-UP CEPHEUS This month, our target is the northern circumpolar constellation Cepheus. CAMELOPARDALIS Another of the original 48 constellations drawn URSA MINOR up by Ptolemy in the 2nd century AD, Cepheus represents the mythical king of Aetheopia, Polaris (Etheopia) - husband of queen Cassiopeia and father to Andromeda. NGC 188 Covering some 588 square degrees and sitting close to the Northern Celestial Pole, Cepheus never sets, as seen from the UK, and is visible ( Errai throughout the year. Despite containing only DRACO one star brighter than 3rd magnitude - the magnitude +2.45 Alderamin, the constellation $ is fairly easy to locate due to it’s proximity to Alfirk , the pole star Polaris,.and the ‘W’ shape of neighbouring Cassiopeia. CEPHEUS 0 M103 4 Though relatively unremarkable, as regards ( deep sky targets for small telescopes, this k Alderamin constellation contains several interesting $ 0 M52 stars, including the prototype of an important :Herschel’s Garnet Star kind of variable. k . However, one interesting target for small to . moderate telescopes is NGC 188. This small CASSIOPEIA LACERTA CYGNUS open cluster is the closest object of it’s type to the Northern Celestial Pole and is one of the oldest open clusters known to astronomers. As mentioned above, Cepheus contains some interesting and important stars, some of which are listed here: (Cep Gamma Cephei, (also known as Errai), is a binary pair consisting of an orange sub-giant, orbited by a red dwarf companion, and current estimates place the pair at a distance of around 50 light-years from us. Interestingly, Gamma Cephei will be the pole star between 3000 and 5200 AD. k Cep Delta Cephei - the first Cepheid variable. Unlike eclipsing binaries, where the light from a star is dimmed by the orbital motion of a smaller or less powerful companion, the variability in Cepheids is due to the pulsation of the star itself. In the case of Delta Cephei, the star’s brightness ranges between magnitude +3.5 and +4.4 and occurs over a period of around five and a half days. Cepheids are important as their variability is very regular, and this enables astronomers to use them as ‘standard candles’ to measure both galactic and extra-galactic distances. Delta Cephei is around 887 light-years distant and has a magnitude +7.5 companion, (separation 41 arcseconds), which is visible in small telescopes. :Cep Popularly known as ‘Herschel’s Garnet Star’ due to it’s deep red colour, Mu Cephei is another variable star whose luminosity ranges between magnitude +3.4 and +5.1 over a period of around 730 days. A red super- giant with a radius of around 11.8 astronomical units, this star is truly enormous. If the centre of Mu Cephei were placed in the position of our Sun, it would reach out as far as the orbit of Saturn! Cepheus is bordered by the constellations Draco, Cygnus, Lacerta, Cassiopeia, Camelopardalis and Ursa Minor. Society meetings are held on the first Wednesday of each month at the Methodist Church Hall, Rhododendron Ave, Sticklepath Hill, Barnstaple. Meetings begin at 7.45pm and all are welcome to attend, regardless of experience. For more information please contact NDAS secretary Julie Buckingham at [email protected] or call Mark Buckingham on 01271 345374..
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