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January 13, 2014

Sky this Month: January 2014

SkyThisMonthJan14by Chris Mann

January is perhaps the best month to understand how all the constellations all fit together.  Find a dark site and just go out and look.  The Milky Way sweeps across the whole sky, overhead, from north-west to south-east and it’s a glorious sight. Almost all the major constellations seem to be embedded it, attached to it and hanging off it.  The first slide shows the sky at 8pm in London. Cygnus is now setting, and then comes Cepheus and Lacerta.  Overhead at this time of the evening are Cassiopeia and Perseus, with to the north the little known Camelopardalis – not surprising as none of its stars are very bright.  Then, as we move towards the ‘rising’ half of the sky, Auriga and Taurus, then Gemini and Orion. Towards the horizon, we see Monoceros and then Sirius in Canis Major.

Almost overhead, at this time of year, the Milky Way axis is crossed by the Ecliptic, with Leo and Cancer rising in the east, Gemini and Taurus at the intersection, and Aries, Pisces and Aquila setting in the west. 

In the evening, Jupiter, riding high in Gemini all night; and Uranus, lowdown to the south-west. Jupiter was at its midnight culmination – opposition – on 5 January.  At 60 degrees above the horizon in London, it’s as high as it will ever get and is visible all night. The second image of Jupiter in the presentation was taken by Rupert Smith at around 1am on Saturday 11 January as the red spot began to come into view. Image details are: Telescope APM 152/1200ED Doublet with 4x Barlow for 4800mm focal length. Camera was a Point Grey Blackfly Colour camera with an e2V 5.2µ EV76 sensor (e2V are a UK sensor company and supply sensors for the Hubble and new Gaia Space Telescopes).

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In the early morning (06:50): Venus, having been a great evening object throughout December, zipped just north of the sun on 9 January and is now an early morning object. Mercury at the same time moves east of the sun – an evening object –  until 31 January but by 16 February it, too, zips north of the sun and starts to catch up Venus as a morning object.

Mars and Saturn are also morning objects at this time, Mars rising about 2pm next week and Saturn later. By 1st February, Mars rises around 23:30. Ceres and Vesta will be just north east of Mars by then and will dance together, getting closer and closer until by 2-4 July they are a mere 10 arc-minutes apart. They are in opposition in mid April when, Ceres at least, at mag 5.8 could be a north-east object at a dark site except the moon will be close.

There is such a wealth of objects, planets and deep sky, at present , I thought that, rather than try to cover them all, I would like to concentrate on just one constellation. Not Orion, which is so well known, nor Gemini for the same reason, but Auriga, riding high at the moment, at the intersection of the Milky Way with the Ecliptic.  One of the great constellations with a profusion of interesting objects.  I’d like to pick out a few items of interest for those with even with low-powered telescopes.

First, Capella. At a magnitude of +0.09, 6th brightest star (after, in the Northern Hemisphere, Sirius in the Big Dog, Arcturus in Bootes, Vega in Lyra and Rigel in Orion). It is the closest 1st mag star to the North Pole. Its proper motion matches the Hyades, the loose cluster in Taurus, of which it may be an outrider. In fact it’s a double star – though at a separation of .05 secs of arc you won’t see it in an amateur scope – and is circled by Capella H at Mag 10, itself a double, at 12 minutes separation.

Menkalinan is an eclipsing binary star and seems to be of a group with some 70 members, to which Sirius, Alpha Ophiucus and Delta Leonis also belong.

Three stars in Auriga, Epsilon, Eta and Zeta, are known as the “Kids”. Epsilon is one of the most studied objects because no one in the 20th century could work out what was causing its variations. Eclipses, which occur every 27 years, last an amazing 2 years. What exactly passes in front of the star was a mystery, though it was thought that a large disk of material with two stars orbiting tightly in the centre is the cause of the eclipse. The disk itself is pretty huge – on the order of 8 astronomical units. There is a slight brightening during the middle of the eclipse that led astronomers to believe there is a hole created by the two stars in the centre. During the 2009-11 eclipse, there was an intensive worldwide observation programme by amateurs and professionals alike to nail the mystery. Using photometry, infrared, CCD, spectroscopy and eclipse spectro-polarimetry, it seems Epsilon Aurigae comprises an unstable F star in orbit around a comparable mass upper-main-sequence star (or stars) enshrouded in a disk resulting from F star mass loss.  The F star may be undergoing rapid evolutionary changes, and the hidden star(s) may have gained mass from the F star. It is the cool, very large disk which eclipses the hidden star.

There are 3 stunning open galactic clusters in Auriga, M36, M37 and M38. M37, perhaps the finest of the three, described variously as ‘a diamond sunburst’, ‘sparkling gold dust’ and ‘best in class’.  Contains some 500 stars down to Mag 12.5. M36 contains around 60 young, bright B-type stars, with a diameter of 14 Lys and an intrinsic brightness of 5,000 suns.  Were it 10 times closer, it would rival the Pleiades. M38 has about 100 stars in a diameter of 25 light-years.

Now I’m sure you’ll be upset if I don’t mention a couple of – to me anyway – really interesting variable stars. The first is SS Aurigae. This is a cataclysmic variable, known as a dwarf nova.  In dwarf novae, 2 tiny sub-dwarf stars very close to each other rotate quickly, in SS’s case in just over 4 hours. Material transfers from one to the other onto a spinning disk which periodically goes nova. Every 50 – 100 days, with an average of 55, the SS system explodes about 5 mags, from 15 to 10, in a couple of days.  So, from not visible to visible in an 8” telescope.  Great fun watching a blank space waiting for something to appear and great fun when it does.

The second is UV Aurigae. Another close binary, this time consisting of a hot star, a star of late type, and an extended envelope excited by the hot star’s radiation. The combined brightness displays irregular variations with amplitudes up to 4 mag.

By the way, the Sun will rise every day next month! Seriously, the solar cycle is rising to a (low) peak so expect more sunspots and flares and perhaps for those far North some aurorae.
Happy New Year, dark skies and great observing!

Posted under: Flamsteed, Sky This Month