The night sky in December 2015

posted 2 Dec 2015, 05:01 by Pete Collins
by Anne Holt

Sunset   1 Dec   15.54,   31 Dec    15.59

Not much change in sunset times this month because of the solstice on  22nd.  The earliest sunset is 15.49, from  10th to 17th. - or maybe 15.48 from 13th to 18th. As usual, websites fail to agree on this.

Highlights this month are the Geminid meteor shower,  a possibly naked eye comet, and Venus shining brightly in the morning sky - a real 'star in the east'  over the Christmas period.  No use getting on your camel and trying to follow it, however, after 3 hours  or so it will be lost in the daylight. Also some nice bright early evening passes of the ISS from 10-20 Dec, so you can give Tim Peake a wave after he arrives there 15 Dec. See heavens-above.com on the Links page for ISS transit times.

Constellations

Orion, with the stars of his belt pointing down to the brightest star in the sky, Sirius, is now well above the horizon by midnight, and is a beautiful sight especially from a dark sky site.  By month end these will be visible from 10pm - weather permitting.  Taurus and the Pleiades precede him across the sky.

Gemini, including the 'twins' Castor and Pollux, and Auriga with the bright Capella are also very prominent.
Aries and Pisces, while not particularly bright - or often not even visible in our polluted skies - are both quite high this month.

Perseus, Andromeda and the Great Square of Pegasus  are also well placed for most of the night. The Plough starts the night quite low in the Northern sky, with Cassiopeia high overhead.  Because of the long winter nights, these last two will have changed places before dawn as they rotate around the celestial north pole.

Planets

As usual, for exact positions of visible planets, major asteroids and comets, check    theskylive.com

There still isn't much going on planet wise in the evening sky.

Mercury - in Sagittarius, mag -0.4. Setting too soon after the sun to be easily seen in the first part of December.  On 18th it sets an hour after the sun and might be visible, very low in the Souith East, getting higher over the next week or so. Greatest eastern elongation is on 29th.

Neptune - in Aquarius, mag 7.8. Above the horizon in the southern sky as night falls throughout December. Sets around midnight at the start of the month, a couple of hour earlier by month end. Should be visible in binoculars from a reasonably dark site but a telescope is needed to see the deep blue disc.

Uranus - in Pisces, mag 5.8. Slightly higher in the sky than Neptune, sets around 3am at the start of the month, by 1am towards the end.
On 20th it will be just 2 degrees to the north east of the 64% lit waxing moon soon after midnight. When the moon is not so close, it might just be visible to the naked eye from a dark sky site.  As with Neptune, a telescope is needed to see the planet's disc and its colour - a much more green hue than Neptune.

Jupiter - in Leo, mag -1.9. Rises before midnight in the later part of December, by which time it will have brightened slightly to -2.2.
On 4th it will be just 2 degrees from the northern limb of the waning crescent moon.

Mars - in Virgo, mag 1.4. Rising around 2am by the end of December, when it will be almost due south by dawn. Still not at its best, showing only a small disc when seen through a scope, because of its distance from Earth.  However, it is starting to get closer so will appear to brighten, and get bigger, over the next few months. Passes close to Spica on 24th, when the red colour of the planet will be a lovely contrast to the blue white star..

Saturn - in Ophiuchus, mag 0.6. Will remain in Ophiuchus, which is not considered to be a Zodiac constellation, even though the ecliptic passes through it, throughout 2016.  Rising very soon before the sun, and therefore not visible, in the first part of December.
On 21st it rises 45 minutes before it and might be seen, very low in the eastern dawn sky, 6 degrees above the red giant, Antares.
At the end of the month it will be below and to the left of the very much brighter Venus.

Venus - in Virgo, mag -4.0. Still by far the brightest 'star' in the night sky.  Rises 4 hours before the sun at the start of the month, when it is close to Spica.  By month end it will have moved into Libra and will be above the horizon just over 3 hours before sunrise.

Meteor showers

The major shower this month is the Geminids, which are active from early December to around 17th.  The peak this year is predicted to be at 18.00 on 14th, so the best times to look are the nights of 13th/14th and 14th/15th. ZHR 120, after the peak the rates fall sharply.
Very bright, often multicoloured meteors,  slower moving than the Perseids and with fewer trails. The peak, this year, is soon after the new moon, so there won't be any interference. The Geminids are the only major shower to originate from an asteroid, 3200 Phaeton, rather than a comet.

Also a few minor showers

Puppa Velids,  peak Dec 9th, ZHR 15.
The radiant for this shower is well below the horizon from our latitudes but a few meteors may be seen shooting upwards in the south east.

Coma Berenecids:  active Dec 12th to 23rd, peak 18th,  ZHR 3
This shower was originally regarded as part of the Leo Minorids, but they are now thought to be 2 separate showers.

Leo Minorids:  active Dec 5th to Feb 4th,  peak Dec 20th, ZHR 5
Slightly faster and stronger meteors than the Coma Berenicids.

Ursids: active Dec 1st to 25th, peak 22nd/23rd, ZHR 10.
The moon will be almost full so will interfere with viewing.  Best seen in the hour before dawn, after the moon has set.

Comet Catalina

Finally, this month we might actually get to see a naked eye comet. C/2013 US10 Catalina is expected to be at mag 5 at the start of December when it is in Virgo, very close to 4th mag Kappa Virginis. In the early part of the month it will be near Venus - they are at their closest, about 4 degrees, on 7th.  However, the crescent moon will also be in the vicinity and will affect viewing conditions.
 It will slowly move northwards - and higher in the sky - during the month.  On 11th, at the time of the new moon, it is expected to be at its brightest, maybe up to mag 4, making it an ideal time to try to see it. At the end of Dec it will be just south of the orange star Arcturus. It will probably be easiest to find throughout the month in the pre-dawn sky by using binoculars to scan up from the horizon to the left (north) of Venus up towards Arcturus.

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