Sky Notes December 2015

Sky Notes for December 2015        Geoff Mitchell

The  December night sky now sees the late autumn constellations prominent early evening and now heralds some familiar winter constellations and the bright planet Jupiter  rising by late evening . In late December, Mercury slips into evening twilight, Uranus and Neptune are evening objects, whilst Venus, Mars, Jupiter and Saturn are dawn objects.  The late autumn / winter night sky contains many fine objects to view with both binocular and small telescopes. The constellations of Cygnus and Lyra can be seen slipping into the west early evening; these are noted for the bright stars of Deneb and Vega.  The Milky Way stretches from the constellation of  Auriga , marked by the bright star Capella in the east up into Perseus  and through the `W` shaped constellation of Cassiopeia high overhead and down along the cross shaped constellation of Cygnus  low in the west . This faint band of stars best seen on dark moonless evenings

Auriga has the bright star Capella, which is circumpolar from UK latitudes and so is always visible. The constellation of Auriga contains some nice star fields and star clusters visible in binoculars.

High In the south the constellation of Pegasus, noted for its `Square ` shape and the adjacent constellation of Andromeda noted for The Andromeda Galaxy (M31) , visible to the unaided eye as a faint fuzzy patch on moonless evening  can now be seen mid evening .  The Square of Pegasus is a useful sign post constellation and also is a good test for sky conditions, (how many faint stars you see within the square is indicates just how good your seeing conditions are).  Follow the two end stars (Scheat and Markab) down to find the star Fomalhaut in the constellation of Pisces Australis (The Southern Fishes), visible very low on the southern horizon early evening mid month.  Another fine globular cluster is M15 in the constellation, best seen telescopically.

In the north Ursa Major, The Plough or The Great Bear is seen low with its handle or tail parallel to the horizon mid evening.   Use the right hand pair of stars  Dubhe  and Merak  (The pointers ) to find the faint pole star Polaris  and hence  the position of North .

Uranus in the constellation of Pisces is visible early evening and can be located using binoculars and a suitable finder chart. A good starting point is to locate the Square of Pegasus and the ring of stars below the Square known as the `Circlet` in the constellation of Pisces (The Fishes), then star hop using the finder chart. Uranus is notable due to the blue colour, telescopes show a tiny disc rather than the sharp pinpoints of stars in the field of view.

Look to the east mid evening to see the seven sisters’ (Pleiades, M45) star cluster and constellation Taurus which heralds the autumn skies. The  Hyades star cluster makes the characteristic `V` shaped asterism in the constellation of Taurus and is noted for the bright, red foreground star  Aldebaren  in Arabic Al Dabaran is `The follower ` of the Pleiades across the skies `, in old English colloquially known as `the eye of the bull`.

By late evening the familiar winter constellations of Orion (The Hunter) with bright red star Betelgeuse (top left) , white star Rigel (bottom right ) and the three stars of Orion’s  belt Mintaka , Alnilam and Alnitak  . Below Orion’s belt can be seen the misty patch that is M42 / M43, visible to the unaided eye, it is one of the gem’s of the winter skies when seen with a telescope. This nebula some 30 light years across is illuminated by a group of four hot young stars that is known as the `Trapezium `asterism, visible under moderate magnification.

Jupiter rises by midnight in the constellation of Leo (The Lion) and will feature more in the spring skies. Small telescopes show the four bright moons discovered by Galileo in 1610 and the famous cloud belts. Jupiter’s Galilean moons show shadow transits and go into eclipse behind the planet and with the current favourable orbital plane alignment some moons can eclipse each other as seen from Earth.

Interest shifts to the pre dawn skies, looking east where Comet C/2013 US10 may be a binocular / naked eye object in Virgo by second week in December (see notes). The comet heads steadily northward and should become a binocular / telescopic evening object maintaining its brightness well into January at its closest approach to Earth in early 2016.

The moonless conditions around December 14th favour the Geminid meteor shower with rates of 50 to 100 / hour possible, the radiant in the constellation of Gemini being well placed in the late evening / early morning.
Planets in December 2015  

Mercury is low in evening twilight reaching greatest elongation on 29th December.
Venus shines brightly in the morning twilight during December onwards. Venus and a thin crescent moon appear close together on the morning of Dec 8th with Comet C/2013 US10 Catalina forming a triangle (see notes)
Mars is placed in Virgo in the pre dawn morning skies in December.
Jupiter shines brightly in the east on the border of Leo / Virgo late evening by late December.
Saturn is positioned low in dawn skies in December. Better placed in spring 2015.
Uranus is visible early evening in the constellation of Pisces. (Binocular / Telescope required).
Neptune in Aquarius (Binocular / Telescope required). The constellation of Aquarius is positioned low in the south west early evening but slips into twilight skies by mid evening

Moons phases in December

New Moon         Dec 11th              Moonless, best time for deep sky and comet observing.

First Quarter      Dec 18th              Best days to see shadow details in lunar craters (early evening)

Full Moon            Dec 25th              Best days to see bright ray craters like Copernicus / Tycho.

Last Quarter      Dec  3rd                Moon visible in daytime skies.  Do not look directly at the Sun.

Winter solstice Dec 21st (04:48 GMT)

Meteor showers

Geminid range December 8th to 17th, maxima 14th December – slow, bright meteors very favourable

Ursid range December 17th to 25th maxima Dec 23rd   – low rates unfavourable (Full Moon)

The Highlights of the Month

December skies, Milky Way visible high overhead on moonless evenings in darker skies.

Uranus binocular object can be found in the evening sky using suitable finder charts

M31 the Andromeda Galaxy is visible on moonless evenings, best seen in binoculars.

Double cluster, on the Perseus / Cassiopeia border, nice pair of star clusters

Pleiades (Seven Sister’s) star cluster (M45) rising in the east best seen with binoculars

Orion Nebula (M42) is a beautiful sight seen telescopically

Geminid meteor shower, moderate rates 20 to 30 / hour

Comet C/2013 US10 Catalina may be binocular or even visible to the unaided eye in the dawn skies (05:00 hrs) from early December for early rise observers (see notes)

All the classic planets in visible in late December although in moonlight using binoculars / naked eye , Mercury in early evening twilight** 4:45 pm Dec 29th (In evening twilight after sunset and  Pre dawn Venus Jupiter, Mars and finally Saturn low in dawn twilight (06:30 am  Dec 29th Dec ). [** Always ensure the Sun has set before looking, binoculars are useful in locating Mercury]  Telescopic observers could complete the `set` of the  major planets with Uranus and Neptune ( mid evening)  More detailed sky notes and LAS Newsletters, Finder charts are available to LAS members via the Members` page on the LAS Website

Comet C/2013 US10 Catalina is moving northward into UK dawn skies (05:00 GMT) at about a degree per day in early December.  First glimpse for UK observers may be in the first week of December, pre dawn at around 05:00 GMT low in the south eastern aspect. Current predictions suggest that the comet has brightened significantly recently on its way into the Sun (Perihelion occurred November 15th 2015 at a distance of 0.82 AU i.e. 122 Million Km from the Sun).

First glimpse may be early December in darker skies. 5am GMT Dec 8th use the bright planet Venus and the thin waning crescent Moon to locate the Comet low in the southeast pre dawn skies.  A good south east aspect would be best.

Comet should be binocular or perhaps naked eye visible from darker observing sites away from street lights and house lights. Allow additional 15 minutes to become dark adapted, so 04:45 GMT start (perhaps).

More detailed finder charts and newsletters are available to LAS members on the member’s page