Night Sky Notes – December 2016

Sky notes for December 2016                        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 Venus low in the west in early evening twilight and the red planet Mars low in the south west . 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. In mid December, Mercury slips into evening twilight reaching greatest elongation on December 11th, Uranus and Neptune are evening binocular objects, Neptune is in conjunction with Mars on December 31st.

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 open star clusters visible in binoculars, notably M36, M37 and M38

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 or The Great Bear, known for The Plough asterism is seen low with its handle 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 currently marking a position close to the north celestial pole.( useful when polar aligning your equatorial telescope mount )

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.

Periodic comet 45P (Honda – Mrkos- Pajdusakova), too faint to see in early evening twilight reaches its closest point some 79 million km from the Sun (Perihelion) on December 31st. Comet 45P may become a binocular pre dawn / early morning then and evening object at its closest approach (13.2 million km ) to Earth in February 2017.

The Moon passes in front of (occults) some stars of the Hyades star cluster in Taurus on the evening of Dec 12th / early morning Dec 13th. The full (perigee) Moon conditions around Dec 14th make the Geminid meteor shower unfavourable. However the Ursid meteor shower peaking around Dec 23rd has better conditions.

Planets in December 2016

Mercury is low in south west evening twilight after sunset reaching greatest elongation on 11th December.

Venus shines brightly in the evening twilight during December. Venus and a thin crescent moon appear close together evening twilight of December2nd and 3rd and again on December 31st after sunset.

Mars is placed in Capricornus low in the south west early evening in December with a waxing Crescent Moon on December 5th and a conjunction with planet Neptune on December 31st.

Jupiter shines brightly in the eastern dawn skies in the constellation of Virgo, a 30% waning crescent Moon is positioned south of Jupiter at dawn December 23rd.

Saturn is located in dawn skies in late December. Saturn will be placed low in late spring evening skies. 2017.

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. Neptune is occulted by the Moon on the evening of December 6th, disappearing behind the dark limb at 22:36 UT just half an hour before moonset.

Moons phases in December 2016

New Moon Dec 29th Moonless, best time for deep sky and comet observing.

First Quarter Dec 7th Best days to see shadow details in lunar craters (early evening)

Full Moon Dec 14th Best days to see bright ray craters like Copernicus / Tycho.

Last Quarter Dec 21st Moon visible in daytime skies. Do not look directly at the Sun.

Winter solstice Dec 21st (10:44 GMT) – Shortest day

Meteor showers

Geminid range December 8th to 17th, maxima 14th December – slow, bright meteors unfavourable, (Full Moon)

Ursid range December 17th to 25th maxima Dec 23rd – low rates ZHR just 10/ hour – favourable

The highlights of the month

  • Venus and the crescent Moon Dec 2nd and 3rd and again on Dec 31st in evening twilight
  • 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.
  • Crescent Moon visibility, a 2.1 % waxing crescent moon is visible in twilight in the south west from around 20 minutes after sunset (from 4.20 pm) with moonset by 5:34 pm on December 30th.

More detailed sky notes and LAS Newsletters, Finder charts are available to LAS members via the Members` page on the LAS Website