This month heralds the beginning of winter; the cold and dark months which might not be to everyone’s taste, but they are what astronomers like best. There is more time to go stargazing! Brave the winter chills this month and enjoy the celestial pyrotechnics of the Geminid meteor shower.
All the main guides, Ursa Major, or the Plough, Orion and Cassiopeia are on view. Orion, the main constellation of winter, is getting higher in the sky and will be at its best after Christmas. Of the stars we see near Orion, only Sirius the Dog Star is difficult to find, as it is still very low in the sky. You can use the three stars in Orion’s belt to point to the lower left to locate Sirius.
The Plough is now standing on its handle in the north. Capella, the bright yellow star, is not yet at the overhead point but it is very high up and cannot be missed. The twins of Gemini, Castor and Pollux, are much higher. Now is a great time to look for the Pleiades, or Seven Sisters, which are in the sky, looking south. This is a cluster of stars moving through space together. If you have good eyesight it is easy to see the seven brightest members of the Pleiades, using binoculars or a telescope however you would discover that there are actually about two hundred and fifty stars in the cluster.
Of the summer triangle Altair is no longer visible, Vega is very low in the sky, and Deneb can still be found in the north west.
The full Moon of the 3rd of the month is the biggest and brightest of the year, but will be upstaged by the next supermoon on 2nd January 2018.
As the Moon rises on the 8th December, it lies right in front of the sat Regulus. This occultation ends around 10.15pm, when you will see the bright star pop into view at the Moon’s dark limb.
As the dusk turns to dark on the 30th December you will find the Moon in front of the Hyades.
Around 1am on the 31st of the month the Moon occults Aldebaran, the star will reappear just about an hour later.
Only two dim planets are visible in the evening sky. Neptune and Uranus. But the planetary pace hots up after midnight. First on the scene after 4.30am is Mars. At magnitude +1.6 it starts the month in Virgo and moves into Libra.
Jupiter is next rising at 4.30am mid month. At magnitude –1.6 it is gradually moving up in the morning sky, and approaches Mars by the years end.
At the start of the month you may catch Venus very low on the dawn sky. At magnitude –3.8 it rises an hour before the Sun, but soon drops down into the twilight zone.
In the final few days of 2017 its place is taken by Mercury. Visible just before 7am, low in the south-east at magnitude –0.1. Saturn is lost in daylight this month.
We are due for a serious celestial display on the night of December 13th and 14th, around 100 meteors per hour might be observed from around 10 pm onwards. As the grains of dust are from an asteroid they are slightly larger than those from a comet, so the Geminids can produce many bright white coloured fireballs in the sky. Look up in any direction and you might be lucky to see at least one Geminid.
Phases of the Moon for December
December 3rd – Full Moon
December 10th – Last Quarter
December 18th – New Moon
December 26th – First Quarter
The Shortest Day
The winter solstice occurs on December 21st. This is the time when we have the shortest day of the year. From this point on the Sun will slowly get higher in the sky and daylight will lengthen.