DECEMBER heralds the beginning of winter; the cold and dark months which might not be to everyone’s taste, but which astronomers like best. There is more time to go stargazing!
If you ever wanted to see a star disappear then reappear, this is the month to be watching. The bright red star Aldebaran in the constellation of Taurus the Bull, which is high in the south, will be occulted by the Moon. This means that the Moon will pass in front of the star. At 5.20am on December 13th, Aldebaran will disappear, then at 5.50am it will reappear from behind the Moon.
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.
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 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.
Venus is absolutely stunning in the evening sky. At a dazzling magnitude of –4.1, it’s putting even the brilliant winter stars to shame.
In early to mid month search along the western horizon after sunset to the lower right of Venus for the planet Mercury. Binoculars will help it will be setting around 5pm.
To the upper left of Venus is Mars with a magnitude of +0.7, it sets soon after 9pm.
Neptune is having some adventures this month on the 6th it’s hidden by the moon and on the very last night of the year Mars gets close up and personal. You will need binoculars or a small telescope to see the distant planet. With a magnitude of +7.9 Neptune lies in Aquarius and sets around 10pm.
Uranus is hanging about in Pices at magnitude +5.8 and sets about 2am.
Mighty Jupiter is a morning observation, rising around 2am. Blazing away in Virgo at magnitude –0.7. It will be moving towards the constellations brightest star, Spica, during this month. The giant planet rises around 2am. Saturn is too close to the sun for observation.
In December we see the Geminid meteor shower, one of the most spectacular of the year, unfortunately this year there will be too much light pollution from the full Moon. 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 7th – First Quarter
December 14th – Full Moon
December 21st – Last Quarter
December 29th – New Moon
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.