By Martin Lunn

GET set for the Geminid meteor shower: a shooting star spectacular for the end of the year.

Many people look out for the annual Perseid meteor shower, which occurs in August. It is, however, not the most spectacular meteor shower. The Geminids hold that title, and they can be seen this month. The Geminids reach maximum on the night of December 14/15 when up to 120 meteors per hour might be seen.

Meteors are connected with comets. As a comet, which is essentially a dirty snowball, travels around the Sun, it leaves a trail of dust behind it. If the Earth happens to pass through such a trail we see a meteor shower. The Earth passes through many such streams each year. Some of the meteor showers are spectacular; others less so, but they are all predictable.

The Geminids are so called because the meteors all seem to come from the constellation of Gemini the Twins. They are special because they are associated not with a comet but with an asteroid, called Phaethon. The pieces of dust produced by asteroids are slightly larger than those produced by comets and because of this they travel through the Earth’s atmosphere more slowly, making them much brighter than the usual meteors.

The Geminids travel at about 20 miles a second, while most other meteors travel at speeds closer to 40 miles per second. The dust particles burn up due to friction in the Earth’s atmosphere.

If there are no clouds we should be in for a spectacular event. If you see a meteor or shooting star in the sky, remember to make a wish.

This month all the main signposts in the night sky are on view: the Plough; Orion; Cassiopeia and the Square of Pegasus. The Plough can be found in the North East, standing on its handle with the pointers (the two stars furthest from the handle) pointing to the North Star. Orion is not yet at its best but it dominates the south eastern part of the sky. Capella, in the constellation of Auriga the Charioteer, has not yet arrived at the zenith but it is very high up. As for the Summer Triangle, only Deneb can be found, low in the west. The Square of Pegasus can be found in the south west. The bright star Fomalhaut in Piscis Austrinus, the Southern Fish, has now set.

The constellation of Perseus is now high in the sky, so this is a good time to find the star Algol which in legend marks the eye of the Medusa slain by Perseus. Medusa was the creature with hair made from snakes, and one look at it would turn the observer to stone. The star names are Arabic, and the word Algol means the ‘Winking Demon’. Algol is what is referred to as a 'variable star', so called because its light changes in brightness over a period of a few days.

These light variations, which were first explained by astronomer John Goodricke in York in the 1780s, are very regular and predictable. It was Goodricke who suggested that the variations were caused by two stars eclipsing each other. It wasn’t until around one hundred years after his death that astronomers were to prove his ideas correct.

While talking about events in the December sky people sometimes think about that most famous of all stars, the Star of Bethlehem. Many people have wondered what it could have been. I have my own ideas about the star, but I expect it will always remain a mystery.

The Planets in December

The planets are putting on a great evening display just in time for Christmas. All of the evening planets are visible as soon as it becomes dark. If you look to the southwest after sunset you will see a bright white dot in the sky, this is the planet Venus often called the Evening Star. In addition, in the south there is a fainter but yellowish looking object this is the planet Saturn.

If you look to the southeast, you will see another bright white dot in the sky. This is Jupiter although not as bright as Venus it is difficult to miss. Jupiter is the largest of the planets in the solar system, further to the southeast and lower in the sky is an orange looking object this is the planet Mars.

If you want to see the last of the naked eye planets, Mercury you will have to be up before the Sun rises. Between December 20 and 25 low in the southeast you can see a pinkish looking object, this is Mercury.

Meteors Showers

After the Geminids another meteor shower, the Ursids, peaks on the night of December 22//23 when it is usual for about ten meteors an hour to be seen. The Ursids appear close to Christmas and with our focus on celebrations they are poorly observed. The Ursids have been known to produce outbursts of large numbers of meteors in the past, so it is worth watching out for them. If you see an Ursid meteor or shooting star, don't forget to make a special Christmas wish. The Ursids appear to come from the constellation of Ursa Minor, the Small Bear. The North Star is the end star of the tail of the small bear.

Phases of the Moon for December

First Quarter 8, Full Moon 15, Last Quarter 22, New Moon 30. The full moon in December is known as the Before Yule Moon. The feast of Yule occurs on the night of December 21 which is the day of the year when the Sun is at its lowest in the sky and produces the shortest period of daylight of the year. This date can vary from year to year by a day or so.

A long time ago people watched for the full moon in December; they then had from that date until the feast of Yule to chop down a Yule log from the forest in readiness to burn it from the feast of Yule for twelve nights. Today of course the Yule log has turned from firewood into a cake.

The Winter Solstice

The winter solstice, when the Sun lies at its lowest point in the sky, occurs on December 21 this year. It is the shortest day and longest night of the year. This is when winter officially begins in the northern hemisphere and summer begins in the southern hemisphere.