Martin Lunn, of Earby Astronomical Society, tells us what to look out for in the December skies.

MANY people look out for the annual Perseid meteor shower, or shooting star shower as some people refer to them, which occurs every 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 13/14 when up to 120 meteors per hour can be seen.

Unfortunately this year the pesky moon will just be past full which will make it a little difficult to see the fainter meteors but fortunately for us the Geminids are among the brightest meteors of the year, so all is not lost.

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 and 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 twenty miles a second compared to most other meteors, which travel at around 40 miles per second. The dust particles burn up due to friction in the Earth’s atmosphere.

This month all the main signposts in the night sky: the Plough; Orion; Cassiopeia and the Square of Pegasus are on view.

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. With regards to the Summer Triangle of stars only Deneb can be found, low in the west. The Square of Pegasus now 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 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’.

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. Venus is in the sky this month so people might believe it was the Star, but astronomers at the time of the birth of Jesus would have been familiar with the movements of the planets and would have known that the appearance of Venus was nothing unusual. I have my own ideas about the star but I doubt that the matter will ever be cleared up.

The Planets in December

The evening sky continues its cycle with the giant gas planets Jupiter and Saturn now having set but there is newcomer with the appearance of Venus as a bright white spot in the south western sky. By Christmas it will be setting around two hours after the Sun. In the morning sky Mercury can be seen as a bright pinkish looking star around the middle of the month about an hour before sunrise. Also in the morning sky is the red planet Mars which is not as bright as Mercury and can be seen as a fairly bright reddish looking star about three hours before sunrise in the south east.

Meteor Showers

As well as the Geminids there is another meteor shower, the Ursids, which peaks on the night of December 22 / 23 when, usually, about ten meteors per hour can be seen. The Ursids appear close to Christmas and with the festival celebrations on people’s mind 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 them. The Ursids appear to come from the constellation of Ursa Minor, the Small Bear. The North Star is actually the end star of the tail of the small bear.

Phases of the Moon for December

First Quarter 4, Full Moon 12, Last quarter 19, New Moon 26.

The full moon in December is known as the 'Before Yule Moon'. The feast of Yule occurs on the night of December 22 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 12 nights. Today of course the Yule log has turned from firewood to a cake.

The Winter Solstice

The winter solstice this year occurs on December 22 when the Sun lies at its lowest point in the sky. It is the shortest day of the year and the longest night.

I would like to wish all the readers of the Craven Herald a very merry and peaceful Christmas and a very Happy New Year.

There is no meeting of the Earby Astronomical Society in December. The next meeting will be on Friday January 31 at All Saints’ Church, Earby, from 7.30pm-9pm. The speaker will be Martin Lunn MBE FRAS, Earby Astronomical Society, and the title of the talk will be ‘Orion the Hunter’.