What to look out in the December night skies

THE December night sky is attracting the attention of astronomers with the possibility of an early Christmas present due to a visitor in the night sky. This is comet Wirtanen, which will be nicely placed for people to try to find. Although this comet will not rival some of the incredibly bright comets that occasionally grace our sky, comet Wirtanen will, as far as predictions go, become bright enough to be seen with the naked eye, in other words you won’t need binoculars or telescopes to find it.

A comet is essentially a dirty snowball anywhere between one and fifty miles across travelling around the Sun. When it gets closer to the Sun the heat causes ice on the comet to melt and a tail forms. Wirtanen is only a small comet, being around one mile across.

I have to issue a note of caution here because predicting the brightnesses of comets can be notoriously unreliable. It has often been said that there is a connection between comets and cats as they both have tails and both do exactly what they like.

At the present time comet Wirtanen is predicted to reach magnitude plus 3 which means that although being a bit fainter than the North Star it should still be noticeable as a faint fuzzy patch in the sky. It will be passing through the constellations of Taurus and Auriga. Comet Wirtanen visits our part of the solar system roughly every five and a half years. On December 16, it will pass a mere 7.2 million miles (11.6 million kilometres) from the Earth.

Comet Wirtanen was discovered in 1948 b y the American astronomer Carl Wirtanen on photographs taken at the Lick Observatory in California, USA.

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. With comet Wirtanen in the sky at the moment it is worth mentioning that one of the suggestions was that the Star was Halley’s comet, which is probably the most famous comet of all, returning every 76 years. When astronomers plot its path around the Sun we find that it was in the sky in 11 BC; a little bit too early to be considered as the Star of Bethlehem. I have my own ideas but I doubt that the matter will ever be cleared up.

This month all the main signposts: 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 that Perseus has slain. 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’.

The Planets in December

There are changes in the number of planets that we can see compared with last month, although Mars is still the only planet we can see in the evening sky, appearing as a bright orange looking ‘star’ low in the sky in the south west.

It is in the morning sky where it is possible to see the brightest planet. This is Venus, which is often called the morning or evening star. Venus can be seen in the south eastern sky before the Sun rises as a bright white dot in the sky. The most difficult planet to observe is Mercury, which is the closest planet to the Sun. If you look towards the south east around an hour or so before sunrise around the 21st then it will be possible to see a bright pinkish looking ‘star’. Mercury can be seen much lower in the sky than the brighter planet Venus.

Meteor Showers

The night of December 13/14 will be the night of the meteors, as the Earth will be passing through the Geminid meteor shower. Meteors are often called ‘shooting stars’. This is the most spectacular meteor shower of the year when we can expect to see around 100 meteors per hour. The meteor shower is called the Geminids because all the meteors appear to radiate from a position in the constellation of Gemini the Twins.

Usually a meteor shower is the result of the Earth passing through the trail of meteor dust left in space by a comet as it travels around the Sun. The Geminids are the exception to the rule because the parent body that produces this stream of dust in space is an asteroid rather than a comet. The asteroid in question is called Phaethon and the pieces of dust are slightly larger than usual. This makes the Geminids much brighter and more spectacular than most meteors and they also travel slightly slower across the sky, making them easier to see.

Phases of the Moon for December

New Moon 7; First Quarter 15; Full Moon 22; Last quarter 29. The full moon in December is known as the Long Night Moon. This is so called because the full moon in December occurs near the winter solstice, which has the longest night of the year.

The Winter Solstice

The winter solstice occurs on December 21 when the Sun lies at its lowest point in the sky. It is also 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 25 at All Saints’ Church, Earby, from 7.30pm-9.00pm. The speaker will be Martin Lunn MBE FRAS, Earby Astronomical Society, and the title of the talk will be ‘The Sun’.