The December night sky

By CLIVE JACKSON

[email protected]

Clive Jackson is the Director of the Astronomical Observatory of Tavira (Sitio do Malhão, Tavira) and the Camera Obscura (next to the Castle in Tavira), specialising in education and public outreach.

THIS MONTH starts off with a coming together of the bright planets Venus and Jupiter, and also the thin crescent Moon.

This will all happen low on the southwestern horizon. Throughout the month of December and well into the New Year, Venus will be shining brightly in the west/southwest soon after sunset. In fact, when Venus is in this position at this time of the year, it often gets mistaken for the ‘star of Bethlehem’.

Two thousand years ago, a similar astronomical occurrence happened in the night sky over the Middle East. Only the astrologers of that time noticed anything and these were the ‘three kings’ of the biblical story. Exactly what happened is still a mystery but most probably it was a close conjunction of bright objects similar to what is happening this year in December. As you watch Venus, Jupiter and the Moon change their position from night to night in the early evening sky it must have seemed something very special to ancient people who were not aware of the true nature of these objects.

Venus will be seen to sparkle and flash all the colours of the rainbow when it is low in the sky and this is entirely due to the effect of our atmosphere acting as a prism and splitting up the white light of Venus into its component colours. As Venus sets in the southwest, try looking over to the southeast where the star Sirius will be seen rising. This is the brightest of the nighttime stars, and also Sirius will change its colours similar to Venus for the same reasons.

Near the end of December after midnight, over in the east, the ringed planet Saturn will be seen rising in the constellation of Leo. This planet shines with the pale yellow colour and, on the night of 19th, the last quarter Moon will be close to the planet. On the last night of the month, the thin crescent Moon will be close to Venus in the evening sky.

The Moon is at First Quarter on December 5, Full on December 12 and Last Quarter on December 19 and New on December 27.

For more information, please call Clive Jackson on 281 321 754, fax 281 324 688, email [email protected] or visit http://www.cdepa.pt