The night sky: Comets loom large in astronomers' sights

The sky at about 10pm tonight, looking north

The year has started with comets grabbing a lot of attention.

On New Year's Day, a new comet was discovered by an automatic survey telescope sited in Chile but run by Poles from the University of Warsaw.

This innovative project uses several telescopes, each similar to a modest telephoto lens fitted with very sensitive digital camera. Every clear night they image all the visible Southern Hemisphere sky and measure the brightness of every object they detect. Effectively that includes most objects visible in an amateur telescope. Not surprisingly, the Poles are doing a pretty impressive job of discovering new objects.

This new comet, called C/2006 A1 (Pojmanski) - is now bright enough to be visible in a good telescope but is not expected to get much brighter.

At the Stardome in Auckland, precise measurements are made of the positions of comets and about five different ones are being followed at the moment, although most are exceedingly faint. The data are used to track changes to their orbits caused by a combination of the tug of the gravity of planets with the push from gases that jet from fissures in the comets' surface - rather like geysers.

On January 15, the Stardust mission successfully returned to Earth tiny samples of cometary dust collected during a close flyby of the comet Wild 2 in 2004. It is hoped that analysis of these dust particles will provide new insights into the formationof the solar system.

Finally, there has been the recent discovery that a double asteroid called Patroclus-Menoetius is actually two comets orbiting each other. This strange pair is a member of the Trojan asteroids that orbit the Sun in company with Jupiter. The densities were measured at only 80 per cent that of water consistent with a composition of mainly water ice.

While there may be no readily observable comets in the sky at present, there is a good selection of bright planets. After sunset in the northwestern sky, Mars (in Taurus) is the bright reddish object forming a line with the red giant stars Betelgeuse and Aldebaran.

In the northeast, Saturn is rising in Cancer. Saturn has a pale yellow colour and being quite bright, it is easy to spot to the right of the Gemini twins, Pollux and Castor.

Jupiter rises in the east just after midnight and is high in the north by dawn. Venus rises just before the Sun in the east.