The annual Leonids meteor shower is expected to reach its maximum at around 21:50 GMT tonight (17 Nov 2009), with up to 100 meteors an hour possible at the peak. Viewing conditions should be quite good, with clear skies over much of the UK (particularly the East and South-East) and with yesterday's New Moon meaning that moonlight won't hide the fainter meteors.

The Leonids are one of the most prolific annual meteor showers, with fast, bright meteors associated with Comet Tempel-Tuttle. The radiant (where the meteors appear to stream from) is at the head or 'sickle' of the constellation Leo, hence the name, and meteors can be seen each year over a period of about two days centred on approximately 17 November. Some of the meteors leave trails which can last for up to half an hour.

The Leonids have very brief periods when hundreds or even thousands of meteors can be seen. This seems to come to a peak every 33 years, the period of Comet Tempel-Tuttle. These 'storms' of shooting stars were seen in 1799, 1833, 1866, 1966 and 1999-2001 (although the expected 1899 and 1933 storms were very disappointing). The 1833 storm was particularly spectacular, with estimates of 100,000 meteors per hour. The 1999-2001 storms produced about 3000 per hour.

Image: Leonid shower; photo by Thomas Paulech and Juraj Toth, Bratislava, Slovakia