Science: The stars next month

Look at the night sky this month, and you can't miss the constellation of Orion riding high in the south. It's one of the most recognisable star patterns of all, and it really does look like a mighty hunter wielding a club. Most of its stars are bright and distinctly blue, with one (literally) glaring exception. That's brilliant red Betelgeuse, at the top left of the constellation - one of Orion's "shoulders".

The constellation of Orion is a rarity in the sky: a group of stars that actually belong together in space, and were all born at about the same time. All except Betelgeuse, that is. At a distance of 450 light years, it is much closer than Orion's other stars, which lie about 1,000 light years away. Its relative closeness, and enormous girth, means that Betelgeuse is one of the only stars that can be seen - with special techniques - as a disc, and not merely a point of light.

Mike Edmonds, professor of astronomy at the University of Wales in Cardiff, has written a fascinating analysis of this star in the latest issue of Astronomy and Geophysics (the Journal of the Royal Astronomical Society). Using all the latest data, he reveals much about a star very different from our sun.

To begin with, it's huge: 900 million km in diameter, 650 times bigger than the Sun, and so vast that, were it in the Solar System, Betelgeuse would stretch all the way to the asteroid belt and swallow up Mercury, Venus, Earth and Mars. Its red colour is a result of its extreme coolness (for a star) - around 3,500C, in contrast to our yellow sun's temperature of 5,500C, and the 20,000+C blue-white heat of Orion's other stars.

Astronomers reckon the star is only 120 million years old - born when the dinosaurs first emerged on our planet - unlike our more ancient sun (4,600 million years old). Yet Betelgeuse is on the way out. Such massive stars consume their nuclear fuel much faster than ordinary stars like our sun.Mike Edmonds says Betelgeuse will finally run out of fuel in 70 million years. The whole star will explode as a supernova, shining as brightly as the full Moon in Earth's skies.

What's up

Venus is brilliant in the pre-dawn sky, reaching its greatest brilliance this month. Through a small telescope you can see its crescent shape. On 23 February Venus will be five moon-widths north of the crescent Moon.

The only other planet easily visible is Saturn. Lying among the dim stars of Pisces, this yellowish planet sets around 10pm.

The sun suffers a total eclipse on 26 February, with a maximum length of 4 minutes 9 seconds. Best seen from the Caribbean, no part of this eclipse is visible from Britain.

Diary (all 24-hour clock, GMT):

3 Feb, 2254: Moon at first quarter

11 Feb, 1023: Full Moon

19 Feb, 1528: Moon at last quarter

26 Feb, 1726: New Moon; total eclipse of the Sun visible from the mid- Pacific Ocean, the northern part of South America, and the mid-Atlantic Ocean.