'Alright,' said Ford. 'How would you react if I said that I'm not from Guildford after all, but from a small planet somewhere in the vicinity of Betelgeuse?'
- The Hitchhiker's Guide to the Galaxy by Douglas Adams

Betelgeuse is probably the most well-known star in the sky... with the possible exception of Alpha Centauri, Sirius and the Pole Star.

It lies in the constellation of Orion, at a distance of around 470 light years, and is 20 times as massive as the Sun. Its name comes from the Arabic, ibt al jauzah, meaning 'armpit of the central one' - a reference to Orion himself. We can only speculate about the unflattering names lifeforms from Betelgeuse might have about our star.

The constellation of Orion is one of the grandest in the northern hemisphere. Orion, the hunter, is depicted with a sword in his belt, raising a club and holding a shield toward Taurus the bull, which is above and to the west. One story tells of the great Orion stung to death by a scorpion. He was then cast to the sky, so that he sets as the constellation Scorpius rises. The most impressive sight in the constellation is that of the Great Orion nebula, M42. This can be seen with the naked eye, and considerable detail can be picked out using a good pair of binoculars.

The constellation is also noteworthy for the Orionid meteor shower, whose radiant is on the Geminid border. These meteors shower around October 21.

Although slightly fainter than Rigel (Orion's left foot), Betelgeuse is given the reference alpha orionis, having a stellar magnitude of around 0.4. It is, however, an irregular variable, which means that the fluctuations in its brightness do not follow a regular pattern. Its brightness can drop to below magnitude 1.3 over a period lasting 5.8 years. During this fluctuation, the star's diameter can vary between 300 and 400 times that of the Sun.

Betelgeuse has a surface temperature of 3000K¹ and a spectral classification of M2 (red). In 1975, astronomers were able to use image-processing to construct a map of brightness (and therefore temperature) variations on Betelgeuse's surface - the first time any such study had been performed on any star.

For the amateur astronomers, Betelgeuse lies at Declination +07d 24m 26s, RA 05h 55m 10.2s (for epoch 2000).

Literary References

Incidentally, the characters Ford Prefect and Zaphod Beeblebrox from The Hitch Hikers' Guide to the Galaxy originally hailed from the vicinity of Betelgeuse.

'You know,' said Arthur, 'it's at times like this, when I'm trapped in a Vogon airlock with a man from Betelgeuse, and about to die of asphyxiation in deep space that I really wish I'd listened to what my mother told me when I was young...'

Other Entries in this Project

• The Celestial Sphere
• Astronomical Distance Scales
• Doppler Effect in Reference to Stars
• Travelling to the Stars