Betelgeuse

Betelgeuse is a red star, among the coolest, in the constellation Orion. It is a supergiant: a very heavy star, swollen to an enormous size and near the end of its life.

Fly to it in 3D Find it on the sky map

A drawing in the star's own colour, worked out from its measured colour index. It is not a photograph.

How far

550 light years

The light you see from Betelgeuse tonight set off about 550 years ago. Everything we know about it is that much out of date.

Betelgeuse is hard to place, because the star is so swollen that its disc is wider than the tiny shift in the sky used to measure distance. This figure comes from a 2020 study of the way the star pulses, and could be anywhere from about 500 to 640 light years. The Hipparcos satellite put it at about 500.

How bright

16,000 Suns

It gives out 16,000 times as much visible light as the Sun. From the Earth it is the ninth brightest star in the night sky. It is one of the brightest stars in the whole sky, easy to see even from a town.

Astronomers put its brightness in our sky at magnitude 0.45. Smaller numbers are brighter, and the faintest stars the eye can see are about 6.

How hot

About 3,800 K

That is the temperature of its surface, worked out from its colour, so it is a guide and not a measurement. It could be out by a few hundred degrees. The Sun's is 5,772 K. Hotter stars are bluer and cooler stars are redder, the same way a poker in a fire goes from red to white.

BetelgeuseThe Sun

In your sky now

Working it out…

Its names

Its own name: Betelgeuse
By constellation (Bayer): Alpha Orionis
Hipparcos catalogue: HIP 27989
Henry Draper catalogue: HD 39801
Spectral type: M2Ib

Where this comes from

Brightness in our sky, colour and spectral type are from the HYG star database, version 4.4, by David Nash, shared under a Creative Commons Attribution-ShareAlike 4.0 licence. The distance is from Joyce and others (2020), and the light the star gives out is worked out from that distance. The temperature is worked out here from the colour with the formula of Ballesteros (2012), and the words are written for this site.