Bellatrix
Bellatrix is a blue-white star, far hotter than the Sun, in the constellation Orion. It is a giant: a star that has used up the hydrogen in its core and swollen up.
How far
250 light years
The light you see from Bellatrix tonight set off about 250 years ago. Everything we know about it is that much out of date.
At this distance the figure could be out by a tenth or so.
How bright
1,200 Suns
It gives out 1,200 times as much visible light as the Sun. It is one of the hundred brightest stars in the night sky. It is easy to see by eye on a clear night.
Astronomers put its brightness in our sky at magnitude 1.64. Smaller numbers are brighter, and the faintest stars the eye can see are about 6.
How hot
About 21,000 K
That is the temperature of its surface, worked out from its spectral type, B2III, with a standard table of how hot stars of each type are. It is a guide and not a measurement, and could be out by a tenth or so. For stars as hot as this, colour is a poor thermometer, because most of their light is ultraviolet, so the type is the better guide. 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.
BellatrixThe Sun
In your sky now
Working it out…
Its names
- Its own name
- Bellatrix
- By constellation (Bayer)
- Gamma Orionis
- Hipparcos catalogue
- HIP 25336
- Henry Draper catalogue
- HD 35468
- Spectral type
- B2III
Where this comes from
Distance, brightness, 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. Its distances are those measured by the Hipparcos satellite. The temperature is read from the spectral type with the table of Pecaut and Mamajek (2013), and the words are written for this site.
To read more: Colour and brightness, How stars live and die, Measuring distance.