Alnitak
Alnitak is a blue star, among the hottest there are, in the constellation Orion. It is a supergiant: a very heavy star, swollen to an enormous size and near the end of its life.
How far
740 light years
The light you see from Alnitak tonight set off about 740 years ago. Everything we know about it is that much out of date.
Distances this great are hard to measure, and this one could be out by a fifth or more.
How bright
8,900 Suns
It gives out 8,900 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 1.74. Smaller numbers are brighter, and the faintest stars the eye can see are about 6.
How hot
About 32,000 K
That is the temperature of its surface, worked out from its spectral type, O9.5Ib SB, 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. Its colour alone would suggest only about 14,000 K. Dust lying between us and the star reddens its light, the way the air reddens the setting Sun, so for this star 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.
Alnitak, as it looks through the dustThe Sun
In your sky now
Working it out…
Its names
- Its own name
- Alnitak
- By constellation (Bayer)
- Zeta Orionis
- Hipparcos catalogue
- HIP 26727
- Henry Draper catalogue
- HD 37742
- Spectral type
- O9.5Ib SB
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.