Castor B
Castor B is a white star, hotter than the Sun, in the constellation Gemini.
How far
52 light years
The light you see from Castor B tonight set off about 52 years ago. Everything we know about it is that much out of date.
How bright
16 Suns
It gives out 16 times as much visible light as the Sun. It is easy to see by eye on a clear night.
Astronomers put its brightness in our sky at magnitude 2.85. Smaller numbers are brighter, and the faintest stars the eye can see are about 6.
How hot
Not known here. The catalogue this site uses has no colour measurement for this star, and colour is what the temperature is worked out from. Its spectral type says it is a white star, hotter than the Sun.
In your sky now
Working it out…
Its names
- Its own name
- Castor B
- By constellation (Bayer)
- Alpha Geminorum
- Henry Draper catalogue
- HD 60178
- Spectral type
- A m
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 words are written for this site.
To read more: Colour and brightness, How stars live and die, Measuring distance.