Alkaid
Alkaid is a blue-white star, far hotter than the Sun, in the constellation Ursa Major. It is in the long, steady part of its life, making helium from hydrogen in its core, as the Sun is.
How far
100 light years
The light you see from Alkaid tonight set off about 100 years ago. Everything we know about it is that much out of date.
How bright
160 Suns
It gives out 160 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 1.85. Smaller numbers are brighter, and the faintest stars the eye can see are about 6.
How hot
About 17,000 K
That is the temperature of its surface, worked out from its spectral type, B3V 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. 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.
AlkaidThe Sun
In your sky now
Working it out…
Its names
- Its own name
- Alkaid
- By constellation (Bayer)
- Eta Ursae Majoris
- Hipparcos catalogue
- HIP 67301
- Henry Draper catalogue
- HD 120315
- Spectral type
- B3V 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.