Algol
Algol is a blue-white star, far hotter than the Sun, in the constellation Perseus. It is in the long, steady part of its life, making helium from hydrogen in its core, as the Sun is.
How far
90 light years
The light you see from Algol tonight set off about 90 years ago. Everything we know about it is that much out of date.
How bright
97 Suns
It gives out 97 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 2.09. Smaller numbers are brighter, and the faintest stars the eye can see are about 6.
How hot
About 12,000 K
That is the temperature of its surface, worked out from its spectral type, B8V, 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.
AlgolThe Sun
In your sky now
Working it out…
Its names
- Its own name
- Algol
- By constellation (Bayer)
- Beta Persei
- Hipparcos catalogue
- HIP 14576
- Henry Draper catalogue
- HD 19356
- Spectral type
- B8V
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.