Stars · Star in Perseus
Star
Algol
The Demon Star — the eye of Medusa — which fades to a third of its brightness for a few hours every 2.87 days.
- Constellation
- Perseus
- Designation
- β Persei
- Apparent magnitude
- 2.09 · 62nd brightest star in the night sky
- Spectral class
- B8V
- Distance
- 89.9 light-years
- Position (J2000)
- RA 3h 08m · Dec +40° 57′
A blue-white main-sequence star, around 14,000 K, like Rigel and Spica. About 58× brighter than the faintest star the eye can see. The light you are seeing left around 1936.
History
The name is Arabic ra’s al-ghūl, “the demon’s head”. In 1783 John Goodricke, a deaf 18-year-old astronomer in York, showed that it dims because a fainter companion passes in front of it.
Look for
Compare it with Mirfak and Almach. On most nights it matches them; on an eclipse night it is clearly fainter.