Algol, the Demon Star
Arab astronomers called one star 'the demon's head'. Every few days it winks, dimming for hours before it brightens again.
What was reported
Algol is a bright star in the constellation Perseus, in the head of the gorgon Medusa that Perseus holds. Its name comes from the Arabic ra's al-ghūl, 'the head of the demon'.
Every 2 days and 21 hours, it fades to a third of its brightness for a few hours, then returns. Astronomers in Europe noted its dimming in 1667. A study of an ancient Egyptian calendar of lucky and unlucky days, the Cairo Calendar, suggests that priests may have tracked its rhythm more than 3,000 years ago.
Explanations offered
Algol is an eclipsing binary: two stars orbiting each other, and when the fainter one passes in front of the brighter, the light dips. A young English astronomer, John Goodricke, suggested this in 1783. Its strange winking may be why it was linked with demons.
- When
- Recorded since ancient Egypt
- Where
- Cairo, Egypt
- Witnesses
- Ancient Egyptian priests, and astronomers since
- Status
- Explained
Famous cases are real, widely reported events. Each file sets out what witnesses said and the explanations that have been offered, without taking a side.
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