Algol known colloquially as the Demon Star, is a bright star in the constellation Perseus. The Arabic form is Al-Ghul, the Ghoul.
Algol is actually a three-star system (Beta Persei A, B, and C) in which the large and bright primary Beta Persei A is regularly eclipsed by the dimmer Beta Persei B. Thus, Algol's magnitude is usually near-constant at 2.1, but regularly dips to 3.4 every 2 days, 20 hours and 49 minutes during the roughly 10-hour-long partial eclipses.
The association of Algol with a demon-like creature (Gorgon in the Greek tradition, ghoul in the Arabic tradition) suggests that its variability was known long before the 17th century, but there is still no indisputable evidence for this.
Investigating a calendar for lucky and unlucky days composed in Egypt some 3200 years ago, scholars have noted a significant periodicity of 2.85 days and several empirical tests indicate that this periodicity may be connected to Algol.
Algol is actually a three-star system (Beta Persei A, B, and C) in which the large and bright primary Beta Persei A is regularly eclipsed by the dimmer Beta Persei B. Thus, Algol's magnitude is usually near-constant at 2.1, but regularly dips to 3.4 every 2 days, 20 hours and 49 minutes during the roughly 10-hour-long partial eclipses.
The association of Algol with a demon-like creature (Gorgon in the Greek tradition, ghoul in the Arabic tradition) suggests that its variability was known long before the 17th century, but there is still no indisputable evidence for this.
Investigating a calendar for lucky and unlucky days composed in Egypt some 3200 years ago, scholars have noted a significant periodicity of 2.85 days and several empirical tests indicate that this periodicity may be connected to Algol.