Ancient astronomers called the star Algol "The Demon" because it appears to blink in the night sky.

Algol, located in the constellation Perseus, is the first eclipsing binary star ever discovered. The system consists of Algol A, a bright blue-white main-sequence star, and Algol B, a larger but cooler orange subgiant. Every 2.867 days, Algol B passes directly between Earth and Algol A, causing the system's apparent magnitude to drop from 2.1 to 3.4 for roughly 10 hours.The name Algol comes from the Arabic "Ra's al-Ghul," meaning "Head of the Ogre" or "Demon." In Greek mythology, it represents the blinking eye of the Gorgon Medusa. While European astronomers formally documented its variability in the 17th century, evidence suggests much older civilizations noticed the phenomenon. A 2012 study by the University of Helsinki analyzed the Cairo Calendar, an Egyptian papyrus dating back to around 1200 BCE, and found that its lucky and unlucky days matched Algol's 2.85-day cycle.British astronomer John Goodricke was the first to provide a scientific explanation for the dimming in 1783. He proposed that a large body was periodically orbiting the star and eclipsing its light. This discovery was revolutionary because it challenged the Aristotelian view that the heavens were perfect and immutable. Today, Algol is also famous for the "Algol Paradox," where the less massive star in the pair is more evolved than its heavier companion—a result of significant mass transfer between the two stars over millions of years.