Algol: The Enigmatic Demon Star That Captivated Ancient Astronomers

A terrifying omen and a puzzling reality

(Public domain)

For thousands of years, many philosophers and religious adherents believed that the heavens were perfect. While the Earth was a realm of chaos, imperfection, and change, the sky above was the opposite. The night sky was predictable, perfect, and unchanging. This idea endured until the 16th century when the invention of the telescope showed us sunspots on the sun and craters on the moon. These seeming imperfections shattered illusions that the heavens were a place of unspoiled perfection.

It was this idea of perfection in the heavens that made the star Algol such a frustrating feature of the night sky. Located in the constellation Perseus, Algol is a variable star, meaning that its brightness changes and is in flux.

Algol’s brightness doesn’t change a little. It changes a lot. At its brightest, Algol is roughly three times brighter than when it is at its dimmest. Algol changes brightness roughly every three days, leaving a strange pulsing spot in the sky. Algol’s variation is so stark that it is noticeable to the naked eye.

The fact that this one star was so insistent on changing (or winking, as people call it) befuddled people for generations. It gave the star a bad reputation. Soon…