Algol is known as the demon star!
A fascinating variable in Perseus that looks like a single magnitude 2.1 star to the unaided eye, but is actually a 3-star system. It dips to mag 3.4 every 2.8 days when 1 of the stars partially eclipses the other. The main binary pair is only separated by 0.062 AU or 5.7 million miles.
Observe this haunting star in October!
Read more from the American Association of Variable Star Observers...