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!Ìý