Algol

Algol (Beta Persei, β Persei, Beta Per, or β Per) is a triple star system including an eclipsing spectroscopic binary, and whose stars show characteristics that do not fit within normal main-sequence evolution, which is presumed to be a consequence of mass transfer between stars. Characteristics (β Per Aa1):

• Perseus - constellation.
• 03h08m10.13245s - right ascension.
• +40deg57m20.3280 - declination.
• +2.12 - apparent magnitude.
• 94 ly - distance.
• B8V - spectral type.
• 3.17 - mass(solar).
• 182 - luminosity(solar).
• 2.73 - radius(solar).
• -0.05 - B-V color index.

The existence of the abnormal stellar characteristics (ascribed to mass transfer) is termed the Algol paradox.

The terms Algol variable (or just Algol) is a class of variable stars for which Algol is the prototype.