The variability of Algol was noted in 1667 by Italian astronomer Geminiano Montanari,[REF] but the periodic nature of its variations in brightness was not recognized until more than a century later, when the British amateur astronomer John Goodricke also proposed a mechanism for the star's variability [REF].
In 1881, the Harvard astronomer Edward Charles Pickering presented evidence that Algol was actually an eclipsing binary [REF].