• Algol Algol is a star in Perseus. ##### ########### ############### ################# ################# ################# ############### ########### ##### Type Blue-white main-sequence star Constellation Perseus Magnitude 2.1 Spectral type B8V Distance 93 light years Double star components 81.9″ apart Variable eclipses every 2.867 days You need naked eye from a dark sky Known as Bayer β Per Yale HR 936 More information about Algol Every 2.87 days, Algol fades by more than a magnitude for about ten hours, because a dimmer companion passes in front of it. The pattern is regular enough that ancient names for it across several cultures suggest people noticed long before John Goodricke worked out why in 1783. You can watch a minimum happen with no equipment at all. The head of the ghoul or the severed head of Medusa, its name carries a dark meaning. Fitting for a darkening star. History Discovered its variability explained by John Goodricke, 1783 Etymology From Arabic Reading al-Ghul · الغول Literally the ghoul ┌ Greek │ the Gorgon's head, in Perseus │ Γοργόνειον │ ├ Arabic · 9th c. │ ra's al-ghul, head of the ghoul │ رأس الغول │ ├ Latin · medieval │ Algol │ └ English · now Algol, and ghoul, the same word Bayer lettered the stars of each constellation in his Uranometria of 1603, in order of brightness. He was working from Tycho's magnitudes by eye, and the order he recorded is often wrong. First published in 1930 by Yale astronomer Frank Schlesinger, and maintained since, the Yale Bright Star Catalogue lists every star down to magnitude 6.5. It contains 9,110 stars. where it is tonight: skymap.sh/Algol