“The Demon Star” –Cairo Calendar Shows Egyptians Discovered the Binary Algol 3200 Years Ago
Algol, aka the Demon Star, is actually a binary star in the Perseus constellation, and has been discovered by a group of Finnish researchers to be first noted by the Egyptians some 3200 years ago. It is one of the best known eclipsing binaries, the first such star to be discovered, and also one of the first (non-nova) variable stars to be discovered.
The eclipses in binary stars give precise information of orbital period changes. Alogl brightens and dims every 2.867 days, a phenomenon first described in semi-modern western astronomy by John Goodricke, who wrote about what he saw with the naked eye back in 1783. The irregular orbital period changes of this longest known eclipsing binary continues to puzzle astronomers. The mass transfer between the two members of this binary should cause a long-term increase of the orbital period, but observations over two centuries have not confirmed this effect.