Algol - Observation History

Observation History

In a 2012 paper, a claim was made that ancient Egyptians made detailed observations of the periodic variability of Algol, over 3200 years ago, in a papyrus document called the Cairo Calendar. Despite many claims in the modern literature that its ancient association with a demon-like creature (Gorgon in the Greek tradition, ghoul in the Arabic tradition) strongly suggests that its variability was known long before the 17th century, there is no conclusive evidence for this.

The variability of Algol was first recorded in 1667 by Geminiano Montanari, but the periodic nature of its brightness variations was not recognized until more than a century later by the British amateur astronomer John Goodricke (who also proposed a mechanism for the star's variability). In May 1783 he presented his findings to the Royal Society, suggesting that the periodic variability was caused by a dark body passing in front of the star (or else that the star itself has a darker region that is periodically turned toward the Earth.) For his report he was awarded the Copley Medal.

In 1881, the Harvard astronomer Edward Charles Pickering presented evidence that Algol was actually an eclipsing binary. This was confirmed a few years later, in 1889, when the Potsdam astronomer Hermann Carl Vogel found periodic doppler shifts in the spectrum of Algol, inferring variations in the radial velocity of this binary system. Thus Algol became one of the first known spectroscopic binaries. Dr. Joel Stebbins at the University of Illinois Observatory used an early selenium cell photometer to produce the first-ever photoelectric study of a variable star. The light curve revealed the second minimum and the reflection effect between the two stars.