Explaining ALGOL
On November 12, 1782, 18-year-old John Goodricke of York, England, compared the brightness of the star Algol (Beta Persei) to neighbouring stars in Perseus and Andromeda. Astonished at what he’d seen, he wrote in his journal:
This night I looked at Beta Persei and was much surprized [sic] to find its brightness altered — It now appears of about the 4th magnitude. I observed it diligently for about an hour — I hardly believed that it changed its brightness because I never heard of any star varying so quickly in its brightness. I thought it might perhaps be owing to an optical illusion, a defect in my eyes, or bad air, but the sequel will show that its change is true and that I was not mistaken.
The next night, Goodricke returned for another look at Algol and wrote, “Beta Persei is now much changed. It now appears of the second magnitude. . . . very unexampled change!”
Goodricke didn’t observe Algol’s dimming by chance. He and Edward Pigott, his mentor and friend, were searching for stars whose light varied. At that time the best-studied variable star, with a period of about 11 months, was Mira (Omicron Ceti). Thus, Goodricke expected any change in
