Watch the “Demon Star” Brighten

The star Algol in Perseus (the Hero) is among the most accessible variable stars for beginner skywatchers. Its visual brightness dims noticeably for about 10 hours once every 2 days, 20 hours, and 49 minutes because a dim companion star orbiting nearly edge-on to Earth crosses in front of the much brighter main star.

On Friday, December 28 at 6:06 pm Eastern Time, Algol will reach its minimum brightness of magnitude 3.4. At that time, for observers in the GTA, it will sit more than halfway up the eastern sky. By 11:06 pm, Algol will be high overhead and will have brightened to its usual magnitude of 2.1.

In the constellation, Algol marks the glowing eye of Medusa the Gorgon, whose severed head Perseus is carrying. That’s why this star has the nickname the “Demon Star”. The constellation sits to the upper left of the bright Pleiades star cluster.