Sunday, November 15, 2015

Tonight's Sky for November 15: Perseus at Zenith at Midnight

Tonight at midnight, mythological Hero Perseus will be at zenith (straight up). This constellation is an interesting one for several reasons, so let's examine them. First up, its alpha (brightest) star is Mirfak and it, along with Fomalhaut, are the only stars brighter than 2nd magnitude in the entire fall sky. Second, Perseus' beta (2nd brightest) star is Algol, and it's an eclipsing binary star. What does that mean? When the dimmer companion moves in front of the brighter main star, Algol will show a noticeable drop in brightness over the course of several hours. This so creeped out the ancients that the very name Algol means “the ghoul” in Arabic. The star is also known as the Winking Demon Star. Third, above Perseus and about half way to W-shaped Cassiopeia ;lies the Double Cluster, a dazzlingly beautiful pair of open clusters populated by blue stars. High power binoculars or a low power eyepiece in a telescope work best here.

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