Featured Deep Sky Objects Beta Persei (Algol)

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		Deep Sky Object Chart | Alpha Persei (Mirfak) | Beta Persei (Algol) | More Perseus Stars | M34 | M76 | Double Cluster | NGC 1245 | NGC 1275 | NGC 1499 Beta Persei (Algol) has already been noted as a variable star, and you too can see these oscillations without much trouble. For one thing, the period is conveniently short: 2.86 days. For another, the star does not slowly swing back and forth it brightness, it suddenly plummets from it's normal magnitude 2.1 to 3.4 over the course of an hour or so! This dimmer phase, which last ten hours, is caused by the passage of a secondary star across the face of blue white primary as the two stars orbit one another. While we cannot see the actual stars involved (they are invisibly small at the distance of about 100 light years) but we can deduce the twin nature of Algol through the characteristics of the light changes and also the presence of two distinct stellar spectra in the light emitted from the system. The companion is a yellow star perhaps 4 times brighter than ours, and the separation between the two stars is just about a million miles - 40 times less than the separation of Mercury and our sun. Studies of the light emitted by Algol have confirmed that a third star, a yellow-white sun about as bright as the yellow companion, orbits at a greater distance. This third star is not involved in the eclipse process, but the scene at Algol must be amazing!