β Persei

Beta Persei is Algol, one of the most notable of variable stars.

Perseus is represented here holding the severed head of the Gorgon Medusa. One look from the Gorgon's evil eye and the victim was dead.

Algol, ‘The Demon’, represents the sparkling eye of Medusa. The name indicates that the ancients also knew that the star shone with a variable magnitude.

Algol is the prototype of an important type of variable known as an eclipsing variable.
     Two close stars orbit each other, with the visual magnitude changing as they block out each other's light. In Algol's case, these eclipses happen every 2.9 days, with the star's visual magnitude fluctuating between 2.2 and 3.5, a very noticeable difference. This minimum lasts about ten hours before the maximum magnitude is again reached.

Algol is quickly found by first locating Mirfak (alpha Persei). Once Mirfak is located, move opposite to the Pole Star (due south) ten degrees: binoculars.

Opposite Algol, on the southwestern edge, is 20 Persei, also known as Struve 318: 5.0, 9.7; 237º, 14.2".

With Algol centred, move one field west and very slightly to the north: M34 is an open cluster of about 80 stars, with about the same apparent size as the full moon. It has an apparent magnitude of 5.2.

Click on this object for more informaton.


From Algol now move a bit more than one field east to find nu and epsilon. Epsilon can also be found by moving two fields southeast from alpha Persei.

Click on epsilon to review the objects in this region.

Epsilon Persei is a double (Struve 471) with two white stars: 2.9, 8.9; 10º, 8.7".

In the same field of view is the lovely binocular double Struve 434; AB (orange and blue): 7.8, 8.3; 83º, 33.4".

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