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Algol (double star)

Algol (double star)


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Algol it is a double star of the constellation of Perseus (also called b Persei), so called, of the name of an Arab demon, because it periodically changes in luminosity. Algol is 82 light years from Earth.

Algol is the prototype of the Eclipse Variables, double stars in which one component periodically hides the other, causing a decrease in brightness. In the case of Algol, the brightest star in the system is eclipsed every 68.8 hours by a weaker star, which is far from the first 10 million kilometers.

As a result of this phenomenon, the total luminosity of Algol drops from 2.2 to 3.5. Then, when at the other end of the orbit the weakest star disappears behind its lighter companion, a decrease in the brightness of the system occurs, but this time it is very small, approximately 1/10 of magnitude, and determinable only by means of a photometer. A third star that does not take part in the eclipses is also part of the Algol system.

Algol's variability, already known to the Arabs, was discovered in 1669 by Bolognese astronomer Geminiano Montanari and the physical explanation of his behavior was given in 1782 by the Englishman John Goodricke. Radio astronomical observations have led, in 1971, to the discovery that Algol is a source of radio emissions due, it seems, to exchanges of gaseous substances between the two main components of the system.


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