Algol, definition and study. A-Z index of Cognitio.

Algol is a star system in the constellation Perseus, 93 light years away from the solar system. It is the best known binary eclipse, the first of this type to be discovered, and is also one of the first variable stars discovered in absolute.

Solar system, definition and study. A-Z Index of Cognitio.

Solar system

Algol is one of the few stars visible to the naked eye to show a marked variability: it is the prototype of the Algol variables and is actually a triple star, where the main star, Algol A, is regularly eclipsed by the weaker partner, Algol B. The association of Algol to a demon (Ghul in the Arab tradition), probably due to its behavior, suggests that the variability of the star was known even before the seventeenth century. Algol is located at the end of the westernmost arm of the inverted “Y” that identifies the constellation of Perseus and, at its maximum brightness, is the second brightest star of the same constellation. Characterized by a strongly northern declination, its observation is easier from the regions of the boreal hemisphere, where it is very high on the horizon in the autumn evenings and the beginning of winter, when Perseus reaches the highest point horizon.

Astronomical observation, definition and study. A-Z index of Cognitio.

Astronomical observation

Being a binary star it is formed by 2 stars, they form a physical couple when they are gravitational linked to each other, rotating around the barycenter of the same couple, in order to balance the gravitational attraction with the centrifugal force.

Gravitational interaction, definition and study. A-Z index of Cognitio.

Gravitational interaction

Therefore they are moving stars on circular or elliptical orbits, but always on the same plane; if they were not moving, they would end up falling on each other. When the less luminous component passes before the brighter one, a real eclipse occurs from the Earth’s point of observation, just as when the Moon passes in front of the Sun: we speak, then, of an eclipsing binary star.

Moon eclipse, definition and study. A-Z index of Cognitio.

Moon eclipse

The eclipses are repeated with extreme regularity and can therefore be predicted with absolute precision. At the end of the eclipse, obviously, the star resumes its usual brightness. Perhaps it is precisely for this particular and unusual characteristic that the most famous star of this category, Algol, in the constellation Perseus (B Perseid) was already known to the Arabs with the rather unsettling name of “Eye of the Devil”. In fact, it decreases its brightness from magnitude of 2.1 to magnitude of 3.4 in an extremely short time: two days, 20 hours and 49 minutes. At each revolution of the less bright star, on time, the eclipse occurs; but the ancients did not know what the cause was. Here is the name given to it by the Arabs.

Algol, definition and study. A-Z index of Cognitio.



To open the video  click on the image, good view from your Alessandro Brizzi.

Algol, definition and study. A-Z index of Cognitio.