This occurs because as we view them their orbital plane contains the line of site to Earth. They are known as eclipsing binary stars meaning they regularly eclipse each other, like clockwork. Within Algol, Beta Persei Aa1 (Algol A) and Beta Persei Aa2 (Algol B), form a very close binary system. Beta Persei Ab, the third star (also known as B Persei C) – a cooler white star, spectral type A7M.Beta Persei Aa2 (also known as B Persei B) – a cooler orange subgiant, stellar classification KOIV.Beta Persei Aa1 (also known as B Persei A) – a hot blue-white main sequence star, spectral type B8V.There is also a third star, a fainter star, in this star system forming a triple star system, within the Constellation Perseus.

There are another five dimmer stars in this star system that are listed as companions.Īlgol is the prototype in a group of eclipsing binary stars known as the ‘Algol Variables’, which have variability in their apparent luminosity. The proper star name of this variable star is Algol (from Arabic) and it is also referred to as ‘the Demon’s Head.’Īlgol is not a single star, but a multiple star system with three confirmed and a further two suspected stellar components. It ranks as the 61st brightest star overall in the night sky. The Constellation of Perseus is the 24th largest Constellation in the Northern Sky and borders Constellation Cassiopeia to the north and Constellation Andromeda to the east.Īlgol has an apparent magnitude of between 2.12 and 3.5, making it a second/third magnitude Star, and at its brightest is around 180 times more luminous than the Sun. It is a popular sight from Earth in the night sky for many amateur astronomers. This is a hot star that is bluish-white in color, located in the Constellation of Perseus, in the northern hemisphere, (and associated with the image of the Greek Hero Perseus, carrying the severed head of Medusa, the Gorgon medusa).Īlgol (Beta Persei, B Persei) is the second brightest star in the Constellation Perseus, after Mirfak (alpha Persei), and one of the best known variable stars in the night sky.Īlgol variable stars have a spherical shape. It is a triple-star system, made up of the 3 bright stars – Algol A, Algol B and Algol C. The Algol Star– Facts in brief: What is it?Īlgol is a variable and multiple main sequence star.

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