Eridani alpha

Alpha Eridani (α Eridani/α Eri) is the the most brilliant star of the Constellation of the Éridan where it is located at the southern end. It is more known under its traditional name of Achernar , sometimes spelled Akhenar (of the Arab Al Akhir Al Nahr , end of the river; the Éridan constellation represents the river éponyme Greek Mythologie Éridan). It is the ninth most brilliant star of the night sky (see Liste of most brilliant stars). Because of its very low variation, it is not visible since the Europe. Before the southern sky is not discovered by the European explorers of the 16th century, the constellation of Éridan in fact was extended less, and it was at the time star more in the south of the visible part of the constellation of today which bore the name of Achernar (because of etymology of the name, cf above). This star, today θ Eridani is from now on known under the name of Acamar.

It is a very luminous star Supergéante of blue-white color (temperature of surface about 20 000 degrees). Its total luminosity is more than 5000 times higher than that of the Sun, though only a little more than 1000 times in the visible field, the large one of its energy being radiated in the Ultraviolet.

It shows the weak ones but regular variations of luminosity which could be due to its fast rotation (see below) and presence of spots on its surface. It presents also a loss of important mass.

Achernar is one of the stars whose clean rotation is among fastest. The speed of its surface to the equator is of 225 Kilomètre S by second, that is to say 75% the critical engine failure speed beyond which the matter located at the equator would be ejected by the Centrifugal force due to the rotation of star. Consequence of this considerable rotation, Achernar is the known most flattened star to date. The shape of star such as it is observed by the interferometric mode Broad Very Telescopes (VLT) Observatoire Southern European (ESO) reveals a Ellipsoïde flattened, whose report/ratio of the axes is 1,5:1. This report/ratio represents a limit lower than the report/ratio between the equatorial diameter and of polar diameter of star (if the axis of rotation of star is not perpendicular to the direction of observation, this report/ratio is larger than 1,5). In any event, this extreme flatness represents a challenge for the models of internal structure of stars.

External bonds

Press release of the ESO in connection with the measurement of the flatness of Achernar
Achernar on the site of Jim Kaler
Achernar on the site solstation.com

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