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Achernar, star α of the constellation Eridanus, of magnitude 0.6, spectral class B5, 70 years distance light, luminosity 280 times that of the Sun It is a blue-white star of the main sequence.
It is one of the few stars of the first magnitude, this being equal to 0.50; this magnitude makes it the ninth brightest star in the sky. Its brightness is not so much due to its distance, that is 144 light years, but above all to the fact of being a star very bright: its mass is approximate of 6:00 to 8:00 solar masses and its absolute magnitude is equal to – 2.72. Achernar is among the brightest stars in the sky, the least known at the popular level: this is due to several factors, chief among them the fact that it is located in an area of sky to very southern declination, thus remaining out of sight in Europe and much of North America and Asia; Secondly, the area around this star are devoid of bright stars or arranged to form asterisms particularly known or recognizable. Nevertheless, it is one of the most interesting stars from a scientific perspective, being one of the more flattened at the poles that you know. Its name means ‘mouth, the mouth, the end of the river’, and in fact is the mouth of the river represented by its constellation. It can be observed, very low, the most southern coast of the Mediterranean, in Libya and around. From the physical point of view, Achernar is in the process of the main sequence, then burning hydrogen but since its mass is much higher than that solar, is destined to live much less. Its peculiarity is given by the rotation time. The motion of rotation, in fact, is carried out at a very high speed and this deforms the star, which has a larger diameter at the equator of 50% compared to the diameter obtained by passing through the poles. This speed makes the star among the most studied of the sky, the more so since it is assumed that the rotation is at a speed of 225 Km / s while the theoretical breaking point is equal to 300 km / s, so very close. At these speeds, moreover, also the loss of material to be part of the star is much greater than the loss incurred by the Sun.
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