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(80 Ursae Majoris). Alcor, forever tied to Mizar, is hardly ever spoken of unless as "Mizar and Alcor," a naked eye double in the tail of Ursa Major that the Arabs referred to as the horse and rider. The name Alcor, however, was stolen from that for Alioth. Both come from an Arabic word that means the "black horse." The term was distorted in different ways as it was applied to each of the two stars. Oddly, the "rider" of the pair is the one with the name of the "horse," "Mizar" referring not to a horse but to the "groin" of the Great Bear. A great many stars with Bayer Greek letter names have no proper names. Alcor is one of the very few in reverse, a star that has a proper names but no Greek letter name. Instead, it is referred to as 80 Ursae Majoris. In the early 1700s, the English astronomer John Flamsteed organized a new catalogue of stars in which they were ordered from west to east within the constellations, Alcor number 80 in Ursa Major. "Flamsteed numbers" are commonly used when the Greek letter names run out. Alcor is a fourth magnitude (4.01) white class A (A5) star with a temperature of 8000 Kelvin and a luminosity 12 times that of the Sun. It appears coupled with Mizar, but is it really a physical companion? We are still not sure. Mizar itself is a quadruple star on the "double-double" theme (two double stars in orbit about each other.) Precision parallaxes with the Hipparcos satellite show Mizar to be 78.1 light years away, but Alcor to be 81.1 light years distant. Mizar and Alcor are part of the Ursa Major cluster, whose core consists of the middle five stars of the Big Dipper. A separation of over three light years, almost the distance between here and Alpha Centauri, would make a gravitational pairing unlikely as the neighboring stars would pull them apart. The measured errors, however, allow a separation as close as 0.7 light years. The errors in the distances are suspected of being greater than listed, and the analysis of the orbit of Mizar A suggests that Mizar might actually be FARTHER than Alcor! If they are actually at the same distance, their minimum separation is only 0.27 light years, making them close enough so that they could truly orbit, though with a long period of three-quarters of a million years. For a time Alcor was thought to be double, but it now appears that early astronomers were fooled and that it is really single, rendering Mizar and Alcor together a "quintuple star." While the Mizar stars are slow rotators with peculiar chemical compositions as a result of element separation, Alcor is a rapid spinner (218 kilometers per second, over 100 times solar). As a result, its atmosphere is stirred and its composition normal. It is, however, a slight pulsating variable. The inner five stars of the Big Dipper are all at roughly the same distance and all are normal hydrogen fusing main sequence dwarfs. Alcor's faintness next to the them is a vivid reminder of the role that mass plays in the stars. Alcor's mass is around 1.6 times that of the Sun. Alioth, on the other hand, with twice Alcor's mass, is almost 10 times brighter!