Mizar and Alcor

Mizar (Arabic مئزر, DMG mi ʾ czar, jacket or belt ' ) is the proper name of the star Zeta Ursae Maiori ( ζ Uma ) in the constellation Ursa Major. Mizar, the mean drawbar star of the Big Dipper constellation and 78 light years away from us. It has long been known that in reality he is a system of four stars and five neighboring suns forms a loose association.

Double or multi- star

Particularly well known is the star of second magnitude, because he already has a freiäugig visible companion Alcor, called the Riders, which can be easily identified under dark skies with normal vision (eye examiner, angular distance 11'50 ", actually three light years).

Mizar itself is a visual double star which is separable with telescopes from two-inch lens opening. Its components are 2.3 and 4.0 might like bright, both have spectral type A2 and are at an angular distance of 14.4 "in the position angle of 153 °. The horseman was probably already known men of the past. A Greek myth of the Pleiades told that one of the heavenly seven sisters had fled from the star cluster in the constellation of Ursa Major.

It is frequently mentioned in the literature, Giovanni Riccioli had been the first who recognized the dual nature of star Mizar in 1650; The basis for this is a short note in his Almagestum novelty from 1651: " ... seems to be only one star in the middle of the handle of the Big Dipper to be, where there are actually two, as the telescope revealed." Recent research, however, show that already Benedetto Castelli and Galileo Galilei in 1617 Mizar have resolved into two single stars. In fact, neither Riccioli still Castelli / Galileo could prove that it is Mizar is a real double star and not just two far behind the other standing stars, since the mutual movement with a turnaround time of an estimated 2000 years is too small. 1889 saw Edward Charles Pickering, that the components A and B in turn are themselves spectroscopic binaries, so that even Mizar is a quadruple system. Only in recent years has managed to make the subsystems A and B by interferometry directly as a separate light sources visible.

Coordinates ( equinox 2000.0 )

• Right ascension: 13 h 23 m 55.50 s
• Declination: 54 ° 55 ' 31.0 "

Member of the "bear stream "

With four other of the seven bright stars are Mizar and Alcor car for so-called bear power, a loose movement pile of about 150 stars distributed over half the sky. Our sun is still in the range of this group, but moves in a different direction.