Horse and Rider
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The Horse and Rider is an informal name given to the stars Mizar (ΞΆ UMa) and Alcor (80 UMa) because of their close proximity in the sky. Mizar is the second star in from the end of the handle of the Big Dipper. Mizar has apparent magnitude 2.27 and spectral class A1 V. With good eyesight one can make out Alcor as a faint companion just to the east. Alcor has magnitude 3.99 and spectral class A5 V. The ability to see Alcor is said to have been used by the Romans to test soldiers' eyesight (cite needed). The two stars lie more than a quarter light-year apart and although their proper motions show they move together, it is still not known whether they form a true visual binary star system that interacts gravitationally and not just an optical binary as currently thought.
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