Horse and Rider

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This article is about the asterism. For the equestrian magazine, see Horse & Rider.
Big Dipper map
Big Dipper map

The Horse and Rider is an informal name given to the asterism composed of the two 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[citation needed].

The Big Dipper's bowl and part of the handle photographed from the International Space Station. Mizar and Alcor are at the upper right.
The Big Dipper's bowl and part of the handle photographed from the International Space Station. Mizar and Alcor are at the upper right.


The two stars actually lie three light-years apart. While their proper motions show they move together as members of the Ursa Major Moving Group, it is not believed that they form a true visual binary star system that interacts gravitationally, but just an optical binary.

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