Mizar and Alcor form one of the best-known naked-eye pairs in the sky, separated enough that many observers can distinguish them without optical aid. A telescope reveals that Mizar itself has a close visual companion, and spectroscopy shows still more stars hidden within the system.

Alcor is also not a solitary star. What appears to the eye as a simple pair is therefore a collection of multiple stars, illustrating how common gravitationally bound stellar systems are even among the bright stars we casually treat as single points of light.

What looks like a simple naked-eye double is actually a much richer stellar system. Mizar itself resolves into multiple stars, including spectroscopic pairs whose companions are detected through orbital motion in their spectra, while Alcor also has a faint companion. The field is a vivid reminder that many apparently single stars are gravitational systems containing two or more suns.

Mizar and Alcor sit in Ursa Major, the Great Bear, at the bend of the familiar Big Dipper’s handle. Greek tradition connects the constellation with Callisto, transformed into a bear and placed among the stars.

The pair also has a long cultural life beyond Greek mythology. Its Arabic-derived names entered modern astronomy, and the ability to separate Mizar and Alcor with the naked eye became a traditional test of sharp eyesight in more than one culture.

Mizar and Alcor also became a famous test of eyesight in several observing traditions: separating the faint Alcor from brighter Mizar was a practical demonstration of visual acuity long before telescopes revealed the system’s true complexity. Their location in the handle of the Great Bear or Big Dipper gave the pair an easy place in the sky to remember and revisit.