The most famous star in the Great Bear is Mizar, the second star in the Bear's tail. When skies are clear of mist and moonlight a fainter companion can be spotted next to Mizar. This fainter star is Alcor which shines at 4th magnitude. Together Mizar and Alcor make up one of the skies easiest naked-eye double stars. The pair have the old English name of 'Jack and his Wagon' and discriminating Alcor used to be an old eye slight test for the Navy. Mizar and Alcor are not true double stars; that is to say they do not orbit around a common centre of gravity- they appear close together simply though a line of sight effect and are known as optical doubles. Having said this, Mizar does have a true double star, discovered by EC.Pickering in 1889 using the technique of spectroscopy - the interpretation of a star's light or spectra.

Name: Mizar
Bayer/Flamsteed Name: 79Zet UMa
Magnitude: 2.27
Spectral Type: A1VpS
Henry Draper Catalogue Number: 116656
Smithsonian Astrophysical Observation Number: 28737
Right Ascension: 13h23m55.5s
Declination: 54°55' 31"
Notes: Variable

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