Polaris (a UMi / a Ursae Minoris / Alpha Ursae Minoris) is the brightest star in the constellation Ursa Minor. It is very close to the north celestial pole (42? away), making it the current northern pole star. "Polaris" comes from Stella Polaris, the Latin form of its common name "Pole Star". The rarely used Greek name Cynosura means "tail of the dog" and is the source of the English word cynosure. Other names include the "North Star", the "Lode Star", or sometimes "Polaris Borealis".

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Polaris is a trinary system, consisting of a large yellow Cepheid variable (a UMi A), distantly (about 2700 AU or 380 billion km) orbited by a bright yellow dwarf (a UMi B). Polaris B can be seen with even a modest telescope and was first noticed by William Herschel in 1780. In 1929, it was discovered by examining the spectrum of Polaris A that it had another very close dwarf companion (variously a UMi P, a UMi a or a UMi Ab). In January 2006, NASA released images from the Hubble telescope, directly showing all three members of the Polaris trinary system. The nearer dwarf star is in an orbit of only 20 AU (3 billion km) from Polaris A, explaining why its light is swamped by its close and much brighter companion.

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