Pole star

Pole star or polar star is a name of Polaris in the constellation Ursa Minor, after its property of being the naked-eye star closest to the Earth's celestial north pole. Indeed, the name Polaris, introduced in the 18th century, is shortened from New Latin stella polaris, meaning "pole star". Polaris is also known as lodestar, or guiding star or as north star from its property of remaining in a fixed position throughout the course of the night and its use in celestial navigation: it is a dependable indicator of the direction toward the respective geographic pole although not exact; they are virtually fixed, and their angle of elevation can also be used to determine latitude. The south celestial pole lacks a bright star like Polaris to mark its position. At present, the naked-eye star nearest to the celestial south pole is the faint Sigma Octantis, which is sometimes known as the South Star.

In a more general sense, a pole star may be any fixed star close to either celestial pole of any given planetary body. It might refer to any such star in the Earths remote history or future, situated along the path of the celestial poles in the course of the procession of the Earth's axis.

The identity of the pole stars gradually changes over time because the celestial poles exhibit a slow continuous drift through the star field. The primary reason for this is the precession of the Earth's rotational axis, which causes its orientation to change over time. Precession causes the celestial poles to trace out circles on the celestial sphere approximately once every 26,000 years, passing close to different stars at different times (with an additional slight shift due to the proper motion of the stars).

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