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Wednesday, January 17, 2018


Posted to Maritime Musings (by on March 26, 2010

The North Star or Pole Star

Polaris (officially known as Alpha Ursae Minoris) is the brightest star in the constellation Ursa Minor or Little Dipper.  It lies approximately 400 light years from the Earth and appears in the night sky to be about half-way between the Big Dipper and Cassiopeia.  In the modern era, it is conveniently located nearly in line with the axis of the Earth’s rotation, so that the star appears to be stationary above the North Pole.  Actually, its declination is approximately 89°14’, but who wants to quibble.  The observed altitude of Polaris is almost exactly equal to the latitude of the observer at sea.  For precise navigation, the azimuth of Polaris at the time of a star sight must be checked using the Nautical Almanac.  Polaris is a multiple star.  The principal star (Polaris A) is about six times larger than our Sun.  It is orbited by two smaller companions.  Polaris B is visible with a good telescope.  Polaris Ab has been observed using the Hubble space telescope.  Due to its nearly stationary position relative to the Earth, Polaris A is an ideal target for celestial navigation and astronomy.  Ancient Greeks and Norse sailors made use of Polaris in their travels, as did sailors in Asia and Micronesia.  Since Polaris is only visible from the Northern Hemisphere, it was unknown to the long-distance sailors of Polynesia until they reached the Hawaiian Islands.  Due to the precession of the equinoxes, Polaris will lose its favored position relative to the Earth in less than 10,000 years.  Since celestial navigation is already a dying skill, few may notice.  How sad!    


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