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A pole star is a visible star that is approximately aligned with the axis of rotation of an astronomical body; that is, a star whose apparent position is close to one of the celestial poles. On Earth , a pole star would lie directly overhead when viewed from the North or the South Pole .
The star Polaris, often called either the "Pole Star" or the "North Star", is treated specially due to its proximity to the north celestial pole. When navigating in the Northern Hemisphere , a simple and quick technique can be used with Polaris to determine the observers latitude or, for larger maritime vessels can be used to calculate any ...
In antiquity, Polaris was not yet the closest naked-eye star to the celestial pole, and the entire constellation of Ursa Minor was used for navigation rather than any single star. Polaris moved close enough to the pole to be the closest naked-eye star, even though still at a distance of several degrees, in the early medieval period, and ...
The International Astronomical Union (IAU) defines the north pole of a planet or any of its satellites in the Solar System as the planetary pole that is in the same celestial hemisphere, relative to the invariable plane of the Solar System, as Earth's north pole. [1] This definition is independent of the object's direction of rotation about its ...
The south celestial pole is visible only from the Southern Hemisphere. It lies in the dim constellation Octans, the Octant. Sigma Octantis is identified as the south pole star, more than one degree away from the pole, but with a magnitude of 5.5 it is barely visible on a clear night.
A star's direction remains nearly fixed due to its vast distance, but its right ascension and declination do change gradually due to precession of the equinoxes and proper motion, and cyclically due to annual parallax. The declinations of Solar System objects change very rapidly compared to those of stars, due to orbital motion and close proximity.
Sigma Octantis is a solitary [9] star in the Octans constellation that forms the pole star of the Southern Hemisphere.Its name is also written as σ Octantis, abbreviated as Sigma Oct or σ Oct, and it is officially named Polaris Australis (/ p oʊ ˈ l ɛər ɪ s ɔː ˈ s t r eɪ l ɪ s /). [10]
True north is the direction along a meridian towards the geographic North Pole. Somewhat more formally, Bowditch defines variation as "the angle between the magnetic and geographic meridians at any place, expressed in degrees and minutes east or west to indicate the direction of magnetic north from true north. The angle between magnetic and ...