Dictionary

Polar (star)

Polar (star)


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It is the visible star of the northern hemisphere closest to the point towards which the Earth's axis is directed, indicating approximately the situation of the celestial north pole. The Polar Star has been used by navigators throughout history and is still used to determine azimuth and latitude.

The Polar Star is not exactly at the celestial North Pole, but at 1 degree from it. Due to the Precession movement of the Earth's axis of rotation, in 2012 the Polar will be at a minimum distance from the celestial North Pole (around half a degree) and then move away again.

During the last 5,000 years, the position of the celestial north pole has moved from the star Thuban or Alpha (a) Draconis, in the constellation Dragon, to the vicinity of the star Alpha (a) Ursae Minoris, in the constellation Ursa Minor.

This star is a multiple star of the second magnitude, and is located at a distance of about 300 light years from Earth. It is easy to locate it in the sky because two easily identifiable stars of the constellation Ursa Major, known as the Pointers, indicate it.

In the year 7500, the brightest star of the constellation Cepheus, Alpha (a) Cephei, will mark the pole, and in the year 15000 the star Vega will do it, in the constellation Lira. After about 9,000 years, Alpha Ursae Minoris will mark the direction of the celestial north pole again.


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