Polaris has several names.

Polaris is also called Beichen, Purple Palace and Purple Weiyuan. Polaris is an important indicator of sky navigation (that is, to identify the direction by observing celestial bodies), which can be used for field activities and navigation activities. Before the compass appeared, sailors, especially those near the Mediterranean, often navigated by observing the North Star.

Polaris refers to the star closest to the north celestial pole, which can be seen in the northern hemisphere. The current Polaris is Alpha Ursa minor (Dog Chen Yi).

Because of precession, Polaris is different in different periods. About 4800 years ago, Polaris was alpha dragon. In ancient Greece, Polaris was the beta star of Ursa minor. It was not until about 2 100 years ago that the angle between Alpha Ursa minor and the North Pole became the smallest (only 27'38 "). After 3 1 century, Shao Wei Zeng Ba (Cepheus γ) will become the North Star. 14000 or so, Alpha Lyra (Vega) will become the North Star.

Extended data

Different from the western astronomical system centered on ecliptic coordinates, China developed an astronomical system centered on equatorial coordinates in ancient times. In this system, Polaris is located just north of the celestial sphere, which undoubtedly has a unique position. In ancient China, it was often used as a symbol of the emperor. But Alpha Bear has not been the North Star since ancient times. Because the earth's rotation axis swings slowly periodically. Therefore, the position of the sky indicated by the north pole of the earth's rotation axis is also changing, and the "throne" of Polaris may also take turns to sit in the village.

The sky pointed to by the north pole of the earth's rotation axis moves at the speed of 15 arc seconds per year. 3000 years ago, Polaris was not the alpha star of Ursa minor, but the alpha star of Draco, a dark star with a magnitude of 3.7, which was called the right pivot in ancient China. By 1000 BC, the beta star Ursa minor (Chinese name Arctic II) was closer to the north celestial pole. Because all the stars revolve around it, the ancients thought it was the son of heaven, so it was named Emperor Star, and because it was in the center of Ziwei Source, it was also called Ziwei Star.

During the Sui and Tang Dynasties, Polaris V (the 32H star in the west) became the Polaris with extremely dim brightness, which was the darkest Polaris in the history of human civilization until 2 1 century. In the early years of the Northern Song Dynasty in China, the sky referred to by the North Pole of the earth was 6 degrees away from the alpha angle of Ursa minor (that is, dog Chen Yi) of Polaris. It can be seen that it was far from Polaris. But by the Ming and Qing Dynasties, Gou Jian had become a veritable North Star.

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