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, Arctic V (32H star in the west) became the Polaris, which was extremely dark and was the darkest Polaris in the history of human civilization. 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. Around 2 100 AD, the angular distance between the sky pointing to the north pole of the earth's rotation axis and the alpha star Ursa major is the smallest, only about 28 minutes. In the future, the sky pointing to the north pole of the earth's rotation axis will gradually move away from Ursa minor. By about 4000 AD, Cepheus Gamma will become the North Star. Around AD 14000, Vega I, the alpha star of Lyra, will gain the reputation of Polaris. The time for the earth's rotation axis to swing like this is about 25,800 years. This shows that everything is in motion, stillness is only temporary and relative, and the change of motion is eternal. And around 28000 AD, the north celestial pole will point to Ursa major again.

List of Polaris from 20000 BC to 20000 AD (this is comprehensively determined according to visibility (brightness) and reference object (position from the North Pole): the brightness position of Polaris (closest to the North Pole) -20000~- 19600 days, 3.25/3.20+90-19600 ~-18600 Tiangouliu 8+07600 ~-16300 hip1024314.50. 8+0 "-14700 ~-13400 Tianjin II 2.90+87 47' 40"-13400 ~-1900 Lyra/kloc-0 0700 ~-9400 days +87 18' Cepheus ν 4.80+8812' 20 "-6400 ~-5000 hip 739095.20+8933' 36"-5000 ~-380. 5+8515'10 "-900 ~-500 Arctic 4.80+8512'17"-500 ~1200 Arctic 5.30+89 27 38 ′ 56 ″ 3300 ~ 4400, Shaowei Zengba 3.20+8803 ′14 ″ 4400 ~ 5500, Shaowei No.7 Dam 4.50+8901′ 22 ″ 5500 ~ 6300, the midpoint of the connecting line between the gully dam and Shang Wei Zengyi. 20+90 6300 ~ 7000 Tiangouliu 4.40+88 51'31"7000 ~ 8500 Tiangouwu 2.45+87 54'13" 8500 ~ 9900 hip65438+. O 23.95+87 23' 29 "11000 ~12400 Tianjin Er 2.90+87 57'18"12400 ~1350. 0+86 14 ' 16 " 14 100 ~ 15000 hip 887885.00+89 54 ' 28 " 15000 ~ 168。 0+89 23' 26 "17600 ~18800 qigonger 3.90+89 26' 02"18800-19200 Wuxian ν4.80+87 05'