What does Polaris describe?

English name: Polaris "current" is located in Ursa minor, about 430 light years away from the earth. It is a star with stable brightness and position that can be seen in the night sky. Because Polaris is closest to true north, people on earth have been navigating by its starlight for thousands of years. Polaris is a bright star in the northern part of the sky. It is very close to the North Pole of the Earth, almost facing the Earth's axis. Seen from the earth, its position is almost unchanged, so it can be used to identify the direction. Due to precession, Polaris is not an eternal star. Now it is alpha Ursa minor, and it will be Vega in the year of 14000. Polaris is now in the sky, pointing to the north pole of the earth. Therefore, it always seems to be in the northern sky. It is because of its important position that it is famous. In fact, according to the brightness, it is just an ordinary second-class star, belonging to the "younger generation." It is more than 300 light years away from us. Polaris belongs to the brightest star in Ursa minor, also known as Alpha in Ursa minor. China called it "Gouchenyi" or "Beichen" in ancient times. On the constellation diagram, it is on the tip of the bear's tail. The replacement of Polaris is here. Maybe you have to ask: Will Alpha in Ursa minor always enjoy the honorific title of Polaris? Or, does the north pole of the earth's rotation axis always point to this star? First of all, it should be pointed out that the rotation axis of the earth is also slowly swinging periodically. Therefore, the position of the sky referred to by the north pole of the earth's rotation axis naturally changed. It can be seen that the "throne" of Polaris also has the possibility of taking turns to sit in the village. Astronomers have made it clear for a long time that 4800 years ago, Polaris was not the present alpha star of Ursa minor, but the alpha star of Draco called right pivot in ancient China. At that time, the right fulcrum won the honor of Polaris. By the year 1000, that is, the early years of the Northern Song Dynasty in China, the sky pointed by the North Pole of the earth was still 6 degrees away from the current Polaris Alpha Ursa major. It can be seen that it was far from Polaris. At present, the north pole of the earth's rotation axis points to the sky, and the angular distance from Alpha Ursa minor is only about 1 degree. At present, the sky pointing to the north pole of the earth's rotation axis is approaching Ursa minor at the speed of 15 arc seconds per year. By AD 2 100, the angular distance between the sky indicated by the north pole of the earth's rotation axis and the alpha star Ursa minor was the smallest, only about 28 minutes. It seems that its "status" reached the peak of Polaris at this time. 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. By 14000, Vega, the alpha star of Lyra, will gain the reputation of Polaris. At this time, people talked about the story of the Cowherd and the Weaver Girl. Vega's position as the throne of Polaris far exceeds that of Cowherd. The time for the earth's rotation axis to swing like this is about 26,000 years. This shows that everything is in motion, stillness is only temporary and relative, and the change of motion is eternal. The Big Dipper is a part of Ursa major. Graphically, the Big Dipper is located at the back and tail of Ursa Major. Of these seven stars, six are secondary stars and one is tertiary. Through the connection of the two stars in the mouth of the bucket, it extends about 5 times in the direction of the mouth of the bucket and finds the Polaris. "Star Recognition Song" has: "Star recognition begins with Beidou, and then begins from north to west." Beginners can look for other constellations in turn from the Big Dipper. Will the pattern of the Big Dipper never change? Will it always be a "tool" to find the North Star? Of course not. Everything in the universe is moving and changing, and stars are no exception. As the stars are also moving, the pattern of the Big Dipper is certainly changing. These seven stars are at different distances from us, ranging from 70 to 130 light years. They run at different speeds and directions. Astronomers have calculated that the pattern of the Big Dipper seen 654.38 million years ago and the pattern seen 654.38 million years later are very different from today's. Polaris refers to the conspicuous star closest to the north celestial pole at any time. At present, the recognized Polaris is Alpha Ursa minor (named Beichen or Gouchenyi in China), which is located at about 0. 7 From North Celestial Pole (2004). It is a late F-type high luminosity star with an apparent magnitude of 2.02 and a distance of 430 light years, and its mass is about four times that of the sun. It is the Cepheid variable closest to the earth.