What is Polaris also called? What was it called in ancient times? How to find it

English name: pole star

The "current" Polar Star

Polaris is located in the constellation Ursa Minor, about 430 light years away from the earth. It is the brightest and brightest star that can be seen in the night sky. A star with a relatively stable position. Because Polaris is closest to true north, people on earth have relied on its starlight to navigate for thousands of years.

Polar Star is a bright star in the northern part of the sky, very close to the North Pole of the Earth, almost facing the Earth's axis. When viewed from the Earth, its position is almost unchanged, and you can rely on it to identify the direction. Due to the precession of the equinoxes, Polaris is not a fixed star forever. It is now Alpha Ursa Minor and will be Vega by 14,000 AD.

Polaris is now very close to the sky pointing toward Earth's North Pole. Therefore, it always appears to be in the northern sky. It is famous because of its important location. In fact, according to its brightness, it is just an ordinary second-magnitude star, belonging to the "junior generation". It is more than 300 light years away from us. Polaris is the brightest star in the constellation Ursa Minor, also called Alpha Ursa Minor. In ancient China, it was called "Gou Chen Yi" or "Beichen". Graphically, it is at the tip of the Little Bear's tail.

The replacement of Polaris

Having said this, you may want to ask: Will Alpha Ursa Minor always enjoy the honorific title of Polaris? In other words, 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 earth's axis of rotation is also slowly swinging periodically. Therefore, the position in the sky where the North Pole of the Earth's rotation axis points naturally changes. It can be seen that the "throne" of Polaris also has the possibility of taking turns. Astronomers have long calculated that 4,800 years ago, the North Star was not Alpha Ursa Minor, but Alpha Draconis, which was called Youshu in ancient China. At that time, Youshu received the honor of Polaris. By 1000 AD, which was the early years of the Northern Song Dynasty in China, the sky where the Earth's North Pole pointed was still 6 degrees away from the current Polaris star Alpha Ursa Minor. It can be seen that at that time it was far from being the North Star. The North Pole of the Earth's rotation axis now points to the sky only about 1 degree from Alpha Ursa Minor. The sky currently pointed toward the North Pole of the Earth's rotation axis is approaching Alpha Ursa Minor at a rate of 15 arc seconds per year. By around 2100 AD, the angular distance between the sky pointing toward the North Pole of the Earth's rotation axis and Alpha Ursa Minor was the smallest, only about 28 arc minutes. It seems that its "status" has reached the peak of the North Star at this time. In the future, the sky pointing toward the North Pole of the Earth's rotation axis will gradually move away from Alpha Ursa Minor. By around AD 4000, Gamma Cephei will become the North Star. By around 14,000 AD, the Alpha Lyra star Vega will gain the reputation of the North Star. At that time, people talked about the story of Cowherd and Weaver Girl again. Vega's status as "throne of the North Star" far surpassed that of Altair. It takes about 26,000 years for the Earth's axis to swing in this way. This shows that everything is in motion, rest is only temporary and relative, and movement and change are eternal.

The Big Dipper

The Big Dipper is part of the Ursa Major constellation. Graphically, the Big Dipper is located on the back and tail of the Big Bear. Six of these seven stars are 2nd magnitude stars and one is a 3rd magnitude star. Pass the line connecting the two stars at the mouth of the bucket and extend it about 5 times farther toward the mouth of the bucket, and you will find the North Star. The star recognition song includes: "Recognize the stars first from the Big Dipper, and then expand from north to west." Beginners who are new to star recognition can start from the Big Dipper to find other constellations in sequence.

Will the shape of the Big Dipper never change? Is it always a "tool" for finding the North Star? Of course not. All objects in the universe are in motion and changing, and stars are no exception. Since the stars are also moving, of course the pattern composed of the Big Dipper is also changing. These seven stars vary in distance from us, ranging from 70 to 130 light years. The speed and direction of their respective movements are also different. Astronomers have calculated that the shape of the Big Dipper seen 100,000 years ago and the shape we will see 100,000 years from now are very different from today's.

Polaris refers to the conspicuous star closest to the North Celestial Pole at any time. The now recognized Polaris is Alpha Ursa Minor (the Chinese name is Beichen or Gouchenyi), located about 0°.7 from the North Celestial Pole (2004). It is an F-type high-luminosity star with a late-type spectral type. Star, with an apparent magnitude of 2.02, a distance of 430 light-years, and a mass of about 4 times that of the sun. It is the closest Cepheid variable star to the earth.

The role of Polaris

Polaris is a very important indicator for outdoor activities and ancient navigation directions. It is also a constellation for identifying directions for beginners in stargazing, astronomical photography and observation rooms. The accurate positioning of the equatorial mount plays a very important role.

Polaris (Polaris B) is also a triple star system, and the distant companion star (Polaris B) can be clearly observed using a small telescope (2,400 AU from Polaris). But the closer companion star (Polaris Ab) cannot be seen because it is too close to Polaris (the visual distance is only 0.2", the actual distance is 18.5 AU) and too faint. It was not photographed by the Hubble Telescope until early August 2005. See its image. Polaris is located in the constellation Ursa Minor, about 430 light years away from the earth. It is the brightest and most stable star in the night sky. Because Polaris is closest to true north, people on the earth have relied on it for thousands of years. Navigate by starlight.

New discoveries about Polaris

As early as more than 200 years ago, astronomer Herschel had discovered that Polaris has a brighter companion star - "Polaris B", which is related to Polaris B. The average straight-line distance from Polaris is 2,400 astronomical units (one astronomical unit is the distance from the earth to the sun, about 150 million kilometers). More than half a century ago, astronomers speculated from the gravitational fluctuations of Polaris that it has another very close companion star, which together with "Polaris B" forms a three-star system. But this companion star has never been observed because it is too close to Polaris and its light is too dim.

Nancy Evans and others from the Harvard-Smithsonian Center for Astrophysics in the United States first observed this mysterious planet in August 2005 with the help of the advanced mapping camera on the Hubble Telescope. The companion star - "Polaris Ab". They found that the companion star is an average straight-line distance of 18.5 AU from Polaris. Observing the distance between Polaris and Polaris Ab on Earth is like distinguishing a coin from 30 kilometers away. Only the advanced mapping camera of the Hubble Space Telescope can do this.

Astronomers also discovered that Polaris is a supergiant star with active internal energy reactions, and its brightness is more than 2,000 times that of the sun, while "Polaris Ab" is a dwarf star that is tending to become dormant. Therefore, its light is always obscured by Polaris, becoming an "invisible partner", but this time its invisibility was seen through by "Hubble".

How to find Polaris

Polaris is now very close to the sky pointing toward the Earth's North Pole. Therefore, it always appears to be in the northern sky. It is famous because of its important location. Polaris is the brightest star in the constellation Ursa Minor, also called Alpha Ursa Minor. The earth's axis of rotation also slowly swings periodically. Therefore, the position in the sky where the North Pole of the Earth's rotation axis points naturally changes. It can be seen that the "throne" of Polaris also has the possibility of taking turns.

The Big Dipper is part of the Ursa Major constellation. Graphically, the Big Dipper is located on the back and tail of the Big Bear. Six of these seven stars are 2nd magnitude stars and one is a 3rd magnitude star. Pass the line connecting the two stars at the mouth of the bucket and extend it about 5 times farther toward the mouth of the bucket, and you will find the North Star. The star recognition song includes: "Recognize the stars first from the Big Dipper, and then expand from north to west." Beginners who are new to star recognition can start from the Big Dipper to find other constellations in sequence.