What is Polaris?

Polaris belongs to Ursa minor, about 400 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 and almost opposite to the north celestial pole.

Polaris

The earth's axis, viewed from the earth, has almost the same position and 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. Every 25,800 years, Polaris will cycle. For example, in the era of Magellan's voyage to the West, Polaris was about 3.5 degrees away from the north celestial pole. Today, Polaris is closer to the north celestial pole with an angle difference of only 42', less than 1 degree. According to the calculation of the earth's axis swing and stellar gravity, by 2 100, Polaris will reach the nearest position directly above the North Pole, and its distance from the North Celestial Pole is only 27', less than half a degree. Then, Polaris will gradually move away from the north celestial pole.

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 about 400 light years away (that is, the light emitted by Polaris 400 years ago). Polaris is the brightest star in Ursa minor, also known as Alpha Star in Ursa minor. It is an F-type high luminosity star with a late spectral type, with an apparent magnitude of 2.02, a distance of about 400 light years, and a mass about four times that of the sun. It is the closest Cepheid variable star to the earth, and was called "Gouchenyi" or "Beichen" in ancient China. On the constellation diagram, it is on the tip of the bear's tail.

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location

The Big Dipper is a part of Ursa major. Graphically, the Big Dipper is located at the back and tail of Ursa Major. Five of these seven stars are second-class stars and one is third-class. 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. Because the earth's axis of rotation will swing periodically for about 26,000 years, the North Pole

Polaris

The stars are not fixed (always alpha Ursa minor). About 4800 years ago, Polaris was the alpha star of Draco. It was not until about 2 100 AD that the included angle between α Ursa minor and the North Pole became the smallest (only 27'38 "). In 4000 years, Cepheus Gamma will become the North Star. Around 14000 BC, Alpha Lyra (Vega) became the North Star. Polaris is a very important indicator of field activities and ancient navigation direction, and it is also a constellation that can tell the direction from small to stargazing to large to astrophotography, and the equatorial observatory in the observation room accurately locates it.

Polaris (Gouchen I) is also a triad system, and the distant companion star (Polaris B) can be clearly observed with a small telescope (2,400 AU away from Gouchen I). However, the nearby companion star (Polaris Ab) is too close to Polaris (the apparent distance is only 0.2 ",but the actual distance is 18.5 AU), which is too dark to be seen. It was not until the beginning of August 2005 that Hubble took its image.

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 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.

The replacement of Polaris

Different from the western astronomical system centered on ecliptic coordinates, China developed in ancient times.

Polaris

An astronomical system centered on equatorial coordinates, in which Polaris is located due north of the celestial sphere, undoubtedly has a unique position, and was often used as a symbol of emperors in ancient China. However, due to the periodic slow swing of the earth's rotation axis, Alpha in Ursa minor has not been the North Star since ancient times. 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. Four thousand eight hundred years ago, Polaris was not the alpha star of Ursa minor, but the alpha star of Draco, which was called the right pivot in ancient China. 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. 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. 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. 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. Moreover, after the year 2000, about 13200, the north celestial pole will once again point to α Ursa minor.

The role of Polaris

Polaris is a very important indicator of field activities and ancient navigation direction. From stargazing to astrophotography, the accurate positioning of the Equatorial Observatory in the observation room is also a very important constellation to identify the direction.

Polaris is located in Ursa minor, about 40 1 light-year 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 brightness level

47. Polaris (Ursa minor)

1 .Sirius 2. Canopus 3. South Gate 2 (Centauri) 4. Arcturus (Capricorn)

5. Vega (Lyra) 6. Betelgeuse (Orion) 7. Capella (Auriga) Betelgeuse (Orion)

9. Nanhesan (Little Dog Constellation) 10. Shuiwei I (Bojiang) 1 1. Marbury I (Centauri) 12. Altair (eagle)

13. Bi Su Wu (Taurus) 14. Cross 2 (South Cross) 15. Antares II (Scorpio) 16. Capricorn I (Virgo).

17. Beihesan (Gemini) 18. Beiluoshimen (South Pisces) 19. Cross three (South Cross) 20. Tianjin No.4 (Cygnus)

2 1. Xuanyuan XIV (Leo, the first-class star in the above picture)

22. Sagittarius VII (Canine) 23. Beichuan II (Gemini) 24. Cross I (South Cross) 25. Wesley VIII (Scorpio)

26. Betelgeuse (Orion). Capella (Taurus) 28 Carina) 29. Betelgeuse (Orion)

30. He Yi (crane constellation) 3 1. Yuheng (Ursa Major) 32. Shu Tian (Ursa Major) 33. Tianzhou No.3 (Perseus)

34. Tiansheyi (Sagittarius) 35. Giussan (Sagittarius) 36. Sagittarius I (Canis Canis) 37. Haishiyi (karina)

38. Shaking Light (Ursa Major) 39. Endura V (Scorpio) 40. Callinan (Auriga)

4 1. Triangle III (South Triangle) 42. Su Jing III (Gemini) 43. Peacock XI (Peacock) 44. Military City I (Canis Canis)

45. constellation I (Ophiuchus) 46. Lou Su III (Aries) 47. Polaris (Ursa minor) 48. Betelgeuse (Sagittarius) 49 Tu Sikong (Pisces) 50. Betelgeuse (Orion)

The secret of Polaris's immobility

Because the earth rotates around the earth's axis, and Polaris is on the north extension line of the earth's axis, Polaris looks at the sky motionless at night, with its head tilted to the north, so it can indicate the north. In addition, because the tilt direction of the earth's axis remains the same all year round, and the distance between Polaris and the earth is much greater than the radius of the earth's revolution, the earth's revolution is ignored, so we can see that the Polaris in the sky does not move for a year, and its position does not change, and the earth's axis always points to Polaris.

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Companion of Polaris

As early as more than 200 years ago, astronomer Herschel discovered the North Star.

Polaris

The average linear distance of the bright companion Polaris B is 2400 astronomical units (one astronomical unit is the distance from the earth to the sun, which is about 65.438+0.5 billion kilometers). More than half a century ago, astronomers speculated that Polaris had another very close companion star, which together with Polaris B formed a Trinary star system. But this companion star has never been observed because it is too close to Polaris and the light is too dim.

Nancy Evans of Harvard-Smithsonian Center for Astrophysics and others first observed this mysterious companion star-"Polaris Ab" in August 2005 with the help of the advanced mapping camera on the Hubble telescope. They found that the average linear distance between this companion star and Polaris is 18.5 astronomical units. Observing the distance between Polaris and Polaris Ab on the earth is like distinguishing a coin from 30 kilometers away. Only the advanced mapping camera of Hubble Space Telescope can do it.

Astronomers also found that Polaris is a Supergiant star with active internal energy response, and its brightness is more than 2,000 times that of the sun, while Polaris Ab is a fading dwarf. Therefore, its light is always blocked by Polaris and becomes an "invisible companion", and this time its stealth state was seen through by Hubble.

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Ways to find Polaris

You can find the Big Dipper first, and then find the North through the Big Dipper.

Polaris

Polaris. 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 and China Traditional Culture

Traditionally in China, Polaris is of extraordinary significance, such as Taiyi in the Five Emperors era in 2263 BC and Di in the Duke of Zhou in 1097 BC. This is because they seem to be fixed in the sky and supported by the stars, so they are regarded as the owners of the stars.