Is it better to observe Polaris and Altair on the first day or the fifteenth day? Why?

Polaris 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.

Speaking of which, maybe you have to ask: Will Alpha Bear always enjoy the 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 referred to by the North Pole of the Earth was 6 degrees away from the current Polaris, that is, the Alpha Star of the constellation Ursa minor. 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.

Because the earth's axis of rotation will swing periodically in about 26,000 years, Polaris is not fixed (always α 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 early August 2005 that Hubble captured its image. Polaris 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.

As early as more than 200 years ago, astronomer Herschel discovered that Polaris has a bright companion star-"Polaris B", and its average linear distance from Polaris 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.

English: Altair/(Altair)

English: Altair

Date: ァルタィル

Hegu II is the alpha star of Aquila, commonly known as "Altair". It is a very famous bright star in the sky in summer and autumn, and it is silvery white. It is 0/6.7 light years away from the Earth/kloc-0, its diameter is 0/0.6 times that of the sun, its surface temperature is about 7000℃, its luminous power is 8 times greater than that of the sun, and its visual magnitude is 0.77. It faces Vega across the Milky Way. According to an ancient legend, the Cowherd and the Weaver Girl met at the Magpie Bridge on July 7th. In fact, the Cowherd and the Weaver Girl are 16 light years apart. Even on the most powerful rocket in modern times, they never met after hundreds of years. The two dark stars on both sides of Altair are Altair's two sons-Hegu I and Hegu III. Legend has it that Cowherd and his two sons chased Weaver Girl on a pole.

As early as the Han Dynasty, the Book of Rites said in Zheng Xiao: "The weaver girl travels eastward in the middle of the month, and the stars also cover the story." That is to say, at least in the Han Dynasty, people have noticed the running law of Vega in the sky, especially in July. "Historical Records Biography of Tianguan" says that Zhinu is the grandson of Tiandi. , that is, the origin of Tiansun. Astrology: It says, "Morning glory is the name of heaven." The cowherd is a cowherd, and the river drum escaped later. The story of the meeting of the Cowherd and the Weaver Maid on July 7th can be found in Fu Xuan's "On July 7th, the Cowherd and the Weaver Maid will meet in Tianhe". This legend may have originated in the early Eastern Han Dynasty.

In the poem of Wang Xiangqi in the late Qing Dynasty, he wrote: "The fellow villagers raised talents, and the grandson married the river drum. A hundred-year match ended in a hurry, and the tears were always silent." What he sees is a mismatch. What he yearns for more is: "The spring river is like a cloud, and Jin Yuanyang does not fly alone." According to the Chronicle of Jingchu in Zonggu of the Southern Dynasties, in Jianghan area at that time, on the night of the seventh day of July, women in every household tied colored silk thread and left very thin needles. Some people use gold, silver and copper as needles, put melons and fruits in the yard and pray for wisdom from Vega God. If spiders weave webs on melons and fruits, it is considered as a sign of the arrival of Vega God. That is to say, on the night of July 7, there is not only the significance of meeting the Cowherd and the Weaver Girl, but also the significance of praying for wisdom from the Vega God. As the textile goddess in folklore, Vega symbolizes the diligence and wisdom of ancient working women. On this night, ancient women made sacrifices to her by tying colored silk thread, hoping to get the source of ingenuity from her, so the night of July 7 is also called "Begging for Cleverness Festival", which is an enterprising festival.

Later, in the Northern Song Dynasty, Mr. Meng Yuan wrote in "Dream of China in Tokyo" that Tanabata was particularly lively when the Northern Song Dynasty was at its peak. "Three or five days before Tanabata, horses and chariots were all over the city, and Luo Qi was full of festivals, but the lotus did not open. Everyone is good at making double-headed lotus flowers, and they will be carried back after playing for a while. Passers-by often can't put it down. " On the evening of the 7th, there were many colorful buildings in your house, which were called' Chocci House'. Paving up the past, grinding and drinking music (note), flower melon, wine moxibustion, pen and inkstone, needle and thread, or children's poetry scissors, the girl is smart, which is called' seeking cleverness'. " . The Qixi Night in Lin 'an in the Southern Song Dynasty is roughly the same as the celebration activities in the Northern Song Dynasty recorded in Wu's Dream Record and Wulin Biography. Compared with the Southern and Northern Dynasties, the activities of Begging for Qiaojie Festival in Song Dynasty were more colorful. I like Jojo Festival, which is not only a part of China's ancient multi-folk culture, but also a festival that inspires wisdom and evokes the reverie of love.