Lagerstroemia speciosa

Aurora is a colorful high-altitude physical phenomenon. In the ancient west, it was described in the sixth century BC that it could be regarded as aurora. Sometimes, they can undoubtedly correctly identify this phenomenon, calling it "rare scenery" or "cracks" in the sky, but at other times, they will confuse it with meteors or comets, which lasted until the seventeenth century. The ancients in China had a similar situation. Judging from their naming of aurora, some of them obviously follow the names of meteors and comets.

However, this is not an important way for China people to describe the aurora phenomenon. They describe the aurora with more intuitive descriptions such as red light, golden light, sky red, sky opening and sky splitting, or use "qi" to express various characteristics of the aurora. Aurora is the light produced by charged particles in the upper atmosphere. Red gas is red gas and purple gas is purple gas. Therefore, even from today's point of view, this term is more scientific. Since the Western Han Dynasty at the latest, with the passage of time, the concept of "Qi" has been adopted more and more widely.

In the eyes of the ancients, the aurora phenomenon, like other strange phenomena such as comets, is a sign of good or bad luck, which makes people have to doubt the authenticity of aurora records after many years, because these records are always associated with the birth of saints or the collapse of dynasties. It can be considered that the earliest recorded aurora in China is the historical data found in the ancient bamboo records, and it is described by a certain color of light. Moire:

This is a spectacular scene of five-color light running through the source area of Weizitian. Coincidentally, shortly after the aurora appeared, King Zhao of Zhou was buried at the bottom of the river. At present, it is not easy to accurately determine the age of this aurora, but according to the research of astronomy and history, it probably appeared around the middle of the tenth century BC. The only disturbing thing is that the word "Wei Zi" appeared in the records, which seems to have left a mark on future generations.

An aurora occurred in BC 193, which may be the earliest reliable record. Tian Wenzhi cloud:

In the second year of filial piety, Tiankai was in the northeast, ten feet wide and twenty feet long. Ground motion, yin surplus; The sky is cracked and the yang is insufficient. It is also a change that the strong will hurt the strong.

However, this record is far less vivid than the aurora which happened in the 14th year of Emperor Wendi (BC 166).

Hanshu? "Suburb Sacrifice" cloud:

Xin Yuanping, a native of Zhao, looked full of hope and said, "The five colors in the northeast of Chang 'an, if people are crowned."

This passage makes the orientation, color and even type of aurora very clear. The ancient aurora in China was recorded for nearly 300 times before18th century, and it was still ahead in number until10th century. Although the ancients expressed the aurora in wonderful words, people had to use more vivid color paintings to record this phenomenon because of the complicated changes of the aurora.

This attempt may have appeared a long time ago, but what we can see today is an atlas completed in the fifteenth century, depicting all kinds of so-called "qi" phenomena, and some images are accurate enough to be comparable to modern aurora photos. Since it is impossible for a person to see all types of aurora in his life, such an atlas obviously reflects the observation history of at least several generations or even longer.

The study of aurora is related to solar activity, geomagnetic change, upper atmosphere research and other important scientific topics. After 1859, people began to realize the close relationship between sunspots and aurora, which means that studying ancient aurora records may become an important way to explore natural laws such as solar activity, climate change and geomagnetic change in history. For these studies, the rich aurora records in ancient China are unique.

The celestial pole includes the south pole and the north pole of the celestial sphere. When the ancient people in China had not observed the starry sky near the South Pole, they could only refer to the celestial North Pole. The so-called celestial pole in astronomy actually refers to the fixed point of the northern sky center in a certain period, that is, the equatorial North Pole, and all the stars move around the celestial pole on Sunday.

Although the North Pole moves slowly in a circle around the yellow pole under the action of precession, it has been considered as a fixed point until people can understand precession. "Lu Chunqiu? There is a beginning: "Polaris swims with the sky, and the sky does not move." "The celestial pole mentioned here is actually the celestial pole. Polaris refers to the star closest to the celestial pole, which may just fall to the north pole. If there are no stars in the North Pole, then people can only choose the nearest and most astronomical star as the North Star.

Considering that China paid attention to the observation of elephants in the early days of astronomy, the Polaris originally determined by people should be a star, not a star. Today's astronomical and archaeological research shows that Beidou served as the North Star for a long time in ancient times. From the historical analysis of the gradual improvement of astronomical observation accuracy, it is obvious that taking Beidou as the north star is closely related to people's understanding of the celestial pole. In fact, the North Pole is just an imaginary point stuck in the center of the northern sky. In any case, its position can only be determined by observing the Polaris.

In the fifth year of Xining in the Northern Song Dynasty (1072), Shen Kuo tried to find the true celestial pole with a peephole. At first, the stars he could see through the peephole quickly moved out of sight, so he gradually expanded the peephole until Polaris only moved in the peephole and did not disappear. In this way, the position of the true celestial pole is determined. In fact, Cai Yong of the Eastern Han Dynasty has recorded similar celestial pole observations in his related literature. This fact tells us that it is difficult to accurately determine the fixed point in the northern sky without the help of corresponding instruments. This means that it was not easy to concentrate the true celestial pole on one point before the ancients invented instruments that could help them locate the celestial pole. The best way is to expand the position of the celestial pole from one point to an area, and the delineation of this area can only be completed by the star closest to the North Pole at that time, and it will be the main star for timing. Such a star can only be Beidou.

Due to precession, the position of Beidou was very close to the position of the true celestial pole around 4000 BC. While planning the celestial pole, its arch movement naturally made it the North Star at that time. The establishment of the equatorial coordinate system of traditional astronomy in China depends on the determination of the celestial pole, so the observation of the celestial pole is actually in the first place in a huge and complex astronomical system. The ancients' understanding of the celestial pole is directly related to their continuous observation of Beidou, which is actually the only effective means for people to understand the celestial pole. This circular sky area in the middle of the North Pole, which was planned by the circumpolar motion of Beidou, was named "Tianen" by the ancients.

In ancient cosmology, Xuan Ji was regarded as a remote place, with the extreme center in the north and the prominent center.