Chapter 2 Chapter 2 Astronomy

The relationship between heaven and earth, the structure of the universe, and the laws of motion of the sun, moon, and stars have aroused people's thinking since ancient times.In ancient my country, starting from the original concept of "the sky is high and the earth is thick", our ancestors developed a rich imagination.Some people say that in a place called Tanggu, there is a towering tree called Fusang, on which ten suns live, one sun on the top and nine suns below; it is also said that in ancient times Gonggong and Zhuanxu [ zhuanxu, Zhuanxu] There was a great battle for the throne, and the defeated Gonggong smashed the giant pillar supporting the sky - Buzhou Mountain in a rage, so the sky tilted to the northwest, the sun, moon and stars moved, and the earth became northwest High and low in the southeast, the water flows eastward.Although these are ancient myths recorded in ancient books, we can glimpse the ancient and simple concept of the universe from them.

With the advancement of astronomical observation technology and the increasing abundance of astronomical observation data, people's understanding of the relationship between heaven and earth and the structure of the universe is getting deeper and deeper.In the Western Han Dynasty, several theories of the universe, mainly Gaitian theory, Huntian theory and Xuanye theory, gradually formed.The origins of these theories of the universe can be traced back to the Spring and Autumn Period and the Warring States Period.In the Han Dynasty, there were fierce debates among schools and factions with different opinions. Among them, the debate between the theory of Huntian and the theory of Gaitian was regarded as a major event in the history of astronomy in our country.While arguing, scholars of various factions also wrote books one after another to expound their own views.According to Xuan Ye theory, the sky is an infinite space without form, and the sun, moon, and stars are suspended in the universe by the action of Qi, and each celestial body has different motion states and speeds.However, the works on Xuanye theory were lost in the Eastern Han Dynasty, and the only information we know about it is a passage written by Qie [qieqie] Meng (1st century A.D.) on Xuanye theory preserved in "Book of Jin · Tianwenzhi" summary.The masterpieces of the theory of the armillary sphere are "Notes on the Armillary Sphere" and "Lingxian" by Zhang Heng (78-139 A.D.).In "Notes on the Armillary Sphere", Zhang Heng compares the armillary sky to an egg. The celestial sphere surrounds the earth like an eggshell, and the earth floats on the water like an egg yolk. Half of the celestial sphere is on the ground and half is underground. All celestial bodies move on the celestial sphere. , and rotate with the celestial sphere.In "Lingxian", Zhang Heng also systematically discussed the creation and evolution of the universe, and pointed out that the round sky is not the boundary of the universe, thus expressing the concept of the infinite universe.It is a pity that Zhang Heng's works have not been handed down completely, and only the preface of "Ling Xian" and other materials are preserved in some ancient documents.Among several cosmological theories, Gaitian theory is undoubtedly the oldest.The early theory of Gaitian believed that the sky is like an open dome, and the earth is like a flat chessboard.In the history of Chinese astronomy, it is called the first Gaitian theory.This statement has obvious shortcomings. For example, Zeng Shen in the 6th century BC felt that the circular sky cover and the square earth could not fit together.So the theory was further improved, and the second Gaitian theory was formed during the Spring and Autumn Period and the Warring States Period.The second Gaitian said that the sky is like a lid, and the earth is like an upside-down plate.The classic work of the Second Gaitian Theory is "Zhou Bi Suan Jing".This book is the earliest systematic theoretical work on astronomy in China, and occupies a prominent position in the history of Chinese astronomy.

"Zhou Bi Suan Jing" was written in the 1st century BC, and its original name was "Zhou Bi".According to the explanation in the book, "big" is the watch rod used for measurement, and it is believed that the method of using an eight-foot long watch rod to measure hope originated in the Zhou Dynasty, so it is called "Zhou Bi".In the Tang Dynasty, after the book was annotated by Li Chunfeng, it was included in the Ten Books of Suanjing as a mathematics textbook, and the word "Suanjing" was added, which has been used to this day. The content of "Zhou Bi Suan Jing" can be roughly divided into the following levels: the beginning part explains the Pythagorean theorem in the form of questions and answers between Zhou Gong and Shang Gao, and the principle that various degrees between heaven and earth can be obtained by using this theorem to measure, which is equivalent to an article introduction.Then, in the form of Rong Fang asking Chen Zi, how to use the method of standing watch to determine the height of the sun, the path of the sun, the range of light, the distance that can be seen by the human eye, and the distance between the south pole and the north pole from the surrounding earth to the four poles are explained in detail. Count and Zhoudi's things, and so on.The last part is related to the calendar, which discusses the shadow length of the twenty-four solar terms, the calculation of the sun and the moon, the return year, the synodic month, and the arrangement of the months of the year, etc.

The author of "Zhou Bi Suan Jing" used the mouth of the Duke of Zhou to sigh "the number of words is great", highly respected mathematics, and tried to use mathematical methods to establish a mathematical, physical and chemical universe model for Gaitian theory.This is extremely rare in ancient Chinese cosmology.The specific content of the Gaitian model in the book is as follows: the sky is centered on the North Pole, and the earth is centered on the land directly below the North Pole. The sky and the earth are all raised in the center and gradually lowered around them, and they are parallel to each other. The distance is also 80,000 miles.The celestial bodies are attached to the canopy, and the canopy rotates around the line connecting the North Pole and the Pole every day, driving the celestial bodies to rise in the east and set in the west.The sun is at the position of the canopy sometimes high and sometimes low. In winter, it circles a big circle at the lower part of the canopy. The diameter of the sun path on the winter solstice is the largest, with a diameter of 476,000 miles. In summer, the circle around the zenith is smaller. The smallest, only 238,000 miles; Chunqiu Ridao is between the two.Draw the sun paths of the main solar terms, and you will get a series of concentric circles with the North Pole as the center, that is, the "Seven Balances and Six Spaces Map", in which the outermost scale is the winter solstice, and the fourth scale in the middle is the vernal equinox and autumnal equinox. Tao, the innermost is the summer solstice road.The place where people live is 103,000 miles south of the extreme bottom, and the distance that the human eye can see and the sun can shine is 167,000 miles (with the human settlement as the center, the radius of 167,000 miles is a circle that intersects Qiheng circle), no matter how far away you can't see it.When the sun is less than this distance from people, we can see day, otherwise it is night.The sunrise points at the winter solstice, vernal equinox, autumnal equinox and summer solstice are L1, L2, L3 respectively, and the sunset points are M1, M2, M3 respectively, which can explain the change of the rising and setting directions of the sun in four seasons.At the same time, because L1M1 only occupies a small part of the winter solstice path, while L3M3 occupies most of the summer solstice path, so the winter solstice day is the shortest and the summer solstice day is the longest.

Although the Gaitian model in "Zhou Bi" has been proven wrong by today's science, the ancients more than 2,000 years ago used it to cleverly explain some natural phenomena.For example, it is mentioned in the book that near the North Pole "there is ice that does not release (melt) in summer" (it is often outside the distance of sunlight, that is, it is far from the center of the sun in summer), and that "there is immortal grass in winter" in the places around Zhongheng; In the extreme north, at noon in the north, midnight in the south, etc.These guesses are surprisingly accurate.

In the history of star map development, "Zhou Bi Suan Jing" also has an important position.This is because the book mentions two things, "green pictures" and "yellow pictures".Among them, the "yellow picture" has the sun path of winter solstice, summer solstice, vernal equinox and autumnal equinox, as well as twenty-eight mansions and other astrological signs.This is actually an all-sky map centered on the North Pole.Later generations called this form of star map "cover map", which has been circulated for a long time and is very common.In addition, the calendar data in "Zhou Bi Suan Jing" is the same as the four-part calendar produced in my country in the late Spring and Autumn Period, but different from the calendar used in the Qin and Han Dynasties, so it is an important historical material about the pre-Qin calendar.

"Zhou Bi Suan Jing" contains a lot of mathematical knowledge.Since the book was written on the basis of previous materials, the mathematical knowledge in it reflects the level of mathematics development in my country from the pre-Qin period to the Western Han Dynasty. "Zhou Bi Suan Jing" pointed out at the beginning of the chapter that "the law of numbers comes from circles and squares", which is the first time to clearly link numbers and graphics.Along this line of thought, the Pythagorean Theorem was first described in the book.It calls the two right-angled sides of a right-angled triangle hooks and strands, and the hypotenuse as chords. It first gives a special case of hooks with three strands, four strings and five strings, and further explains the general relationship between the square of hooks and strands and the square of chords. "Zhou Bi Suan Jing" attaches great importance to the application of Pythagorean, not only explaining the relationship between triangles, rectangles and circles, but also giving general methods for measuring height, distance and depth.These methods are used in the book to measure the world and give Gaitian a quantitative concept.If a pole is set up in different places, assuming that the shadow is one inch apart from each other, the height of the sun on that day can be calculated according to the similar proportional relationship.This is the method of measuring the height of the sun in "Zhou Bi Suan Jing".Obviously, this is calculated by taking the earth as a plane, and the result is also conceivably wrong.However, it is feasible to use this method to measure high and distant targets on the ground.Later, this method developed into the gravity difference theory in measurement in ancient China.

The four arithmetic operations of fractions are very common today, but it was not easy in ancient times.Until the 18th century, the West was still very afraid of the calculation of fractions.In ancient my country, fractions were studied very early. "Zuo Zhuan" records that the emperor distributed the land to the princes, "Guanzi Diyuan" talked about the rhythm, and "Kao Gong Ji" introduced the specifications of various handicraft products, etc., there is a lot of knowledge about scores. "Zhou Bi Suan Jing" has more complex fraction calculations.For example: It is known that January = 29 and 499/940 days, the monthly movement is 13 and 7/19 degrees every day, and the week is 3651/4 degrees. Find the degree of the month after 12 months.The answer is 3546612/17860 degrees.Since the "Zhoubi Suanjing" has not done a good job of dividing, the calculation process is very complicated, but being able to do such complex fraction calculations at that time really shows the great wisdom of our ancestors.

The author of "Zhou Bi Suan Jing" believes that astronomy and calendar can be solved by mathematical methods. Therefore, although the whole book mainly discusses astronomical phenomena, and the time of writing is just when religious superstition is prevalent, we have not found a single word related to theology. idea.Such a naive materialist view was commendable at the time. The Gaitian model in "Zhou Bi Suan Jing" has its own serious flaws.For example, the sky and the earth in the model of the universe are all high protrusions in the middle, but the calculations are based on the horizon, and there are assumptions that the shadows differ by an inch, and some data are also suspected of being made up, and so on.Gaitian theory also has many difficulties in explaining specific celestial phenomena.If the sun revolves around the North Pole and cannot be seen far away from us, then the sun should be in the shape of a vertical semicircle at sunrise and sunset, but what we actually see is a horizontal semicircle; if the sun turns to the north of the North Pole, we will Can't see, and the stars are dimmer than the sun, why can we see them when we circle north of the North Pole?etc.In terms of explaining astronomical phenomena, the theory of Huntian is more convenient than that of Gaitian. Therefore, Gaitian theory lost its status in astronomical practice during Emperor Wu of the Han Dynasty. After the Sui and Tang Dynasties, it was less discussed. The authoritative theory of the structure of the universe.In the late Ming and Qing dynasties, when Western astronomy was introduced to my country, many scholars studied the universe theory in "Zhou Bi Suan Jing" and compared it with Western astronomy.For example, it is believed that the "Seven Balances and Six Spaces Map" is consistent with the theory of the five zones of the earth, and it is believed that the idea of ​​a round earth has existed in "Zhou Bi Suan Jing", etc.Although the methods and conclusions of these studies are wrong, this research upsurge also aroused people's interest in "Zhou Bi Suan Jing", and promoted the in-depth study of the specific content of the book.