# The earliest monograph on astronomy

The Book of Zhou Yi is the first of the top ten books in ancient China. The original name is Book of Zhou Yi and it is the earliest astronomical book in China. The book of Zhou Yan Suan Jing was written between the two Han dynasties (around AD), and some historians believe that it appeared earlier and was pregnant in the Zhou Dynasty and formed in the Western Han Dynasty.

People often think of the Zhou Huan Su Jing as a mathematical monograph. In fact, Zhou Huan Su Jing is an astronomical work, most of which is related to astronomical calculations. In order to discuss the astronomical calendar, the book describes some related mathematical knowledge. The important topics are the Pythagorean theorem, the ratio measurement and the calculation of the celestial body.

The Gai Tian theory is the earliest ancient theory of cosmic structure in China. This theory holds that the sky is round, covering the ground like an open umbrella, the ground is square, like a chessboard, and the sun, moon, and stars pass through the sky like reptiles, so this theory is also called Said Tianyuan. Gai Tian said that the appearance of the sun, the moon and the stars is not really a haunting, but it is only visible when they are far away, and they are shining when they are close. By the time of the writing of Zhou Jing Suan Jing, a complete and quantitative system had been formed. It reflects a stage in which people understand the structure of the universe, and has certain historical significance in describing the apparent motion of celestial bodies.

Looking up at the stars on a clear night, you might wonder how high the sky is? In fact, our ancestors thought about this problem thousands of years ago. There is such a story in Zhou Jing Suan Jing: One day, Zhou Gong asked the mathematician Shang Zhou at the time: How high is the sky? Shang Zhou thought for a while and said, The method of hook three strands, four strings and five can be used. Calculate how high the sky is . So, what is hook three strands, four strings and five ? You can draw a rectangle on paper with a length of 3 cm and a width of 4 cm, and then connect the diagonals with straight lines. There will be two right triangles. Measure this diagonal line, it must be 5 cm. This is the Pythagorean theorem we know today, also known as Shang Gao Theorem or Pythagoras Theorem.

In the Book of Zhou Counting, how ancient people used simple methods to calculate the distance from the sun to the earth. According to records, the calculation method of the solar distance is: first set up a number of eight-foot-long poles in various parts of the country. At noon on the day of the summer solstice, write down the length of the pole shadows in each place. Thousands of miles away, the pole shadow is one foot five inches; one thousand miles away from Chang an Zhengbei is one foot seven inches. Therefore, it is known that the length of the pole shadow varies by an inch every one thousand miles from the north to the south. Measured on the day of the winter solstice, the Chang an local film was one foot three feet five inches long. Zhou Yan Suan Jing is calculated between the summer solstice and winter solstice. The pole shadow is exactly six feet long, and the answer is 100,000 miles. This 100,000 miles is the distance between the sun and the ground as recorded in the B ook of Zhou Zongshu . We know that the distance between the earth and the sun is about 149,5 million kilometers, and the records in the Zhou Huan Jing Jing are not accurate. But we must emphasize that the calculation of the distance of the sun is correct.