What astronomical theory did Zhang Heng put forward at the end of the Eastern Han Dynasty?
Zhang was born in the third year of Emperor Jian, a shabby bureaucratic family in Shiqiao, E County, Nanyang County (now 50 miles north of Nanyang City, Henan Province). Grandfather Zhang Kan is a local official, who was once the prefect of Shu County and the prefect of Yuyang. When Zhang Heng was young, his family had declined, and sometimes he had to rely on relatives and friends for help. It was this poor life that enabled him to get in touch with the working people in the lower class and some production and life realities, which brought positive influence to his later scientific creation. In mathematics, geography, painting and literature, Zhang Heng showed extraordinary talent and extensive knowledge. Zhang Heng is one of the representatives of Huntian theory in the middle of Eastern Han Dynasty. He pointed out that the moon itself does not shine, and moonlight is actually a reflection of the sun's light; He also correctly explained the cause of the solar eclipse and realized the infinity of the universe and the relationship between the speed of planetary motion and the distance from the earth. Zhang Heng [1] observed and recorded 2,500 stars, created the world's first light-leaking celestial globe instrument that can accurately perform astronomical phenomena, and the first instrument to test earthquakes-the seismograph of the waiting wind. He also made a south guide car, an automatic drum car, a wooden bird flying to Wan Li and so on. Zhang Heng * * * is the author of 32 scientific, philosophical and literary works, among which astronomical works include Ling Xian and Ling Xian Tu. In order to commemorate Zhang Heng's achievements, people named a crater on the back of the moon as "Zhang Heng Crater" and the asteroid 1802 as "Zhang Hengxing". Guo Moruo, a famous writer and historian in China in the 20th century, commented on Zhang Heng: "Such an all-round development figure is rare in world history and admirable for thousands of years." Later people called Zhang Heng a wooden saint.