Ancient emperors all knew astronomical phenomena, because astronomical phenomena were part of their early study. If you don't know astronomy and geography, you will be laughed at by everyone in the world. However, for their own life, national construction and frontier defense, each dynasty had an astronomical institution dedicated to observing astronomical phenomena, called Huntian Prison, Taishi Prison or Qin Tian Prison.
The names of institutions are different, but the responsibilities are the same. They are all responsible for making national calendars according to meteorological data, guiding agricultural seasons, observing the changes of the sun, the moon and the stars, and providing astronomical information for the emperor's decision-making.
Astronomical officials should, according to the emperor's orders, choose a date and year that is conducive to the occurrence of the event, and report to the emperor on all state affairs such as the knighthood of the Crown Prince, the accession of the new emperor, court buildings and military expeditions. When the emperor died, he chose the land of Yongfu and built a cemetery. Astronomical officials must also choose the date and time and go to the scene to investigate. Every day, if the sky is abnormal, report it to the emperor immediately.
The ancients believed that great men, including emperors, had one or a group of corresponding stars in the sky, and the emperor's star was called the emperor's star. Actually, it's also Taiyi or Wudi. The ancients believed that they were not only the stars of the Emperor of Heaven, but also in charge of the actions and fate of the emperor on the ground. Therefore, the emperor star and the emperor star on the ground take care of each other, and astronomical officials should also pay close attention to the dynamics of the emperor star.
It is said that Liu Xun, the emperor of the Han Dynasty, was lucky and a beautiful man. They are very close, eating, playing and even sleeping in the same bed. Pu Xian slept recklessly. Once he stretched out his thigh and stepped on Emperor Han Chengdi. The two were sleeping in the room, and the astronomical officials outside the house observed the astronomical phenomena and suddenly found that "the guest star violated the emperor." That is, an unknown little star from outside invaded the constellation Emperor. So I immediately reported it and got the answer, which is the story above.