What did Qin Tian Jian do in ancient times?

Official signature. Observe astronomical phenomena, calculate solar terms and make calendars. From the Qin and Han Dynasties to the Southern Dynasties, the Emperor Tai Shang belonged to the Taishiling Star Calendar. Sui secretary provincial Taishi Cao, Yang-ti changed Cao to supervisor. At the beginning of the Tang Dynasty, Taishi supervisor was changed to Taishi Bureau, and the successor was renamed Secretary Pavilion, Mixed Day Supervisor, Mixed Justice Supervisor, or Secretary Province several times. In the 14th year of Kaiyuan (726), it was re-established as Taishi Bureau and was the secretary province. In the first year of Gan Yuan (758), it was renamed Si Tiantai. In the Five Dynasties and the Early Song Dynasty, it was called Division, and Yuanfeng was changed to Taishi Bureau after restructuring. There is a supervisor in southern Liaoning, and the gold is called Tiantai, which belongs to the supervisor. In the Yuan Dynasty, there was imperial academy, which was juxtaposed with Si Tianjian and Hui Sijian.