Departments

Astronomical observation — Officials tasked with systematic observation of the sky, recording the positions and movements of celestial bodies, and noting unusual phenomena. Observations were conducted from dedicated platforms, most notably the Beijing Ancient Observatory (established in 1442 and rebuilt with Jesuit-designed instruments in the 1670s).

Calendar production — The annual production of the official calendar was one of the bureau's most important functions. The calendar prescribed not only the dates of months, solar terms, and festivals, but also designated auspicious and inauspicious days for a wide range of activities — a function that connected the bureau's astronomical calculations to its astrological role.

Timekeeping — The bureau maintained the official timekeeping apparatus of the court, including water clocks (漏壺, lòuhú) and later mechanical clocks, and was responsible for announcing the time within the imperial palace.

Divination and date selection — Officials trained in astrological and divinatory methods, including the Four Pillars of Destiny, Qimen Dunjia, and related systems, provided consultations for the court on the timing of ceremonies, construction, military campaigns, and other state activities.

Bureau officials were typically recruited through examination or recommendation and were expected to possess specialised knowledge in astronomy, mathematics, the Yijing (Book of Changes), and calendrical science. The position of bureau director carried moderate bureaucratic rank, and the bureau as a whole occupied a specialised but somewhat peripheral position within the vast apparatus of the Chinese imperial bureaucracy.