The Beijing Ancient Observatory is a pretelescopic observatory located in Beijing, China. The revolutionary tools used within this ancient observatory were built in 1442 during the Ming Dynasty, and later amended during the Qing.
As one of the oldest observatories in the world, the Beijing Ancient Observatory grounds cover an area of 10,000 square meters. The observatory itself is located on a 15 meter tall brick platform and about 40 x 40 square meters wide, an extant portion of the old Ming Dynasty era city wall that once encircled Beijing. Several of the bronze astronomical instruments are on the platform, and other armillary spheres, sundials, and other instruments are located nearby at ground level. It is operated as a museum in affiliation with Beijing Planetarium.
- The armillary sphere is an instrument used to measure the coordinates of the celestial bodies. This instrument is constructed of two bronze disks—one being known as the ecliptic armillary (for tracking the sun), and the other deemed the equatorial armillary (tracks bodies that are not the sun).
- The quadrant is an instrument built in 1673 and used in order to measures the altitudes and zenith locations of the celestial bodies.
- The theodolite is an instrument built in 1715 and used for measuring both altitude and azimuth coordinates of celestial bodies. The azimuth theodolite is a relatively similar instrument lacking only the ability to record altitude.
- The astronomical sextant is an instrument used for measuring the angular distance between celestial bodies, and is also used for measuring the angular diameter of the moon and sun.
- The celestial globe was built in 1673 and used to determine the time in which the celestial bodies will rise and set; as well as the altitude and azimuth of the bodies at any given time.