The Armillary Sphere was an astronomic observatory instrument in ancient China. The ancient people believed the heaven was round, just like an egg, with the stars in the sky resembling the round pills beset in the shell and the earth like the yolk. People used the armillary sphere to examine the position of celestial bodies from the earth.

The armillary sphere's structure was very simple at the very beginning, with three rings and a metal axis. The outermost ring -- meridian ring -- was fixed in the north-south direction, the middle ring -- equator ring -- was parallel to the earth's equatorial plane, and the innermost one -- Chijing ring -- could revolve around the metal axis.

The Chijing ring and the metal axis intersected at two points, with one pointing to the North Pole and the other to the South Pole. An observatory tube (an equivalent of the modern telescope) was fixed on the Chijing ring and could rotate around the center of the ring.

When used for examining the position of stars, the tube was first aimed at a certain star; then the graduation on the equator and Chijing rings was used to pinpoint the star's position in the sky.

Later, in order to facilitate the observation of more celestial bodies, such as the sun, the planets, and the moon, more rings were added inside the armillary sphere, making it a multi-purpose astronomic instrument.

Author: Jessie