History of the Armillary Sphere and the Armillary Sundial

Ancient astronomers used celestial globes which show the celestial heavens as “globes of the world.” In 225 B.C., Eratosthenes, an astronomer and mathematician of Alexandria, constructed an armillary (named from the Latin word armilla: a bracelet or ring) which consisted of many rings put together in the form of a hollow sphere, with a globe in the center. It was made to show the heavens circling the earth.

Armillary spheres have been constructed in many different ways, from complex versions with dozens of rings, to the most popular versions which typically consist of three or four rings. The rings represent celestial lines such as the horizon, the celestial equator, true north, meridian circle, the arctic circle, tropic of Cancer, tropic of Capricorn, Antarctic circle, and the paths in which the planets move, called the ecliptic.

The armillary sphere was used for centuries by astronomers for observational purposes, and was also useful for solving many problems of the sphere. The armillary sphere has proved to be one of the most attractive forms of a sundial. Typically, armillary sundials are constructed with three rings – two rings representing the equator and the meridian with a rod passing through their common center representing the earth’s axis, and a third ring to represent the horizon.

For further reading, please see “A History of Sundials.”

Copyright 2006 www.OutdoorDecor.com

Nate Burke, OutdoorDecor.com Staff Writer