The History of the Armillary or Equatorial Sundial

History

• According to "History of Astronomy: An Encyclopedia," the armillary sphere was developed from ancient Roman astronomer Ptolemy's astrolabon, which "allowed astronomers to find elliptic coordinates of stars without having to convert from altazimuth measurements." The Ancient Observatory in Beijing contains a full-size replica of a sphere used in the Ming Dynasty. With time and development, the armillary sphere was able to give equatorial coordinates. Astronomers Nicolas Copernicus and Tycho Brahe developed armillary spheres while China developed an observatory sphere.

Features

• Armillary spheres have changed over the years to incorporate the knowledge gleaned over the centuries. Armillary spheres are comprised of rings to represent "great circles of the celestial sphere." Polar circles, the equator, and elliptical lines were also designated. When utilized correctly, an armillary sphere represents a geocentric system. Armillary spheres will almost always consist of three rings with a center orb.

Facts

• The armillary sphere was invented as an instrument of observation. It can be viewed as a scaled-down version of the celestial sphere of its day. Earlier models of the sphere were made of wood, but eventually, they were made of brass. They are most often set in cradles so that they can represent the "heavens seen from any latitude."

Identification

• When looking for an armillary sphere, look for three rings with a sphere set in the middle. Two of these rings represent the equator and the meridian, respectively. The third ring represents the horizon. A rod that passes through the rings represents the earth's axis. Three rings will be set at an angle to represent the axis of the earth.

Significance

• While armillary spheres may seem archaic these days, they are complex pieces of ancient machinery that illustrate the incredible thinking processes of mankind. They cannot be used for timekeeping, today but they demonstrate the ability of mankind to attempt to understand the universe in which he lives. Divided by the 12 sections of the zodiac, the armillary sphere was used by the ancient Greeks to measure a star's place from the vernal equinox. While it is possible to tell time from an armillary sphere, it is difficult at best.