History of the Armillary Sphere

A model of the cosmos as it was perceived before the 1600s, the armillary sphere consists of a number of graduated brass rings representing the chief celestial circles and demonstrates the basic principles of astronomical motion and horology (the science of time measurement). The word armillary is derived form the Greek term armilla meaning bracelets or rings.

An armillary sphere consists of a skeletal celestial sphere (the basket) inside a vertical ring (the meridian ring). The basket has two colure rings representing the celestial poles and one ring each for the two tropics. A band marked with 360 degree intervals circles the basket and represents the equator. The final component of the basket is the ecliptic ring which is divided into the twelve signs of the Zodiac eachone being divided into thirty units or days. At the center of the basket sits a globe representing earth.

The first armillary sphere was probably invented in the third century BC by the Greek astronomer Eratosthenes. Around 130 AD Ptolemy constructed a model to assist him in making observations of the paths of the major astronomical bodies across the night sky. By the early 1500s Copernicus had overthrown the accepted geocentric premise and the spheres began to be built with the sun in the center. Over the course of the years they became extremely complicated instruments used for instruction and calculation of movement of celestial objects and events. The armillary sphere could be used to:

determine the time of sunrise and sunset.
explain the meaning of the Spring and Vernal Equinox.
demonstrate the meaning of the Tropics (turning point) at the Summer and Winter Solstice.
determine the position of a star and explain the meaning of right ascension and declination.
locate the Polar Star.

The armillary sphere combines the concept of time, history, and the changing universe into one element. This timeless symbology is still pertinent today as man continues to search the heavens for knowledge of how we relate to the universe.

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