Armillary sphere

From Free net encyclopedia

Image:Armillary sphere.png An armillary sphere (also known as a spherical astrolabe, armilla, or armil) is a model of the celestial sphere, invented by Eratosthenes in 255 BC. Its name comes from the Latin armilla (circle, bracelet), since it has a skeleton made of graduated metal circles linking the poles and representing the equator, the ecliptic, meridians and parallels. Usually a ball representing the Earth or, later, the Sun is placed in its center. It is used to demonstrate the motion of the stars around the Earth.

Armillary spheres were developed by the Greeks and were used as teaching tools already in the 3rd century B.C.. In larger and more precise forms they were also used as observational instruments, being preferred by Ptolemy. Armillary spheres became popular again in the Late Middle Ages; the Danish astronomer Tycho Brahe (1546-1601) constructed several of such instruments.

Renaissance scientists and public figures often had their portraits painted showing them with one hand on an armillary sphere, which represented the height of wisdom and knowledge.

Armillary spheres were among the first complex mechanical devices. Their development led to many improvements in techniques and design of all mechanical devices.

A representation of an armillary sphere is present in the modern flag of Portugal and has been a national symbol since the reign of Manuel I.

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Chinese history

Image:ChineseCelestialGlobe.JPG Throughout Chinese history, astronomers have created celestial globes to assist the observation of the stars.

The earliest celestial globe was dated back to 52 BC in the West Han dynasty by the astronomers Geng Shou-chang (耿壽昌) and Luo-xia Hong (落下閎). The first water powered celestial globe was created by Zhang Heng in the East Han dynasty.

Then Li Chun-feng (李淳風) of the Tang dynasty created one in 633 AD with three spherical layers to calibrate multiple aspects of astronomical observations.

In 723 AD, Tang dynasty buddhist monk Yi-xing (一行) and government official Liang Ling-zan (梁令瓚) combined Zhang Heng's water powered celestial globe with an escapement device. The result was allegedly the world's first water powered mechanical clock.

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