Armillary Spheres in China
The equatorial armillary sphere was a traditional Chinese astronomical instrument used to observe celestial bodies in an equatorial coordinate system. Its origin is still not very clear. Astronomer Luoxia Hong (ca. 100 BCE) of the Western Han Dynasty was probably the first maker of this instrument which possessed a very basic form.
The early equatorial armilla was composed of two layers: the outside layer included a meridian circle, equatorial circle, and vertical circle – all three of these were fixed. The inside layer included a polar axis, right ascension circle, and sighting tube. The right ascension circle could rotate around the polar axis, and the sighting tube could rotate in the right ascension circle freely so it could point to everywhere in the sky.
In the Tang Dynasty (AD 618–907), a third layer was added to the equatorial armillary which included an ecliptic (the band of the zodiac through which the Sun apparently moves in its yearly course) circle and a circle of the...