FlourishedXianyang (Shaanxi), China, 30–101
Jia Kui, a Chinese astronomer of the Later Han dynasty (25–220), improved Chinese understanding of the Moon’s motions and detected the precession of the equinoxes, improving Chinese calendars in the process. In the year 85, a group of astronomers including Jia Kui was put in charge of improving the Sifen (quarter-remainder) calendar then in use. He confirmed that the Moon’s velocity varies, with the highest speed being at perigee. He also deduced that the point of maximum velocity shifts forward by 3 min of arc each month. Whereas ancient Chinese astronomers generally used polar and equatorial coordinates, Jia Kui advocated the use of ecliptic coordinates as the more accurate frame of reference for studying solar and lunar motions.
Jia Kui had bronze ecliptic instruments cast and put in use at the Imperial Observatory. Jia Kui pointed out that the equinoxes used in the previous Taichu calendar (104 BCE) had already moved to new locations. The...
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