Canon of the Season-Granting System, Part 2
[This section sets out the elements of timekeeping; see the orientation, p. 82. The Centered Star (chung-hsing 中星) refers to whatever star is culminating (crossing the meridian) at a given moment. Most often it designates a star in one of the lunar lodges, since astronomers knew its distance from the determinative, and thus its equatorial location. Determining culminations is not part of generating the ephemeris, but in the Yuan laymen still widely used rules of thumb based on sighting a star crossing the meridian to tell the time of night.
Tabulate declination and polar distance of ecliptic, and day and night lengths
Compute daily polar distance of ecliptic, using table
Compute length of day and night
Compute times of sunrise and sunset
Compute lengths of night watches and subdivisions
Compute times of night watches and subdivisions
Compute the nightly arc of stellar motion
Compute positions of stars that culminate at dusk, dawn, and each night watch
Compute day and night marks for any latitude]
KeywordsSolar Eclipse Polar Distance Motion Part Summer Solstice Winter Solstice
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