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For more than two millennia, a Bureau of Astronomy made astronomical observations, calculated astronomical events such as eclipses, prepared astrological predictions, and maintained the calendar.
After all, a successful calendar not only served practical needs, but also confirmed the consonance between Heaven and the imperial court. Various intercalation schemes were developed for the early calendars, including the nineteen-year and 76-year lunar phase cycles that came to be known in the West as the Metonic cycle and Callipic cycle.
Although the accession of an emperor would mark a new era, an emperor might also declare a new era at various times within his reign.
Chinese New Year is the main holiday of the year for more than one quarter of the world’s population.
Although the People’s Republic of China uses the Gregorian calendar for civil purposes, a special Chinese calendar is used for determining festivals. The Chinese calendar is based on exact astronomical observations of the longitude of the sun and the phases of the moon.
However, calculations were based on the mean motions resulting from the cyclic relationships.
Inequalities in the Moon’s motions were incorporated as early as the seventh century C.
This roughly corresponds to the east coast of China.