The Chinese year
The Chinese calendar is a combined solar/lunar calendar which strives to have each year coincide with the tropical year and each month coincide with the synodic month. It is not surprising that a few similarities exist between the Chinese and the Hebrew calendars:
An ordinary year has 12 months and a leap year has 13 months. An ordinary year has 353, 354, or 355 days, a leap year has 383, 384, or 385 days.
When determining what a Chinese year looks like, a number of astronomical calculations need to be made:
Firstly, the dates for the new moons must be determined. In the lunar calendar a new moon is a completely "black" moon (when the moon is in conjunction with the sun), not the first visible crescent that used in the Islamic and Hebrew calendars. The date of a new moon is the first day of a new month.
Secondly, the dates when the sun's longitude is a multiple of 30 degrees must be determined. (The sun's longitude is 0 at Vernal Equinox, 90 at Summer Solstice, 180 at Autumnal Equinox, and 270 at Winter Solstice.) These dates are called the Principal Terms and are used to determine the number of each month:
Principal Term 1 occurs when the sun's longitude is 330 degrees.
Principal Term 2 occurs when the sun's longitude is 0 degrees.
Principal Term 3 occurs when the sun's longitude is 30 degrees.
etc.
Principal Term 11 occurs when the sun's longitude is 270 degrees.
Principal Term 12 occurs when the sun's longitude is 300 degrees.
Each month carries the number of the Principal Term that occurs in that month.
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