Chinese New Year

Chinese New Year is the most-observed festival on earth and its date is determined by a rule that is astronomical rather than tabular, which distinguishes it from the Hebrew and ecclesiastical systems.

The calendar is lunisolar. Months begin on the day of the astronomical new moon, the true conjunction, calculated, not a mean value, and a month is 29 or 30 days accordingly. The solar year is divided into twenty-four jieqi, solar terms, each corresponding to 15 degrees of the sun's ecliptic longitude, alternating between twelve major terms and twelve minor ones.

The anchor is the winter solstice, which must fall in the eleventh month. That requirement drives everything else. If the interval between one eleventh month and the next contains thirteen new moons, a leap month must be inserted, and the rule for choosing it is that the first month in that interval which contains no major solar term becomes the leap month, repeating the number of the month before it.

New Year is then the new moon that begins the first month, which in practice is the second new moon after the winter solstice, occasionally the third. This places it between 21 January and 20 February.

Calculations are made for Chinese Standard Time, at 120 degrees east, which matters because a new moon occurring just before or just after local midnight shifts the date. Vietnam uses its own meridian, which is why the Vietnamese Tet occasionally falls a day apart from Chinese New Year, and once in a while a whole month apart when the leap months differ.

The festival is not a day. It runs from New Year's Eve to the Lantern Festival on the fifteenth day, the first full moon of the year, and the intervening days have assigned characters, which relatives are visited on which day, when the god of wealth is welcomed, when it is unlucky to sweep.

The reunion dinner on the eve is the observance with the greatest social weight, and the travel it generates, the chunyun period, is the largest annual human migration in the world, measured in the billions of trips.

The red envelope given to children and unmarried adults, the red couplets on doorframes, the avoidance of certain words, the ban on sweeping in the first days lest fortune be swept out: these are widely observed regardless of religious belief, which is characteristic of the Chinese festival calendar. Much of the year's ritual apparatus operates as custom rather than as confessional practice.

The Nian monster story, a beast frightened away by red, noise and fire, said to explain the firecrackers and the colour, is often presented as ancient and appears to be relatively late in its current form, with no early textual basis. It is a good etiological tale of the kind that accumulates around long-established customs.

The official name in the People's Republic since 1912 is the Spring Festival, a republican-era coinage introduced when the Gregorian calendar was adopted for civil purposes and the term "new year" was reassigned to 1 January. The traditional calendar remains in official use for festivals and is published by the Purple Mountain Observatory.