22 January 2012

A Short Primer on The Science of The Chinese New Year

The Chinese Calendar is a combination of two calendars, the solar and the lunisolar calendar. The solar calendar starts on the December solstice and follows the 24 solar terms of which the solstice and equinoxes are a part. The lunisolar calendar starts on the Chinese New Year and consists of 12 or 13 months.

The Chinese Calendar based on traditional culture and beliefs has been in use for more than 5,000 years. The year beginning January 23, 2012 based on the chinese calendar system is the year 4710. It is the Year of the (Male) Black Water Dragon.

A lunisolar calendar is a calendar whose date indicates both the moon phase and the time of the solar year. In the chinese calendar, the lunar months are typically simply numbered, following the standard practice with the solar months. The Chinese zodiac is only used in naming years—it is not used in the actual calculation of the calendar. The calendar is not as simple as the Gregorian calendar. Since it is based on moon phases and solar time, there is no exact or consistent tracking system for the calendar. All calculations are based on the exact time the moon has entered a phase.

The day on which the New Moon phase occurs is the first day of the month. A month is calculated from the start of the new moon up to the time of the end of the phase. Instead of leap years, the calendar adjusts based on a "leap month". This is done when the cycle of the moon phase starts to get ahead of how the calendar is calculated. This is remedied by adding a day to synchronize with the moon phase again.

Video: A Chinese New Year Story

As a rule of thumb, the year starts on the second new moon after the December solstice. But, another rule is that Chinese New Year should also fall on the day of the new Moon closest to the “beginning of spring”. Although there will be inconsistencies pertaining to these two conditions, the first one usually takes precedence.

Chinese Calendar Rules as noted in Wikipedia:

The following rules outline the Chinese calendar since 104 BC. Note: the rules allow either mean or true motions of the Sun and Moon to be used, depending on the historical period.

  • The months are lunar months. This means the first day of each month beginning at midnight is the day of the astronomical dark moon. (This differs from a traditional Chinese "day" which begins at 11 p.m.).
  • Each year has 12 regular months, which are numbered in sequence (1 to 12) and have alternative names. Every second or third year has an intercalary month (traditional Chinese: 閏月; simplified Chinese: 闰月; pinyin: rùnyuè), which may come after any regular month. It has the same number as the preceding regular month, but is designated intercalary.
  • Every other jiéqì of the Chinese solar year is equivalent to an entry of the sun into a sign of the tropical zodiac (a principal term or cusp).
  • The sun always passes the winter solstice (enters Capricorn) during month 11.
  • If there are 12 months between two successive occurrences of month 11, not counting either month 11, at least one of these 12 months must be a month during which the sun remains within the same zodiac sign throughout (no principal term or cusp occurs within it). If only one such month occurs, it is designated intercalary, but if two such months occur, only the first is designated intercalary. Note that for calendars before true motions of the sun were used for naming (i.e., before 1645), or in years where there is no double-cusp month in that year or the previous or following years (i.e., usually), the following rule suffices: a month with no principal term (or cusp) in it is designated intercalary.
  • The times of the astronomical new moons and the sun entering a zodiac sign are determined using the time in the Chinese Time Zone by the Purple Mountain Observatory (Chinese: 紫金山天文台; pinyin: Zǐjīnshān Tiānwéntái) outside Nanjing using modern astronomical equations.


When is Chinese New Year?
The Mathematics of the Chinese Calendar
Chinese Calendar
MIT NEWS: The Advantage Of Ambiguity in Language
MIT NEWS: The faster-than-fast Fourier transform
NASA GRAIL Twin Satellites Named
NASA Twin Satellites to Orbit the Moon
Super-Sized Lunar Eclipse on December 10