Chinese New Year  : A  Product of the Lunisolar  Calendar 陰陽合壁的夏曆  

The Chinese calendar harmonizes BOTH the Lunar cycle 陰曆 AND
the Solar year 陽曆 by incorpratong astronomical observations of :
1. The phases of the moon 太陰, and
2. The apparrent path of the sun 太陽: 黃道所至.

The Chinese New Year is celebrated on the second new moon (Lunar)
after the Winter Solstice (Solar).

The Winter Solstice 冬至 occurs when the apparent path of the sun reaches
its lowest point on the horizon. To an observer in the northern hemisphere,
the sun reaches its lowest height of the year on that day. The shadow it
casts is the longest. For an observer in the southern hemisphere, the opposite
is true.

In the northern hemisphere, Winter Solstice usually occurs on December 21 or 22.
Though we generally assume that the duration of daylight is the shortest on
Winter Solstice, astronomers would hasten to point out that it is not exactly

Depending on the "age" of the moon on Winter Solstice, the second new moon
could arrive any where from 30 to 59 days later.

For example:
let x = the "age" of the moon on Winter Solstice
the second new moon occurs at = ( 29.5 - x ) + 29.5 days

The Winter Solstice of 2000 occurred on December 21st. It corresponds to the 26th day of the lunar month. Five days later, on December 26th, the first new moon after the Winter Solstice appears. The second new moon follows 29 days later, on January 24th, 2001. This is the day of the Chinese New Year! In North America, the first new moon may possibly be sighted at the predawn hours of 6:30 am along the Pacific Coast from Vancouver to Los Angeles. Residents in Alaska and Hawaii might notice the new moon at 5:30 am or 4:30 am in their respective time zones. In Hong Kong and China, the first glimpse on the new moon might be visible late at night after 10:30 pm on January 24th, 2001. Welcome to the year of the Golden Snake (Rattle!) ! If you are still interested, please read on...

The Chinese calendar normally has 12 moons (months) in a year.
Since the "age" of the moon has a 29.5 day cycle, each month is rounded off
to either 29 or 30 days.
The New Moon occurs on Day 1 (First Day), the First Quartrer on Day 7th.
The Full Moon is on the 15th while the Last Quarter occurs on Day 21,
and the last day of the month is either the 29th or the 30th.

The New Year is celebrated, not surprisingly, on the First Day of the First Month.
The Chinese calendar is said to haved started by the Xia 夏 people (ca 2,205 B.C.),

The ability to determine the seasons, especially the arrival of Spring,
is vital to an agricultural society. By measuring the length of the shadow
casted upon a pole (or stem, 干), ancient astronomers readily quantified the
seasons into 24 intervals 廿四節氣 of roughly 15 days each.Due to variations
in the motion of the earth, the summer intervals are slightly longer than the
winter ones.

In 104 B.C. the length of a year was determined to an accuracy of 365.2502 days,
by 480 A.D., Ju Chongzhi 祖沖之 refined it to 365.2428 days, or 52 seconds more than
the modern value of 365.2422 days.

The challenge: how to synchronize the lunar cycle of 354 days in 12 months
(29.5 x 12 = 354) with the 365 day solar cycle?

Unless adjustments are made to account for the difference of 11+ days per year,
the seasons will be 30 days late in arrival within 3 years!

The answer: to add a LEAP MONTH once every 2.7 to 3 years:
when ever a month fails to span two consecutive intervals 無中氣之月置閏.
This works out to approx. 7 leap months in 19 years.

Chinese astronomers settled for a value of 235 lunations (months) in 19 years.