Solar vs. Lunar
In many renowned publications about Chinese Calendar Science and Astrology, it is clearly defined and explained that the 10 Heavenly (or Celestial) Stems 天干and 12 Earthly (or Terrestrial) Branches 地支 are based on Solar Terms 節氣 of the sun, not lunar calendar of the moon. As the 12 Zodiac Animals represent the 12 Earthly Branches, the Chinese Zodiac publications also clearly stated that Chinese Zodiac is based on Solar Terms, and it begins on “Start of Spring” 立春, not Lunar New Year.
Zodiac Year Cutoff
The Chinese Zodiac Year Cutoff is based on “Start of Spring” (Chinese
立春, meaning Initiating Spring literally) which is usually February 4th,
but sometimes 5th or 3rd depending on the time zone. “Start of Spring” is about 6 weeks
before the spring Vernal Equinox which is usually March 20th in the
Northern Hemisphere. Astronomically, the spring Vernal Equinox is the
middle of spring, but it is commonly referred as the “first day of
spring” in the US due to its longitude and temperature. Chinese Zodiac
uses the astronomical Start of Spring for the year cutoff.
This means each Chinese Zodiac Animal begins on “Start of Spring” and ends on the day before the next “Start of Spring” of next year. For example,
1984 was the “Year of Rat”. It started on Feb. 4, 1984, the Start of
Spring of 1984.
1985 was the “Year of Ox”. It started on Feb. 4, 1985, the Start of Spring of 1985.
So the “Year of Rat of 1984” was from Feb. 4, 1984 to Feb. 3, 1985.
Lunar New Year and Chinese Zodiac
There is a common but incorrect saying that the Chinese Zodiac Year cutoff is based on Chinese New Year. The fundamental difference is that Chinese New Year is based on lunar calendar while Chinese Zodiac is based on Solar Terms. The Lunar New Year usually occurs in the first two weeks of February, but occasionally occurs in the last week of January or the 3rd week of February. Due to the close timeframe, it has been a tradition to welcome and celebrate the next Zodiac Animal during the Chinese New Year festival. So it can be confusing when a baby is born right after the Chinese New Year but before Start of Spring, because in this case, the prior year Zodiac Animal is still in effect, literally “at the tail end of the animal”. For example,
Lunar New Year of 1984 was on Feb. 2, 1984 and
Lunar New Year of 1985 was on Feb. 20, 1985.
So the “Lunar year of 1984” was from Feb. 2, 1984 to Feb. 19, 1985.
Feb 2 - 3, 1984
Feb 4 - 19, 1985
Therefore, if your birthday is close to the Lunar New Year, and if you use websites that based on Lunar New Year cutoff, you may get a wrong Zodiac Animal and wrong analysis.