Around September 23 each year, the sun reaches the longitude of 180 degrees, walking into the Autumn Equinox. As the Spring Equinox, the Autumn Equinox is one of the solar terms established in the earliest period of Chinese history. "Chun Qiu Fan Lu, Yin and Yang" says: "Autumn Equinox means the day when yin is accompanied by yang, day and night are the same length and the cold and heat are balanced."

The Autumn Equinox has two meanings:

First, in ancient China, the four seasons are divided by solar terms such as the Beginning of Spring, Beginning of Summer, Beginning of Autumn, and Beginning of Winter. Autumn Equinox lies at the midpoint of autumn, dividing autumn into two equal parts. In Chinese, the Autumn Equinox is written as “Qiu Fen” (秋分). “Qiu” means autumn and “Fen” means division.

Second, on Autumn Equinox, day and night are of equal length, each occupying 12 hours. The sun on the day of the Autumn Equinox shines almost directly onto the equator. After that day, the location of direct sunlight moves to the south, making days shorter and nights longer in the northern hemisphere.

How to Calculate the Date

Formula: [Y×D+C]-L

Note: Y refers to the last two digits of a year, such as 10 in 2010, 08 in 2008 D=0.2422 L=the number of leap years 21st century C=23.042 20th century C=23.822

Example: The date of Autumn Equinox in 2088=[88×0.2422+23.042]-[88/4]=44-22=22, so Autumn Equinox falls on September 22.

Exception: Add one to the calculated result of 1927.