1, the autumn equinox, is the sixteenth of the twenty-four solar terms, the time is generally for the annual calendar September 22 ~ 24 days. Autumn equinox day the sun reaches 180 ° longitude (the autumnal equinox), almost directly on the Earth's equator, the day and night around the globe is equal (not taking into account the atmosphere on the refraction of sunlight and morning and evening shadow). In ancient times, there was a "spring festival of the sun, autumn moon festival" folk activities, the autumnal equinox was the traditional "Festival of the Moon" (Mid-Autumn Festival), the Mid-Autumn Festival evolved from the Autumn Sunset moon festival.

2, the autumnal equinox symbolizes one, day and night time is equal, the sun reaches 180 degrees of longitude on this day, direct sunlight on the Earth's equator, so most of the world on this day of the 24 hours of day and night are divided, each 12 hours. After the autumnal equinox, the sun's direct point of view began to enter the southern hemisphere from the equator, the northern hemisphere began to shorten the day and night, the day began to be shorter than the night within a day; near the North Pole is also about to usher in a year of six consecutive months of long night and six consecutive months of inextinguishable starry sky.

3, the autumnal equinox symbolizes two, the climate from hot to cool. According to China's ancient to spring, summer, autumn, winter for the beginning of the four seasons of the seasonal division of law, the autumnal equinox in the 90 days of autumn, the equal division of the autumn.