The meaning and symbol of autumnal equinox

The autumnal equinox has a double meaning. One is that the autumnal equinox is divided into equal parts day and night, and the time between day and night is the same. The other is that the autumnal equinox is equally divided, and the weather gradually turns from hot to cold. The equinox is "half".

At the autumnal equinox, the world is as long as day and night. After the autumnal equinox, the days are getting shorter and shorter in the northern hemisphere, and the nights are getting longer and longer in the southern hemisphere. China's ancient book "Spring and Autumn Stories, Yin and Yang in and out" said: "The autumn equinox, Yin and Yang are also half-phase, so it is cold and summer day and night.

According to the lunar calendar, "beginning of autumn" is the beginning of autumn and ends with "the first frost", and the "vernal equinox" is just half of the 90-day journey from beginning of autumn to the first frost.

September 23rd or 24th of the Gregorian calendar is one of the twenty-four solar terms of traditional festivals in China. The autumnal equinox used to be a traditional festival to offer sacrifices to the moon, and there were customs such as offering sacrifices to the moon, eating autumn vegetables, sending autumn cows, flying kites and sticking birds' mouths. And every year on the day of the autumnal equinox, the whole world is playing the game of vertical eggs.

On the day of the autumnal equinox, the point of direct sunlight reaches longitude 180 (autumnal equinox), almost directly to the equator of the earth, and the length of day and night is the same all over the world (regardless of the refraction of sunlight by the atmosphere and the dim shadow in the morning).

After the autumnal equinox, the direct point of the sun continued to move from the equator to the southern hemisphere, and the days in the northern hemisphere began to shorten and the nights became longer, that is, the days in a day began to be shorter than the nights; The southern hemisphere is the opposite. Therefore, the autumnal equinox is also called the landing point. At the North Pole and South Pole, on the day of the autumn equinox, the sun is on the horizon all day.