What does the autumnal equinox mean? What does the autumn equinox symbolize? It represents the equal division of autumnal equinox and the equal length of day and night. China's ancient book "The Story of the Spring and Autumn Period, Yin and Yang in and out" said: "The autumn equinox, Yin and Yang are also half-phase, so it is cold and hot day and night. The autumnal equinox is one of the 24 solar terms of traditional festivals in China. On September 22nd, 23rd or 24th of Gregorian calendar, the sun reaches 180 degrees. Twenty-four solar terms: "See the vernal equinox in mid-August." Minute "means to divide day and night equally." Like the vernal equinox, the sun shines directly on the equator of the earth on this day, and day and night are equal. From then on, direct sunlight began to enter the southern hemisphere, and the northern hemisphere began to have shorter days and longer nights, and the temperature dropped, which was of universal significance throughout the country. At the autumnal equinox, "fen" means "half". At the autumnal equinox, most parts of the earth are equally divided day and night, each with 12 hours; Near the North Pole and South Pole, the sun can be observed on the horizon all day on this day. After the autumnal equinox, the days in the northern hemisphere are short and the nights in the southern hemisphere are short. The characteristics of the autumnal equinox The autumnal equinox solar terms are special among the 24 solar terms. Why is the autumnal equinox divided equally between day and night? The alternation of day and night is produced by the rotation of the earth. Because the earth is not luminous and opaque, at the same time, the sun can only illuminate half of the earth, the illuminated hemisphere is daytime, the unlighted hemisphere is night, the earth rotates for one day and night, and the dividing line between day and night is called terminator line; While the earth is rotating, it is still tilting its body around the sun, and the tilt angle remains the same for one year. In this way, the earth's exposure to the sun at different positions in its orbit is not exactly the same (the latitude of direct sunlight is different), thus forming four seasons; Because people on the earth usually can't feel the movement of the earth (revolution), just like people sitting in driving vehicles feel the backward movement of objects around them, what people on the earth see is the backward movement of the sun on the starry background composed of stars, which is called the annual apparent movement of the sun, and the sun's running line (that is, the reflection of the earth's revolution orbit on the celestial sphere) is called the ecliptic. The zodiac is the measuring coordinate (longitude) on the ecliptic. According to astronomical practice, it is measured from west to east from the vernal equinox and divided into 360 degrees. The ancients in China divided the 360-degree meridian of the sun into 24 equal parts, each equal part is 15 degrees, which is a solar term. On the day of the autumnal equinox (the sun reaches the longitude 180), the sun points directly at the equator again, and the terminator line also passes through the north and south poles, which coincides with the meridian circle of the earth and divides all latitudes into two parts, so it is said that "the vernal equinox and autumnal equinox are equally divided day and night". The difference is that after the vernal equinox in the northern hemisphere, the direct point of the sun gradually moved northward, the solar radiation gradually increased, the weather became warmer day by day, the days became longer and the nights became shorter. After the autumnal equinox, the direct point of the sun gradually moved southward, the solar radiation gradually decreased, the weather became colder day by day, the days became shorter and the nights became longer. The southern hemisphere is just the opposite.