Which solar term is the autumnal equinox?

Autumnal equinox: the barrel refers to itself. The solar line is 180. On the day of the autumnal equinox, like spring people, the sun is almost direct to the equator, and day and night are almost equal. From this day on, the position of direct sunlight continued to move from the equator to the southern hemisphere, and the days became shorter and the nights became longer in the northern hemisphere. According to China's autumnal equinox theory, this day is exactly half of the ninety days in autumn, so it is called autumnal equinox. But in astronomy, it is stipulated that autumn in the northern hemisphere begins with the autumnal equinox.