Equator and solar terms

The vernal equinox and the autumnal equinox are artificially set. This is because the direct sunlight at the equator is a special critical point. Moreover, the exact time of vernal equinox and autumnal equinox is instantaneous, and the vernal equinox is the midpoint of 90 days in spring. One of the 24 solar terms, around March 20 of the Gregorian calendar every year, when the sun is located at 0 (vernal equinox) of the yellow meridian. On the day of vernal equinox (vernal equinox usually refers to the moment when the sun meridian is located at 0, to be exact), the sun shines directly at the equator of the earth, and the seasons in the northern hemisphere are opposite, which is the vernal equinox in the northern hemisphere and the autumnal equinox in the southern hemisphere. Generally speaking, the period from vernal equinox to rainy season is called vernal equinox, just like many times: 50 seconds after one o'clock, we still call one o'clock.