Why are the vernal equinox and autumnal equinox equally divided day and night?

When the earth revolves around the sun, when the sun shines on the earth, it forms a vertical direct, and the direct point moves between the tropic of cancer. The ancients formulated 24 solar terms according to the change of the position of the direct point of the sun. Mutton toutoulai

The center line between the Tropic of Cancer is the equator, and the direct point of the sun is formed near the equator of the earth. This direct point is twice a year, around March 22nd and September 22nd respectively, that is, the vernal equinox and the autumnal equinox. The equator is also the center line between the north and south of the earth. At this time, the earth rotates once, and day and night are equally divided in time.