What do you mean by vernal equinox and autumnal equinox?

"Equivalence between day and night at vernal equinox" means that when the vernal equinox and autumnal equinox arrive every year, day and night are equal in length, that is, they are equally divided between day and night, which is 12 hours respectively, and the climate is mild.

The vernal equinox is one of the 24 solar terms. Since then, the direct position of the sun has continued to move from the equator to the northern hemisphere. In the northern hemisphere, the day begins to be longer than the night, while in the southern hemisphere, it is the opposite. In ancient times, it was spring from long summer in beginning of spring, and the vernal equinox happened to be in the three months of spring, and the spring was equally divided.