Why are the days and nights of the vernal equinox and the autumnal equinox equal in the northern hemisphere?

From winter solstice to vernal equinox in the northern hemisphere, the change of day and night length is that the day first becomes longer and the night gradually becomes shorter, but the day is shorter and the night is longer. The revolution from winter solstice to vernal equinox is a gradual process, and the vernal equinox will be as long as day and night.

The variation law of the length of day and night in the northern hemisphere is that in summer (March 21-September 23), the days in the northern hemisphere are long and the nights are short; The days are short and the nights are long in winter (September 23rd-March 2nd1); June 22nd is the longest day-summer solstice; /kloc-February 22nd, 0/2, with the shortest day-winter solstice; March 2 1 day and September 23, the day and night are equally divided-vernal equinox and autumn equinox.

Judging the length of day and night in a certain place, you can see that the direct point points directly to that hemisphere. The rule is that the straight hemisphere has long days and short nights, and there is daytime near the pole of this hemisphere. The length of day and night in spring and autumn is similar in a year.