How to judge the four solar terms by the signal of the earth's revolution

Because the orbital plane of the earth's rotation is not the same as the equatorial plane, but maintains a certain inclination angle, the position of direct sunlight on the earth is different all year round.

When identifying solar terms on the plan of revolutionary orbit, we should first consider the "vernal equinox" and then determine the "dichotomy" point. The key to interpretation is to determine the position of the direct point of the sun.

On the summer solstice, the sun shines directly on the Tropic of Cancer (23.5? N), the northern hemisphere is biased towards the sun, the Arctic Circle has an extreme day, and the Antarctic Circle has an extreme night;

On the solstice of winter, the sun shines directly on the tropic of Capricorn (23.5? S), the southern hemisphere is biased towards the sun, the polar day appears in the Antarctic circle, and the polar night appears in the Arctic circle;

Then determine the vernal equinox and autumnal equinox according to the revolution direction of the earth.