How to judge the solar terms according to the terminator line! !

Judge the solar terms, date and latitude of the direct sun point, and circle the pole (or coincide with a meridian) in the morning and evening, and the direct sun point is the equator, that is, vernal equinox; The termination line is tangent to the polar circle. If there is an extreme solar phenomenon in the Arctic Circle, it is the summer solstice in the northern hemisphere, and the direct sunlight point is at 23o 26' north latitude. If there is an extreme night phenomenon in the Arctic Circle, it is the winter solstice in the northern hemisphere, and the direct sunlight point is at 23 26' south latitude.