How to judge what is vernal equinox, winter solstice, autumn equinox and summer solstice on a geographical map?

1. In the dichotomy diagram, a straight line can be connected between the two spherical centers of the sun and the earth. The intersection of this straight line and the earth's ground is the direct point of the sun, and its position can be judged. It is the summer solstice of the Tropic of Cancer, the winter solstice of the Tropic of Cancer, and the vernal equinox or autumn equinox of the equator. 2. If the solar rays are given in the solar illumination map of a single earth, the one perpendicular to the earth's surface can be found (it must be unique). Similarly, the intersection of this ray and the ground is the direct point, and the rest of the process is the same as the above point 1. 3. If the sunlight is not given, we can also use the day and night conditions in A Trip to the Terminator and The Earth to judge the solar terms. Winter solstice occurs when there is extreme night in the Arctic Circle and its north (or extreme day in the south of the Antarctic Circle), and summer solstice occurs when there is extreme night in the Arctic Circle and its north (or extreme night in the Antarctic Circle and its south). If the global day and night are equal, that is, the terminator line passes through the north and south poles at the same time, then it must be the vernal equinox or the autumn equinox.