High school geography solar terms

The direct points of the sun in winter solstice and summer solstice are the Tropic of Cancer and the Tropic of Cancer. If you draw a top view of a pole, it is concentric circles. The outer circle is the equator, the inner circle is the tropic of cancer, and the center of the circle is the pole.

Partial side view of winter solstice:

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The terminator line is a morning and evening circle. The dividing line between the daytime hemisphere and the night hemisphere on the earth is the great circle of the earth. Vernal equinox coincides with the same meridian coil, and the global day and night are equal in length. From winter to summer, its angle with meridian is the largest, and the temperature difference between day and night ranks first in the world. Because of atmospheric refraction and the apparent radius of the sun, it is actually slightly smaller than the great circle.

Generally speaking, in the spring and autumn, the terminator line coincides with the meridian, that is, the terminator line will cross the north and south poles. At any other time, the termination line is oblique to the meridian (that is, the termination line does not pass through the north and south poles), and its included angle ranges from 0 to 23 26'.

On the second solstice, the maximum included angle is 23 26'. When the termination line intersects the meridian, the included angle is equal to the latitude value of the direct point of the sun at this time.

If the terminal line passes through the pole and coincides with a meridian, the solar terms are vernal equinox and autumnal equinox, and the sun shines directly on the equator;

If the termination line is tangent to the polar circle, that is, the angle of intersection with the earth axis is the largest, it can be divided into two situations: first, the arctic circle and its north are extremely daytime, then the summer solstice, and the sun is directly on the tropic of cancer; The second is the polar night in the Arctic Circle and the north. At this time, it is the winter solstice and the sun shines directly on the Tropic of Capricorn.