Flag pole shadow twenty-four solar terms

The earth revolves around the sun at the same time, which is called the revolution of the earth. The phenomena produced by the revolution of the earth are the change of seasons and the change of the sun's altitude angle. When the sun shines directly on the Tropic of Cancer, it is the summer solstice in the northern hemisphere. On this day, the height angle of the sun is the largest in the northern hemisphere, so the shadow of the school flagpole is the shortest at noon. When the sun shines directly on the tropic of Capricorn, it is the winter solstice in the northern hemisphere. On this day, the sun's altitude angle in the northern hemisphere is the smallest, so the shadow of the flagpole in the school is the longest at noon; When the sun shines directly on the equator, it is the vernal equinox or autumnal equinox in the northern hemisphere. On this day, the solar altitude angle in the northern hemisphere is between the winter solstice and the summer solstice, so the noon shadow length of flagpoles in schools is also between the winter solstice and the summer solstice. Therefore, it can be judged that A is the shadow length measured from the winter to the sun, B and C are the shadow lengths measured from the vernal equinox or the autumnal equinox respectively, and D is the shadow length measured from the summer to the sun.

As can be seen from Figure 2, the length of the flagpole shadow in the figure is the same as that in Figure 1, so it can be judged that the date of measuring the flagpole shadow in Figure 2 is the winter solstice; Option A means summer solstice, B means autumnal equinox, C means winter solstice and D means vernal equinox.

So choose: C.