9.23 sunshine length

3.2 1 and 9.23 are vernal equinox and autumnal equinox, and the sun shines directly on the equator, so the sunshine height in the northern and southern hemispheres is equal to the complementary angle of latitude.

3.2 1-6.22 From the vernal equinox to the summer solstice, and from the summer solstice to the autumn equinox, the direct point of the sun is between the equator and the Tropic of Cancer. During this period, the sunshine height in the north temperate zone (north of the Tropic of Cancer) is between the complementary angle of latitude and the complementary angle of latitude+23 26', and the Tropic of Cancer (inclusive) is between the equator.

6.22 is the summer solstice, and the sun shines directly on the Tropic of Cancer. At this time, the sunshine height in the northern temperate zone is the complementary angle of latitude+23 26', the sunshine height from the Tropic of Cancer to the equator is latitude+23 26', and the sunshine height in the southern hemisphere is the complementary angle of latitude-23 26'.

9.23- 12.22 From the autumnal equinox to the winter solstice, 12.22-3.2 1 From the winter solstice to the vernal equinox, the direct point of the sun is between the equator and the tropic of Capricorn. During this period, the sunshine height in the south temperate zone is between the complementary angle of latitude and the complementary angle of latitude+23 26', and the tropic of Capricorn (inclusive).

6.22 is the winter solstice, and the sun shines directly on the tropic of Capricorn. At this time, the sunshine height in the south temperate zone is the complementary angle of latitude+23 26', the sunshine height from tropic of Capricorn to equator is latitude+23 26', and the sunshine height in the northern hemisphere is the complementary angle of latitude-23 26'.