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Why are the times of vernal equinox, summer solstice and autumn solstice different from those in the book?

The time for geography in senior high school to pass through vernal equinox, summer solstice and autumnal equinox, and winter solstice is 3.216.229.2312.22 respectively (average year).

When the year is February 29th, there are 3.20 6.2 1 9.22 1 (leap year).