The vernal equinox, summer solstice, autumn equinox, winter solstice and the sun shine on that part of the earth respectively.

The direct sunlight of vernal equinox and autumnal equinox is on the equator, the direct sunlight of summer solstice is on the tropic of cancer, and the direct sunlight of winter solstice is on the tropic of cancer.

The earth's revolution and rotation form the ecliptic angle, which results in the periodic change of the direct direction of the sun between the tropic of cancer, as well as the periodic change of climate, the length of day and night and the height of the sun.

Summer is the season with the longest day and the highest sun at noon. Starting from beginning of spring (February 4th or 5th), Changxia (May 5th or 6th), beginning of autumn (August 7th or 8th) and beginning of winter (165438+1October 7th or 8th) among the 24 solar terms.

The movement of the earth in the orbit of revolution will produce regular changes in weather and seasons, and farmers in traditional agriculture will carry out agricultural production accordingly, just like the proverb "Grain Rain planted melons and beans before and after".

The ecliptic angle is the direct cause of the astronomical season. This is because:

The distribution of noon sun height with latitude is as follows: low latitude is large, high latitude is small, and the spring and autumn equinox decreases from equator to poles; In summer solstice, it decreases from the tropic of cancer to the north and south sides; In winter solstice, it decreases from the tropic of Capricorn to the north and south sides.

The seasonal variation is: north of the Tropic of Cancer, the height of the sun reaches the maximum from summer to noon, and reaches the minimum from winter to noon. South of the Tropic of Capricorn is the opposite. Between the Tropic of Cancer, there is direct sunlight twice a year.