Causes of seasonal variation of midday sun height and length of day and night

1, causing the change of the sun height at noon:

(1) The angle between the sun's rays and the ground plane is called the solar altitude angle, which is referred to as the solar altitude angle (expressed by H). At noon, the height of the sun decreases from the direct point to the north and south sides. So the position of the direct point of the sun determines the height of the sun at noon in a place. At the direct point of the sun, the height of the sun is 90, and at the termination line, the height of the sun is 0.

(2) The reason for the noon sun height change: Because of the yellow-red intersection angle, the direct point of the sun moves north and south, which causes the noon sun height change.

(3) Variation law of noon solar height: noon solar height is the largest solar height in a day, and its size changes regularly with different latitudes and seasons.

2. The length of day and night varies with latitude and season:

The dividing line between the day hemisphere and the night hemisphere of the earth is called the end line (circle). The terminator line divides the latitude into day arc and night arc. Because of the ecliptic angle, every latitude circle is divided into two parts with different lengths (except the equator), except that there is a termination line passing through the poles in vernal equinox, which divides all the latitudes equally. The earth rotates once, and the length of the day arc is long; The night arc is long and the day is short. The variation of the length of day and night with latitude and season is shown in the table below:

3. Seasonal changes:

(1) From the astronomical season:

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.

(2) The months included in the four seasons. Spring (March, April and May), summer (June, July and August), autumn (September, 10, 165438+ 10) and winter (12,/kloc-0).

(3) Western seasons: starting from the vernal equinox, summer solstice, autumn equinox and winter solstice. One and a half months later than the astronomical season in China.