How to calculate the 24 solar terms?

The 24 solar terms are divided according to the position of the earth on the ecliptic. Depending on the sun starting from the vernal equinox (longitude zero, at this moment the sun shines vertically on the equator), every advance of 15 degrees is a solar term; After a week's operation, I returned to the vernal equinox, which is a tropical year with 360 degrees, so it is divided into 24 solar terms.

The twenty-four solar terms reflect the annual apparent motion of the sun, so their dates are relatively fixed in the Gregorian calendar. The solar term in the first half of the year is on the 6th, the solar term in the second half is on the 8th and the solar term is on the 23rd, with a difference of 1 ~ 2 days. The earth revolves around the sun once every 365 days at 6: 09 and 10 second (exactly) and rotates once every 24 hours.

Because the orbital plane of the earth's rotation is not the same as the equatorial plane, but maintains a certain inclination angle, the position of direct sunlight on the earth is different all year round. In the northern hemisphere, the sun shines directly on the Tropic of Cancer (23 26' north latitude), which is called summer solstice in astronomy. When the sun shines directly on the tropic of Capricorn (23 26' south latitude), it is called the winter solstice; The solstice in summer and the solstice in winter mean that it is halfway between summer and winter.

Twice a year, when the sun shines directly on the equator, it is the vernal equinox and the autumnal equinox, in the middle of spring and autumn. The day is as long as the night.

The activity law of the direct solar point is: vernal equinox (March 2 1 or so), the direct solar point is at equator 0, and then moves northward. During the summer solstice (around June 22nd), the direct point of the sun is on the Tropic of Cancer (23 26' N), and then moves south. At the autumnal equinox (around September 23), the direct point of the sun is 0 on the equator, and then it continues to move south. During the winter solstice (around 65438+February 22nd), the direct point of the sun is on the tropic of Capricorn (23 26), and then moves northward.

Extended information 24 solar terms songs

The plum blossoms in the early spring are particularly bright, and the apricot blossoms after the rain are particularly fresh;

Lulin thunder, butterfly dance between flowers at the vernal equinox.

Qingming kite broken, Grain Rain tender tea jade companion;

Mulberry fruits are like cherries in the long summer, and silkworms are cultivated in the small man.

Before mango seedlings enter the palace, the summer solstice rice and flowers are like white practice;

Summer breeze urges early-maturing beans, and Chi Pan enjoys red lotus in hot summer.

Beginning of autumn knows how to make people fall asleep, and sunflowers smile in summer.

The white dew returns to the geese, and the autumn equinox smells like osmanthus.

Cold dew vegetable seedlings are green, and the first frost reed flowers are floating all over the sky;

Beginning of winter reported good news, reported three rewards, and light snow and goose feathers flew in pieces.

The snow is very cold, the plum blossoms are crazy in the wind, and the winter solstice is full of snow.

Little cold wanderers are homesick, and they celebrate reunion at the end of the cold year.

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