How is beginning of spring time calculated?

According to the position of the sun on the regression ecliptic, that is, on a "ecliptic" with a circumference of 360 degrees (the apparent path of the sun on the celestial sphere for one year), it is divided into 24 equal parts, each equal part is 15, and the starting point is 0 degrees in spring (beginning of spring still ranks first), and arranged according to the degree of the ecliptic.

Every time the sun moves 15 degrees on the ecliptic, it is a solar term, and the degrees between each solar term are equal (the time is different), which is called "the method of regulating qi". In the twenty-four solar terms, the activity law of the sun's direct point is: at the vernal equinox, the sun's direct point is at the equator 0, and then moves north; On the summer solstice, the direct point of the sun is on the tropic of cancer (23 26' n), and then it moves south.

At the autumnal equinox, the direct point of the sun is 0 on the equator, and then it continues to move south; During the winter solstice, the direct point of the sun is on the tropic of Capricorn (23 26), and then it moves northward. Twenty-four solar terms are 24 time points, and when the "point" falls is the natural result of celestial movement. The solar terms (according to the degree of the yellow meridian) divided by the method of "fixing qi" began in the beginning of spring and ended in the great cold.