Beginning of autumn and astronomical knowledge

The earth revolves around the sun for about 365 days and 5 hours, with a journey of 940 million kilometers. This orbit of the earth is called the ecliptic. This orbital plane is the ecliptic plane, and the angle with the equatorial plane of the earth is 23 degrees and 26 minutes, which is called the ecliptic angle. This is why the globe tilts the earth, because people use the water plane to represent the ecliptic plane at this time. ?

24 solar terms just divided the longitude of the sun from 360 degrees into 24 equal parts, each part is 15 degrees, which is a solar term. The longitude of the sun in 24 solar terms is: 3 15 degrees in beginning of spring, 330 degrees in rain, 345 degrees in fright, 360 degrees in vernal equinox, 30 degrees in Qingming 15 degrees in Grain Rain, 45 degrees in long summer, 60 degrees in childhood, 75 degrees in awn grass, 90 degrees in full summer solstice and 0/0 in summer. Millennium 165 degrees, autumnal equinox 180 degrees, cold dew 195 degrees, first frost 2 10 degrees, beginning of winter 225 degrees, light snow 240 degrees, heavy snow 255 degrees, winter solstice 270 degrees, slight cold 285 degrees and severe cold 3000 degrees.

Therefore, according to modern science based on the revolution of the earth around the sun, beginning of autumn should be the longitude of the earth reaching the sun 135 degrees, not the longitude of the sun 135 degrees. ?

As for the ancients, they observed the movement of the sun around the earth. The twenty-four solar terms must be determined according to the position of the sun in the starry sky. It is actually a "moment", not a "day". Observed from the earth, the sun will move eastward about 65438 0 degrees every day, and the time around it is called the "sidereal year", and the time around the spring equinox is called the "tropic year". Its trajectory is called the ecliptic. Because the inclination of the earth's rotation axis relative to the public rotation axis is 23.5 degrees, the elevation angle of the sun is higher at noon in summer and lower in winter, which affects the temperature and season throughout the year. In order to let our ancestors know about the climate change in cold and summer, decide the progress of farming or serve as a reference for daily life, ancient historians stipulated that the tropical year from winter solstice to winter solstice of the following year should be divided into twelve equal parts, called Zhongqi; Then, the two equal parts of neutral gas are called solar terms, which are the source of 24 solar terms. The formulation of this solar term is called "flat gas method". ? However, because the earth's orbit around the sun is elliptical. Near the sun, the speed of the earth's revolution is faster, but far away, it is slower. For the Central Plains region where this calendar was made at that time, some solar terms could not reflect the real climate. Therefore, since the Qing Dynasty, the vernal equinox has been set at 0 degrees, and every time the sun runs 15 degrees on the ecliptic, it is set as a solar term or neutral atmosphere, so the 24 solar terms have 24 specific moments instead of 24 specific days. This method of making solar terms is called "fixing gas method".