When did the solar term first appear?

In ancient China, before the invention of using standard tables to determine seasons, the stars in twilight, sunrise and sunset, and the direction pointed by Beidou bucket handle were used to determine seasons. These data are recorded in China and his early almanac in the summer. "Moon Order" specially records the astrology and phenology at the beginning and middle of the month. Whenever stars and phenology appear, you will know what season it is, and you will know what crops to plant and what to do in farm work. Around the middle and late Warring States period, people divided 1 tropical year into 34 intervals according to the astrological and phenological knowledge at the beginning of the month, and gave themselves names, which is the origin of the 24 solar terms. In the Spring and Autumn Period, there was the name of the sun solstice in the south and the name of the sun solstice in the north, which may be the proper name for measuring the shadow length of the winter, summer and solstice by using the standard table. At the end of the Warring States Period, Lu's Spring and Autumn December recorded the names of eight solar terms: beginning of spring, Spring Equinox, Long Summer, Summer, beginning of autumn, Autumn Equinox, beginning of winter and Winter. Except for the vernal equinox and autumnal equinox, as well as the winter and summer solstice, the rest are in line with modern times. The eight solar terms are the most important of the 24 solar terms, which are separated by about 46 days. Huainanzi records all the names of the 24 solar terms, which is completely consistent with modern times. This is the earliest record of all the names of the 24 solar terms. From the unearthed documents, it can be proved that solar terms were definitely used to remember calendars in the Western Han Dynasty, so at that time, it had developed to the point where we could grasp the seasons just by reading the almanac.

Agricultural production is closely related to seasons, and the working people in ancient China have long known the importance of timely sowing. In their long-term production practice, they summed up many experiences in the relationship between seasons and farming seasons, and compiled many songs to master farming seasons and festivals, which were widely circulated among working people. When a certain season comes, people will be familiar with the time to do farm work. Twenty-four solar terms and seasonal songs compiled according to different climatic characteristics in different places have greatly helped and promoted the development of agricultural production. Although the Gregorian calendar has been used in China for several decades, the 24 solar terms are still very popular in China and still play a favorable guiding role in agricultural production.

Some people say that solar terms belong to the solar calendar, which is quite right. But it is also a unique product of the lunar calendar. The sun marks the year and the moon marks the moon, which is the characteristic of the Yin and Yang calendars used in ancient China. It is necessary to set a leap month to adjust the cold and warm seasons. Because of the leap month, the season is not very fixed in the month. For example, some phenology sometimes appears at the beginning of Dan and sometimes at the end of the month. The 24 solar terms were created to accurately show climate change. This is a pure solar calendar. Many countries in the ancient world used the lunar calendar, and only China created the 24 solar terms, which can prove the wisdom of the working people in ancient China and the developed agricultural production and technology in ancient China.