The 24 solar terms based on the sun’s position in the zodiac, created by ancient farmers on the middle and lower reaches of the Yellow River, reflect the changes in climate, natural phenomena, agricultural production, and other aspects of human life, including clothing, food, housing, and transportation, etc.
The terms consist of 12 major solar terms and 12 minor solar terms interlaced with each other; namely, they are as follows: Start of Spring (lì chūn立春),Rain Water(yǔ shuǐ雨水), Awakening of Insects (jīng zhé惊蛰),Vernal Equinox (chūn fēn春分), Clear and Bright (qīng míng清明), Grain Rain (gǔ yǔ谷雨), Start of Summer (lì xià立夏), Grain Full (xiǎo mǎn小满), Grain in Ear (máng zhǒng芒种), Summer Solstice (xià zhì夏至), Minor Heat (xiǎo shǔ小暑), Major Heat (dà shǔ大暑), Start of Autumn (lì qiū立秋), Limit of Heat (chù shǔ处暑), White Dew (bái lù白露), Autumnal Equinox (qiū fēn秋分), Cold Dew (hán lù寒露), Frost Descent (shuāng jiàng霜降), Start of Winter (lì dōng立冬), Minor Snow (xiǎo xuě小雪), Major Snow (dà xuě大雪), Winter Solstice (dōng zhì冬至), Minor Cold (xiǎo hán小寒), and Major Cold (dà hán大寒).
The 24 solar terms embody a complete circle of the sun and divide the circle into 24 segments, with each segment about half a month long. In both the lunar and solar calendars, the date of each solar term is basically fixed, with minor differences of within one or two days.
As early as the Spring and Autumn Period (770–476 BC), our ancestors had already established two major solar terms, ri nan zhi (日南至) and ri bei zhi (日北至). As of the end of the Warring States Period (475–221 BC), eight key solar terms (Start of Spring, Vernal Equinox, Start of Summer, Summer Solstice, Start of Autumn, Autumnal Equinox, Start of Winter, and Winter Solstice) marking the four seasons, were established according to the different positions of the sun and the moon in the beginning and middle of a lunar month, as well as the changes in natural phenomena. The rest of the solar terms were initiated in the Western Han Dynasty (206 BC–24 AD).