The origin of light snow is the same as other solar terms, that is, "24 solar terms" and "December construction" are the basic contents of the dry calendar, which was concluded in ancient times (or ancient times). According to ancient records, Emperor Tiandi began to determine his age in the name of cadres and branches. "Twenty-four solar terms" is a special festival in the calendar, indicating the season, phenology, climate change and the establishment of "December construction". The repeated rotation of the Big Dipper is closely related to the change of seasons. Taking the direction pointed by bucket handle, namely the Big Dipper, as the standard for judging seasons, it is called sword fighting, also known as Jian Yue. The method of the era of cadres and branches, the first month to build Yin, beginning of spring as the beginning of the year, the beginning of the month to pay the festival. One year is divided into twelve years ("completed in December"), in which "completed" represents the direction of the top of the bucket handle of the Big Dipper. In ancient times, the "twenty-four solar terms" were determined by the direction at the top of the bucket handle of Beidou, and bucket handle rotated to the "twelfth day" in turn, which was called "December Construction" (or "December Order"). In ancient culture, the time and position of branch and gossip are linked together. Yin position is the root position of the acquired gossip, the position at the end of the year and the beginning of the year, representing the end and beginning. For example, "Yi Shuo Gua Zhuan": "Gen, the divination in the northeast is also the beginning of all things." That is to say, bucket handle is one of the "years old", starting from the east to the north (Yin position, gossip position the day after tomorrow) and making a circle through the south, west and north. Therefore, silver moon is "spring is positive", and the beginning of spring is the beginning of a year. The twenty-four solar terms established by Beidou bucket handle began in the beginning of spring and ended in severe cold.
In the Western Han Dynasty, the name of "Twenty-four solar terms" first appeared in the book Huainanzi Astronomical Training. During the period of Emperor Wu of the Han Dynasty, "Twenty-four solar terms" were absorbed into taichu calendar as a supplement to the calendar guiding agriculture. The solar terms are divided by the "average time method". The method of "flat gas" determines that the days in the Yellow River basin are as short as the winter solstice through vertical polar photogrammetry, and divides the date between the winter solstice and the next winter solstice into twelve equal parts, which is called "neutral gas", and then divides the date between adjacent "neutral gases" into equal parts, which is called "solar terms"; On average, there is a "neutral gas" and a "solar term" every month, which are collectively called "24 solar terms". "leveling method" is a time average method, and the interval of each solar term is about 15 days. The uneven motion of the sun on the ecliptic is not considered in the calculation. Using the method of "balancing qi" to divide the solar terms starts from the solstice of winter and ends with heavy snow. The current "twenty-four solar terms" come from the "fixed gas method" concluded more than 300 years ago (it has been used since 1645). "Fixed space method" is a method to determine solar terms according to the position of the sun on the ecliptic, that is, on a 360-degree circle "ecliptic" (the apparent path of the sun on the celestial sphere for one year), it is divided into 24 equal parts, once every 60 years.