The Great Cold is the last of China's 24 solar terms, typically occurring around January 20 each year. Its arrival marks the nearing end of the cold winter and the gradual approach of spring. The name "Dahan" is closely linked to the agricultural cycles of ancient China. As early as three thousand years ago, China began using the solar calendar, dividing the year into 24 solar terms, with Dahan being one of them.
During the Great Cold, the sun reaches the ecliptic longitude of 300°. The *Collected Explanations of the Seventy-Two Phases of the Moon* states, "In the twelfth month, the explanation is as mentioned earlier (for Minor Cold)." The *Treatise on the Timing of the Seasons: Celestial Timing* cites *The Three Rites and Their Meanings* to explain: "Great Cold is called 'Great' because it follows Minor Cold, hence the name... As the cold reaches its peak, it is termed Great Cold." This indicates that during the Great Cold, frequent cold waves move southward, marking the coldest period of the year in most regions of China, with strong winds, low temperatures, and unmelting ground snow, presenting a severe winter scene of ice-covered skies and frozen earth.
In ancient China, the Great Cold was divided into three periods: the first period is when the chicken begins to milk; The second symptom is severe illness in birds; San Hou Shui Ze has a firm belly. The mother hen begins to incubate the chicks, while migratory birds such as eagles and falcons are in a state of extremely strong hunting ability. The ice in large areas of water has also frozen to the center of the water, and is the strongest and thickest. The origin and legend of the Great Cold solar term reflect the outstanding wisdom of ancient Chinese people in astronomical observation, calendar formulation, and folk culture.
