The origin of the dog days in summer

Every summer from mid-July to mid-August is a unique "three volts" solar term in China, which is printed on our calendar.

From 776 BC to the present, the method of "recording solar branches" has been popular in China, that is, taking A, B, D, E, G, F, D, D, D, D, D, D, D, D, D, D, D, D, D, D. Every day with the word "Geng" is called "Geng Day". During the Qin and Han dynasties, the idealistic view of "five elements give birth to grams" prevailed. It is believed that the hottest days in summer belong to fire, while Geng belongs to gold, and fire produces gram gold (gold is afraid of being melted by fire), so on Geng Day, gold will be hidden. Therefore, it is stipulated that the third Geng day from summer to the future (June 2 1 or 22 in Gregorian calendar) is the first day (with ten days), the fourth Geng day is the middle day (with ten days in some years and twenty days in some years), and the first Geng day after beginning of autumn (August 7 or 8 in Gregorian calendar) is the third day with ten days. In this way, the dog has a fixed day. According to this regulation, it can be inferred that the dog days are from mid-July to mid-August in the solar calendar.

The reason why the dog days are extremely hot is that from the relationship between the sun and the earth, from the vernal equinox to summer, the sun gradually changes from direct equator to direct tropic of cancer. The summer solstice is the longest day of the year in the northern hemisphere. On this day, the ground in the northern hemisphere receives the most solar heat and the least heat dissipation. But the hottest day of the year is not the solstice of summer, but the dog days from summer to the future, especially midsummer and dog days.

Fukuda's statement is said to have a long history, which originated from the state of Qin in the Spring and Autumn Period. In Liu's Historical Records, he said: "Qin Degong first fell in the second year (676 BC)." Zhang Shoujie, a Tang Dynasty man, said, "On the third day of June, Qin Gong set sail, so when the clouds first fell, those who fell hid themselves for the summer." Like other festivals in the dog days of ancient times, many food customs spread among the people.