In the Gregorian calendar, the Summer Solstice usually falls around June 21, and more often refers in particular to the day when the sun is exactly at the celestial longitude of 90°. The date marks the beginning of summer: the daytime is the longest and the night is the shortest in the northern hemisphere, but it is not the hottest day of the year. The Summer Solstice is not only one of the twenty-four solar terms, it is also one of the traditional folk festivals. People even think of it as the origin of the Dragon Boat Festival.
In ancient times, the Summer Solstice was a festival to escape the heat of summer and to worship the gods. Many popular customs are related to offering sacrifice to the gods, such as eating noodles or won ton.
For example, people in Shangdong Province normally eat cold noodles, while residents of the Guangdong region are accustomed to cooking different kinds of soups, porridges, and tea, such as pork chop soup, chopped green onion and tofu soup, as well as millet porridge, bean jelly, bean curd, sweet potato soup, cold soybean milk, sugar water, herbal tea, and plum juice, and drinking them when they are cold.