The summer solstice is one of the 24 solar terms, which falls on June 20th, or 2 1 day, or 22nd of the Gregorian calendar every year. On the day of the summer solstice, the sun moves to 90 degrees of the yellow meridian, and the position where the sun points directly at the ground reaches the northernmost point of the year, almost pointing directly at the Tropic of Cancer. The summer solstice is the longest day and the shortest night in the northern hemisphere.

After the summer solstice, the ground is heated strongly, and the air convection is strong, and thunderstorms are often easy to form in the afternoon to evening. During the summer solstice, the Jianghuai area entered the "Meiyu" season. At this time, it was the yellow ripening period of plums in the south of the Yangtze River, and the air was very humid. The cold and warm air masses met here and formed a trough of low pressure, which led to rainy weather. After the arrival of the summer solstice, the stars in the night sky gradually turned into summer stars.