Every year around August 23rd (August 22nd-24th), when the sun reaches the longitude of the Yellow River 150, it is the midsummer of the twenty-four solar terms. Summer is a solar term reflecting the temperature change. "Twenty-four solar terms" said: "Go, go, the heat is over." "Chu" means termination, which means that the summer heat is about to pass, the summer heat will end on this day, and the temperature in most parts of China will gradually drop.

Being in summer is not only different from mild summer heat and severe summer heat, but also different from mild cold and severe cold solar terms. This is a solar term representing the transition from hot to cold. In midsummer, the temperature enters a stage of significant change, and it drops day by day, and the summer heat is no longer threatening.

This change in festivals is naturally reflected in farming. A large number of practical proverbs left by the ancients, such as "an autumn rain and a cold", "beginning of autumn is cool in summer" and "the summer has not yet arrived", are all direct descriptions of climate change in the hot summer season.

Astronomical calendar:

In summer, the bucket handle of the Big Dipper points southwest (E position). When the sun reaches the longitude of 150, the node time is around August 23rd in Gregorian calendar.

In summer, the direct point of the sun has moved from 23 26' north latitude to1128' north latitude. As the height of the sun decreases, the heat it brings will also decrease. At this time, if you watch the Big Dipper at night, you will find that the curved bucket handle still points southwest.