The sun has reached midday, which is the hour of noon. Daytime means 11 to 13 o'clock every day. This period of time is named after the Earthly Branches and is called Wu Shi.
In ancient times, people used the time when the sun reached the middle of the sky as a time mark to go to the market for transactions. The initial activities of such commodity exchanges were carried out at noon hour. There are examples to prove: "The middle of the day is the market, bringing together the people of the world, gathering the goods of the world, trading and retreating, everyone gets what he has." ("Yi·Xici")
"Liezi·Tang Wen" : "One son said: 'At the beginning of the day, it is as big as a car hood, and at midday it is like a pan. Isn't this why the far one is small and the near one is big?'" In addition, "Historical Records Biography of Sima Ranju": "With Zhuang Jia Yue will meet at the military gate on the first day of the day. "Rizhong" is used quite frequently in ancient books.