Why is it cold at five or six?

It is not the coldest at five or six in the evening, but it is the coldest at five or six in the morning.

The ground temperature comes directly from the light and heat of the sun. Generally speaking, how much heat the ground receives from the sun during the day will radiate into space in the form of infrared radiation at night, so the ground temperature (calculated by the annual average) can basically remain unchanged. In a day, the strongest time to receive solar radiation is noon. At the same time, as the sun rises and radiates the ground, the ground begins to accumulate heat. Generally, the heat accumulated on the ground reaches its maximum in the afternoon, and it begins to radiate heat while continuing to receive solar radiation. So on sunny days, the temperature is the highest from noon to 3 pm. As the sun sets in the west, the solar radiation received by the ground begins to drop, and the site temperature will also drop. After the sun went down, the temperature began to drop obviously. If the sun does not rise, the temperature will be lower and lower as the ground temperature (including atmospheric temperature) continues to drop. But at 6-7 in the morning, the sun will rise again, the ground will begin to receive solar radiation, and the temperature will rise again. Therefore, in a day, when the sun will rise at five or six in the morning, the temperature will drop to the lowest, which is also the coldest time of the day.