When is the coldest time of the day?

The coldest day is four or five in the morning.

After 14: 00, the solar radiation gradually decreases, and the ground temperature drops, so does the temperature. After sunset, there was no solar radiation income, only heat expenditure, and the ground temperature continued to decrease until around sunrise the next day, when there was solar radiation income again, and the temperature reached the lowest value of the day.

The temperature is influenced by the movement of the sun and the rotation of the earth. The earth's orbit around the sun is an ellipse close to a perfect circle, and the sun is located at a focus of the elliptical orbit, so that the distance between the sun and the earth changes constantly in a year or even a day.

Compared with the average distance between the sun and the earth (6.5438+49.6 million kilometers), the change difference of the distance between the sun and the earth within one year (05 million kilometers) is almost negligible. Then in one day, the change of the distance between the sun and the earth is even more insignificant.

Extended data:

The highest temperature in mainland China generally appears around 14, and the lowest temperature generally appears before sunrise. After noon, although the solar radiation began to weaken, the solar radiation heat gained on the ground was still more than the heat lost by the ground radiation.

The heat stored on the ground keeps increasing until the solar radiation heat begins to be less than the heat lost by the ground radiation, that is, when the surplus turns into a loss, the ground temperature reaches the highest value.

At night, the ground heat is lost and the temperature is reduced, until the heat stored on the ground is minimized before sunrise, so the lowest temperature appears around 5 am. The difference between the highest temperature and the lowest temperature on this day is called the daily range.

Baidu Encyclopedia-Daily Variation of Temperature