The sun in winter is the farthest from our China. Why is it not the coldest at this time, and why is it cold on March 9?

First of all, correct it: the winter solstice is not the farthest from us, but the shortest sunshine time.

Winter solstice is one of the twenty-four solar terms and one of the most important solar terms. Winter solstice is a solar term divided by astronomy, which was called "short day" and "short day" in ancient times. From winter to the sun, the sun is located at 270 degrees of the Yellow Meridian, and the sun shines almost directly to the Tropic of Capricorn, which has the shortest day in the northern hemisphere. Accordingly, the daytime from winter solstice in the southern hemisphere is the longest in the whole year.

Second, this day is not the coldest, because:

The earth's orbit around the sun is not a perfect circle, but an ellipse that approximates a circle. The sun is at one focus of the ellipse (the ellipse has two focuses), so the position of the earth relative to the sun can be divided into perihelion (near the sun) and apohelion (far from the sun).

Because the axis of the earth (the central axis of the earth) is not perpendicular to the orbital plane (the included angle is 23 degrees and 36 minutes), and the angles of the revolution of the earth and the sun are different (one revolution is one year), the temperatures in different places in a year are different, which also forms the changes of seasons and days.

However, when the northern hemisphere (the United States) is in summer, the earth is at apohelion; However, in winter, it is at the perihelion, so the sunshine time from summer solstice is the longest, but not the hottest day, and the sunshine time from winter solstice is the shortest, but not the coldest day.

Why is it cold?

From winter to around, the daytime is the shortest, the solar energy absorbed by the surface layer is the least, and the heat emitted at night is the most; But at this time, the heat accumulated on the surface layer in summer and autumn is still left, which can be compensated, so the temperature will not drop very low. By "March 9th", the heat accumulated in the surface layer in summer and autumn has been exhausted. Although it has increased during the day, the heat absorbed during the day cannot offset the heat emitted at night, and the income and expenditure are seriously upside down. In addition, before and after the March 9th, the cold air in the north frequently went south, and the weather was particularly cold, so it was called the March 9th cold day.