What does the phrase "early autumn is cold and late autumn is hot" mean? Why did the early autumn come late this year?

This is a popular saying that early autumn is cold and late autumn is hot. It vividly describes the temperature changes before and after beginning of autumn. Specifically, in the early autumn, the weather began to get cold, and the chill gradually hit, giving people a cold feeling; In the early autumn night, the weather becomes very hot, just like cows will be killed by the sun.

Why did the early autumn come late this year? This is related to the trajectory of the sun. According to the China lunar calendar, beginning of autumn refers to the day when the longitude of the sun reaches 135. Because the earth's orbit around the sun is elliptical, the distance between the earth and the sun is not always the same. In an elliptical orbit, the closest position from the earth to the sun is called perihelion, and the farthest position is called apohelion. According to Kepler's second law, the closer the earth is to the sun, the faster the revolution speed; On the contrary, the slower.

Therefore, in the process of the earth's revolution, when the earth approaches the perihelion, its speed around the sun accelerates, which leads to the lengthening of summer; When the earth approaches the apohelion, its speed around the sun will slow down, which leads to a longer winter. Therefore, the reason why beginning of autumn is late this year is that the earth is far from the sun and the revolution speed is slow, which makes the summer time relatively prolonged.

This phenomenon is related to weather changes. After autumn, the sunshine time decreases and the solar altitude angle decreases, which leads to the decrease of surface heating and the gradual decrease of temperature. However, due to the late arrival of beginning of autumn this year, the summer solstice is only over a month away, and the heat in the atmosphere has not completely dissipated. In addition, the earth's revolution speed is slow, which leads to the long duration of direct sunlight and hotter weather.

As the saying goes, "It is cold in early autumn and hot in late autumn" describes the temperature difference before and after beginning of autumn. The reason for beginning of autumn tonight is that the Earth is far away from the sun, and its rotation speed is slow, which makes the summer time relatively long, resulting in hotter weather. This phenomenon is related to the angle of the sun, the orbit of the earth and other factors, affecting the change of temperature. Therefore, we need to do a good job of heatstroke prevention and cooling according to specific meteorological conditions in daily life to protect our health.