The “smallest sun of the year” is here. Will the weather get cooler as the sun moves further away?

(Original title: "The smallest sun of the year" Xiaoshu appears)

The Lesser Heat solar term arrived on the 7th. At 4:07 on that day, the Earth reached its orbital aphelion, which is the moment when the Earth is farthest from the Sun in a year. People will see the "smallest Sun of the year". Why is the distance between the Earth and the Sun sometimes closer and sometimes farther? Will the weather get cooler when the Sun is farther away? Astronomy experts from the Chinese Academy of Sciences reveal the secrets for you.

Wang Kechao, the director of science popularization at the Purple Mountain Observatory of the Chinese Academy of Sciences, introduced that the orbit of the earth around the sun is not a perfect circle, but an ellipse with an eccentricity of 0.0167. On this elliptical orbit, the point closest to the sun is called the "perihelion" and the farthest point is called the "aphelion".

The distance between the sun and the earth is not fixed. The average distance between the sun and the earth is about 149.6 million kilometers. The distance between the sun and the earth at aphelion is 152.1 million kilometers, and the distance between the sun and the earth at perihelion is 147.1 million kilometers, with a difference of 5 million kilometers. The earth passes the perihelion in early January and the aphelion in early July. Therefore, in the summer in the northern hemisphere, the distance between the sun and the earth is relatively far.

This year, the Earth reached its aphelion at 4:07 am on July 7. At this time, the apparent diameter of the Sun was 31 arc minutes and 28 arc seconds, which is about 3.4% smaller than the apparent diameter of the Sun visible when the Earth passed its perihelion on January 5 this year. It can be called the "smallest Sun of the year."

"Although the earth is farther away from the sun, it does not mean that the weather will get cooler. On the contrary, after the Lesser Heat, we will soon enter the Dog Days, and the hottest time of the year is about to come," said Wang Kechao.

Wang Kechao explained that the change in the distance between the sun and the earth is not the main reason for the change of seasons. The change of seasons is mainly affected by the surface receiving solar radiation. Around the summer solstice, the solar altitude angle is large during the day in the northern hemisphere, the sunshine time is long, and the radiation energy received is large. "Taking into account the cumulative effect of the surface heat balance, generally for a period of time after the summer solstice, the heat absorbed by the ground is still greater than the heat it releases, and the ground temperature will continue to rise." Wang Kechao said. (Reporters Wang Jueyin and Zhu Xiao)