Why is the moon round in Mid-Autumn Festival?

1, from the meteorological point of view.

At this time, the dry and cold airflow from the north forces the warm and humid airflow that has been swirling over China in summer to recede, so the fog in the weather gradually decreases, the inclination of the sun gradually increases, the sunlight and heat on the ground get less and less, and the temperature drops day by day. Autumn wind usually reduces water vapor and makes the air transparent. So the night sky is usually brighter and the moonlight is usually brighter.

2. From an astronomical point of view.

Only in the Mid-Autumn Festival, the moon is usually not necessarily sunny. Because the moon usually reflects sunlight, so from the perspective of the moon, the strength of moonlight should be related to the size of its reflecting surface, as well as the distance between the moon and the earth and the distance between the moon and the sun. The moon is round when it emits the most sunlight, and it is usually the brightest at this time.

The moon usually revolves around the earth, and the earth's orbit is elliptical. And the nearest place is not necessarily fifteen. The first day of the lunar calendar is usually called "new moon", and "looking" depends on the movement of the moon, usually appearing on the fifteenth, sixteenth or even seventeenth day of the lunar calendar (such as this year); In addition, the earth's orbit around the sun is also elliptical, and the perihelion is generally in 1 1 month and1February of the lunar calendar, instead of August.