The moon itself does not emit light, and the moon we observe has light because of the sunlight it reflects.

The moonlight we observe is sometimes white, sometimes yellow, and sometimes red or blue, which is caused by the scattering of water vapor molecules in the atmosphere.

In the Mid-Autumn Festival, the water content in the atmosphere is generally high. The moon reflects the light of the sun. When it passes through the earth's atmosphere, a large part of the blue light is scattered into the night sky by water vapor molecules in the atmosphere, and the rest of the light will be yellow when it reaches people's eyes.

If the local air quality is very good and the clouds are thin or almost cloudless, the moon we see will be bright and bright, but if the air quality is poor and the clouds are thick, the moon will become yellow or even invisible.

It is usually seen that the moon is yellow, mostly when the moon appears on the horizon. You can refer to the pattern of the sun. The sun will appear yellow or even red at sunrise and sunset, but it is not yellow at noon, and so is the moon. This is mainly related to the atmosphere. When the moon is in the middle, the distance of light passing through the atmosphere is the shortest, so the light absorbed by the atmosphere is limited. But when the moon is around the horizon, the distance of light passing through the atmosphere is the longest, and most of the light is absorbed by the atmosphere, so it will make the moon appear different colors.

In the Mid-Autumn Festival, the angle between the moon and the sun is just close to180. According to the mid-August of the lunar calendar, there is enough water vapor in the atmosphere, so the moon we see is big and yellow.

The origin of the Mid-Autumn Festival is inseparable from the moon. Since ancient times, China has had the traditional custom of enjoying the moon in the Mid-Autumn Festival. Li Bai's poem "lifting myself to look, I found that it was moonlight, sinking back again, I thought suddenly of home" not only describes the bright moon in the Mid-Autumn Festival, but also expresses his infinite homesickness. In addition to enjoying the moon, Mid-Autumn Festival in China also has some folk activities, such as offering sacrifices to the moon, burning lanterns, watching tides, guessing riddles, eating moon cakes, enjoying osmanthus, drinking osmanthus wine, playing with lanterns and so on. It is one of the four traditional festivals in China.