Why is there foggy weather?

1. "Night with moon" means there are not many clouds in the sky.

There is no cloud in the sky, just like a person without a quilt, the heat on the ground will radiate into the air in large quantities, making the temperature on the ground drop very low.

When the temperature is too low, the water vapor in the air liquefies into small water droplets and becomes fog, and the water vapor condenses into small ice particles, which is frost.