Why is it cloudy? How did it come into being?

1, cloudy day: the total amount of low clouds in the sky is 8/ 10 or above, and the clouds are usually gray or black, which is thicker than normal.

2. Cloudy: A weather phenomenon in which low cloud cover accounts for 4/ 10-7/ 10 of the sky area or high cloud cover accounts for 6/ 10 of the sky area.

Second, the intensity from sunlight.

1. cloudy day: the sky is gloomy, and little or no sunlight passes through the clouds.

2, cloudy: the sun is not enough, but you can still see sunny days from the clouds. Refers to a kind of weather that can be called "between sunny and cloudy".

Matters needing attention

Be careful of ultraviolet rays when you are active in cloudy weather. Ultraviolet ray is the general name of radiation with the wavelength from 10 nm to 400 nm in the electromagnetic spectrum, which can't be detected by human eyes, but too much ultraviolet ray may harm eyes.

The German Good Vision Association reminds that in cloudy summer, people should not forget to protect sensitive eyes, because some ultraviolet rays can still reach the surface through clouds, and long-term use may cause certain damage to eyes.

The association also said that people who stay near the water for a long time should pay more attention to protecting their eyes because the water reflects light. If the eyes are damaged by too much ultraviolet rays, there will be symptoms such as redness, tears and eye muscle tension.