Why is the sky blue? Why are you so sad?

There is a simple reason. The scattering of sunlight by the atmosphere makes the sky look blue.

The surface of the earth is surrounded by the atmosphere. When sunlight enters the atmosphere, air molecules and particles (dust, water droplets, ice crystals, etc. ) will scatter sunlight around. Sunlight consists of seven kinds of light: red, orange, yellow, green, blue, indigo and violet, of which red light has the longest wavelength and violet light has the shortest wavelength. Red light with longer wavelength is the most transparent and can directly penetrate particles in the atmosphere and shoot to the ground. However, blue, indigo, purple and other short-wavelength colored light are easily scattered by particles in the atmosphere. In the short-wave band, blue light has the largest energy and light waves scatter the most, so the sky we see shows that.

Blue.

And you think it is sad because of your inner sadness;

Cheer up, nothing can't be solved. When you are happy, you will find that life is beautiful and everything is happy.