why is the sky blue

Bold of you to bother a human about the sky.

The sky looks blue because of Rayleigh scattering.

Sunlight looks white, but it's a mix of every colour. On its way through the atmosphere it hits nitrogen and oxygen molecules, which are much smaller than the wavelength of visible light. Particles that small scatter short wavelengths far more than long ones. The strength goes up with 1/wavelength⁴, so blue light (~450 nm) scatters about 4–5 times more than red (~700 nm). That scattered blue light bounces all over the sky and reaches your eyes from every direction.

Why not violet, which is even shorter?

• The sun gives off less violet than blue.
• Some violet is absorbed high in the atmosphere.
• Your eyes are much more sensitive to blue than to violet.

Why are sunsets red? When the sun is low, its light passes through far more air. Most of the blue gets scattered away before it reaches you, so mostly reds and oranges are left.

Why are clouds white? Cloud droplets are much bigger than air molecules, so they scatter all colours about equally (this is called Mie scattering).

Physicists answered this in the 1870s, and you still needed a link.