Why is the sky blue?

The sky appears blue because of a phenomenon called Rayleigh scattering.

This scattering is caused by the interaction of sunlight with particles in the atmosphere, primarily nitrogen and oxygen molecules.

When sunlight enters the atmosphere, it is composed of a mixture of all colors in the visible spectrum. However, as the sunlight travels through the atmosphere, it interacts with these molecules and is selectively scattered.

Shorter wavelength light (blue and violet) is scattered more than longer wavelength light (red and orange), which causes the blue and violet light to be scattered in all directions.

This scattered blue light is what we perceive as the blue sky. The amount of scattering depends on the wavelength of light and the size of the particles.

The smaller the particles, the more the light is scattered. This is why the sky is typically a darker blue near the horizon, where the particles are larger, and a lighter blue overhead, where the particles are smaller.