Earth Trivia : Why is the sky blue?

Different colors of light have different wavelengths.:

White light (which is a combination of all colors) from the Sun is scattered by the Earth’s atmosphere.
The blue light is scattered more than other visible light and so the sky appears blue and direct sunlight appears as white light slightly devoid of blue (i.e. yellowish).
More? ⇒Infant Hercules

Sunlight reaches Earth's atmosphere and is scattered in all directions by all the gases and particles in the air. Blue light is scattered in all directions by the tiny molecules of air in Earth's atmosphere.
Blue is scattered more than other colors because it travels as shorter, smaller waves.
More? ⇒NASA
Atmosphere scatters blue light more than other colors.:

Atmosphere scatters blue light more than other colors.:

Why is sunset red?

As the sun gets lower in the sky, its light is passing through more of the atmosphere to reach you.
Even more of the blue light is scattered, allowing the reds and yellows to pass straight through to your eyes.
Red sky at sunset: