Why the Sky is blue ?

The daytime sky on Earth appears blue in colour. Light is made up of PHOTONS which are matterless particles. White light is made up of seven colours: red, orange, yellow, green, blue, violet & indigo.

This light travels at different wavelengths. Some colours are better at passing through gases than others. Red light is seen at longer wavelengths and indigo has the shortest wavelength.

When photons from the Sun travel into Earth's atmosphere some of this light hits and bounces the nitrogen and oxygen molecules there. The result is that light is split up and scattered.

Red, orange, yellow and green light carries straight on through this atmosphere but blue, violet and indigo get bounced around from molecule to molecule.

We see a blue sky as a result of all this bouncing around.

Why don't we see an Indigo or Violet sky? Simply because our eyes do not see these colours very well. Blue is a more dominant colour.

Further evidence of this can be seen during sunset and sunrise. The sky appears red then as the light travels through more of Earth's atmosphere. Most of the blue light is scattered away. Also during a lunar eclipse the Moon appears red as light travels through Earth's atmosphere.