Question: Why is the sky blue?

Stephen Davitt answered on 10 Nov 2016:

Very good question! The answer is a littel tricky but I’ll try to explain it in an easy way.

A few things you need to know first: white light isn’t actually white it is what we see when all of the colours red, orange, yellow, green, blue, indigo, violet are mixed together. Each colour of light has a different size or ‘wavelength’ red being the biggest and as you move to violet you get smaller and smaller.

The next thing we need to know is that in the air and sky there are tiny molecules and droplets of water among other things

The sky is blue due to scattered light, sunlight is white light (made up of the different colours). When the sunlight enters our atmosphere it starts to hit off the small water droplets in the sky.

The ‘bigger’ colours (red orange yellow green ) often are strong enough not be be bothered by the droplets, the blue indigo and violet aren’t so lucky and bounce off them and are directed down.

So when we look at the sky we see this scattered blue, indigo and violet light, so why is the sky just blue? Well if you measure how much of each colour comes from the sun you’ll see that there is a lot more blue light then indigo or violet.

An extra bit of info for you is that in clouds the droplets are much bigger so all of the colours get scattered and this is why we see the clouds as white