Why is the sky blue?

Why is the sky blue?

The light from the sun looks white, so why doesn't the sky?

We asked you to ask Planet Science a question and we've had some great ones so far. Check out last week's question - How do electric toothbrushes charge through plastic? This week, pupils from Sunbury State School in Australia asked us Why is the sky blue?

We set off to investigate. First we needed to find out about sunlight.

The light from the sun looks white, but it's made up of all the colours of the rainbow. Sunlight travels in waves. Each colour of the rainbow has a slightly different wave length.  Some colours travel in short waves. Other colours travel in longer waves. Blue light waves are shorter than red light waves.

Visible light spectrum

Why is the sky blue?

Earth's atmosphere isn't empty, it is full of gases, like oxygen. When sunlight hits the Earth's atmosphere it is scattered by all the gases in the air. Blue light is scattered more than most other colours in the rainbow because it has a shorter wave length. This means that we see the blue light scattered over the sky, making the sky look blue.

Why is the sky blue

Why is the sunset red?

At sunset the sky looks orange and red. The sun is lower in the sky so the light has much further to travel to reach us. The blue light is scattered so much that it doesn't reach us. The red light, with a longer wavelength, does reach us, so the sky looks red.