Question: Why is the sky blue?

Edward Codling answered on 22 Jun 2011:

Great question!

🙂

This is because the light that reaches us from the sun is partially absorbed by gas particles in our atmosphere. The light from the sun is made up of different wavelengths corresponding to different colours. The red, orange and yellow light from the sun passes through our atmosphere easily. However, the blue light tends to be absorbed by these gas molecules and then radiated outwards in all directions from the molecule. This means the sky then appears blue.

It is also our atmosphere that makes the sun look yellow – if you were in space it would look white!

Similarly, it is our atmosphere and the gas molecules in it that create the red colour in the sky at sunset – because the sun is lower in the sky. If there are more particles in the air to absorb the light then the sunset will be more spectacular. Often you get spectacular sunsets over cities – but this is because of all the air pollution! 🙁

There are some great explanations of these ideas with pictures here: http://www.sciencemadesimple.com/sky_blue.html