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Asked by to Kate, Kieren, Nicola, Rowena, Roy on 11 Mar 2014. This question was also asked by .
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Kate Nicholson answered on 11 Mar 2014:
Two reasons. The one that everyone will tell you is that is the way sunlight is scattered by particles in our atmosphere, the blue colour is what is left over and that is what we see. The second reason is that the ozone in our atmosphere also helps filter out the harmful UV light, by absorbing it but also adds to the blue light by giving off some of this light energy there. This is why when you take a photo of the sky it always looks a lot bluer than your eyes will see – the camera can pick up much better than our eyes can.
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Rowena Fletcher-Wood answered on 11 Mar 2014:
Adding to Kate’s answer – ozone is actually blue and oxygen in the air is also blue. If you condense them as liquids you can see the intense blue colour:
(ozone) and 
(oxygen). They are very volatile (easily evaporating) and flammable liquids. -
Nicola Rogers answered on 12 Mar 2014:
This is a summary of the scattering argument:
The sky is full of particles and when the sunlight shines through these in the air, the light scatters (diffracts and refracts) every time it hits a particle. Shorter wavelengths of light (blue light) scatter much more than longer wavelengths (red) and when we look at the sky we see the scattered light from the sun and hence it looks blue as there is more blue scattering than anything else. However, if we look directly at the sun (do not do this on a sunny day!) you see the colours that do not scatter around sky as much, and that’s why we see the reds and the yellows, and the sun looks yellow/orange. The sun actually emits white light.
A great way to simulate this is to mix flour in water in a glass and shine a torch through it – the flour particles will scatter the light and looking at the whole glass it will have a blue tinge to it – but it you look at the torch light going through the mixture it will look more yellow- best to use an LED torch with white light.
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