• Question: Is it true the sky is really black and that the only reason it is blue in the day is because it reflects from the sun? ;)

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      Asked by robyn to Kate, Kieren, Nicola, Rowena, Roy on 13 Mar 2014.
      • Photo: Kieren Bradley

        Kieren Bradley answered on 13 Mar 2014:

        Well when the sun is gone you can see that it is black, so yes you’re right. The sun light bounces off the gasses in the atmosphere and because there is so much it appears that there is blue light (the colour that scatters off gasses the most) coming from everywhere.

        The question to ask is why isn’t the sky filled with white when the stars are out. We think the universe is practically infinite, so we should see stars at every point in the sky. The fact that there aren’t stars everywhere is good proof of the fact there is a speed of light; light from stars that are too far away haven’t reached us yet and therefore we don’t see them.

      • Photo: Kate Nicholson

        Kate Nicholson answered on 13 Mar 2014:

        Almost, the blue is the result of scattering, not reflection, so when the sun is lighting the sky, we see the blue colour. (It’s even more blue than our eyes can see but that’s a different story thanks to our ozone layer) If the gas particles in our atmosphere were a different size the light would scatter differently and the sky would be a different colour.
        The other thing is how much atmosphere the light has to scatter through – now think why the sky isn’t blue at sunsets 😉

      • Photo: Rowena Fletcher-Wood

        Rowena Fletcher-Wood answered on 14 Mar 2014:

        Space is emptiness… but the sky within the atmosphere is made up of many gases that have their own colours. Many of them you can’t see their colours until you condense them to liquids!

        Oxygen and ozone are dark blue colours. Ozone makes up a lot of the ozone layer and oxygen is 20% of air.
        Nitrogen is 78% of air and is colourless.
        Carbon dioxide is colourless or white.
        There are also pollutants like nitrogen oxides which are colourless or brown.

        However, gases occupy a large space so are very dilute. Mostly the colours we see are scattering effects because most of the gas is colourless nitrogen anyway – but some of the sky really IS blue.

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