• Question: Why is the sea blue why is it not red

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      Asked by 284matb36 to Elizabeth, James, Martin, Martin, Rob on 6 Mar 2015.
      • Photo: Elizabeth Cooper

        Elizabeth Cooper answered on 6 Mar 2015:

        The sea is blue because as light passes through the water, blue light is reflected and travels through the water easier than red light which does not travel as far as it is absorbed. This is due to blue light having a shorter wavelength than red light (look up colour wavelengths for more information)

        Another reason is that the sky is reflected in the water making it look the same colour as the sky!

      • Photo: Martin Ward

        Martin Ward answered on 6 Mar 2015:

        I think Elizabeth has answered your question there.

        Another reason that can cause this effect is when there are small particles in the water. Small particles scatter blue light more than red light, this means that when we are stood on the beach we see mostly blue/green light coming from the water.

      • Photo: Martin Wieczysty

        Martin Wieczysty answered on 6 Mar 2015:

        Very interesting question!
        You may be interested to know that the sea can sometimes be red http://en.wikipedia.org/wiki/Red_tide – this is due to algae (a sea organism that has a red colour).

        To answer your question I would like to first talk about colour in general.
        Firstly, white light (similar to that coming from the sun), is actually made up of millions of shades of red, orange, yellow, green, blue, (indigo), and violet. This white light can be split using a triangular piece of glass called a prism, see the front cover of Pink Floyd’s “Dark Side of the Moon” http://en.wikipedia.org/wiki/The_Dark_Side_of_the_Moon.
        Or, better still, when it has been raining you can sometimes see a rainbow – this is where water droplets suspended in the atmosphere split white light into all its colours.
        This becomes important when we want to make coloured items, such as clothes. For example, when WHITE light hits a BLUE jumper, it ABSORBS all the colours (all reds, oranges, yellows, greens, (indigos) and violets), and reflects blue. We can make dyes based on what colours they absorbs.

        So similarly, when sunlight (or white light) hits water, it weakly absorbs red orange and yellow colours, and reflects greens and blues. When you have a lot of water (such as a swimming pool) this is much more easy to see.
        Another reason seas and oceans are blue is because they reflect the sky (which is also blue).

        Hope this answers your question.

        Fun Facts:
        – Water is made up of oxygen atoms and hydrogen atoms. Oxygen is a colourless gas that is in the air that we breathe. However it can be cooled down to a liquid (at minus 183 °C), and this is a very beautiful blue colour.
        – Ice is solid water, and when it gets very cold and compressed (squeesed) it becomes very blue. You can see this effect in areas such as Antartica.

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