• Question: why is the sea blue?

    Asked by Robert to Sian, Dawn, David, Dan, Christie on 15 Jun 2016.
    • Photo: Sian Thomas

      Sian Thomas answered on 15 Jun 2016:

      It is a reflection of the sky. I think 🙂

    • Photo: Dawn Lau

      Dawn Lau answered on 16 Jun 2016:

      I remember learning this in my physics class. Visible light consists of several wavelengths, ranging from longer wavelengths (red, orange, yellow) to shorter wavelengths (blues and ultraviolet). Water is better at absorbing the longer wavelengths, so the shorter wavelengths can reach further into the water. Since blue light is a shorter wavelength, the sea is more likely to appear blue. Sometimes other particles in seawater can affect absorption and scatter of light which might make the sea appear blue-green or similar shades.

    • Photo: Christie Waddington

      Christie Waddington answered on 19 Jun 2016:

      This is all about light :-). The red, orange, yellow, and green wavelengths of light are absorbed by water molecules so that the remaining light we see is made up of the shorter wavelength of blues and violets. This is the main reason why ocean colour is blue. Some constituents of sea water can influence the shade of blue of the ocean.

      But have you noticed how the sea doesn’t always look blue? That’s because impurities in the sea scatter the light, adding in greens and browns making it less blue.

    • Photo: David Robertson

      David Robertson answered on 21 Jun 2016:

      I think it is a combination of Dawn and Sian’s answers.

      The colour of the sea is mainly a reflection of the colour of the sky.

      The reason the sky is blue is to with scattering of the different wavelengths of light. Long wavelengths (red colours) scatter by very small angles so tend to go straight on and short wavelengths (blue colours) are scattered by much bigger angles, so when you look up at the sky during the day you are seeing the blue colours that have been scattered (bent) much more than the red colours.
      Around sunrise and sunset you can see the light that has been scattered through much smaller angles (the red colours) so sunsets and sunrises are much more likely to be red.

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