• Question: if water is clear, how is the sea blue?

    Asked by shannon :) to Ahmed, Francesca, George, James, Nitheen on 13 Nov 2014.
    • Photo: James Sullivan

      James Sullivan answered on 13 Nov 2014:

      Hi Shannon,
      The blue you see in the sea or the ocean is a reflection from the sky.

    • Photo: Francesca Paradisi

      Francesca Paradisi answered on 13 Nov 2014:

      Go James! Great answer here, can’t add much!

    • Photo: George Dowson

      George Dowson answered on 15 Nov 2014:

      I have to disagree with James here. (Deep indoor pools also look blue). Water is actually just very very pale blue!

      This blueness is indeed magnified by the sky outdoors but also further made blue when it’s deep because of similar reasons as to why the sky is blue. Blue light is scattered by the water particles adding to the intrinsic blueness of water.

      Transparent things often look colourless when there are thin layers being observed. So similarly most glass is dark green when it is thick enough (look edgewise down a pane of glass or mirror next chance you get – don’t do anything dangerous though! )

    • Photo: Ahmed Osman

      Ahmed Osman answered on 17 Nov 2014:

      Hi Shanon
      Thanks for this wonderful question
      the sea is blue as it reflect the colour of the sky. And the sky is blue because of the way the Earth’s atmosphere scatters light from the sun. A clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light. When we look towards the sun at sunset, we see red and orange colours because the blue light has been scattered out and away from the line of sight.
      hope my answer is clear