Question: how did the sea go blue

Tom Nicholas answered on 12 Jun 2017:

The sea is blue, but you know that water isn’t blue, so how is the sea blue when its not made of blue stuff?

The sea is actually blue for the same reason that the sky is, so we’ll think about the sky first. The sun sends out light of all different colours, which have to go through the air in the sky before we can see it. When this light hits the air, it can go through, or it can be reflected. It turns out that different colours get reflected (we say it is “scattered”) by different amounts. Blue light coming from the sun is scattered loads, going off every which way. This means that wherever you look in the sky then you will see some blue light that has come from the sun, but been scattered lots of times. This means in the daytime you will see blue no matter where you look. If you looked straight at the sun (do not actually do this!!!!), then the other colours like red would be coming straight to you, as they don’t get scattered so much. This is why the sun looks more red or orange.

So when you look at the sea, the reason you don’t see lots of clear water (like in a bath), with a single reflection of the sun, is that the sea is so big that the blue light from the sun can be scattered over and over, until it looks like the sea is blue in all directions!