Question: Which is true? The sea is a reflection of the sky or the sky the reflection of the sea?

Hayley Evers-King answered on 13 Mar 2013:

Neither is true. But they are both blue (usually) for the similar reasons. First you must remember that light can be split in to different colours, like when there is a rainbow.

The sky is blue because of a process called “Rayleigh scattering”. Light is scattered by gas and other particles in the sky. This scattering is most effective in the blue area of the light spectrum which is what makes the sky look blue to us.

The sea is a little different. Pure water absorbs red light more than blue light. So when white light (a mix of all colours), shines on the sea, the red is absorbed, leaving blue light to be reflected back towards your eyes. In some cases, like in the waters I work in, the sea looks green or red, because there are other things in it other than water, which interact with the light in different ways! This proves that the sky doesn’t reflect the sea or vice versa, else they would both be the same colour all the time! Usually when we have our red tides, the sky is bright blue 🙂