What makes the sea blue?
Zak Walton from Somerset (Age: 5-14)
Bradley Kelly from Tyne and Wear (Age: 5-14)
Why is the sea blue?
Corey from West Midlands (age 5-14)
Filed under: age 5-14, Answered Big Questions, Astronomy Big Questions, Environment & Natural World Big Qs, Physics Big Questions, Science Big Questions, Shelley Richardson's Big Answers
Reflection from the sky. Sometimes it looks grey.
The sunlight coming to Earth is white; i.e. all colours, which splits up into a spectrum (rainbow). The sea is blue because the water molecules absorb visible light from the red end of the spectrum much more easily than they absorb blue light. The blue light is reflected so that’s what we see. The blue colour also comes partially from the reflection of the sky (which is blue for the same reason the sea is!)
The main reason the sea is blue is that the sky is also blue. The light from the sky is reflected off the surface of the water which is why on cloudy days the sea often appears grey and water surrounded by trees sometimes appears greeny-blue. The chemicals in water can also affect how it looks sometimes.
The reason the sky is blue on the other hand is that the light from the sun is scattered with the blue light being scattered more than the red light because of the difference in wavelengths. More blue light is scattered means that we see more blue light and the sky is therefore blue.
Why is the sea blue even on cloudy days?