Why do the sky and ocean appear blue?
Look up on a bright sunny day and you will likely see blue sky. Similarly, the water found in our oceans, lakes and rivers may also look blue on a sunny day.
But have you ever wondered why the sky and water are actually blue? Mike Leclair did, and that is the subject of this week’s Ask Allister.
As with many things, we can turn to the visible light spectrum for the answer to this question.
White light emitted by the sun is actually made up of the seven colours of the rainbow, or visible light spectrum.
The colours in the visible light spectrum have different wavelengths, with red and orange having the longest wavelengths, and violet, indigo and blue having the shortest.
The sunlight gets scattered in all directions by particles such as gases and dust that can be found in our atmosphere.
The blue light is scattered the most and is why our sky appears blue. This is what is known as Rayleigh scattering.
The absorption and scattering of visible light are also why water can look blue.
The water absorbs the longer wavelength colours such as red and reflects the shorter wavelength colours such as blue.
After reading this, you may wonder that since violet has a shorter wavelength than blue, why isn’t the sky or ocean that colour?
There are a few reasons, mainly that the violet light gets scattered more than blue light, and that some of the violet and indigo light gets absorbed higher in the atmosphere.
Also, our eyes are not as sensitive to violet which also allows the sky to appear blue.
Thank you, Mike, for your weather question.