Why is the Sky blue?

Reading time: 3 minutes

Don’t tell me the sky’s the limit, there are footprints on the moon. Paul Brandt

The sky appears blue on most days, in most parts of the world. This is mainly because of what happens to sunlight when it enters our atmosphere. Light is made up of photons that carry electromagnetic waves and there is a wide spectrum of these waves carrying different amounts of energy. The waves our eyes perceive as colour is known as the visible spectrum.

The electromagnetic spectrum

Each of the colours in the visible spectrum differ from each other based on their wavelength. Reddish light carries long wavelengths, meaning it carries less energy and has a lower frequency. Bluish light has a short wavelength and more energy and a higher frequency. When light from the sun enters our atmosphere, it refracts (it appears to bend) as it passes through the layers of the atmosphere. This light is scattered in all directions by the gases and particles in the air. Due to its shorter wavelength, bluish light is scattered the most and reaches our eyes, causing the sky to appear blue.

Misconceptions

It was wrongly understood that the ocean was responsible for the sky’s colour as light hitting the ocean was reflected back to the atmosphere and made it appear blue. This is false, as water being colourless and transparent, won’t reflect any light. In fact, the reason water appears blue is similar to why the sky is blue. The ocean absorbs red wavelengths, and thus the water appears bluish. It may vary in colour due to sediments.

An understanding

Also it is a little weird that most gases are transparent and our atmosphere is completely transparent (which is proven by the fact the satellites provide imagery of Earth from space), so the atmosphere being transparent should act like a window, and the colour of the sky should be the same as the colour of space. This is what happens during night time. We can peer into space during the night as there is no sun to radiate electromagnetic waves in huge magnitudes, which would hinder our view.

A conclusion

So, the sky is blue because when light enters our atmosphere, it gets scattered by air molecules and other particles. Blue light having a shorter wavelength gets scattered the most and the sky appears blue. Thanks for reading!