One of the most commonly seen sights is the blue sky, yet what's not widely known is what makes it blue.

The sun emits light that travels through space towards the Earth. Because space is a vacuum (ie it has no atmosphere), the light remains largely undisturbed until it nears the Earth, whose atmosphere is made up of a mixture of gas molecules (mainly oxygen and nitrogen) and other materials. The closer you get to the Earth, the thicker the atmosphere.

Light from the sun appears white but is in fact a combination of colours, and the range of these colours that are visible to the human eye - from red to violet, by way of orange, yellow, green, blue and indigo - is shown when light is passed through a prism. these different colours have different wavelengths and energies, with violet having the shortest wavelength and highest energy and red having the longest wavelength and lowest energy.

Al light hits the Earth's atmosphere, the different colours react in different ways. Some of them get absorbed by the gas molecules while others do not.

The gas molecules then radiate these colours and scatter them across the sky, causing the sky to appear blue. The reason why we perceive the sky as blue and not violet is because our eyes are most sensitive to blue.