Why is the sky blue due to light scattering?

The sky appears blue because of a process called Rayleigh scattering, where shorter wavelengths of light are scattered more than longer ones.

Rayleigh scattering is a phenomenon named after the British scientist Lord Rayleigh, who first studied it in detail. It refers to the scattering of light or other electromagnetic radiation by particles much smaller than the wavelength of the light. The scattering of light is the main reason why we see the sky in colour.

When sunlight reaches Earth's atmosphere, it is made up of different colours, each of which has a different wavelength. Blue and violet light have the shortest wavelengths and are scattered in all directions by the oxygen and nitrogen molecules in Earth's atmosphere. This scattering process, called Rayleigh scattering, causes the sky to appear blue.

However, you might wonder why we don't see a violet sky, given that violet light is scattered more than blue light. This is because our eyes are more sensitive to blue light and because sunlight reaches us with less violet light to begin with. Additionally, some of the violet light gets absorbed by the ozone layer in the atmosphere.

In contrast, the longer wavelengths of light such as red, orange, and yellow pass straight through the atmosphere to our eyes without being scattered much, which is why the sun itself appears in these colours.

During sunrise and sunset, the sun is lower in the sky and its light has to pass through more of Earth's atmosphere. This means that even more of the short-wavelength blue and violet light is scattered out of the line of sight, and the sun and the sky can appear red or orange.

In summary, the sky appears blue because of Rayleigh scattering, where the shorter wavelengths of light are scattered more than the longer ones, and our eyes are more sensitive to blue light.