Why is blue light scattered

Violet light is actually scattered even a bit more strongly than blue. More of the sunlight entering the atmosphere is blue than violet, however, and our eyes are somewhat more sensitive to blue light than to violet light, so the sky appears blue. When we view the setting sun on the horizon, the opposite occurs.

We see only the light that has not been scattered into other directions. The red wavelengths of sunlight that pass through the atmosphere without being scattered much reach our eyes, while the strongly scattered blue light does not. The longer distance that the sunlight travels through the atmosphere when it is on the horizon amplifies the effect--there are more opportunities for blue light to be scattered than when the sun is overhead.

Thus, the setting sun appears reddish. In a polluted sky, small aerosol particles of sulfate, organic carbon, or mineral dust further amplify the scattering of blue light, making sunsets in polluted conditions sometimes spectacular. Clouds, on the other hand, are made of water droplets that are much larger than the wavelengths of visible light. The way they scatter sunlight is determined by how the light is refracted and internally reflected by, and diffracted around, the cloud droplets.

For these particles the difference between the scattering of blue and red light is not nearly so large as it is for gas molecules. Hence, our eyes receive substantial scattered light at all visible wavelengths, causing clouds to appear more white than blue, especially when viewed against a blue sky background. Since scattering by the atmosphere causes the sky to be blue, a planet with no atmosphere cannot have a bright sky. For example, photographs taken by the Apollo astronauts on the moon show them and the moon's surface bathed in sunlight, but a completely dark sky in all directions away from the sun.

At noon, when the Sun is overhead it appears white. Hence the Sun and skies look redder at dawn and dusk. The low density of air molecules means that the Rayleigh scattering that causes our skies to be blue on Earth has a very small effect on Mars.

We might expect it to have a very faint blue coloured sky, but due to the haze of dust that remains suspended in the air the daytime sky on Mars appears more yellow. This is because the larger dust particles absorb the short wavelength blue light, and scatter the remaining colours to give a butterscotch hue over the Martian sky.

When the air is too thin for gas molecules to collide with each other, we call it an 'exosphere' instead. But what makes the sea blue — is it reflecting the blue of the sky?

Water molecules are good at absorbing longer wavelengths of light, so when sunlight hits the water the reds and oranges get absorbed.

The shorter wavelength blue light is absorbed very little and much of it is reflected back to our eyes. This article has been written by an astronomer at the Royal Observatory, Greenwich. Written and illustrated by astronomical experts, Storm Dunlop and Wil Tirion, and approved by the astronomers of Royal Observatory Greenwich Buy Now. Special Price. Visible light includes the wavelengths our eyes can see.

The longest wavelengths we can see look red to us. The shortest wavelengths we can see look blue or violet. The wavelengths in this picture are not to scale. A red light wave is about nanometers, while a blue or violet wave is about nanometers. A nanometer is one-billionth of a meter. A human hair is about 50, nanometers thick! So these visible light wavelengths are very, very tiny. Another important thing to know about light is that it travels in a straight line unless something gets in the way to.

The blue and violet waves, however, are just the right size to hit and bounce off of the molecules of gas in the atmosphere. This causes the blue and violet waves to be separated from the rest of the light and become scattered in every direction for all to see.

The other wavelengths stick together as a group, and therefore remain white.