Nasa why is the sky blue

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. They are still mixed together, unscattered by the atmosphere, so they still appear white.

The scattered violet and blue light dominates the sky, making it appear blue. What happens to the violet? Some of the violet light is absorbed by the upper atmosphere. Also, our eyes are not as sensitive to violet as they are to blue. A multicoloured sunset over the Firth of Forth in Scotland.

When the air is clear the sunset will appear yellow, because the light from the sun has passed a long distance through air and some of the blue light has been scattered away. If the air is polluted with small particles, natural or otherwise, the sunset will be more red. Sunsets over the sea may also be orange, due to salt particles in the air, which are effective Tyndall scatterers. The sky around the sun is seen reddened, as well as the light coming directly from the sun. This is because all light is scattered relatively well through small angles—but blue light is then more likely to be scattered twice or more over the greater distances, leaving the yellow, red and orange colours.

A blue haze over the mountains of Les Vosges in France. Clouds and dust haze appear white because they consist of particles larger than the wavelengths of light, which scatter all wavelengths equally Mie scattering. But sometimes there might be other particles in the air that are much smaller. Some mountainous regions are famous for their blue haze.

Aerosols of terpenes from the vegetation react with ozone in the atmosphere to form small particles about nm across, and these particles scatter the blue light. A forest fire or volcanic eruption may occasionally fill the atmosphere with fine particles of — nm across, being the right size to scatter red light. This gives the opposite to the usual Tyndall effect, and may cause the moon to have a blue tinge since the red light has been scattered out. This is a very rare phenomenon, occurring literally once in a blue moon.

The Tyndall effect is responsible for some other blue colorations in nature: such as blue eyes, the opalescence of some gem stones, and the colour in the blue jay's wing. The colours can vary according to the size of the scattering particles. When a fluid is near its critical temperature and pressure, tiny density fluctuations are responsible for a blue coloration known as critical opalescence.

People have also copied these natural effects by making ornamental glasses impregnated with particles, to give the glass a blue sheen. But not all blue colouring in nature is caused by scattering. Light under the sea is blue because water absorbs longer wavelength of light through distances over about 20 metres. When viewed from the beach, the sea is also blue because it reflects the sky, of course.

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. Sky-Watcher Skyhawk Telescope. The ideal telescope of choice for beginner to intermediate astronomers who are looking to expand their skygazing experiences What is light?

Spirit Captures a Sunset on Mars. Astronaut John W. Young, commander of the Apollo 16 lunar landing mission, leaps from the lunar surface as he salutes the United States flag at the Descartes landing site during the first Apollo 16 extravehicular activity NASA. See the universe in a new light Visit Astronomy Photographer of the Year and see the world's greatest space photography Find out more Find more exhibitions and events. Visit Us. Search Want to search our collection?