Why is the sky blue

Why is the sky blue?

Here’s the short answer…

As white light passes through our atmosphere, tiny air molecules cause it to ‘scatter’.

The scattering caused by these tiny air molecules (known as Rayleigh scattering) increases as the wavelength of light decreases.

Violet and blue light have the shortest wavelengths and red light has the longest.

Therefore, blue light is scattered more than red light and the sky appears blue during the day.

When the Sun is low in the sky during sunrise and sunset, the light has to travel further through the Earth’s atmosphere.

We don’t see the blue light because it gets scattered away, but the red light isn’t scattered very much – so the sky appears red.

Source; https://www.rmg.co.uk/

The Atmosphere

The atmosphere is the mixture of gas molecules and other materials surrounding the Earth. We think of it as a thick layer encircling our planet, but astronauts call it the “thin blue line” because from space, it appears narrow and delicate.

The atmosphere is made mostly of the gases nitrogen (78%), and oxygen (21%). Argon gas and water (in the form of vapor, droplets and ice crystals) are the next most common things. There are also small amounts of other gases, plus many small solid particles, like dust, soot and ashes, pollen, and salt from the oceans.

The composition of the atmosphere varies, depending on your location, the weather, and many other things. There may be more water in the air after a rainstorm, or near the ocean. Pollution can add different gases or dust and soot.

Volcanoes can put large amounts of dust particles high into the atmosphere. They also release gases including carbon dioxide, sulfur dioxide, hydrogen sulfide, hydrogen chloride, and methane. Many of these are toxic, or can contribute to acid rain.

The atmosphere is densest (thickest) at the bottom, near the Earth. It gradually thins out as you go higher and higher up. There is no sharp break between the atmosphere and space. Learn more about the atmosphere.

Light in the Air

Light travels through space in a straight line as long as nothing disturbs it. As light moves through the atmosphere, it continues to go straight until it bumps into a bit of dust or a gas molecule. Then what happens to the light depends on its wave length and the size of the thing it hits.

Dust particles and water droplets are much larger than the wavelength of visible light. When light hits these large particles, it gets reflected, or bounced off, in different directions. The different colors of light are all reflected by the particle in the same way. The reflected light appears white because it still contains all of the same colors.

Gas molecules are smaller than the wavelength of visible light. If light bumps into them, it acts differently. When light hits a gas molecule, some of it may get absorbed. After awhile, the molecule radiates (releases, or gives off) the light in a different direction. The color that is radiated is the same color that was absorbed. The different colors of light are affected differently. All of the colors can be absorbed. But the higher frequencies (blues) are absorbed more often than the lower frequencies (reds). This process is called Rayleigh scattering. (It is named after Lord John Rayleigh, an English physicist, who first described it in the 1870’s.)

Source: https://www.sciencemadesimple.com/