Put these three things together, and a blue sky is inevitable. Here's how it all comes together. Light of many different wavelengths, not all of which are visible, are emitted by the Sun. Sunlight is made up of all the different colors of light The photosphere of our Sun is so hot, at nearly 6, K, that it emits a wide spectrum of light, from ultraviolet at the highest energies and into the visible, from violet all the way to red, and then deep into the infrared portion of the spectrum.
The highest energy light is also the shortest-wavelength and high-frequency light, while the lower energy light has longer-wavelengths and low-frequencies than the high-energy counterparts. When you see a prism split up sunlight into its individual components, the reason the light splits at all is because of the fact that redder light has a longer wavelength than the bluer light.
Schematic animation of a continuous beam of light being dispersed by a prism. If you had ultraviolet The fact that light of different wavelengths responds differently to interactions with matter proves extremely important and useful in our daily lives. The large holes in your microwave allow short-wavelength visible light in-and-out, but keep longer-wavelength microwave light in, reflecting it.
The thin coatings on your sunglasses reflect ultraviolet, violet, and blue light, but allow the longer-wavelength greens, yellows, oranges, and reds to pass through. And the tiny, invisible particles that make up our atmosphere — molecules like nitrogen, oxygen, water, carbon dioxide, as well as argon atoms — all scatter light of all wavelengths, but scatter the shorter-wavelength light much more efficiently.
When the Sun is high overhead, the sky towards the zenith is a much darker blue, while the sky This is due to the larger amount of atmosphere, and the larger amount of scattered light, that is visible at low angles on the sky. Because these molecules are all much smaller than the wavelength of light itself, the shorter the light's wavelength is, the better it scatters. In fact, quantitatively, it obeys a law known as Rayleigh scattering , which teaches us that the violet light at the short-wavelength limit of human vision scatters more than nine times more frequently than the red light at the long-wavelength limit.
Some opalescent materials, like the one shown here, have similar Rayleigh scattering properties to When the Sun is high in the sky, this is why the entire sky is blue. It appears a brighter blue the farther away from the Sun you look, because there's more atmosphere to see and therefore more blue light in those directions.
In any direction you look, you can see the scattered light coming from the sunlight striking the entirety of the atmosphere between your eyes and where outer space begins. This has a few interesting consequences for the color of the sky, depending on where the Sun is and where you're looking. From very high altitudes in the pre-sunrise or post-sunset skies, a spectrum of colors can be seen, If the Sun is below the horizon, the light all has to travel through large amounts of atmosphere.
To understand why the sky is blue, we first need to understand a little bit about light. Although light from the Sun looks white, it is really made up of a spectrum of many different colours, as we can see when they are spread out in a rainbow.
We can think of light as being a wave of energy, and different colours all have a different wavelength. At one end of the spectrum is red light which has the longest wavelength and at the other is blue and violet lights which have a much shorter wavelength.
When the Sun's light reaches the Earth's atmosphere it is scattered, or deflected, by the tiny molecules of gas mostly nitrogen and oxygen in the air. Because these molecules are much smaller than the wavelength of visible light, the amount of scattering depends on the wavelength. This effect is called Rayleigh scattering, named after Lord Rayleigh who first discovered it.
Shorter wavelengths violet and blue are scattered the most strongly, so more of the blue light is scattered towards our eyes than the other colours. 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. Closer to the horizon, the sky fades to a lighter blue or white. The sunlight reaching us from the horizon has passed through even more air than the sunlight reaching us from overhead.
The molecules of gas have rescattered the blue light in so many directions so many times that less blue light reaches us.
As the Sun gets lower in the sky, its light passes through more of the atmosphere to reach you. Even more of the blue and violet light is scattered, allowing the reds and yellows to pass straight through to your eyes without all that competition from the blues. Also, larger particles of dust, pollution, and water vapor in the atmosphere reflect and scatter more of the reds and yellows, sometimes making the whole western sky glow red.
The Short Answer:. Gases and particles in Earth's atmosphere scatter sunlight in all directions.
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