Why does the sky look blue if outer space is black?
As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air. However, much of the shorter wavelength light is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue. Answer originally posted in response to Why is the sky blue?
The sky is not blue, it only appears blue. The sky is clear and transparent – just like it is at night when the moon and stars shine through it without being altered in their color. The blue sky color is an optical illusion – just like a rainbow.
A rainbow isn’t a real object although the colors you see are real. You can make a rainbow with a garden hose and a sprinkler head and the Sun. The rainbow looks like it is real and really there but when you turn the water off the rainbow goes away.
The reason the rainbow has colors is because the light going into a rain drop is refracted and then is totally internally reflected and then is refracted as it exits the drop. The angle of refraction of the light is color dependent. That produces the rainbow’s colors. Notice that the rainbow always appears opposite the Sun. The Sun has to be at your back.
In a similar way the blue color of the sky is created all over the sky and it looks like there is a real blue sky but it goes away when the sun goes down. The object we call the blue sky is an optical illusion.
The blue sky color is created when sunlight shines through the Earth’s atmosphere during the day. The atmosphere is mostly composed of oxygen, argon and nitrogen gasses. As sunlight shines through the atmospheric gasses some of the light is scattered in all directions by the very molecules of the gasses. This scattering process, called Raleigh Scattering is very wavelength dependent. Blue light is scattered in all directions about 10 times as much as red light is scattered and so we see mostly blue light coming from the direction of the sky.
The blue sky is light scattered from the molecules in the Earth’s atmosphere… The rainbow is created by refraction of light within a rain drop.
Looking from space to the Earth – the blue sky is overwhelmed by the intensity of the light reflected from the surface of the Earth.
