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Why does the sky appear in different colours at different times?
The colors of the sky are created because the atmosphere between the sun and the earth consists of many different particles and chemicals. The sky directly surrounding the earth though, mainly consists of nitrogen and oxygen molecules as well as the dust and and air pollution caused by humans and animals on the earth's surface. So, when the light hits these particles it is broken up and the different wavelengths are scattered in different directions. This process is called scattering.
During the day the sky is seen as blue unless clouds are in the way or the weather is not nice. But why is it that the sky is blue instead of purple or orange? The answer to this question is that the wavelength of blue light is very small and can be broken up about ten times more than red light because red light has almost double the wavelength of blue light. So, blue light is scattered in more directions than the shorter wavelengths when it comes in contact with the nitrogen and oxygen molecules. Therefore, blue is the light that enters our eye. But, using this same scientific reasoning, it would seem logical that we would see a violet sky instead since it has the longest wavelength of all. But, human eyes are more sensitive to blue than violet so therefore we see a blue sky.

At dusk and dawn the colors of the sky change and the first portion of the visible spectrum is what appears to the viewer. During these times of the day the sun is positioned at a different angle to the earth than during the normal daytime. Because of this angle, the longer wavelengths are the ones that reach the eye. The blue and other shorter wavelengths are scattered millions of times and do not reach the viewer. When the sun does not shine directly on a certain portion of the earth there are more gas molecules between the viewer and the sun. Therefore, the normal blue color of he sky is no longer visible because the short wavelengths of blue and green are scattered millions of times and do not reach the viewer. Therefore the longer wavelengths that couldn't be scattered as many times are able to now hit the viewer in a more direct way.
The colors of the sunset result from a phenomenon called scattering. Molecules and small particles in the atmosphere change the direction of light rays, causing them to scatter. Scattering affects the color of light coming from the sky, but the details are determined by the wavelength of the light and the size of the particle.
Scattering affects the color of light coming from the sky, but the details are determined by the wavelength of the light and the size of the particle. The short-wavelength blue and violet are scattered by molecules in the air much more than other colors of the spectrum. This is why blue and violet light reaches our eyes from all directions on a clear day. But because we can't see violet very well, the sky appears blue.


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