It is kind of a clichè – I know, pictures of the sunset. Still, I think most people find them beautiful. But why does the sky turn orange?
Molecules and small particles in the atmosphere change the direction of light rays, causing them to scatter, which affects the colour of the light. The wavelength of the light, and the size and amount of molecules the light has to pass through, determines the colour. The short wavelength colours blue and violet are scattered in the air much more than other colours, hence the sky appears blue. However, at sunset and sunrise, the sun is low on the horizon, and the light has to pass through more air, which also means more molecules to scatter the light. The result is that the blue and violet light is scattered out of your sight, while the other colours with longer wavelength brakes through the atmosphere and find their way to your eyes. This is why sunsets may appear yellow, orange and/or red.
Here are some other colourful pictures