As mentioned before, light incorporates colors such as blue and red. Common light combines various kinds of light, each of which has its own wavelength. The individual components of light are called the spectrum. Blue light has a short wavelength; red light a longer wavelength. The sky looks blue because blue light is scattered far more than red light, owing to the shorter wavelength of blue light. (Violet light, which has an even shorter wavelength, cannot be seen because the human eye is not very sensitive to violet light.)

The sky is red at dawn and dusk. Because at these times sunlight travels further through the atmosphere than at other times of the day, blue light is scattered more. Reds and oranges are scattered less, so these colors appear with greater intensity to our eyes.