The sky appears blue for several reasons. Firstly, sunlight is scattered by tiny air molecules in the Earth’s atmosphere. This scattering, called Rayleigh scattering, is more effective at shorter wavelengths, such as blue and violet. However, since our eyes are more sensitive to blue light, we perceive the sky as blue rather than violet.
“The sky is the daily bread of the eyes.” – Ralph Waldo Emerson
Secondly, the atmosphere filters out some of the violet light, further enhancing the blue appearance.
Factors Affecting Sky Color
- Time of Day: The sky is often a deeper blue at midday when the sun is high in the sky. At sunrise and sunset, the light has to travel through more of the atmosphere, scattering away more of the blue light and leaving longer wavelengths like red and orange.
- Weather: Clouds can obviously obscure the blue sky, but even on clear days, dust and pollution can affect the color.
- Altitude: At higher altitudes, the sky appears darker blue, and eventually almost black, due to the thinner atmosphere.
