Question

Why does a clear sky appear blue?

Hint:

This same principle (Rayleigh scattering) explains why the sun appears red at sunrise and sunset (blue is scattered away, leaving red).

Answer 1

Step 1: Understanding the Concept:
When sunlight passes through the Earth's atmosphere, it interacts with gases and particles, causing scattering of light.

Step 2: Detailed Explanation:
Sunlight is composed of various colors (the visible spectrum).
According to Rayleigh scattering, the amount of scattering is inversely proportional to the fourth power of the wavelength (\(\text{Scattering} \propto \frac{1}{\lambda^4}\)).
Blue light has a shorter wavelength compared to red light.
Therefore, the fine particles and molecules (like nitrogen and oxygen) in the atmosphere scatter the blue light in all directions much more strongly than they scatter the longer wavelengths (red/yellow).
When we look at the sky, we see this scattered blue light entering our eyes.

Step 3: Final Answer:
The sky is blue because atmospheric molecules scatter shorter-wavelength blue light more efficiently than other colors.