Atmospheric Refraction: Cause Analysis

Atmospheric refraction is the bending of light rays as they pass through Earth's atmosphere due to variations in air density and temperature. Let's analyze the given options:

Phenomena Explained

• Apparent Sun Position: The Sun appears higher in the sky than its actual geometric position because light rays bend downwards when entering the denser atmosphere from the vacuum of space. This is caused by atmospheric refraction.
• Sunrise and Sunset Times: We observe sunrise slightly before the Sun geometrically appears above the horizon and sunset slightly after it disappears. This difference is due to light bending, making the Sun visible even when it's geometrically below the horizon. This is caused by atmospheric refraction.
• Twinkling of Stars: Starlight travels through various atmospheric layers of different densities and temperatures. These variations cause the light rays to refract inconsistently, making the star's apparent position and brightness fluctuate, resulting in twinkling. This is caused by atmospheric refraction.
• Reddish Color of Sun: The reddish hue of the Sun during sunrise and sunset is primarily due to Rayleigh scattering, not refraction. When the Sun is near the horizon, sunlight travels through a thicker layer of the atmosphere. Shorter wavelengths (blue and violet) are scattered away effectively by air molecules, while longer wavelengths (red and orange) pass through more directly, giving the Sun its characteristic color.

Conclusion

Based on the analysis, the reddish color of the sun at sunrise and sunset is the phenomenon NOT caused by atmospheric refraction. It is caused by the scattering of sunlight.