Which of the following is not caused by the atmospheric refraction of light?

Question

Accepted Answer

Explanation:

1. **Option 4: Sun appearing red at sunset.**  
   The sun appearing red at sunset is not caused by atmospheric refraction but rather by a phenomenon known as scattering. During sunset, the sun's light has to pass through a greater thickness of Earth's atmosphere. Shorter wavelengths of light (blue and violet) are scattered out of the direct path of sight, while the longer wavelengths (red and orange) are less affected by scattering and thus dominate the sky's color. This is why the sun appears red at sunset.

2. **Option 1: Twinkling of stars at night.**  
   The twinkling of stars, also known as stellar scintillation, is indeed caused by atmospheric refraction. As starlight passes through the Earth's atmosphere, it is refracted multiple times due to varying air densities and temperatures. This causes the light to bend in different directions, making stars appear to twinkle.

3. **Option 2: Sun appearing higher in the sky than it actually is.**  
   This phenomenon is also a result of atmospheric refraction. When the sun is near the horizon, its light passes through a thicker layer of the atmosphere, causing the light to bend. This bending makes the sun appear higher in the sky than its actual geometric position.

4. **Option 3: Sun becoming visible two minutes before actual sunrise.**  
   Atmospheric refraction is responsible for this effect as well. As the sun approaches the horizon, its light is bent by the Earth's atmosphere, allowing us to see the sun before it has actually risen above the horizon. This bending of light causes the sun to appear earlier than it physically is.

In summary, Option 4 is correct because the red appearance of the sun at sunset is due to scattering, not atmospheric refraction, whereas the other options are directly related to the effects of atmospheric refraction.