Question

Advance sunrise and delayed sunset are due to

• A. atmospheric refraction
• B. atmospheric scattering
• C. atmospheric dispersion
• D. atmospheric reflection

Hint:

Think about how objects appear slightly distorted or displaced when viewed through a medium with varying refractive index, like air above a hot surface. Atmospheric refraction is a similar effect on a larger scale.

Answer 1

The Correct Option is A

Step 1: Understand the phenomenon of atmospheric refraction.
Atmospheric refraction is the bending of light caused by the varying optical density of the Earth's atmosphere. As sunlight enters the atmosphere, it passes through layers of air with gradually changing refractive indices due to variations in temperature and density. 
Step 2: Explain how atmospheric refraction causes advance sunrise and delayed sunset.
When the sun is near the horizon, the sunlight has to travel through a larger portion of the atmosphere. Due to atmospheric refraction, the light rays bend as they pass through these layers. This bending causes the apparent position of the sun to be slightly higher than its actual position.

• Advance Sunrise:
  Even before the sun has actually risen above the horizon, its light rays bend due to atmospheric refraction, making it appear as if the sun has already risen. This results in an advance sunrise of about 2 minutes.
• Delayed Sunset:
  Similarly, even after the sun has actually set below the horizon, its light rays continue to bend due to atmospheric refraction, making it appear as if the sun is still visible. This causes a delayed sunset of about 2 minutes.

Step 3: Analyze the other options.
 

• Atmospheric scattering:
  This is the phenomenon responsible for the blue colour of the sky and the reddish appearance of the sun during sunrise and sunset. It does not directly cause the advance sunrise and delayed sunset.
• Atmospheric dispersion:
  This is the separation of white light into its constituent colours by the atmosphere, similar to how a prism works. While it occurs, it is not the primary reason for advance sunrise and delayed sunset.
• Atmospheric reflection:
  Some sunlight is reflected back into space by the atmosphere and clouds, but this does not explain the apparent shift in the sun's position near the horizon.

Therefore, advance sunrise and delayed sunset are due to atmospheric refraction.