Question

The Sun is visible to us about 2 minutes before the actual sunrise and about 2 minutes after the actual sunset because of

• A. atmospheric refraction
• B. atmospheric scattering
• C. dispersion of light
• D. motion of Earth

Hint:

Atmospheric refraction causes celestial objects (like the Sun and stars) to appear slightly higher in the sky than their actual positions.
This refraction adds about 4 minutes of daylight to our day.

Answer 1

The Correct Option is A

Step 1: Understanding the Question:
The question asks for the physical phenomenon responsible for the early visibility of the Sun before actual sunrise and its prolonged visibility after actual sunset.

Step 2: Key Formula or Approach:
This phenomenon is explained by the bending of light rays as they pass through layers of air of varying optical density in the Earth's atmosphere.

Step 3: Detailed Explanation:

• The Earth's atmosphere is made of air layers with varying temperatures and densities.

• Air closer to the Earth's surface is denser and has a higher refractive index than the upper layers of air.

• When light from the Sun (which is still below the horizon) enters the Earth's atmosphere obliquely, it travels from a rarer medium to a denser medium.

• Consequently, the light rays undergo continuous refraction, bending progressively towards the normal (downwards towards the Earth).

• To an observer on the ground, these bent rays appear to come from a position slightly higher than the horizon.

• As a result, the Sun appears to rise about 2 minutes earlier than it actually crosses the horizon, and remains visible for about 2 minutes after it has actually set below the horizon.


Step 4: Final Answer:
The early sunrise and delayed sunset occur due to atmospheric refraction.