Chapter 10 · Question 6
Briefly explain the phenomenon of atmospheric refraction. How does it lead to advance sunrise and delayed sunset?
Q6
Briefly explain the phenomenon of atmospheric refraction. How does it lead to advance sunrise and delayed sunset?
Answer Revealed
Direct Answer:
Atmospheric refraction is the bending of light by Earth's atmosphere, which has varying refractive indices due to temperature and density differences. This makes the Sun visible about 2 minutes before it actually rises above the horizon and about 2 minutes after it sets below the horizon.
Simple Explanation
Earth's atmosphere gets denser as you go down, so light from the Sun bends as it passes through different layers. This bending makes the Sun appear above the horizon even when it is physically just below it — so we see the sunrise about 2 minutes early and the sunset about 2 minutes late.
Exam-Ready Structure
Atmospheric refraction is the bending of light as it passes through the Earth's atmosphere, which has layers of different optical densities. Key points: 1. The refractive index of the atmosphere increases as we go downwards because the air becomes denser. 2. When light from a celestial object (like the Sun or a star) enters the atmosphere, it passes through layers of increasing refractive index, bending continuously towards the normal. 3. Advance sunrise: When the Sun is physically just below the horizon in the morning, light rays from it enter the atmosphere and bend downwards towards the observer. The observer sees the Sun at an apparent position above the horizon even though the actual Sun is below it. This makes sunrise appear about 2 minutes early. 4. Delayed sunset: In the evening, after the Sun has physically sunk below the horizon, its light rays continue to bend through the atmosphere, making the Sun visible to an observer for about 2 additional minutes. 5. Without an atmosphere, the Sun would appear and disappear exactly at the moment it crosses the horizon. The atmosphere therefore lengthens the duration of daylight by about 4 minutes daily.
Key Points
- Atmosphere has varying refractive index — denser near the Earth's surface
- Light from celestial objects bends continuously through the atmosphere
- Sun appears above horizon before actual sunrise by about 2 minutes
- Sun remains visible after actual sunset by about 2 minutes
- Daylight lengthened by approximately 4 minutes daily due to atmospheric refraction