Explain with the help of a diagram, how we are able to observe the sunrise about two minutes before the sun gets above the horizon.
Explain with the help of a diagram, how we are able to observe the sunrise about two minutes before the sun gets above the horizon.
We observe the sunrise about minutes before the sun actually crosses the horizon due to atmospheric refraction.
- Density Gradient: The Earth's atmosphere consists of layers of air with varying densities. Air near the surface is denser than air at higher altitudes.
- Bending of Light: When sunlight enters the Earth's atmosphere from vacuum, it travels from a rarer medium to a denser medium, continuously bending towards the normal.
- Apparent Position: For an observer on Earth, the light appears to come from a straight line, making the sun appear at an apparent position slightly above its actual position.
- Result: Consequently, the sun is seen even when it is still below the horizon.
Marking Scheme
- 11.0 mark: Mentioning atmospheric refraction and density gradient
- 21.0 mark: Explaining the difference between actual and apparent position with a diagram
Hint
Think about how light bends when it moves from a vacuum into the air layers of the Earth.
Quick Oral Answer
It is due to atmospheric refraction. The light from the sun bends as it enters the atmosphere, making the sun appear above the horizon before it actually rises.
Analysis & Explanation
Atmospheric refraction is the deviation of light from a straight line as it passes through the atmosphere due to the variation in air density. Since the refractive index of air increases as we move closer to the Earth's surface, light from the sun (which is below the horizon) follows a curved path. Our eyes perceive light as traveling in a straight line, so we see the sun at a position higher than it actually is. This phenomenon also causes the delayed sunset by about minutes, effectively increasing the length of the day by minutes.
Common Mistakes
- 1Attributing the phenomenon to reflection or scattering instead of refraction.
- 2Forgetting to mention that the sun is actually below the horizon.
- 3Confusing the time duration (it is 2 minutes, not 4 minutes for sunrise alone).
Interesting Facts
Atmospheric refraction is also the reason why stars appear to twinkle and why they seem higher in the sky than they actually are.
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Frequently Asked Questions
How many marks does this question carry in CBSE Class 10 Science 2011?
This question carries 2 marks in the CBSE Class 10 Science 2011 examination.
Which chapter does this question come from in Science?
This question is from the chapter "Chemical Reactions and Equations" in the CBSE Class 10 Science syllabus.
What topic does this question cover in Science?
This question covers the topic "Atmospheric Refraction" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2011 paper?
This is a Short Answer question from Section A in the CBSE Class 10 Science 2011 paper.