With the help of a labelled diagram, explain why the sun appears reddish at the sun-rise and the sun-set.
With the help of a labelled diagram, explain why the sun appears reddish at the sun-rise and the sun-set.
Official answer
At sunrise and sunset, the Sun is near the horizon. The light rays from the Sun have to travel a much larger distance through the thick layers of the Earth's atmosphere before reaching our eyes.
During this long journey, most of the shorter wavelengths of light (blue and violet) are scattered away by the fine particles in the atmosphere. The light that successfully reaches our eyes consists primarily of longer wavelengths, which are red and orange. Consequently, the Sun and the surrounding sky appear reddish.
``diagram {"xrange": [29.0, 246.0], "yrange": [-242.8, -7.2], "lines": [{"from": [65.0, -140.0], "to": [221.0, -140.0], "label": "Long path through atmosphere (Blue scattered)"}, {"from": [225.0, -45.0], "to": [225.0, -136.0], "label": "Short path"}], "points": [{"x": 225.0, "y": -220.0, "label": "Earth"}, {"x": 225.0, "y": -220.0, "label": "Atmosphere"}, {"x": 225.0, "y": -140.0, "label": "Observer"}, {"x": 50.0, "y": -140.0, "label": "Sun near horizon"}, {"x": 225.0, "y": -30.0, "label": "Sun overhead"}], "caption": "Reddening of the Sun at Sunrise and Sunset"} ``
Marking scheme
- 1.Stating that light travels a longer distance through the atmosphere near the horizon. (1 mark)
- 2.Explaining that shorter wavelengths (blue/violet) are scattered away by atmospheric particles. (1 mark)
- 3.Concluding that the remaining longer wavelengths (red/orange) reach our eyes, making the Sun look reddish. (1 mark)
Hint
Think about how the distance traveled by sunlight through the atmosphere changes when the Sun is at the horizon compared to when it is directly overhead.
Quick oral answer
The Sun appears reddish because at the horizon, sunlight travels a longer atmospheric path, scattering away the blue light and leaving the longer-wavelength red light to reach our eyes.
Common mistakes
- 1.Confusing atmospheric refraction with scattering of light.
- 2.Stating that red light is scattered the most instead of the least.
Analysis and explanation
When the Sun is overhead, the light travels a relatively shorter distance through the atmosphere, resulting in very little scattering of light, which is why it appears white. However, near the horizon, the path length is maximized. Since scattering intensity is inversely proportional to the fourth power of wavelength (Rayleigh scattering), shorter blue wavelengths are scattered out of the line of sight, leaving the unscattered longer red wavelengths to reach the observer.
Interesting facts
If the Earth had no atmosphere, the sky would look completely dark, and the Sun would appear white even at sunrise and sunset!
Question details
Q17 of 36 questions
- Board
- CBSE
- Class
- Class 10
- Subject
- Science
- Year
- 2015
- Section
- Section A
- Marks
- 3
- Type
- Short Answer
- Chapter
- The Human Eye and the Colourful World
- Topic
- Scattering of Light
- Bloom's level
- Understanding
- Syllabus topic
- Colour of the sun at sunrise and sunset
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Frequently asked questions
How many marks does this question carry in CBSE Class 10 Science 2015?
This question carries 3 marks in the CBSE Class 10 Science 2015 examination.
Which chapter does this question come from in Science?
This question is from the chapter "The Human Eye and the Colourful World" in the CBSE Class 10 Science syllabus.
What topic does this question cover in Science?
This question covers the topic "Scattering of Light" from CBSE Class 10 Science.
What type of question is this in the CBSE Class 10 Science 2015 paper?
This is a Short Answer question from Section A in the CBSE Class 10 Science 2015 paper.