Draw a labelled diagram to show (i) reddish appearance of the sun at the sunrise or the sunset and (ii) white appearance of the sun at noon when it is overhead.

Q: Draw a labelled diagram to show (i) reddish appearance of the sun at the sunrise or the sunset and (ii) white appearance of the sun at noon when it is overhead.

### Explanation of the Phenomena 1. **Reddish Appearance at Sunrise/Sunset:** When the Sun is near the horizon, the light rays must travel a longer distance through a thicker layer of the Earth's atmosphere before reaching the observer's eye. During this long journey, most of the shorter wavelengths (blue and violet light) are scattered away by the minute particles in the atmosphere. The light that successfully reaches our eyes consists primarily of longer wavelengths (red and orange), giving the Sun a reddish appearance. 2. **White Appearance at Noon:** When the Sun is directly overhead (at noon), the light rays travel a relatively shorter distance through the atmosphere. Consequently, very little of the light is scattered. Since all colours reach our eyes in almost equal, complete proportions, the Sun appears white. --- ### Labelled Diagram ```diagram {"xrange": [17.4, 302.6], "yrange": [-353.6, -6.4], "lines": [{"from": [275.0, -60.0], "to": [275.0, -220.0], "label": "Short Path (Less Scattering - Sun appears White)"}, {"from": [65.0, -220.0], "to": [175.0, -220.0], "label": "Long Path (Blue Scattered Away - Sun appears Red)"}], "points": [{"x": 275.0, "y": -320.0, "label": "Earth"}, {"x": 275.0, "y": -320.0, "label": "Atmosphere"}, {"x": 275.0, "y": -40.0, "label": "Sun Overhead (Noon)"}, {"x": 45.0, "y": -220.0, "label": "Sun near Horizon (Sunrise/Sunset)"}, {"x": 275.0, "y": -215.0, "label": ""}], "caption": "Atmospheric Scattering of Sunlight at Noon and Horizon"} ```

Scattering of Light

Official Answer

Explanation of the Phenomena

Reddish Appearance at Sunrise/Sunset:

When the Sun is near the horizon, the light rays must travel a longer distance through a thicker layer of the Earth's atmosphere before reaching the observer's eye. During this long journey, most of the shorter wavelengths (blue and violet light) are scattered away by the minute particles in the atmosphere. The light that successfully reaches our eyes consists primarily of longer wavelengths (red and orange), giving the Sun a reddish appearance.

White Appearance at Noon:

When the Sun is directly overhead (at noon), the light rays travel a relatively shorter distance through the atmosphere. Consequently, very little of the light is scattered. Since all colours reach our eyes in almost equal, complete proportions, the Sun appears white.

Labelled Diagram

Atmospheric Scattering of Sunlight at Noon and Horizon

horizonoverheadlonger distanceshorter distanceshorter wavelengths scatteredlonger wavelengthsreddish appearancewhite appearance

Marking Scheme

1Correct explanation of the reddish appearance at sunrise/sunset (longer path, blue scattered away): 1 Mark
2Correct explanation of the white appearance at noon (shorter path, minimal scattering): 1 Mark
3Neat, correctly labelled diagram showing both positions of the Sun, the Earth, and the atmosphere: 1 Mark

Hint

Draw the Earth with a surrounding layer of atmosphere. Place the Sun directly overhead for noon (short path) and at the side near the horizon for sunrise/sunset (long path). Show how blue light is scattered out of the long path.

Quick Oral Answer

At sunrise and sunset, sunlight travels a longer distance through the atmosphere, scattering away most of the blue light, leaving red light to reach our eyes. At noon, the path is short, scattering is minimal, so the Sun appears white.

Analysis & Explanation

The scattering of light is governed by Rayleigh's scattering law, which states that the intensity of scattered light is inversely proportional to the fourth power of the wavelength ( $I \propto \frac{1}{\lambda^4}$ ). Blue light has a shorter wavelength than red light, so it is scattered much more strongly. At the horizon, the path length through the atmosphere is maximum, so almost all blue light is scattered out of the line of sight, leaving the unscattered red light to reach the observer. At noon, the path length is minimum, scattering is negligible, and the Sun appears white.

Common Mistakes

1Drawing the atmosphere as a thin line or omitting it entirely.
2Stating that red light is scattered *more* than blue light at sunset.
3Confusing atmospheric refraction (which causes advanced sunrise) with scattering of light (which causes the reddish color).

Interesting Facts

If the Earth had no atmosphere, the sky would look completely dark, and the Sun would appear white at all times of the day, just as it does to astronauts in space!

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Frequently Asked Questions

How many marks does this question carry in CBSE Class 10 Science 2020?

This question carries 3 marks in the CBSE Class 10 Science 2020 examination.

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 2020 paper?

This is a Short Answer question from Section B in the CBSE Class 10 Science 2020 paper.