Optical Illusions in Nature
Question
Consider the following phenomena:
Which of the above are optical illusions?
- 1.
Size of the sun at dusk
- 2.
Colour of the sun at dawn
- 3.
Moon being visible at dawn
- 4.
Twinkle of stars in the sky
- 5.
Polestar being visible in the sky
Options
1, 2 and 3
3, 4 and 5
1, 2 and 4
2, 3 and 5
Explanation
(1) Size of sun at dusk is an optical illusion (moon illusion) caused by atmospheric refraction and psychological factors making the sun appear larger near the horizon than at zenith. (2) Colour of sun at dawn appears reddish due to Rayleigh scattering of shorter wavelengths in the atmosphere, which is an optical effect creating an illusion of color change. (3) Moon being visible at dawn is NOT an illusion—it is an actual astronomical fact; the moon can be visible during daylight hours. (4) Twinkle of stars is due to atmospheric turbulence causing refraction variations, which IS an optical illusion/effect. (5) Polestar's visibility is due to actual astronomical position and Earth's orientation, not an illusion. Therefore, 1, 2, and 4 are optical illusions caused by atmospheric and psychological effects.
Answer: (c).
Question details
Year
2014
Paper
GS Paper 1
Question
Q89
Subject
Science & Technology
Sub-topic
Physics - Optics and Light
Type
Statement-based
Difficulty
Hard
Nature
Static
Source hint
Physics - Optics and Atmospheric Phenomena
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