UPSC CSE Prelims
Question 62
Consider the following phenomena:
- Size of the sun at dusk
- Colour of the sun at dawn
- Moon being visible at dawn
- Twinkle of stars in the sky
- Polestar being visible in the sky
Which of the above are optical illusions?
View correct answer and explanation
Correct answer: C
Correct Option: C
Explanation: Near-horizon apparent solar size, reddish dawn sunlight and star twinkling involve optical perception or atmospheric propagation; seeing the Moon or Pole Star is ordinary visibility.
Statement/Pair-wise Analysis:
Statement/Item 1: Correct - The apparently larger Sun near the horizon is largely a perceptual/optical illusion.
Statement/Item 2: Correct - The reddish colour of the dawn Sun results from wavelength-dependent atmospheric scattering.
Statement/Item 3: Incorrect - A Moon visible at dawn is a real geometric/illumination phenomenon, not an illusion.
Statement/Item 4: Correct - Atmospheric refraction through turbulent layers causes starlight to twinkle.
Statement/Item 5: Incorrect - The Pole Star’s visibility reflects its celestial position and the observer’s latitude.
Option-wise Analysis:
A: Incorrect - includes false item 3 and excludes true item 4.
B: Incorrect - includes false items 3, 5 and excludes true items 1, 2.
C: Correct - selects all and only the accurate statements/pairs.
D: Incorrect - includes false items 3, 5 and excludes true items 1, 4.
Review Note: Strictly, dawn redness is physical selective scattering rather than an “illusion” in the same sense as the horizon-size illusion; option C is the conventional examination classification.