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UPSC 2013: Consider the following phenomena: 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 Which of the above are optical illusions?
(a)1, 2 and 3
(b)3, 4 and 5
(c)1, 2 and 4
(d)2, 3 and 5
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Not attemptedCorrect Answer: (c) 1, 2 and 4
1 The apparent larger size of the Sun (or Moon) near the horizon is a classic perceptual illusion. 2 The reddish colour of the Sun at dawn results from Rayleigh scattering along a long atmospheric path and is likewise a visual effect. 4 Stars ‘twinkle’ because atmospheric turbulence refracts their light rapidly, an illusion called scintillation. Moon-visibility at dawn and the fixed Pole Star are real positional phenomena, so only statements 1, 2 and 4 are optical illusions, matching option (c). ([britannica.com](https://www.britannica.com/topic/illusion/Optical-phenomena?utm_source=openai))
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What is the correct answer to this UPSC 2013 Science & Technology question?▼
The correct answer is option (c): 1, 2 and 4. Watch the detailed video explanation in our Sherlocking Prelims course on UnlockIAS.
Which year was this Physics question asked in UPSC Prelims?▼
This question was asked in UPSC CSE Prelims 2013, GS Paper 1, as Question 89. It falls under Science & Technology > Physics.
What is the difficulty level of this UPSC question?▼
This question is rated "moderate". It requires sound conceptual understanding of the topic.
How many UPSC Prelims questions have been asked from Physics?▼
UPSC has asked 104 questions from Physics (under Science & Technology) across multiple years. Visit the topic page to see the full list and year-wise trends.