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?
Correct Answer: (c) 1, 2 and 4
Note: The size of the Sun at dusk is an optical illusion. The Sun appears smaller during noon but longer at dawn or more clearly at dusk. At dawn, the Sun is seen with other objects on the horizon and looks big. The colour of the Sun at dawn is also an optical illusion. Finally twinkling of stars is also an optical illusion caused by the refraction of light while moving through various layers of atmosphere.
