Question
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 beingvisible 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
Answer:
C
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Explanation:
Size of the sun at dusk: This phenomenon is not an optical illusion but rather a result of atmospheric conditions affecting the appearance of the sun. The size of the sun appears larger near the horizon due to the atmospheric refraction.
Color of the sun at dawn: The color of the sun at dawn is an optical illusion caused by the scattering of light in the Earth's atmosphere. The longer path length of sunlight through the atmosphere at dawn scatters shorter wavelengths, making the sun appear reddish.
Moon being visible at dawn: This is not an optical illusion. The visibility of the moon at dawn is a natural occurrence based on the moon's position in relation to the Earth and the sun.
Twinkle of stars in the sky: The twinkling of stars in the sky is an optical illusion caused by the Earth's atmosphere refracting the starlight. The atmospheric turbulence causes the apparent brightness of stars to fluctuate, creating the twinkling effect.
Polestar being visible in the sky: This is not an optical illusion. The Polestar (Polaris) is a star located near the North Celestial Pole, and its position makes it visible in the northern hemisphere throughout the night.