Consider the following phenomena : 1. Size of the sun at dusk 2. Co

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?

1, 2 and 3

3, 4 and 5

1, 2 and 4

2, 3 and 5

Answer is Right!

Answer is Wrong!

This question was previously asked in

UPSC IAS – 2013

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The size of the sun at dusk, the colour of the sun at dawn, and the twinkle of stars in the sky are considered optical phenomena or illusions.

1. The apparent increase in the size of the sun (or moon) near the horizon (dusk) is an optical illusion known as the Moon illusion. 2. The reddish/orange colour of the sun at dawn is due to atmospheric scattering (Rayleigh scattering), where shorter wavelengths (blue/green) are scattered away more than longer wavelengths (red/orange) when light travels a longer path through the atmosphere. This phenomenon leads to a perceived colour change. 4. The twinkling of stars is caused by atmospheric refraction due to turbulence in the air, which makes the light from distant stars appear to fluctuate in brightness and position.

Phenomena 3 (Moon being visible at dawn) and 5 (Polestar being visible in the sky) are real astronomical occurrences related to the celestial positions of these bodies and are not optical illusions in the sense of being perceptual distortions or atmospheric effects causing altered appearance. Therefore, 1, 2, and 4 fit the description of optical illusions or related atmospheric optical phenomena causing altered visual perception.

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