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

Ans-[C] 

Explanation– An optical illusion also called a visual illusion is characterized by visually perceived images that differ from object than reality. The information gathered by the eye is processed in the brain to give a perception that does not tally with a physical measurement of the stimulus source. Moon being visible in dawn and polestar being visible in sky are not any illusion. Size of the sun which appears big, color of the sun at dawn and twinkle of stars in the sky are not actual phenomenon but happens due to various factors such as refraction, different density of the air layers etc.