Consider the following phenomena:

Answer: (c) 1, 2 and 4

Phenomena 1, 2 and 4 are apparent effects: what we see differs from the real object, because of the atmosphere or the way the brain judges size. The Moon at dawn and the Pole Star are real objects that are actually there to be seen, so 3 and 5 are not illusions.

• ✓ 1. The Sun's disc is no bigger near the horizon than high in the sky; it only looks bigger. Photographs prove the Moon is the same width near the horizon as when it is high up, yet our eyes see it as larger. The same horizon illusion makes the setting Sun look bigger.
• ✓ 2. The Sun looks red or orange at dawn because its light travels a long path through the air and is scattered. The Sun's real colour does not change, only its appearance.
• ✗ 3. At certain phases the Moon is really above the horizon at dawn and can be seen. This is a real sighting, not a false appearance.
• ✓ 4. Twinkling is caused by atmospheric refraction of starlight. As the light passes through moving layers of air it is bent unevenly, so the star's apparent position and brightness keep changing, though the star itself is not flickering.
• ✗ 5. Polaris is a real star that stays nearly fixed in the northern sky, so it is actually seen from the northern hemisphere. Nothing about its appearance is false.

Remember · The Sun's apparent size and colour at the horizon and the twinkling of stars are appearances caused by perception and the atmosphere. Seeing the Moon or the Pole Star is plain visibility.

📘 Read it in NCERT: Class 10 Science, Ch 10 (practise this chapter) · Class 10 Science, Ch 10 (practise this chapter)

Question: UPSC Civil Services (Preliminary) 2013, General Studies Paper I. Explanation: Minimalist IAS, checked 25 Oct 2026 (how we verify). · Report an error