🧷 Authentic Classroom Explanation by IAS Monk

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📌 The Question:

Consider the following pairs:

Objects in space : Description

1. Cepheids : Giant clouds of dust and gas in space
2. Nebulae : Stars which brighten and dim periodically
3. Pulsars : Neutron stars that are formed when massive stars run out of fuel and collapse

How many of the above pairs are correctly matched?

(a) Only one
(b) Only two
(c) All three
(d) None

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✅ Answer: (a) Only one

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🧑‍🏫 Classroom Explanation:

Let us verify each pair carefully:

• Pair 1 – Cepheids:
Cepheids are variable stars that brighten and dim periodically due to rhythmic expansion and contraction. They are not clouds of dust and gas. Hence, incorrectly matched.

• Pair 2 – Nebulae:
Nebulae are indeed giant clouds of dust and gas in space, often serving as stellar nurseries. They are not stars that brighten and dim periodically. Hence, incorrectly matched.

• Pair 3 – Pulsars:
Pulsars are rapidly rotating neutron stars, formed when massive stars exhaust their nuclear fuel and collapse under gravity, often after a supernova explosion. Hence, correctly matched.

Thus, only one pair (Pair 3) is correctly matched.

Correct answer is (a).

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🔍 Curiosity Raiser:

🌌 How do astronomers measure distances to faraway galaxies without travelling there?

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📚 Enrichment Notes (UPSC Edge):

• Cepheid variables are crucial “standard candles” used to measure cosmic distances
• Nebulae can be:
  • Emission nebulae
  • Reflection nebulae
  • Planetary nebulae
• Pulsars emit beams of radiation that appear as pulses due to their rotation, acting like cosmic lighthouses

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🧘 IAS Monk Whisper:

🌀 In the silence of space, rhythm, dust, and collapse write the story of the universe.