CAPF AC 2021 Q20: Science & Technology – Physics
Which one among the following is not a luminous object?
- (a) Sun
- (b) Proxima Centauri
- (c) Jupiter
- (d) Alpha Centauri
Answer: (c) Jupiter
Explanation
Luminous and non-luminous objects
How to think: a luminous object makes its own light.
A non-luminous object only reflects light that falls on it.
Stars make their own light.
Planets and moons do not.
| Object | What it is | Luminous? |
|---|---|---|
| Sun | Star | Yes |
| Proxima Centauri | Star, the nearest to the Sun | Yes |
| Alpha Centauri | Star system, close to the Sun | Yes |
| Jupiter | Planet | No, it shines by reflected sunlight |
Useful facts: Proxima Centauri is about 4.2 light years away.
It belongs to the Alpha Centauri system.
Jupiter is the largest planet of the solar system.
Answer: (c) Jupiter.
Why each option is right or wrong
- (a) Incorrect. The Sun is a star and produces its own light by nuclear fusion.
- (b) Incorrect. Proxima Centauri is a star, the nearest one to the Sun, so it is luminous.
- (c) CORRECT. Jupiter is a planet and only reflects the light of the Sun.
- (d) Incorrect. Alpha Centauri is a star system and gives out its own light.
Key point
Stars are luminous (own light); planets and moons are non-luminous (reflected light). Proxima Centauri is the nearest star to the Sun, about 4.2 light years away.
Remember
Stars shine, planets reflect.
Common mistakes
- Thinking Jupiter is luminous because it looks bright in the night sky.
- Not recognising Proxima Centauri and Alpha Centauri as stars.
- Believing the Moon and planets produce light; they only reflect sunlight.
Exam tip
Educated guess: three options are stars and one is a planet. The odd one out is the answer.
Sources
- NCERT Class VI Science — Light, Shadows and Reflections (luminous and non-luminous objects)
- NCERT Class VIII Science — Stars and the Solar System