UPSC Prelims 2002 Q56: Geography – Atmosphere & Climatology
Sun’s halo is produced by the refraction of light in
- (a) Water vapour, in Stratus clouds
- (b) Ice crystals in Cirrocumulus clouds
- (c) Ice crystals in Cirrus clouds
- (d) Dust particles in Stratus clouds
Answer: (c) Ice crystals in Cirrus clouds
Explanation
Sun's halo and the clouds that produce it
| Option | Assessment |
|---|---|
| Ice crystals in cirrus clouds | Yes — high, thin cirrus clouds hold hexagonal ice crystals that refract sunlight at 22° |
| Ice crystals in cirrocumulus clouds | Possible in rare cases, but cirrus is the standard cause |
| Water vapour in stratus clouds | Low cloud of water droplets does not give a halo |
| Dust particles in stratus clouds | Dust does not make a halo |
A halo around the Sun is produced by the refraction of light in ice crystals in high cirrus clouds. The hexagonal crystals bend the light by a minimum of 22 degrees, forming a ring.
Answer: (c) Ice crystals in Cirrus clouds.
Why each option is right or wrong
- (a) Incorrect. Stratus is a low water-droplet cloud.
- (b) Incorrect. Cirrocumulus is a less usual halo cloud; cirrus is the standard answer.
- (c) CORRECT. Ice crystals in cirrus clouds refract sunlight into a halo.
- (d) Incorrect. Dust in stratus clouds does not cause a halo.
Key point
Halo: 22° ring from ice crystals in cirrus or cirrostratus; rainbow: refraction in water drops.
Remember
Sun halo = refraction in ice crystals of cirrus.
Common mistakes
- Choosing cirrocumulus because it is also a high cloud.
- Mixing halo with rainbow, which needs water drops.
- Thinking that dust particles in low clouds make the ring.
Exam tip
Halo means ice; ice means high cirrus.
Sources
- NCERT Class XI — Fundamentals of Physical Geography (Atmosphere)
- Savindra Singh — Climatology