2002 General Studies, all questions
UPSC Prelims 2002 · General Studies
Question 56: Geography
Sun’s halo is produced by the refraction of light in
aWater vapour, in Stratus clouds
bIce crystals in Cirrocumulus clouds
cIce crystals in Cirrus clouds
dDust particles in Stratus clouds
AnswerThe answer is (c).
A halo is a ring of light around the sun or moon, caused by refraction of the light through hexagonal ice crystals in high, thin clouds. The commonest is the 22-degree halo. In practice it is thin cirrostratus that most often gives one, and cirrus is the nearest option offered. Stratus clouds are low water-droplet clouds, so water vapour or dust in them cannot make a halo.
Why each option is right or wrong
- (a) Stratus clouds are low water-droplet clouds and do not make a halo.
- (b) Cirrocumulus is a high patchy ice cloud, but the given answer picks cirrus.
- (c) Right: ice crystals in cirrus-type clouds refract the light into a ring.
- (d) Dust in low stratus cloud does not make a halo.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2002, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.