2013 GS Paper I, all questions
UPSC Prelims 2013 · GS Paper I
Question 14: Geography
Variations in the length of daytime and nighttime from season to season are due to
athe earth's rotation on its axis
bthe earth's revolution round the sun in an elliptical manner
clatitudinal position of the place
drevolution of the earth on a tilted axis
AnswerUPSC’s answer is (d).
Day and night change in length with the seasons because the earth's axis is tilted about 23.5 degrees from the perpendicular to its orbital plane and keeps pointing the same way as the earth revolves around the sun. This makes each hemisphere lean towards or away from the sun at different times of year. Rotation only produces the daily cycle, and the shape of the orbit is not the cause.
Why each option is right or wrong
- (a) Wrong. Rotation causes the daily cycle of day and night, not seasonal change in their lengths.
- (b) Wrong. The elliptical orbit alone would not change day length; the tilt does.
- (c) Wrong. Latitude decides how large the variation is, but it is not the cause of the seasonal change.
- (d) Correct. The tilted axis combined with revolution causes the variation.
Answer: UPSC’s key. Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 2013, General Studies Paper I, Series A. The paper on upsc.gov.in.