UPSC Prelims 1997 · General Studies
Question 64: Geography
If the earth's direction of rotation is reversed, what would be the IST when it is noon at the International Date Line?
AnswerThe answer is (c).
Today, noon on the International Date Line (180°) falls at 00:00 UTC, so IST, which is UTC+5:30, would then show 05:30. If the Earth rotated the other way, places east of Greenwich would be behind Greenwich time instead of ahead, so IST would be UTC minus 5:30. With 180° still at 00:00 UTC at its noon, IST would be 00:00 minus 5:30, that is 18:30 on the previous day.
Why each option is right or wrong
- (a) 06:30 hrs adds an hour to the normal result for no reason.
- (b) 05:30 hrs is the answer with the present direction of rotation.
- (c) Right: 00:00 UTC minus 5:30 gives 18:30 hrs.
- (d) 17:30 hrs does not follow from subtracting 5:30 from 00:00 UTC.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 1997, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.