Consider the following lines of Longitude and Latitude: 1. Prime Meridian; 2. Tropic of Cancer; 3. Equator. Which of the above lines is/are a Great Circle?
- (a)1, 2 and 3
- (b)1 and 2 only
- (c)1 and 3 only
- (d)3 only
Correct — D, 3 only (the Equator). A great circle is any circle on the globe whose plane passes through the Earth's centre, cutting the sphere into two equal halves. The Equator is the only line of latitude that does this. The Tropic of Cancer is a small circle whose plane sits north of the centre, and a single named meridian such as the Prime Meridian is only half of a great circle — it needs its 180-degree antimeridian to complete the full centre-cutting circle. On this strict reading only the Equator qualifies; note some textbooks loosely call each meridian a great circle, which would instead give (c) 1 and 3.
- (a)1, 2 and 3 — The Tropic of Cancer cannot be a great circle: its plane lies about 23.5 degrees north of the centre, so it is a small circle. Including it (and treating a single meridian as a full great circle) overcounts.
- (b)1 and 2 only — This excludes the Equator, the one line that is unquestionably a great circle, while wrongly including the Tropic of Cancer, which is a small circle. It gets the clearest case backwards.
- (c)1 and 3 only — This is the near-miss: it counts the Prime Meridian as a great circle. On the strict definition a single meridian is only half a great circle (it must join its antimeridian), so only the Equator (3) qualifies. This option is defensible only under the looser textbook usage.
A great circle is the largest circle that can be drawn on a sphere; its plane passes through the centre and divides the globe into two equal hemispheres. Any circle whose plane misses the centre is a small circle. Great circles also give the shortest path between two points on a sphere.
Among latitudes, only the Equator passes through the centre, so all other parallels (including the Tropic of Cancer) are small circles. Each meridian is a half great circle; a meridian and its antimeridian together make one complete great circle. Applying the strict test leaves the Equator alone, option (d).
- A great circle's plane passes through the Earth's centre and splits it into equal halves.
- The Equator is the only parallel of latitude that is a great circle.
- All other parallels, such as the Tropic of Cancer, are small circles.
- A meridian is half a great circle; it pairs with its 180-degree antimeridian to form a full one.
Only a circle whose plane cuts the Earth's centre is a great circle — among these three, that is the Equator.
- Calling the Tropic of Cancer a great circle (it is a small circle).
- Treating a single meridian as a whole great circle rather than half of one.
- Forgetting the Equator is the only parallel that is a great circle.
NDA/UPSC ask which named line is a great circle — the Equator always qualifies; parallels other than the Equator do not.
No directly related past PYQ was found.
- practice — not a real PYQ
Which one of the following is a great circle?
- (a)Tropic of Capricorn
- (b)Arctic Circle
- (c)Equator
- (d)Tropic of Cancer
Answer(c) Equator — its plane passes through the Earth's centre; the other parallels are small circles.
- practice — not a real PYQ
A great circle is one whose plane
- (a)lies near the poles
- (b)passes through the centre of the Earth
- (c)is tilted 23.5 degrees
- (d)never touches the Equator
Answer(b) passes through the centre of the Earth — dividing the globe into two equal halves.