BPSC 69th CCE Prelims General Studies · Question 96 of 144

Correct — C, 179. Count the circles, not the degrees. Start at the Equator and step north one degree at a time: you can draw parallels at 1° N, 2° N and so on up to 89° N, which is 89 circles. Do the same southward for another 89. Add the Equator itself, which is the 0° parallel and a line in its own right. 89 + 89 + 1 = 179. The two remaining values of latitude, 90° N and 90° S, are the poles, and a pole is a single point — the place where the Earth's axis meets the surface. A parallel of latitude is by definition a circle running round the globe at a constant angular distance from the Equator, and at 90° that circle has shrunk to zero radius, so there is nothing left to draw. This is not a quibble invented for an exam. It is the same geometry that makes the length of a parallel 2πR cos φ: about 40,075 km at the Equator, roughly 20,000 km at 60°, and exactly zero at 90°. The same reasoning disposes of the two rival numbers. 178 is what you get by adding the hemispheres and forgetting that the Equator is a parallel. 180 is the angular span from 90° N to 90° S expressed in degrees — a measurement of arc, not a count of lines drawn along it — and no consistent counting rule produces it: admit the poles and you reach 181, exclude them and you reach 179, but never 180. It is worth knowing what one of those 179 lines is worth on the ground, because that is what the rest of the syllabus does with them. Work on the WGS84 ellipsoid that modern Indian surveying uses — equatorial radius 6,378,137 m exactly, flattening 1/298.257223563 — and one degree of latitude comes out at 110.574 km at the Equator and 111.694 km at the poles. It is longer near the poles, not shorter, because the Earth is flattened there and the meridian curves less sharply, so you must travel further to turn through the same one degree. The 179 parallels therefore step down a pole-to-pole meridian of about 20,004 km at intervals of roughly 111 km. Two working units were built on that step. The metre was defined by the French Academy of Sciences in 1791 as one ten-millionth of the distance from the North Pole to the Equator along the Paris meridian — the modern value of that quadrant is 10,002 km, which is how close an eighteenth-century survey came. And one minute of latitude is the nautical mile, fixed at exactly 1,852 metres by the International Extraordinary Hydrographic Conference at Monaco in 1929; the true arc of one minute at 45° latitude works out to 1,852.2 m. One honest caveat, because this answer is ours and carries medium rather than high confidence. 179 is the count used in standard Indian textbook practice, and it is plainly what the paper is testing. A minority of sources do count 181 by admitting the two poles as degenerate parallels, and a candidate holding that convention would have to choose (d). There is no Commission key for the 69th to settle the point; we follow the standard count.

• (a)180 — The distance from 90° N to 90° S is 180 degrees, and that is the figure being recalled here — but an angular span is not a count of the circles drawn along it. No convention yields 180: include the poles and the total is 181, exclude them and it is 179. This is the most tempting option precisely because 180 feels like the natural round answer for a hemisphere-to-hemisphere sweep.
• (b)178 — 89 north plus 89 south, with the Equator dropped. The Equator is 0° latitude and is itself a parallel — indeed the only one that is a great circle — so it has to be in the count. This is a slip rather than a misconception, and the quick guard against it is that the answer must be an odd number: a set symmetric about the Equator, with one member lying exactly on the axis of symmetry, can never total an even figure.
• (d)None of the above — This is only right under the minority convention that treats the two poles as parallels, which would give 181 and put the true value outside the list. Under the count used in Indian geography teaching — and the one the paper is testing — 179 is on offer, so the escape option is not needed. Choosing it means backing an alternative convention against the standard one.

A globe is ruled by two families of lines that together form the graticule. Parallels of latitude run east–west, measure angular distance north or south of the Equator, extend from 0° to 90° in each hemisphere and never meet. Meridians of longitude run north–south, measure angular distance east or west of the prime meridian at Greenwich, extend 0° to 180° each way, and all of them converge at the two poles. The asymmetry between the two families is exactly what this question tests. Every meridian is half of a great circle — a circle whose plane passes through the centre of the Earth — so any two opposite meridians together make one complete great circle. Among parallels, only the Equator is a great circle; every other parallel is a small circle whose radius falls off with the cosine of the latitude until, at 90°, it vanishes to a point. That is why a 1° graticule carries 179 parallels but 360 meridians, and why 90° N and 90° S are the only two latitude values that cannot be drawn as lines at all. One further distinction is the source of every disagreement about the count: a latitude is an angular coordinate, a parallel is a drawn circle. There are 181 whole-degree values of latitude from 90° S to 90° N inclusive; only 179 of them can be drawn.

Reason this out rather than recalling a number — three of the four options are near neighbours, and the derivation takes ten seconds. Build the count in three pieces: 89 parallels north of the Equator, 89 south, and the Equator itself. Then ask the one question that actually decides the item — do the poles count as parallels? A parallel must be a circle; a pole is a point; so they do not, and the answer is 179 rather than 181. That single decision is the whole question, and each distractor is a different way of failing it: 178 forgets the Equator, 180 confuses the angular span with the line count, and "None of the above" is what you are forced into if you decide the poles do count. Two cross-checks are worth carrying into the exam hall. First, the equivalent figure for meridians at 1° spacing is 360, not 179, because meridians converge at the poles instead of shrinking away — the prime meridian, 179 more eastward, the 180° meridian and 179 westward. Second, 179 is odd, as it must be, and any even answer means you have dropped the Equator. The word in the stem that decides the whole item is "drawn". Values of latitude and circles of latitude are not the same set — there are 181 whole-degree values from 90° S to 90° N, and 179 circles — so a question that asks how many can be drawn is asking for circles. A second habit worth building is to notice which parallels are not in the 179 at all. Of the five that every syllabus names, only the Equator falls on a whole degree: the Tropics of Cancer and Capricorn sit at about 23°26′ and the Arctic and Antarctic Circles at about 66°34′, because both are set by the tilt of the Earth's axis rather than by any round number — and that tilt is itself shrinking by roughly half an arcsecond a year, which walks the tropics about 15 metres towards the Equator annually.

• Parallels at 1° spacing number 179 — 89 in the Northern Hemisphere, 89 in the Southern, plus the Equator; 90° N and 90° S are points, not circles, so they cannot be drawn
• Meridians at 1° spacing number 360 — the prime meridian, 179 to the east, the 180° meridian and 179 to the west — so a full 1° graticule carries 539 lines
• The Equator is the only parallel that is a great circle, about 40,075 km round; every other parallel is a small circle of length 2πR cos φ — roughly 20,000 km at 60° latitude and zero at the poles
• Opposite meridians pair into complete great circles, so the 360 meridians make up 180 great circles; each individual meridian is a semicircle from pole to pole
• On the WGS84 ellipsoid (equatorial radius 6,378,137 m, flattening 1/298.257223563) one degree of latitude is 110.574 km at the Equator and 111.694 km at the poles, while one degree of longitude falls from 111.319 km at the Equator to 78.847 km at 45°, 55.800 km at 60° and zero at the poles
• One minute of latitude is the nautical mile, fixed at exactly 1,852 m by the International Extraordinary Hydrographic Conference at Monaco in 1929; the metre was defined in 1791 as one ten-millionth of the pole-to-Equator meridian quadrant, whose modern value is 10,002 km
• Of the five parallels every syllabus names, only the Equator lies on a whole degree and so belongs to the 179 — the Tropics sit at about 23°26′ and the Polar Circles at about 66°34′, both fixed by the Earth's axial tilt, which is itself decreasing by roughly 0.47 arcsecond a year
• Latitude runs 0°–90° north and south, longitude 0°–180° east and west — the different ranges are why the two families of lines give different counts

• Counting the poles as parallels. That convention gives 181, not 180, and would force "None of the above"; the standard Indian count excludes them and gives 179.
• Dropping the Equator, which produces 178. The Equator is 0° latitude and a parallel in its own right — and the only one that is a great circle.
• Carrying the parallel count over to meridians. Meridians at 1° spacing number 360, because they converge at the poles rather than shrinking to nothing.

BPSC asks the bare graticule count as a one-line factual with a "None of the above" safety valve, and that fourth option is not decorative — it is there because the count is convention-dependent, which is also why this answer is a medium-confidence derivation rather than a certainty. UPSC almost never asks the count itself; it uses the same geometry indirectly, in items about which latitudes pass through which places, about great-circle routes and shortest paths, or about converting longitude into time. Learn the structure of the graticule rather than the single number.

No directly related past PYQ was found.

• practice — not a real PYQ

  How many meridians of longitude can be drawn on a globe at 1 degree interval?

  • (a)179
  • (b)180
  • (c)360
  • (d)361

  Answer(c) 360 — the prime meridian, 179 more to the east, the 180° meridian, and 179 to the west. Unlike parallels, meridians converge at the poles rather than shrinking to a point, so none of them is lost.

• practice — not a real PYQ

  Which one of the following parallels of latitude is a great circle?

  • (a)Tropic of Cancer
  • (b)The Equator
  • (c)Arctic Circle
  • (d)45° N

  Answer(b) The Equator — its plane passes through the centre of the Earth, so it divides the globe into two equal halves. Every other parallel is a small circle whose length falls as the cosine of its latitude.