Prime Meridian Trivia
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47 free Prime Meridian trivia questions with answers — geography quiz, new questions added Oct 2026.
This prime meridian trivia quiz covers the imaginary line at zero degrees longitude and the century-long argument over where to draw it. The easy questions cover the London borough it runs through, the observatory on the hill, the hemispheres it divides, the year the world agreed on it and the country that sulked. From there the quiz moves through the history: Ptolemy's Fortunate Isles, the ancient Indian meridian through Ujjain, Cardinal Richelieu's El Hierro, Mercator's globe, Maskelyne's Nautical Almanac and why French translations quietly kept Greenwich figures. The hard end covers the 1884 International Meridian Conference in Washington: who called it, how many nations came, how the vote went, what France proposed instead and when Paris finally gave in. Then the modern twist: why a GPS receiver standing on the brass strip does not read zero, the deflection of the vertical, the IERS Reference Meridian, the countries the line crosses today, Null Island and its Soul buoy, and the prime meridians of the Moon, Mercury, Venus and Mars. Every answer was checked against the encyclopaedia entries for the prime meridian, the Greenwich meridian, the International Meridian Conference, the Royal Observatory and Null Island before publishing, and the supporting sentence is stored with each question. Our geography, maps and time zones quizzes are natural next stops.
30 of 47 questions with answers and explanations. Play the quiz
Q 01Where does the prime meridian meet every other line of longitude?
At the two poles
At the two poles: every meridian is half of a great circle running from the North Pole to the South Pole, so they all converge there; the prime meridian is simply the one chosen to count as zero.
Q 02What marked the prime meridian line in the Royal Observatory's courtyard for many years?
A brass strip
A brass strip marked the line once the old observatory became a museum; it has since been replaced by stainless steel, and visitors stand astride it to put one foot in each hemisphere.
Q 03Which two hemispheres does the prime meridian divide the Earth into?
Eastern and Western
Eastern and Western: unlike the equator, which the Earth's spin fixes in place, this dividing line is pure convention, so the two halves are simply whatever the chosen meridian makes them.
Q 04In which city was the International Meridian Conference held?
Washington, D.C.
Washington, D.C. hosted because the call came from the United States: Congress authorised the president in 1882 to invite the world's governments, and their delegates gathered in October 1884.
Q 05Which US president called the 1884 International Meridian Conference?
Chester A. Arthur
Chester A. Arthur issued the invitations under an 1882 Act of Congress; yet his own country did not write standard time into law until 1918.
Q 06Which industry put North America on Greenwich-based time zones in November 1883, a year before the Meridian Conference?
The railways
The railways: tired of juggling scores of local times, the companies switched to a handful of standard zones at noon on 18 November 1883, decades before Congress made the system law.
Q 07Which country abstained from the meridian conference vote and kept its own meridian for decades?
France
France abstained, kept the Paris meridian on its maps for decades, and when it finally adopted Greenwich time in 1911 the law called it 'Paris mean time, retarded by 9 minutes and 21 seconds'.
Q 08Which time standard replaced Greenwich Mean Time as the world's civil time reference in 1972?
Coordinated Universal Time
Coordinated Universal Time, or UTC, is kept by atomic clocks but nudged with leap seconds so that it stays within about a second of mean solar time on the prime meridian.
Q 09Which queen approved a £20,000 reward in 1714 for a practical way to find longitude at sea?
Queen Anne
Queen Anne approved the Longitude Act at the very end of her reign; the commissioners it named had so little to judge that they did not hold a meeting until 1737.
Q 10Which Astronomer Royal fixed the Greenwich prime meridian in 1851 with his new transit circle?
George Airy
George Airy's new transit circle set the line from January 1851, a few metres east of the one before; Britain's own Ordnance Survey never switched, and its maps are still drawn from the older meridian.
Q 11How far east of Greenwich's historic meridian line do satellite navigation devices place zero longitude?
About 100 metres
About 100 metres: satellite zero lies 102 m east of the courtyard line, because the old telescope was levelled against local gravity, which pulls slightly off true there, while satellites orbit the Earth's centre of mass.
Q 12Since 1924 the BBC has broadcast the Greenwich Time Signal as six short tones known as what?
The pips
The pips went on air on 5 February 1924, timed by the Royal Observatory; the last one is now longer than the others so that listeners can tell which tone marks the hour, which begins the instant it starts.
Q 13After leaving Africa, the prime meridian heads south across which ocean?
The Atlantic
Q 21Per the ancient Surya Siddhanta, India's zero longitude passed through which city?
Ujjain
Ujjain, then called Avanti, was the zero point of Indian astronomy; it is still nicknamed the Greenwich of India, and Jai Singh II built one of his five stone observatories there.
Q 22Which 1494 treaty divided newly found lands between Castile and Portugal along a meridian west of Cape Verde?
Tordesillas
Tordesillas moved the dividing line from the Pope's 100 leagues to 370 leagues west of the Cape Verde islands, a shift that later gave Portugal its claim to the eastern bulge of Brazil.
Q 23Which island, then seen as the western edge of the Old World, did Cardinal Richelieu's 1634 conference choose as prime meridian?
El Hierro
The Atlantic: the line leaves land in West Africa and meets none again until Antarctica, one reason that most of the prime meridian's length lies over the sea.
Q 14What carries Greenwich's historic meridian telescope north-east by about 2.5 cm a year relative to modern zero longitude?
Plate tectonics
Plate tectonics: the observatory rides on the Eurasian plate, which creeps north-east at roughly 2.5 cm a year, while today's zero meridian is tied to a satellite-era frame that averages out the motion of all the plates.
Q 15What was installed at Greenwich in December 1999 to mark the meridian across the night sky?
A green laser
A green laser has marked the line across the night sky since 16 December 1999; it shines north from a point above the telescope that defined the meridian and can be seen more than 20 km away in clear air.
Q 16Which of these European countries does the prime meridian pass through?
Spain
Spain sits on the Greenwich line yet keeps Central European Time, an hour ahead: Franco moved the clocks forward in 1940 to align with Germany, and they have never been moved back.
Q 17Which is the southernmost African country crossed by the Greenwich meridian?
Ghana
Ghana: the line clips the far north of Togo on its way south, but it is Ghana's coast, at the port city of Tema, that it finally leaves.
Q 18What name do mapmakers give the spot in the ocean where the prime meridian meets the equator?
Null Island
Null Island is no island at all: so much badly geocoded data defaults to zero latitude and zero longitude that mapmakers gave the empty patch of sea a name; a weather buoy was moored there until 2021.
Q 19Which ancient geographer's Geographia gave coordinates for places across the known world from a single prime meridian?
Ptolemy
Ptolemy: his Geographia counted longitude eastward from the Fortunate Isles, placed west of Africa so that every known place had a positive longitude, a convention Marinus of Tyre had used before him.
Q 20With which modern islands are the ancient prime meridian's 'Fortunate Isles' usually identified?
The Canaries
The Canaries are the usual identification, though other island groups off north-west Africa have their backers; either way the isles were the westernmost land the ancients recorded, a natural place to start counting.
El Hierro, then known as Ferro, stayed on continental maps into the 19th century; geographers later simply fixed its line at exactly 20 degrees west of Paris, so it became the Paris meridian in disguise.
Q 24Before sea clocks, who first proposed finding longitude by timing the eclipses of Jupiter's moons?
Galileo Galilei
Galileo Galilei, who had found the four moons in 1610, pitched them to two governments as a celestial clock; the method proved hopeless on a rolling deck, but on land it later helped surveyors redraw national maps.
Q 25How were longitudes counted in Ortelius's first modern atlas of 1570?
From 0 to 360 degrees
From 0 to 360 degrees: Ortelius's Theatrum Orbis Terrarum numbered longitude right round the globe from its zero, a single eastward count that navigators kept well into the 18th century.
Q 26Whose Nautical Almanac, first issued for the year 1767, made Greenwich the reference point for navigators?
Nevil Maskelyne's
Nevil Maskelyne's almanac tabulated the Moon's position against Greenwich time, so any navigator using its lunar-distance tables was reckoning longitude from Greenwich, whatever flag his ship flew.
Q 27Which clockmaker developed the marine chronometer that transformed the finding of longitude at sea?
John Harrison
John Harrison's fourth timekeeper, the watch-sized H4, kept such good time on a 1761-62 voyage to Jamaica that it showed a clock could carry home-port time across an ocean and so fix longitude at sea.
Q 28Which king founded the Royal Observatory at Greenwich in 1675?
Charles II
Charles II ordered 'a small observatory within our park at Greenwich, upon the highest ground' in June 1675, persuaded that astronomy held the key to finding longitude at sea.
Q 29Greenwich's time ball, first dropped in 1833, was set to fall at what time instead of noon?
1 pm
1 pm: the ball climbs halfway up its mast at 12:55 as a warning, reaches the top at 12:58 and drops exactly on the hour, a signal set up so that ships below could check their chronometers.
Q 30Which country became the first to define its civil time by the Greenwich meridian, in 1868?
New Zealand
New Zealand set a single national time in 1868, eleven and a half hours ahead of Greenwich, so that telegraph offices up and down the country could keep the same opening hours.