Prime Meridian Trivia
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48 free Prime Meridian trivia questions with answers — geography quiz, new questions added Aug 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 48 questions with answers and explanations. Play the quiz
Q 01What is the longitude of the prime meridian?
Nought
Nought: the prime meridian is the line of 0° longitude by definition, the starting point from which every other longitude is measured east or west.
Q 02What marked the prime meridian line in the Royal Observatory's courtyard for many years?
A brass strip
A brass strip: for decades a brass strip set into the courtyard of the Royal Observatory at Greenwich marked the line, and it was later replaced by stainless steel.
Q 03Which two hemispheres does the prime meridian divide the Earth into?
Eastern and Western
Eastern and Western: the prime meridian and its antimeridian split the globe into the Eastern and Western Hemispheres, a boundary fixed by convention rather than by the Earth's rotation.
Q 04In which year did the International Meridian Conference adopt Greenwich as the world's prime meridian?
1884
Forty-one delegates met that October.
Q 05In which city was the International Meridian Conference held?
Washington, D.C.
Washington, D.C.: the delegates met in the US capital that October, invited by the American government under an Act of Congress of 3 August 1882.
Q 06Which US president requested the International Meridian Conference?
Chester A. Arthur
Chester A. Arthur: president from 1881 to 1885, he issued the invitations under the Act of 3 August 1882 that authorised him to call the conference.
Q 07How many countries voted to adopt the Greenwich meridian at the meridian conference?
22
Forty-one delegates attended in total; the French abstained.
Q 08Which country abstained from the meridian conference vote and kept its own meridian for decades?
France
It argued for a neutral line through the Azores or the Bering Strait.
Q 09In what year did the holdout nation finally adopt Greenwich as the beginning of the universal day?
1911
1911: a French law of March 1911 aligned the country's legal time with Greenwich, though its wording avoided the name; French marine charts followed in 1914.
Q 10What phrase did the French use instead of the word Greenwich once they gave in?
Paris mean time, retarded by 9 minutes and 21 seconds
Paris mean time, retarded by 9 minutes and 21 seconds: the French law set legal time that way because the Paris Observatory lies about 2°20' east of Greenwich, a 9-minute-21-second difference in mean time.
Q 11Which Astronomer Royal fixed the Greenwich prime meridian in 1851 with his new transit circle?
George Airy
Earlier transit instruments, the first bought by Halley in 1721, sat about 43 metres further west.
Q 12How far east of the Greenwich courtyard marker does a GPS receiver place the meridian?
About 102 metres
About 102 metres: satellite-based zero longitude lies 102.5 m east of the courtyard line at Greenwich, 5.3 arcseconds away, because a plumb line there is deflected by local gravity while satellites reference the Earth's centre of mass.
Q 13What is the name of the international standard prime meridian adopted in 1984?
IERS Reference
Q 21With which modern islands are the ancient geographer's 'Fortunate Isles' usually associated?
The Canaries
The Canaries: the Fortunate Isles of Greek tradition are usually identified with the Canary Islands, the westernmost land then known, so longitude counted eastward from them stayed positive.
Q 22Per the 4th-century Surya Siddhanta, India's ancient zero longitude passed through which city?
Ujjain
Ujjain: the Surya Siddhanta's meridian ran through Ujjain, then known as Avanti, and through Rohitaka, modern Rohtak, on its way north.
Q 23Which 1494 Spain–Portugal treaty used a mid-Atlantic line where the compass pointed due north?
Tordesillas
The line was settled at 370 leagues west of Cape Verde.
Its plane passes through the Earth's centre of mass rather than following a plumb line at Greenwich.
Q 14Since what year has the Earth-centred reference meridian been the international standard?
1984
1984: that year the satellite-based, Earth-centred zero meridian took over as the international standard, a century after the Greenwich line was chosen.
Q 15How fast does Airy's transit circle drift relative to Earth-centred zero longitude?
About 2.5 centimetres a year
About 2.5 centimetres a year: the Eurasian plate carries the Greenwich instrument north-eastward at roughly 2.5 cm a year relative to the satellite-defined frame, whose origin is the Earth's centre of mass.
Q 16What was installed at Greenwich in December 1999 to mark the meridian across the night sky?
A green laser
A green laser: a green laser installed at the Royal Observatory for the millennium shines north along the meridian line at night, visible for miles on a clear evening.
Q 17How many countries does the Greenwich meridian pass through between the North and South Poles?
Eight
Eight: three in Europe, the United Kingdom among them, then Algeria, Mali and Burkina Faso, and two more states on the Gulf of Guinea coast before open ocean and Antarctica.
Q 18Which is the southernmost African country crossed by the Greenwich meridian?
Ghana
After leaving Ghana the line runs down through the Gulf of Guinea and the Atlantic to Antarctica.
Q 19What is 'Null Island'?
The point where the prime meridian meets the equator
The point where the prime meridian meets the equator: 0° latitude, 0° longitude is open ocean in the Gulf of Guinea, and mapmakers joke that mis-geocoded data lands on this imaginary island.
Q 20Which ancient geographer's Geographia listed coordinates for some 8,000 places 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 24Which island did Cardinal Richelieu's 1634 conference choose as the prime meridian?
El Hierro
El Hierro: the westernmost Canary island, then called Ferro, was chosen at Richelieu's 1634 conference; Delisle later fixed it at exactly 20 degrees west of the French capital's meridian.
Q 25Through which island did Mercator draw the prime meridian on his 1541 globe?
Fuerteventura
Fuerteventura: Mercator's terrestrial globe of 1541 drew the zero meridian through Fuerteventura; his later maps moved it to the Azores on the theory that magnetic north marked a natural line.
Q 26How 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 27Whose Nautical Almanac, first issued for the year 1767, made Greenwich the reference point for navigators?
Nevil Maskelyne's
Nevil Maskelyne's: as Astronomer Royal he launched the Nautical Almanac, whose lunar-distance tables were computed for the Greenwich meridian, so navigators everywhere, even in French translation, reckoned from Greenwich.
Q 28Which clockmaker developed the marine chronometer that transformed the finding of longitude at sea?
John Harrison
John Harrison: his fourth sea clock, H4, lost only seconds on a 1761-62 voyage to Jamaica, proving a timekeeper could carry Greenwich time and so fix longitude at sea.
Q 29Which king founded the Royal Observatory at Greenwich in 1675?
Charles II
Charles II: he founded the observatory by royal warrant in June 1675 to fix longitude for navigation, and Christopher Wren chose the hilltop site of the old Greenwich Castle.
Q 30At what time does the red time ball on the Greenwich observatory drop each day?
1 pm
1 pm: the ball is hoisted just before the hour and falls at exactly 1 pm, a signal Astronomer Royal John Pond introduced in 1833 so ships on the Thames could set their chronometers.