Observance Daily What day is today, and why are we celebrating it?
Prime Meridian Day is marked every November 1, celebrating the line of 0° longitude at the Royal Observatory, Greenwich, London, which defines global time and longitude.
History of Prime Meridian Day
Before a single standard existed, different countries used different meridians, confusing navigation and timekeeping. A ship’s captain might reckon longitude from Paris while the chart in his hands was drawn from Greenwich; railway timetables multiplied the confusion on land. As trade, travel and the telegraph stitched the world closer together in the 19th century, the need for one agreed zero line became impossible to ignore.
The answer came at the International Meridian Conference, held in Washington, D.C., in October 1884, with delegates from 25 countries. On October 13, 1884, Greenwich was chosen as the international prime meridian by 22 votes to 1, with France and Brazil not voting and Haiti voting against, according to contemporary accounts. The conference concluded on November 1, 1884 — which is why Prime Meridian Day is marked on November 1.
The choice of Greenwich was not a foregone conclusion. France long championed Paris as the zero meridian, and French maps continued to use it for decades. But Greenwich had practical advantages: by the 1880s the great majority of the world’s shipping already used charts based on Greenwich, and the Royal Observatory there had been publishing precise astronomical data for navigators since the 18th century. The vote simply ratified what most seafarers were already doing.
Why Prime Meridian Day matters
The prime meridian is the reference from which longitude is measured east and west up to 180°, and it is the basis for Greenwich Mean Time and the world’s time zones. Every time zone on Earth is defined by its offset from the line at Greenwich; every GPS receiver in every phone triangulates its position against a coordinate system that begins there.
For visitors, the line itself has become a small pilgrimage. At the Royal Observatory in Greenwich Park, a brass strip set into the courtyard marks 0° longitude, and standing astride it you can be in the Eastern and Western Hemispheres at once — one foot in each half of the world. It is one of the most photographed lines on the planet, and a reminder that even the most abstract human agreements can be given a physical home.
Prime Meridian Day is worth marking because it celebrates something easy to take for granted: the quiet infrastructure of agreement that lets the modern world work. Time zones, flight plans, shipping lanes and satellite navigation all rest on the decision taken in Washington in 1884. A single line, drawn by diplomats and astronomers, still organises the day of nearly everyone alive.
How to mark Prime Meridian Day
You do not need to travel to London to mark Prime Meridian Day. Look up your own longitude and work out how many degrees — and how many time-zone hours — stand between you and Greenwich. If a trip to London is ever on your plans, put the Royal Observatory’s meridian line on the itinerary and take the classic photograph with a foot in each hemisphere. And the next time your phone finds your location in seconds, spare a thought for the brass strip in a Greenwich courtyard where the whole system begins.
Prime Meridian Day: frequently asked questions
When is Prime Meridian Day? It is marked every November 1, the anniversary of the conclusion of the International Meridian Conference in 1884.
Where is the prime meridian? At the Royal Observatory, Greenwich, London — the line of 0° longitude.
What was decided in 1884? Delegates from 25 countries at the International Meridian Conference in Washington, D.C., chose Greenwich as the international prime meridian by 22 votes to 1.
Why November 1? The conference concluded on November 1, 1884, so the anniversary is marked on that date.
Can you stand on the line? Yes — at the Royal Observatory in Greenwich, a brass strip marks 0° longitude, and visitors straddle the Eastern and Western Hemispheres.
Related November 1 observances
Prime Meridian Day shares its date with World Vegan Day and All Saints’ Day.
Read more about November 1 on November 1 Holidays, Observances and History.