Prime Meridian Day is marked on November 1 each year. In 1884, the prime meridian was defined by the location of the large Airy Transit Circle telescope at the Royal Observatory in Greenwich, England. Sir George Biddell Airy — the seventh Astronomer Royal — designed the legendary telescope in 1850. The Airy Transit Circle’s crosshairs defined 0° longitude. Today, we celebrate the prime meridian and its applications, including dividing the Earth into the Eastern and Western Hemispheres and setting up the global time zones.
History of Prime Meridian Day
U.S. President Chester A. Arthur played host to the International Meridian Conference held on October 1, 1884, in Washington D.C. The conference was called to set up global time zones and select the 0° official longitude, also called the prime meridian. Over 41 delegates representing 25 countries were in attendance. Out of the nations present, Greenwich got affirmative votes from 22 countries, France and Brazil did not vote and Haiti voted against.
Prior to the conference, the world lacked a standard prime meridian. Several locations were regarded as 0° longitude since lines of longitude are imaginary lines. On October 13, Greenwich in England was declared as the international prime meridian. Prime Meridian Day is celebrated every year to commemorate the occasion.
The prime meridian passed through the middle of a transit instrument in the observatory in Greenwich. The observatory would later become the Royal Observatory, Greenwich. The observatory was relocated to Hailsham, East Sussex after the Second World War, even though the prime meridian still went through Greenwich. The Hailsham site would later be called the Observatory Science Center, and after some time, the Royal Observatory was reestablished at Greenwich.
The treaty signed at the International Meridian Conference established the International Date Line in the Pacific Ocean at 180° longitude. Several meridians exist, there is one for every 15° with a one-hour time difference between them. However, some countries do not follow the hour change rule. China, for example, employs a single time zone, despite having five meridians crossing its terrain.
Prime Meridian Day timeline
Great Britain establishes its meridian at the Royal Observatory, Greenwich.
Sir George Biddell Airy builds the Airy Transit Circle telescope.
U.S. President Chester Arthur hosts the International Meridian conference on October 1 in Washington, D.C.
The International Meridian Conference selects the Greenwich Meridian to serve as the International Prime Meridian on October 13.
Prime Meridian Day FAQs
What is the antimeridian?
The antimeridian sits at a longitude of 180°. Together with the prime meridian, it forms a giant circle around the Earth, dividing it into the Eastern Hemisphere and Western Hemisphere.
What happens if you cross the International Date Line?
The IDL, an imaginary line, cuts across the Earth from the North to the South Pole in the center of the Pacific Ocean. Crossing it usually means you lose or gain a day, depending on the direction you are traveling.
Are there other prime meridians?
Yes, the prime meridian is an imaginary line, meaning it’s arbitrary and can be located anywhere. There are over 24 prime meridians.
Prime Meridian Day Activities
Visit the observatory
Pay a visit to Greenwich’s Royal Observatory to learn more about the prime meridian. You can also swing by Hailsham’s Observatory Science Center for the complete experience.
Explore the global time zones
Learning is always fun. Research the global time zones and note their peculiarities. You never know, it might come in handy on trivia night.
Search for your location
Find the exact coordinates for your home, office, or school. It should make a fun reply the next time someone asks for your address.
5 Facts About Time Zones That Will Blow Your Mind
Dead zone
Antarctica has no official time zone because it’s mostly uninhabited.
Neverending sunshine
The world’s poles experience uninterrupted daylight for six months followed by uninterrupted darkness for the remaining six months of the year.
High numbers
France is the country with the most time zones while the United States and Russia follow close behind with 11 apiece.
Time travel
Despite the prime meridian passing through the country, France is a full hour behind Greenwich Mean Time.
Popular choice
The IERS Reference Meridian is the most widely adopted modern meridian.
Why We Love Prime Meridian Day
It gave us two hemispheres
There are lots of reasons to love Prime Meridian Day. Among these is the fact that it divides the earth into the Eastern and Western Hemispheres.
The starting point for measuring distance
The prime meridian represents 0°longitude. When measuring the distance around the Earth, the prime meridian is the starting point.
It’s the basis for global time zones
The prime meridian serves as the basis for time zones around the world. Without it, we would be stuck in limbo.
Prime Meridian Day dates
| Year | Date | Day |
|---|---|---|
| 2025 | November 1 | Saturday |
| 2026 | November 1 | Sunday |
| 2027 | November 1 | Monday |
| 2028 | November 1 | Wednesday |
| 2029 | November 1 | Thursday |
