November 1, 2012 - Prime Meridian Day

You know how the world is divided up into different latitudes and longitudes? This makes sense, because we can use these numbers to communicate about, and map, and travel to very precise locations.

 But did you ever wonder who divvied up the world in this way?

When people explored regions, even back in ancient times, they often drew maps of what they saw. Many people used coordinate systems on their maps—numbered or lettered lines running both vertically and horizontally, as an aid to finding and talking about features on the map. However, mapmakers' systems were different from one another, and that could be confusing!

The wealthiest and most powerful nations in the world used some of that wealth and power to explore faraway places, and so the latitude/longitude systems they used became widespread. Still, many different nations counted longitude with a different starting point, a different line of longitude being zero, a different “Prime Meridian.” For example, geographers in France counted the line of longitude running through Paris as the Prime Meridian, but geographers in England counted the line of longitude running through Greenwich (just outside of London) as the Prime Meridian.

This line marks the spot
where East meets West!

And when you are traveling all over the world, and writing letters to people all over the world, and doing cooperative science experiments with people all over the world, that is really confusing!

By the way, it was obvious to everyone where the zero-line of latitude should be—the equator. The equator is an imaginary line that runs around the planet's “waist,” the mid-point between the two poles that serve as the axis of rotation, and it's a very obvious and “fair” location for the starting point of latitude. But there just isn't an obvious and objective spot to start longitude. Should it be the line that intersects Tokyo, Japan? Cairo, Egypt? New York, United States?

Any of these lines would work as well as any other line—so how did people choose the Prime Meridian?

If you go to Greenwich, England, you can
have one foot in the Western Hemisphere
and the other in the Eastern Hemisphere.

On this date in 1884, representatives of 25 nations around the world met in Washington, D.C., to set up a standard latitude/longitude system (and also standard time zones). Probably because Great Britain was an important colonial power, but also because the United States of America already used it, the British system of longitude, with the Prime Meridian running through Greenwich in Great Britain, was finally chosen. One nation (Haiti) voted against this, and two nations (Brazil and France) refused to vote on the issue, but 22 “yea” votes carried the day, and the world finally had one standard Prime Meridian.

Find out more about longitude at Kids Geo.

Also on this date:

Day of the Dead (Dia de los Muertos) 

Continental-drift guy / geophysicist Alfred Wegener's birthday