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first published week of: 08/24/2015
Once called the Prime Meridian of the World, the invisible line running north to south that divides the world into Eastern and Western hemispheres passed through the Airy Transit Circle — a 19th-century telescopic instrument at the Royal Observatory at Greenwich, England.
However, this line of longitude now runs 334 feet (102 meters) east of where it did. What made it shift? A change in finding out which way is down — from using a basin of liquid mercury to relying on satellites around Earth, researchers have found.
Nowadays, any point on Earth's surface can be described by its latitude and longitude — lines of latitude run from east to west, while lines of longitude run from north to south. Although the concept of running a grid of lines over a map to specify places on the Earth was first suggested by ancient Greek astronomer and mathematician Hipparchus in about 150 B.C., the idea did not take off until the Age of Discovery, when explorers began wandering across the globe, beginning in the early part of the 15th century.
Developing ways to pinpoint one's latitude and longitude was one of the greatest scientific endeavors in history, a quest that ultimately took centuries and was a matter of life and death. Navigation at sea was extraordinarily challenging, resulting in countless tragedies because ships could not get a fix on where they were. One example of such a disaster happened in 1707, when four British warships and more than 1,400 lives were lost because storms forced the fleet's navigators off course, making them believe they were safely to the west of the island of Ushant instead of closing in on dangerous rocks near the Isles of Scilly continued…