![]() It is the positioning of this neighbouring equipment, just 5.79 metres (19ft) away, which eventually became the basis for international time. The fourth Meridian was established in 1851 by yet another Astronomer Royal, Sir George Airy, who set up new measuring equipment in a room alongside Bradley’s original equipment. The third was defined by another Astronomer Royal, James Bradley, in the mid 18th century, and is still used as the basis for map-making in Britain today. In 1725, Edmund Halley, the second Astronomer Royal established a second Meridian. The earliest is Flamsteed’s, named after the first Astronomer Royal, which was established in 1675. It is, in fact, one of a countless number of meridians in the world – every possible line of longitude is one – and until a little over a century ago, many different ones were adopted by different countries for map-making, navigation and timekeeping.Įven today, it can be confusing as there are four Meridians all passing through the Old Royal Observatory. It is the basis for timekeeping and navigation throughout the world. The zero degrees longitude line runs from the North Pole to the South Pole, passing directly through the Old Royal Observatory building at Greenwich in South East London. The Americas, the western part of the British Isles (including Ireland and Wales), and the northwestern part of Africa are land masses in the Western Hemisphere.In the same way that the Equator separates the Northern and Southern hemispheres, the Greenwich Meridian divides the East from the West. The Western Hemisphere is west of the prime meridian and east of the International Date Line. Most of Earth's landmasses, including all of Asia and Australia, and most of Africa, are part of the Eastern Hemisphere. The Eastern Hemisphere is east of the prime meridian and west of the International Date Line. This is similar to the way the Equator serves as the 0° latitude line and divides Earth into the northern and southern hemispheres. The prime meridian and the International Date Line create a circle that divides Earth into the Eastern and Western Hemispheres. As you pass the International Date Line, you either add a day (going west) or subtract a day (going east.) Hemispheres The meridian at 180° longitude is commonly known as the International Date Line. Earth's longitude measures 360°, so the halfway point from the prime meridian is the 180° longitude line. The prime meridian also helps establish the International Date Line. in Orlando, Florida, United States 4:00 p.m. in Houston, Texas, United States, it would be reported at 12 p.m. ![]() All countries and regions measure their time zones according to UTC. Just as the prime meridian is the standard for longitude, UTC is the standard for time. UTC never changes for daylight savings or anything else. The prime meridian also sets Coordinated Universal Time (UTC). The Greenwich Meridian became the international standard for the prime meridian. They chose the meridian passing through the Royal Observatory in Greenwich, England. President Chester Arthur in 1884, representatives from 25 countries agreed to pick a single, standard meridian. Finally, at an international convention called by U.S. Even different parts of the same country published materials based on local meridians. Cartographers in China published maps with 0° longitude running through Beijing. France published maps with 0° longitude running through Paris. ![]() Different countries published maps and charts with longitude based on the meridian passing through their capital city. Governments did not always agree that the Greenwich meridian was the prime meridian, making navigation over long distances very difficult. However, there is an international agreement that the meridian that runs through Greenwich, England, is considered the official prime meridian. Any line of longitude (a meridian) can serve as the 0° longitude line. The prime meridian is arbitrary, meaning it could be chosen to be anywhere. ![]() The prime meridian is the line of 0° longitude, the starting point for measuring distance both east and west around Earth.
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