UK doesn't follow GMT in the summer Skewed Gravity Apart from serving as a navigational reference point, the local mean time at the Greenwich Meridian now also served as the basis for the global time standard, Greenwich Mean Time (GMT), before being replaced by UTC in the 1960s. While latitudes are defined by the Earth's shape and movement-the poles at 90° latitude are where the Earth's axis meets the Earth's surface and the equator at 0° latitude marks the middle point between the poles-there is no natural reason for any longitude to be used as the prime meridian.Īt the International Meridian Conference in 1884, with multiple candidates to choose from, that honor was bestowed upon the longitude of the Airy Transit Circle in Greenwich. To understand how there can be two different prime meridians, both being in the correct location for their purposes, it's important to bear in mind that meridians and longitudes are a human invention, so there is essentially no right or wrong way to place them. Since the location of this original prime meridian is defined by the location of the telescope, it cannot be wrong: it is always where the telescope is. It is defined by the location of the telescope, which was originally used to measure the passage of certain stars to feed data into an astronomical coordinate system, which, in its day, served as the basis for global navigation and timekeeping. However, although the world is now using an updated version, the location of the prime meridian is not wrong as such-it's just a different kind of meridian. Navigation systems such as the GPS now use the IERS Reference Meridian (IRM), which runs about 334 feet (102 meters) east of the observatory. It is true that the meridian that runs through the observatory has lost its status as the world's sole reference point for longitude. The Northern and Southern Hemispheres Not Wrong, Just Different So, have they been luring tourists to the wrong place for decades? However, if you follow your GPS device to 0° longitude, you will end up a good distance away from the famous line marking the meridian in the observatory's Meridian Courtyard. The observatory is home to the Airy Transit Circle, a telescope designed by George Biddell Airy in the 19th century, which marks the location of the prime meridian, the line running along 0° of longitude, where the Earth's western and eastern hemispheres meet. Since everyone is running around with their own GPS tracker or mobile phones with GPS capability, a visit to the Royal Observatory in Greenwich, London may have become a slightly disappointing affair for some. ©Daniel Case GPS Shows Different Meridian The line and monument marking the location of the original Greenwich Meridian in the Meridian Courtyard at the Royal Observatory in Greenwich, London, UK.
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