Meridian

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Meridians are imaginary lines used to describe places on the Earth. Meridians are lines of longitude drawn from the North Pole to the South Pole. Similar lines that go around the Earth in the opposite direction are called circles (or lines) of latitude. The best known circle of latitude is the Equator.

With latitude, scientists said the best place to start measuring from was the Equator. With longitude, they were not sure where to start, so at different times in history, different places were used. Scientists today mostly agree to measure from what they call the Prime Meridian. It is the line of longitude that goes through the Royal Greenwich Observatory in Greenwich, England. They decided this at the 1884 International Meridian Conference.

Meridians, as lines of longitude, are measured in degrees, just like angles. The Prime Meridian, as the starting point, is 0 (zero). Lines west of the Prime Meridian are sometimes said as west, such as "the longitude of Los Angeles, California is 118 degrees west". Other times it is said as a negative number; "the longitude of Los Angeles, California is -118 degrees". Going the other direction (east) is always said as a positive number; "The longitude of Mecca is [about] 40 degrees east." or "The longitude of Mecca is [about] 40 degrees."

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