![]() ![]() The same Latin stem gives rise to the terms a.m. Likewise, the Sun crosses the celestial meridian at the same time. The term meridian comes from the Latin meridies, meaning "midday" the subsolar point passes through a given meridian at solar noon, midway between the times of sunrise and sunset on that meridian. Multiple locations for the geographical meridian meant that there was inconsistency, because each country had their own guidelines for where the prime meridian was located. Many years later around the 19th century there were still concerns of the prime meridian. This prime meridian was used to provide measurement of the earth, but had many problems because of the lack of latitude measurement. The first prime meridian was set by Eratosthenes in 200 BCE. The length of a meridian on a modern ellipsoid model of Earth ( WGS 84) has been estimated as 20,003.93 km (12,429.87 mi). A meridian is half of a great circle on Earth's surface. On a Mercator projection or on a Gall-Peters projection, each meridian is perpendicular to all circles of latitude. The position of a point along the meridian is given by that longitude and its latitude, measured in angular degrees north or south of the Equator. In other words, it is a line of longitude. In geography and geodesy, a meridian is the locus connecting points of equal longitude, which is the angle (in degrees or other units) east or west of a given prime meridian (currently, the IERS Reference Meridian). Meridians run between the North and South poles. ![]()
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