Information for "Longitude"
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A location's north–south position along a meridian is given by its latitude, which is (not quite exactly) the angle between the local vertical and the plane of the Equator.
If the Earth were perfectly spherical and homogeneous, then longitude at a point would just be the angle between a vertical north–south plane through that point and the plane of the Greenwich meridian. Everywhere on Earth the vertical north–south plane would contain the Earth's axis. But the Earth is not homogeneous, and has mountains—which have gravity and so can shift the vertical plane away from the Earth's axis. The vertical north–south plane still intersects the plane of the Greenwich meridian at some angle; that angle is astronomical longitude, the longitude you calculate from star observations. The longitude shown on maps and GPS devices is the angle between the Greenwich plane and a not-quite-vertical plane through the point; the not-quite-vertical plane is perpendicular to the surface of the spheroid chosen to approximate the Earth's sea-level surface, rather than perpendicular to the sea-level surface itself.
Intro History Noting and calculating longitude Length of a degree of longitude See also References External links
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|Date of page creation||17:06, 27 October 2015|
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