Longitude
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Longitude is a geographic coordinate that specifies the east-west position of a point on the surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees
The clockwork in John Harrison's H4 marine chronometer on display at the Royal Observatory, Greenwich
Marine sandglass MMM
Meridian (geography)
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In geography and geodesy, a meridian is the locus connecting points of equal longitude, which is the angle east or west of a given prime meridian. In other words, it is a coordinate line for longitude
Longitude
…surface of the Earth, or another celestial body. It is an angular measurement, usually expressed in degrees and denoted by the Greek letter lambda (λ). Meridians are imaginary semicircular lines running from pole to pole that connect points with the same longitude. The prime meridian defines 0° longitude; by…
Meridians run between the North and South poles.
The astronomic prime meridian at Greenwich, England. The geodetic prime meridian is actually 102.478 meters east of this point since the adoption of WGS84.
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