Geographical mile: Difference between revisions
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The '''geographical mile''' is a unit of length determined by 1 [[minute|minute of arc]] along the [[Earth]]'s [[equator]], approximately equal to 1855.325 [[metre]]s (6087.025 international [[foot (length)|feet]]). Any greater precision depends more on choice of standard than on more careful measurement: the length of the [[equator]] in the [[World Geodetic System]] WGS-84 is 40,075,016.6856 m which makes the geographical mile 1855.3248 m, while the [[International Astronomical Union]] standard IAU-2000 takes the [[equator]] to be 40,075,035.5351 m making the geographical mile 1855.3257 m, almost a millimetre longer. | The '''geographical mile''' is a unit of length determined by 1 [[minute|minute of arc]] along the [[Earth]]'s [[equator]], approximately equal to 1855.325 [[metre]]s (6087.025 international [[foot (length)|feet]]). Any greater precision depends more on choice of standard than on more careful measurement: the length of the [[equator]] in the [[World Geodetic System]] WGS-84 is 40,075,016.6856 m which makes the geographical mile 1855.3248 m, while the [[International Astronomical Union]] standard IAU-2000 takes the [[equator]] to be 40,075,035.5351 m making the geographical mile 1855.3257 m, almost a millimetre longer. | ||
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*[[mile]] for the various other miles in use | *[[mile]] for the various other miles in use | ||
*[[nautical mile]] | *[[nautical mile]] | ||
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[[Category:Units of length]] | [[Category:Units of length]] | ||
Latest revision as of 20:51, 11 April 2009
The geographical mile is a unit of length determined by 1 minute of arc along the Earth's equator, approximately equal to 1855.325 metres (6087.025 international feet). Any greater precision depends more on choice of standard than on more careful measurement: the length of the equator in the World Geodetic System WGS-84 is 40,075,016.6856 m which makes the geographical mile 1855.3248 m, while the International Astronomical Union standard IAU-2000 takes the equator to be 40,075,035.5351 m making the geographical mile 1855.3257 m, almost a millimetre longer.
The unit is not used much; it is closely related to the nautical mile, which was originally determined as 1 minute of arc along a great circle of the Earth but is nowadays defined as exactly 1852 metres.
The Danish and German geographical mile (geografisk mil and geographische Meile or geographische Landmeile, respectively) is 4 minutes of arc, and was defined as approximately 7421.5 metres by the astronomer Ole Rømer of Denmark. In Norway and Sweden, this 4 minute geographical mile was mainly used at sea (sjømil), up to the beginning of the 20th century.
See also
- conversion of units
- Medieval weights and measures for details of the geographical league of France
- mile for the various other miles in use
- nautical mile