Geographical mile: Difference between revisions

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.

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-The '''geographical mile''', or '''U.S. survey mile''', is a unit of length determined by 1 [[minute|minute of arc]] along the [[Earth]]'s [[equator]], approximately equal to 1855 [[metre]]s (6087.15 international [[feet]]).
+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.
-(Wikipedia alert! [[mile]] page say it is 1609.347 metres!)
+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 [[Denmark|Danish]] and [[Germany|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.
-It is not the same as the more commonly used [[statute mile]], which is 1609.344 metres (5280 feet), or the [[nautical mile]] which is 1 minute of arc along a [[great circle]] of the Earth (1852 metres, 6076.1 feet). The U.S. survey mile is used almost exclusively by the [[U.S. Coast and Geodetic Survey]].
+==See also==
-'''See also:'''
+*[[conversion of units]]
-* [[Conversion of units]]
+*[[Medieval weights and measures]] for details of the geographical [[league]] of [[France]]
-* [[mile]]
+*[[mile]] for the various other miles in use
+*[[nautical mile]]
+{{ntnes}}
+[[Category:Units of length]]

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Latest revision as of 20:51, 11 April 2009

See also