A '''nautical mile''' is a [[physical unit|unit]] of distance, or, as physical scientists like to call it, [[length]]. It is widely used around the world for maritime and aviation purposes. The derived unit of [[speed]] is the [[knot_(speed)|knot]], defined as one nautical mile per [[hour]].
==Definition==
The nautical mile was historically defined as a [[minute of arc]] along a [[great circle]] of the Earth.
It can therefore be measured on a [[meridian (geography)|meridian]] as change of latitude on a [[nautical chart]]. Slight variations in national definitions were settled in [[1929]], when the
[[International Extraordinary Hydrographic Conference]], [[Monaco]] adopted a definition of 1 nm = [[1 E3 m|1,852 metres]]. The [[United States]] adopted it in [[1954]]. The Royal Hydrographic Office of the [[United Kingdom|UK]] converted in [[1970]]. Prior to the adoption of the international nautical mile, the nautical mile used by the [[United Kingdom|UK]] was 6080 [[foot (unit of length)|feet]], or 1853.184 [[metre]]s, and that of the [[United States|US]] was 6080.2 ft (1853.249 m).
==Abbreviations==
The [[Bureau International des Poids et Mesures|BIPM]] in its SI brochure lists the nautical mile in the table of units "currently accepted" for use with SI without using a symbol, saying in a [http://www1.bipm.org/en/si/si_brochure/chapter4/table8.html footnote]: "As yet there is no internationally agreed symbol."
The abbreviation "'''nm'''" is used. The same abbreviation, "nm", is also used to denote nanometre in the [[SI]] though little confusion is generated from this, as the contexts of use are very different. For example, the 'nm' abbreviation is typically seen in listings of aircraft flight range, but listed next to the range in kilometers (km). ([http://www.airliners.net/info/stats.main?id=400 Example] of nm, km together- in performance section). Also, the large ratio of 1.852 trillion makes confusion unlikely in most cases. The abbreviation [[nmi]] is also used.
==See also==
*[[conversion of units]]
*[[orders of magnitude (length)]]
[[da:Sømil]]
[[de:Seemeile]]
[[et:Meremiil]]
[[es:Milla náutica]]
[[fr:Mille nautique]]
[[nl:Zeemijl]]
[[ja:海里]]
[[pl:mila morska]]
[[ru:Морская миля]]
[[sl:Morska milja]]
[[zh:海里]]
[[sv:Sjömil]]
[[fi:Meripeninkulma]]
[[he:מייל ימי]]
[[Category:Navigation]]
[[Category:Units of length]]
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