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{{unit of length||m= 1852|accuracy=4 -->A
nautical mile or
sea mile is a unit of length. It is a non-International System of Units unit used by special interest groups such as
navigators in the shipping and aviation industries. Section 4.1 Table 8 in the
International System of Units 8th ed. (2006) by the Bureau International des Poids et Mesures. It is commonly used in
international law and
Treaty, especially regarding the limits of
territorial waters. It developed from the geographical mile.
Definition
The international standard definition is: 1 nautical mile = exactly. This corresponds approximately to one
Minute of arc of
latitude along any meridian.
Unit symbol
There is no widely accepted international standard symbol for the unit nautical mile. The preferred abbreviation of the IEEE is
nmi, IEEE guidelines for authors while
M is used by the BIPM and the maritime authorities of the USA Positions, Distances, Directions, Compass; Office of Coastal Survey, NOAA, USA, and Canada POSITIONS, DISTANCES, DIRECTIONS, COMPASS, Ministry of Fisheries and Oceans, Canada. For aviation use, the preferred abbreviation of the
ICAO is
NM. NOTIFICATION OF ANNEX DIFFERENCES (Presented by Australia)International Civil Aviation Organisation, Sixth Meeting of CNS/MET Sub Group of APANPIRG, Bangkok, Thailand, 15 to 19 July 2002, The abbreviation
nm, though conflicting with the SI symbol for the
nanometre, is also in widespread use.
Conversions to other units
One nautical mile converts to:
- (exact)
- 1.150779 mile (exact: )
- (exact:
- (exact: )
- (exact: )
- 10 common-definition Cable length (exact, as one common definition of "cable")
- 10.126859 "ordinary" (100-fathom) Cable length (exact: ordinary cables)
- 12.152231 US Navy (120-fathom) Cable length (exact: US Navy cables)
- 0.998383 equatorial arc minutes = traditional geographical miles (approx.)
- 0.9998834 mean meridian arc minutes = mean historical nautical miles (approx.)
History
The nautical mile was historically defined as a minute of arc along a
meridian (geography) of the Earth, making a meridian exactly 180×60 = historical nautical miles. It can therefore be used for approximate measures on a meridian as change of
latitude on a nautical chart. The originally intended definition of the metre as 10-7 of a half-meridian makes the mean historical nautical mile exactly (2)/ = historical metres. Based on the current IUGG meridian of (standard) metres the mean historical nautical mile is .
The historical definition differs from the length-based standard in that a minute of arc, and hence a nautical mile, is not a constant length at the surface of the Earth but gradually lengthens with increasing distance from the equator, as a corollary of the Earth's
oblateness, whence the need for "mean" in the preceding sentence. According to WGS84, the
radius of curvature in a meridian plane is at the poles and at the Equator. By the definition of latitude#Common "latitude", the length of a minute of arc depends on the radius of curvature. This radius generally does not pass through Earth's center, except for the latitudes of 0° (equator) and 90° (poles). This length equals about at the poles and at the Equator, a variation of one percent.
The length of a minute of arc defined by
latitude#Geocentric latitude also depends on the radius of curvature along a meridian on the surface of the Earth, but a specific length occurs at a different latitude because a surface feature's geocentric latitude differs by as much as 12 arc-minutes (at 45°) from its geodetic latitude. The naive definition of an arc minute as the distance over which one's (three-dimensional) trajectory turns one minute when sailing due north corresponds to geodetic latitude; if instead one measures it by the turning of a line between the vessel and the center of the earth this corresponds to geocentric latitude.
Other nations had different definitions of the nautical mile. This variety in combination with the complexity of angular measure described above along with the intrinsic uncertainty of geodetically derived units mitigated against the extant definitions in favor of a simple unit of pure length. International agreement was achieved in 1929 when the International Hydrographic Organization held in Monaco adopted a definition of one (1) international nautical mile as being equal to 1 E3 m exactly, in excellent agreement (for an integer) with both the above-mentioned values of historical metres and standard metres.
Since the 1929 agreement, all nations have now adopted the international definition. The
United States, formerly using a value of , did not however adopt this definition until July 1, 1954.
British nautical mile (admiralty)
The British definition of the nautical mile originally related to the length on the surface of the Earth just south of Great Britain. It was not specified according to a calibrated measurement of the Earth, but chosen as exactly 800 feet longer than a
Mile#Statute miles, namely . For disambiguation, this is sometimes called the "admiralty mile" after the
British Admiralty. The precise definition of the
Foot (unit of length) varied slightly around the world until the international yard, always equal to exactly three feet, was standardized at exactly 0.9144 m in 1959, making the admiralty mile exactly . The Royal Hydrographic office of the United Kingdom converted to the international definition in 1970.
US navy nautical mile (rocketry)
As a simpler approximation, designers of radar systems for ballistic and
cruise missiles for use by the United States Navy in the 1950s would take as their equivalent of a nautical mile. In the past, some ship-borne computer systems developed for the Royal Navy also used the "data mile" of , and the more unusual "foot*", equivalent to about nine inches, defined as (223 mm).
Associated units
The derived unit of speed is the
knot (speed), defined as one nautical mile per hour. The term "log" is used to measure the distance a vessel has moved through the water, it can also be used to measure the speed through the water (see chip log) as the speed and distance are directly related.
The term knot and log originally are derived from the practice of using a "log" tied to a knotted rope as a method of gauging speed of a ship. The log would be thrown into the water and the rope trailed behind the ship. The number of knots that passed off the ship and into the water in a given time would determine the speed in "knots". The present day measurement of knots and log are determined using a mechanical tow, electronic tow, retractable hull-mounted unit,
doppler or ultrasonics, or
Global Positioning System.{{cite web|url=http://www.history.navy.mil/library/online/origin.htm#kno|publisher=Naval Historical Center, US Naval Dept. Library|title=Origin of Naval Terminology|date=May 03, 2006-->David, Fairhall (2005). "Pass your day skipper (2nd Edition)"
See also
Notes
References
- (IUGG/WGS-84 data)
| last = Taff
| first = Laurence G.
| title = Computational Spherical Astronomy
| publisher = John Wiley and Sons
| date = 1981 --> (IAU data)
External links
- National Bureau of Standards: Refinement of values for the yard and the pound (1959)
{{unit of length||m= 1852|accuracy=4 -->A nautical mile or sea mile is a unit of length. It is a non-International System of Units unit used by special interest groups such as navigators in the shipping and aviation industries. Section 4.1 Table 8 in the International System of Units 8th ed. (2006) by the Bureau International des Poids et Mesures. It is commonly used in international law and Treaty, especially regarding the limits of territorial waters. It developed from the geographical mile.
Definition
The international standard definition is: 1 nautical mile = exactly. This corresponds approximately to one Minute of arc of latitude along any meridian.
Unit symbol
There is no widely accepted international standard symbol for the unit nautical mile. The preferred abbreviation of the IEEE is nmi, IEEE guidelines for authors while M is used by the BIPM and the maritime authorities of the USA Positions, Distances, Directions, Compass; Office of Coastal Survey, NOAA, USA, and Canada POSITIONS, DISTANCES, DIRECTIONS, COMPASS, Ministry of Fisheries and Oceans, Canada. For aviation use, the preferred abbreviation of the ICAO is NM. NOTIFICATION OF ANNEX DIFFERENCES (Presented by Australia)International Civil Aviation Organisation, Sixth Meeting of CNS/MET Sub Group of APANPIRG, Bangkok, Thailand, 15 to 19 July 2002, The abbreviation nm, though conflicting with the SI symbol for the nanometre, is also in widespread use.
Conversions to other units
One nautical mile converts to:
- (exact)
- 1.150779 mile (exact: )
- (exact:
- (exact: )
- (exact: )
- 10 common-definition Cable length (exact, as one common definition of "cable")
- 10.126859 "ordinary" (100-fathom) Cable length (exact: ordinary cables)
- 12.152231 US Navy (120-fathom) Cable length (exact: US Navy cables)
- 0.998383 equatorial arc minutes = traditional geographical miles (approx.)
- 0.9998834 mean meridian arc minutes = mean historical nautical miles (approx.)
History
The nautical mile was historically defined as a minute of arc along a meridian (geography) of the Earth, making a meridian exactly 180×60 = historical nautical miles. It can therefore be used for approximate measures on a meridian as change of latitude on a nautical chart. The originally intended definition of the metre as 10-7 of a half-meridian makes the mean historical nautical mile exactly (2)/ = historical metres. Based on the current IUGG meridian of (standard) metres the mean historical nautical mile is .
The historical definition differs from the length-based standard in that a minute of arc, and hence a nautical mile, is not a constant length at the surface of the Earth but gradually lengthens with increasing distance from the equator, as a corollary of the Earth's oblateness, whence the need for "mean" in the preceding sentence. According to WGS84, the radius of curvature in a meridian plane is at the poles and at the Equator. By the definition of latitude#Common "latitude", the length of a minute of arc depends on the radius of curvature. This radius generally does not pass through Earth's center, except for the latitudes of 0° (equator) and 90° (poles). This length equals about at the poles and at the Equator, a variation of one percent.
The length of a minute of arc defined by latitude#Geocentric latitude also depends on the radius of curvature along a meridian on the surface of the Earth, but a specific length occurs at a different latitude because a surface feature's geocentric latitude differs by as much as 12 arc-minutes (at 45°) from its geodetic latitude. The naive definition of an arc minute as the distance over which one's (three-dimensional) trajectory turns one minute when sailing due north corresponds to geodetic latitude; if instead one measures it by the turning of a line between the vessel and the center of the earth this corresponds to geocentric latitude.
Other nations had different definitions of the nautical mile. This variety in combination with the complexity of angular measure described above along with the intrinsic uncertainty of geodetically derived units mitigated against the extant definitions in favor of a simple unit of pure length. International agreement was achieved in 1929 when the International Hydrographic Organization held in Monaco adopted a definition of one (1) international nautical mile as being equal to 1 E3 m exactly, in excellent agreement (for an integer) with both the above-mentioned values of historical metres and standard metres.
Since the 1929 agreement, all nations have now adopted the international definition. The United States, formerly using a value of , did not however adopt this definition until July 1, 1954.
British nautical mile (admiralty)
The British definition of the nautical mile originally related to the length on the surface of the Earth just south of Great Britain. It was not specified according to a calibrated measurement of the Earth, but chosen as exactly 800 feet longer than a Mile#Statute miles, namely . For disambiguation, this is sometimes called the "admiralty mile" after the British Admiralty. The precise definition of the Foot (unit of length) varied slightly around the world until the international yard, always equal to exactly three feet, was standardized at exactly 0.9144 m in 1959, making the admiralty mile exactly . The Royal Hydrographic office of the United Kingdom converted to the international definition in 1970.
US navy nautical mile (rocketry)
As a simpler approximation, designers of radar systems for ballistic and cruise missiles for use by the United States Navy in the 1950s would take as their equivalent of a nautical mile. In the past, some ship-borne computer systems developed for the Royal Navy also used the "data mile" of , and the more unusual "foot*", equivalent to about nine inches, defined as (223 mm).
Associated units
The derived unit of speed is the knot (speed), defined as one nautical mile per hour. The term "log" is used to measure the distance a vessel has moved through the water, it can also be used to measure the speed through the water (see chip log) as the speed and distance are directly related.
The term knot and log originally are derived from the practice of using a "log" tied to a knotted rope as a method of gauging speed of a ship. The log would be thrown into the water and the rope trailed behind the ship. The number of knots that passed off the ship and into the water in a given time would determine the speed in "knots". The present day measurement of knots and log are determined using a mechanical tow, electronic tow, retractable hull-mounted unit, doppler or ultrasonics, or Global Positioning System.{{cite web|url=http://www.history.navy.mil/library/online/origin.htm#kno|publisher=Naval Historical Center, US Naval Dept. Library|title=Origin of Naval Terminology|date=May 03, 2006-->David, Fairhall (2005). "Pass your day skipper (2nd Edition)"
See also
Notes
References
- (IUGG/WGS-84 data)
| last = Taff
| first = Laurence G.
| title = Computational Spherical Astronomy
| publisher = John Wiley and Sons
| date = 1981 --> (IAU data)
External links
- National Bureau of Standards: Refinement of values for the yard and the pound (1959)
Nautical Miles
Nautical mile - Wikipedia, the free encyclopedia
A nautical mile or sea mile is a unit of length. It corresponds approximately to one minute of latitude along any meridian. It is a non-SI unit used especially by navigators in the ...
The Nautical Mile, St. Clair Shores Michigan
Information about business and recreation in this area, which has the largest concentration of boats and marinas in the mid-west. Year-round event schedule for the entire family.
Nautical Mile Merchants Association -> Gallery
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FAQ: What is a knot? What is a nautical mile?
Information about the term knot, and nautical mile. ... Knots and Nautical miles are good old navy terms. The nautical mile was based on the circumference of the earth at the ...
nautical mile - definition of nautical mile by the Free Online ...
n. Abbr. nm. A unit of length used in sea and air navigation, based on the length of one minute of arc of a great circle, especially an international and U.S. unit equal to 1,852 ...
Nautical miles - Hutchinson encyclopedia article about Nautical miles
nautical mile. Unit of distance used in navigation, an internationally agreed standard (since 1959) equalling the average length of one minute of arc on a great circle of the Earth ...
AskOxford: nautical mile
nautical mile • noun a unit used in measuring distances at sea, equal to 1,852 metres (approximately 2,025 yards). Perform another search of the Compact Oxford English Dictionary
Nautical Mile - 1alt1 | Google Groups
Nautical Mile FAQ: What is a knot? What is a nautical mile? Information about the term knot, and nautical mile. ... The nautical mile was based on the circumference of the earth at ...
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