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Information about Nautical Mile

1 nautical mile =
SI units
0 m0 km
US customary / Imperial units
0 ft0 mi
A nautical mile or sea mile is a unit of length. It is a non-SI unit used by special interest groups such as navigators in the shipping and aviation industries.[1] It is commonly used in international law and treaties, especially regarding the limits of territorial waters. It developed from the geographical mile.

Definition

The international standard definition is: 1 nautical mile = 1,852 metres exactly.[1] This corresponds approximately to one minute 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,[2] while M is used by the BIPM[1] and the maritime authorities of the USA[3], and Canada [4]. For aviation use, the preferred abbreviation of the ICAO is NM.[5] 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:

History

The nautical mile was historically defined as a minute of arc along a meridian of the Earth, making a meridian exactly 180×60 = 10,800 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 (2107)/10,800 = 1,851.851851… historical metres. Based on the current IUGG meridian of 20,003,931.4585 (standard) metres the mean historical nautical mile is 1,852.216 m.

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 6,399,593.6258 metres at the poles and 6,335,439.3273 metres at the Equator. By the definition of geodetic 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 1,861.57 metres at the poles and 1,842.90 metres at the Equator, a variation of one percent.

The length of a minute of arc defined by 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 Extraordinary Hydrographic Conference held in Monaco adopted a definition of one (1) international nautical mile as being equal to 1,852 metres exactly, in excellent agreement (for an integer) with both the above-mentioned values of 1,851.851 historical metres and 1,852.216 standard metres.

Since the 1929 agreement, all nations have now adopted the international definition. The United States, formerly using a value of 1,853.248 m (6,080.2 ft), did not however adopt this definition until July 1, 1954.[6]

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 statute mile, namely 6,080 feet. For disambiguation, this is sometimes called the "admiralty mile" after the British Admiralty. The precise definition of the foot 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 1,853.184 m. 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 6,000 feet (1,828.8 m) 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 6,000 feet, and the more unusual "foot*", equivalent to about nine inches, defined as 6,000/8,192 feet (223 mm).

Associated units

The derived unit of speed is the knot, 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 GPS.[7][8]

See also

Notes

1. ^ Section 4.1 Table 8 in the International System of Units 8th ed. (2006) by the Bureau International des Poids et Mesures.
2. ^ IEEE guidelines for authors
3. ^ Positions, Distances, Directions, Compass; Office of Coastal Survey, NOAA, USA
4. ^ POSITIONS, DISTANCES, DIRECTIONS, COMPASS, Ministry of Fisheries and Oceans, Canada
5. ^ 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,
6. ^ Louis E. Barbrow and Lewis V. Judson (1976). Appendix 4 The international nautical mile (PDF). Weights and Measures Standards of the United States, A brief history. NIST Physics Laboratory. Retrieved on 2007-08-02.
7. ^ Origin of Naval Terminology. Naval Historical Center, US Naval Dept. Library (May 03, 2006).
8. ^ David, Fairhall (2005). "Pass your day skipper (2nd Edition)"

References

  • Moritz, H. (1980). "Geodetic Reference System". Bulletin Geodesique 54 (3).  (IUGG/WGS-84 data)
  • Taff, Laurence G. (1981). Computational Spherical Astronomy. John Wiley and Sons.  (IAU data)

External links

International System of Units (abbreviated SI from the French Le Système international d'unités) is the modern form of the metric system.
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1 metre =
SI units
1000 mm 0 cm
US customary / Imperial units
0 ft 0 in
The metre or meter[1](symbol: m) is the fundamental unit of length in the International System of Units (SI).
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1 kilometre =
SI units
0 m 0106 mm
US customary / Imperial units
0 ft 0 mi
A kilometre (American spelling: kilometer, symbol km
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U.S. customary units, also known in the United States as English units[1] (but see English unit) or standard units, are units of measurement that are currently used in the USA, in some cases alongside units from SI (the International System of Units
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Imperial units or the Imperial system is a collection of units, first defined in the British Weights and Measures Act of 1824, later refined (until 1959) and reduced.
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1 foot =
SI units
0 m 0 mm
US customary / Imperial units
0 yd 0 in
A foot (plural: feet or foot;[1] symbol or abbreviation: ft or, sometimes, ′
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1 mile =
SI units
0 m 0 km
US customary / Imperial units
0 ft 0 yd
“Miles” redirects here. For other uses, see Miles (disambiguation).

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Length is the long dimension of any object. The length of a thing is the distance between its ends, its linear extent as measured from end to end. This may be distinguished from height, which is vertical extent, and width or breadth
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International System of Units (abbreviated SI from the French Le Système international d'unités) is the modern form of the metric system.
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navigator is the person onboard a ship or aircraft responsible for its navigation. The navigator's primary responsibility is to be aware of ship or aircraft position at all times.
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Shipping is physical process of transporting goods and cargo. Virtually every product ever made, bought, or sold has been affected by shipping. Despite the many variables in shipped products and locations, there are only three basic types of shipments: land, air, and sea.
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Aviation refers to all activities involving the operation of heavier-than-air aircraft, machines designed for atmospheric flight. The term also describes the organizations and regulatory bodies as well as the personnel related with the operation of aircraft and the industries
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International law can refer to three distinct legal disciplines.
  • public international law, which involves for instance the United Nations, maritime law, international criminal law and the Geneva conventions.

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treaty is an agreement under international law entered into by actors in international law, namely states and international organizations. A Treaty may also be known as: (international) agreement, protocol, covenant, convention, exchange of letters
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Territorial waters, or a territorial sea, is a belt of coastal waters extending at most twelve nautical miles (but possibly less, at the coastal country's discretion) from the mean low water mark of a littoral state that is regarded as the sovereign territory of the state,
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1 geographical mile =
SI units
0 m 0 km
US customary / Imperial units
0 ft 0 mi
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.
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The term International Standard may refer to
  • International standard
  • International Standard (dance), a category of ballroom dance


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1 metre =
SI units
1000 mm 0 cm
US customary / Imperial units
0 ft 0 in
The metre or meter[1](symbol: m) is the fundamental unit of length in the International System of Units (SI).
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A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60) of one degree. [1] Since one degree is defined as one three hundred sixtieth (1/360) of a circle, 1 MOA is 1/21600 of the amount of arc in a closed circle, or
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equator divides the planet into a Northern Hemisphere and a Southern Hemisphere, and has a latitude of 0. Latitude, usually denoted symbolically by the Greek letter phi, , gives the location of a place on Earth north or south of the equator.
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Institute of Electrical and Electronics Engineers

Type Professional Organization
Founded January 1, 1963
Origins Merger of the American Institute of Electrical Engineers and the Institute of Radio Engineers
Key people Leah H.
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International Civil Aviation Organization

The ICAO flag

Formation April 1947
Headquarters Montreal, Canada
Membership 190 member states
Official languages Arabic, Chinese, English, French, Russian and Spanish
Secretary General Taïeb Chérif
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1 nanometre =
SI units
010−9 m 010−3 μm
US customary / Imperial units
010−9 ft 010−9 in
A nanometre (American spelling: nanometer, symbol nm
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1 metre =
SI units
1000 mm 0 cm
US customary / Imperial units
0 ft 0 in
The metre or meter[1](symbol: m) is the fundamental unit of length in the International System of Units (SI).
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1 mile =
SI units
0 m 0 km
US customary / Imperial units
0 ft 0 yd
“Miles” redirects here. For other uses, see Miles (disambiguation).

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1 yard =
SI units
0 m 0 mm
US customary / Imperial units
0 ft 0 in
A yard (abbreviation: yd) is the name of a unit of length in a number of different systems, including English units, Imperial units, and United States customary
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1 foot =
SI units
0 m 0 mm
US customary / Imperial units
0 yd 0 in
A foot (plural: feet or foot;[1] symbol or abbreviation: ft or, sometimes, ′
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1 fathom =
SI units
0 m 0 cm
US customary / Imperial units
0 ft 0 in
A fathom is a unit of length in the Imperial system (and the derived U.S. customary units).
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A cable length or cable's length is a nautical unit of measure equal to one tenth of a nautical mile or 100 fathoms. The unit is named after the length of a ship's anchor cable in the age of sail. The definition varies:
  • International: 1/10 nautical mile, or 185.

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1 fathom =
SI units
0 m 0 cm
US customary / Imperial units
0 ft 0 in
A fathom is a unit of length in the Imperial system (and the derived U.S. customary units).
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