NAUTICAL MILE

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What is a Nautical Mile?

BoatSafeKids.com

A nautical mile is a distance on the earth's surface of 6,080 feet, which is equal to one minute of latitude at the earth's equator. Since there are 360 degrees around the earth, and each degree equals 60 minutes, the distance around the earth, at the equator or any other great circle, is 21,600 nautical miles. (A great circle is like a circumference.)

 

The origin of the nautical mile started with the realization that the earth was spherical and not flat. It was Pythagoras who first put forward the theory in 580 b.c.

 

 

 

A former British unit of length equivalent to 6,080 feet (1,853.184 meters); 800 feet longer than a statute mile a unit of length used in navigation; exactly 1,852 meters; historically based on the distance spanned by one minute of arc in latitude
wordnetweb.princeton.edu/perl/webwn

The nautical mile (symbol M, NM, Nm or nmi) is a unit of length corresponding approximately to one minute of arc of latitude along any meridian. ...
en.wikipedia.org/wiki/Nautical_mile

Unit of distance used in marine navigation, equal to approximately 1.15 statute miles (length of 1 minute of latitude).
www.srh.noaa.gov/key/marine/definitions.php

A distance equal to 6,082.2 feet. A land mile is 5,280 feet.
www.bestcruises.com.au/information/cruise_glossary

How distance is measured over water. It is the unit of length used to define the knot (speed of one nautical mile per hour) used by ships and airplanes. A nautical mile is 6,076.1 feet (1,852 meters). A statute or 'normal' mile is 5,280 feet (about 1.60935 kilometers).
www.kidzworld.com/article/1328-map-terms-c-to-p

Distance at sea is measured in nautical miles, which are about 6067.12 feet, 1.15 statute miles or exactly 1852 meters. Nautical miles have the unique property that a minute of latitude is equal to one nautical mile (there is a slight error because the earth is not perfectly round. ...
www.terrax.org/sailing/glossary/gn.aspx

The nautical mile is closely related to the geographical mile which is defined as the length of one minute of arc on the earth's equator. By international agreement, the nautical mile is now defined as 1852 meters.
www.novalynx.com/glossary-n.html

A measure of distance equal to one minute of arc on the earth's surface (6,076.1 feet or 1,852 meters).
www.flyfrompti.com/ptipart150/Glossary_Page.htm

one minute of latitude; approximately 6076 feet - about 1/8 longer than the statute mile of 5280 feet
www.boathook.com/nautical_terms.html

Distance of 6080 feet.
www.firstflight.com/features/glossaryPopUP.htm

The most common distance measurement in aviation. A nautical mile is equivalent to 1.15 statute (standard US) miles.
www.sportpilot.org/learntofly/glossary.html

One sea mile. 6080 feet which is 1/60 of a degree on the equator.
www.sdmaritime.com/contentpage.asp

Unit of length equal to 1852m (6076ft). Also equal to one minute of latitude.
www.technologyawards.org/marine_technology/

An international unit of distance used in sea navigation. A nautical mile is equivalent to 1852 meters or 6076.17 feet.
www.pacificshipwrecks.ca/english/glossary.html

 

 

 

 

HowStuffWorks.com

A nautical mile is based on the circumference of the planet Earth. If you were to cut the Earth in half at the equator, you could pick up one of the halves and look at the equator as a circle. You could divide that circle into 360 degrees. You could then divide a degree into 60 minutes. A minute of arc on the planet Earth is 1 nautical mile. This unit of measurement is used by all nations for air and sea travel.

 

A knot is a unit of measure for speed. If you are traveling at a speed of 1 nautical mile per hour, you are said to be traveling at a speed of 1 knot.

 

A kilometer is also defined using the planet Earth as a standard of distance. If you were to take the Earth and cut it in half along a line passing from the North Pole through Paris, and then measure the distance of the curve running from the North Pole to the equator on that circle, and then divide that distance by 10,000, you would have the traditional unit for the kilometer as defined in 1791 by the French Academy of Sciences.

 

A nautical mile is 1,852 meters, or 1.852 kilometers. In the English measurement system, a nautical mile is 1.1508 miles, or 6,076 feet.

 

To travel around the Earth at the equator, you would have to travel (360 * 60) 21,600 nautical miles, 24,857 miles or 40,003 kilometers.

 

 

wisegeek.com

AA nauticalnauticalnautical milemilemile is aaa unit of measurement used in aeronautics and maritime navigation. Some people also prefer to refer to aaa nauticalnauticalnautical milemilemile as aaa sea milemilemile, maritime unit, or sea unit, in aaa reference to the maritime usage of the measurement. When speed is given in nauticalnauticalnautical miles, the correct term is “knots,” as in “the ship traveled at 23 knots,” indicating that the ship was moving at aaa rate of 23 nauticalnauticalnautical miles per hour.

 

Technically, aaa nauticalnauticalnautical milemilemile is equal to the length of one minute of arc in aaa great circle. If this statement has caused you to blink furiously in confusion, think about the Earth as aaa large orange. If you cut the orange in half along the middle, or equator, you have bisected the orange along one of its “great circles.” There are numerous other great circles, as aaa great circle is any line around aaa sphere which can be traced to cut the sphere precisely in half. There are 360 degrees in aaa great circle, and each degree can be further broken down into 60 minutes, sometimes called minutes of arc. Therefore, the Earth measures 21,600 nauticalnauticalnautical miles around the equator.

 

After much international debate, it has been agreed that aaa nauticalnauticalnautical milemilemile is equal to 6,076 feet (1,852 meters). International agreement on the measurement of aaa nauticalnauticalnautical milemilemile is important, since many treaties and agreements include nauticalnauticalnautical miles as aaa unit of measurement. Furthermore, it ensures smooth navigation between various nations, which is especially important for major trading partners. As aaa result, aaa nauticalnauticalnautical milemilemile is recognized within the framework known as the International System of Units (SI), which is aaa system of measurements which have been clearly defined and agreed upon by most countries in the world.

 

Usage of nauticalnauticalnautical miles varies around the world. Since aaa nauticalnauticalnautical milemilemile is not technically an SI measurement, some nations prefer to use distances which are recognized under this system, which prefers metric measurements like meters and kilometers to measurements such as inches and feet. In some regions, the nauticalnauticalnautical milemilemile is heavily used and understood by seafarers, while other areas, distances may be expressed in other measurements, especially when an international team is cooperating on aaa project.

 

For anyone who is dying to know about the origin of “knot” as aaa term for aaa unit of speed in maritime navigation, the word is closely linked to the technique sailors used to employ to measure their speed. AAA weighted line would be thrown out from aaa ship by one sailor while another held aaa timer. Knots in the line were placed at precise lengths, so that the sailor could count off the knots to figure out how far the ship had traveled in aaa set amount of time, typically 30 seconds. This measurement could be extrapolated into an estimate of the overall speed of the ship, and while more precise navigational tools are used now, “knots” for speed continues to be used.

 

 

 

 

 

OnlineConversation.com

What is a knot? What is a nautical mile?

Knots and Nautical miles are good old navy terms. The nautical mile was based on the circumference of the earth at the equator. Since the earth is 360 degrees of longitude around, and degrees are broken into 60 so-called "minutes", that means there are 360 * 60 = 21,600 "minutes" of longitude around the earth. This was taken as the basis for the nautical mile; thus, by definition, 1 minute of longitude at the equator is equal to 1 nautical mile. So the earth is ideally, by definition, 21,600 nautical miles (and 21,600 "minutes" of longitude) in circumference at the equator. If anyone ever asks you how far is it around the earth, you can quickly do the math in your head (360 degrees * 60 minutes per degree) and answer "about 21,600 nautical miles!"

In fact, even modern navigators use the "minute of latitude" on charts to measure distance; this is what you see them doing when they use their compass spreaders while they are hovering over their nautical charts (maps). [For geometrical reasons, we use the minute of latitude on charts to correspond to a nautical mile rather than the minute of longitude. Minutes of longitude shrink as they move away from the equator and towards the poles; minutes of latitude do not shrink. Take a look at a globe with longitude and latitude lines marked on it to understand why.]

 

Using the definition of a nautical mile for distance at sea, the challenge was to measure speed -- i.e. what is the ship's speed in nautical miles per hour? (By the way, the nautical mile is about 1.15 larger than the "statute" mile used by land lubbers.) Since [speed] = [distance] divided by [time], if we measure a small distance (or length) in a small time we can do the math and figure our speed.

 

The device that sailors used to make their speed measurement was called the "chip log." Chip as in chip of wood, and log as in to record in a log. The chip was a wedge of wood about 18" in size; it was tied to one end of a rope on a large spool. The rope had knots tied into it about every 47'3" (more about how that was calibrated below).

 

The wooden chip was thrown overboard at the ship's stern (back end). Because of its wedge shape, it would "grab" the water and start pulling out rope as the ship moved forward at some yet unknown speed. One man would hold the spool of rope as it played out; another man would start a sandglass filled with 30 seconds of sand; and a third man would count the knots as they passed over the stern board. When the 30 seconds of sand expired, the time keeper would call out and the counting of knots would stop.

 

The faster the ship was sailing, more knots and a longer length of rope were played out. The number of knots in the rope that were counted in 30 seconds, then, was equal to the speed of the ship in nautical miles per hour. A "knot", therefore, is not a nautical mile, it is a nautical mile per hour. Thus 1 knot was equivalent to 1 nautical mile per hour; 5 knots were equivalent to 5 nautical miles per hour; etc. The similar sound of "knot" and "naut" is entirely coincidental.

Finally, what about the actual values of 47'3" between knots on the rope and the 30 seconds that were used with the chip log? The length was based on converting [1 nautical mile per hour] to [feet per second(fps)], and then multiplying [fps] by 30 seconds (which was a practical time to spend counting knots with a sandglass). The result was the calibrated length in feet at which to tie the knots for a 30-second run of the chip log.

 

... Now that we have much more precise technology to measure things, and because we need to establish international standards and conversion factors, and because the earth is not uniformly flat or round anywhere, and because even the precise definition of the second has changed, the official value for how many international feet in an international nautical mile has changed.

 

Likewise, the measuring time of about "30 seconds" in the sandglass is now calibrated at 28 seconds. Time itself didn't change by 6.7%! But the cumulative effects of new international standard definitions for time, feet, statute miles, and nautical miles and more accurate measurements of the actual size of the earth -- and the fact that we don't use sand to measure time anymore -- have changed the modern calibration of the chip log.