# Difference between nautical and terrestrial miles

Does someone know the historical reason behind the difference in physical units between nautical and terrestrial miles?

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en.wikipedia.org/wiki/Nautical_mile and howstuffworks.com/question79.htm have some information, but neither explain the difference – ChrisF Mar 23 '13 at 12:18
Maybe you want to read en.wikipedia.org/wiki/Mile to see that there have been tons of different miles. The word "mile" comes from a Latin word for one thousand - it was one thousand paces, really, but the statute (land) mile was defined to be slightly less, for pretty random reasons. There's nothing special about these two miles except that they survived to the present. There have been dozens of different miles with somewhat different values in both directions. This messy history shows how it's sometimes a good idea to try to be conservative in conventions. ;-) – Luboš Motl Mar 23 '13 at 12:21
This seems like a primo question for the History of science and mathematics site proposal on Area51. – naught101 Sep 10 '14 at 0:13

## 1 Answer

A nautical mile is the length of one minute of arc (1/60 deg) along any meridian

If you are navigating by measuring the angles of the sun and stars then it's a simple and obvious unit to use since it avoids a lot of calculation and it's close enough to a normal mile to be understood.

It's also been an internation standard for quite a long time - unlike all the other historical definitions of a mile from different countries.

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Maybe one should also add the definition of the statute (land) mile: The statute mile was so-named because it was defined by an English Act of Parliament in 1593, during the reign of Queen Elizabeth I. The statute states: "A Mile ſhall contain eight Furlongs, every Furlong forty Poles, and every Pole ſixteen Foot and a half." (35 Eliz. cap. 6.)[45] It was thus 1760 yards (5280 feet, about 1609 metres). - Pretty contrived definition with bizarre numbers, but that's what they did to match the common-person understanding of the vaguely defined units. – Luboš Motl Mar 24 '13 at 9:28
It;s a great definition if you need to divide fields up. Just like contrived units in physics, eV are great if you are dealing with cyclotrons, but less use for the crane lifting the experiment. In a way a mile is no real use in the C16, most people would have talked about travel time - just like us Astronomers. – Martin Beckett Mar 24 '13 at 13:33