What is a Nautical Mile?

What is a Nautical Mile?

The origins of the nautical mile trace back to ancient seafaring civilizations, where mariners relied on celestial observations and instruments like astrolabe, magnetic compass, chip logs and sextant to navigate vast expanses of open water. Measuring angles to/with the stars/Sun/Moon along the celestial sky dome (above the flat earth plane) was a basic navigation technique used to determine the position of ships at sea. Latitude was measured using an angle with Polaris and a chronometer was used to determine longitude.

So a Nautical Mile (also called a "minute-mile") is a distance travelled by a ship at sea in one arc minute when measured along the 180° celestial sky dome around us. One nautical mile corresponds to one minute of latitude (and one degree is 60 minutes or 60 nautical miles) and it has absolutely nothing to do with the globe Earth or it's circumference.

Initially, Spanish, French, Dutch and British navigators measured different values of the nautical mile, but at the International Hydrographic Conference in 1929 it was fixed to 1852 metres.

1 Nautical Mile = 1.15 Statute Miles = 1852 Meters

Nautical miles are used at sea and in the air because both sailors and airmen use degrees of latitude and longitude as their position coordinates and they need to use flat paper charts (or the 2D electronic equivalent). The big point about using nautical miles (and their corresponding speed unit, knots) is to make chart reading quicker. Charts have the Latitude and Longitude grid printed on them. The grid spacing that equals one minute of latitude also equals one nautical mile.