A nautical mile is equal to one minute of arc measured along any meridian. It is equal to approximately 1.15 statute miles or 1.85 kilometers.
Credit: Lidingo (cc)
Ahoy there cruisers! Let's talk about the nautical mile, the trusty unit of distance measurement used in maritime (and air) navigation. A nautical mile is approximately 1,852 meters, or one minute of arc measured along a meridian, which is a line of longitude running from the North Pole to the South Pole.
17th Century
In the 17th century, sailors used all sorts of units of measurement such as fathoms, cubits, and feet, which varied from ship to ship and made navigation difficult.
18th Century
In the 18th century, Edmund Halley, the famous astronomer, proposed using longitude as a unit of measurement for navigation at sea, with each degree of longitude equaling 60 nautical miles. However, this idea wasn't widely accepted at the time as measuring longitude was still very difficult.
It wasn't until later in the 18th century that the invention of the marine chronometer by John Harrison allowed sailors to accurately measure the time difference between their current position and the reference meridian, making it possible to use longitude as a unit of measurement for navigation at sea.
19th Century
Fast forward to the 19th century, and sailors were using longitude as a unit of measurement to calculate distance traveled at sea, but there were still variations in the length of the nautical mile used by different countries. Finally, in 1929, the London International Conference on Safety at Sea adopted the nautical mile as the standard unit of measurement for international maritime navigation.
20th Century
After the adoption of the nautical mile as the international standard for maritime navigation, the United States and the United Kingdom initially used their own slightly different measurements. However, the US officially adopted the international nautical mile in 1954, while the UK followed suit in 1970.
Today
The nautical mile is used by sailors (and pilots) to measure the distance traveled at sea (or in the air). It's even used in other fields like cartography and geography.