Aviation Explained: What is a nautical mile and why planes use it instead of kilometres

Nautical miles and knots are units generally used for the measurement of distance and speed on ships and planes.

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The unit nautical miles is often heard yet lesser-known teams for measuring distance. Though it might be a bit confusing for us as we are used to the regular kilometre or miles, this unit is generally used to measure distance in flights and on sea routes. It is a unit that has been used for a long time and remains in general practice.

How was the nautical mile developed?

In the beginning, the nautical mile came into existence as a practical navigational development and got further developed with time. Everything started after the parallel system of latitude and meridians of longitude was set back in the 16th century. This way was used as an alternative to visual navigation.

What is a nautical mile?

A nautical mile can be defined based on latitude and longitude. In other words, the earth has been divided into latitudes and longitudes, with the sphere of the earth divided into 360 degrees, among which one degree equals one minute. The distance between these minutes is represented by nautical miles. Which is one-sixtieth of a degree.

How did a nautical mile become a standardised unit?

For millennia, a measure based on degrees was successfully used in maritime navigation and continues to do so now. The metre was invented in the late 1800s as a replacement for the yardstick. It was calculated to be one ten-millionth of a quarter meridian (running from the North Pole to the Equator, Paris). This gives the world a circumference of 40,000 kilometres.

The International Hydrographic Organization officially standardised the nautical mile against the metre in 1929. It was determined that one nautical mile equalled 1,852 meters. For a long time, the US and the UK utilised slightly different measurements, but they have all been standardised.

Relation between nautical mile and knots

Nautical mile and knot are interrelated units both used in navigation. It is like km and kmph; meaning knots are used to measure the speed; it can be defined as one nautical mile per hour.

How did the term knot come into existence?

The term 'knot' comes from early marine speed measurement procedures. In this method, a rope with evenly spaced knots is fastened to a piece of wood. The length of rope (by knots) that passed out behind the ship over a specific amount of time defined the speed of this wood in the water behind a ship.

Why use nautical miles and knots?

The use of nautical miles and knots is the only sensible thing to do as it uses the distance between latitudes and longitudes to measure distance which is more accurate than any other unit over long distances. In addition, planes and ships travel long distances over the circumference of the earth, which makes these units even more adequate.