Why distance by air and sea measured/referred in nautical miles, why not in nautical kilometres?
A kilometer is 1000 times the length of an arbitrary distance called a meter. It has no physical significance. A nautical mile is a measure of distance on a curved surface the size of the Earth. It is in fact a measure of angle. 360 Degrees = full circle 1 Degree = 60 Minutes of Arc 1 Minute of Arc = 1 Nautical mile (on Earth) On a large planet like Jupiter a Minute of Arc would be longer distance than that measured on Earth. On a smaller surface like the Moon 1 Minute of arc would be shorter. Navigation is performed by measuring angles and/or times to celestial bodies. Fixed bodies like stars are the simplest means. Slow moving bodies like Sun, Moon, and Planets are more difficult. Fast moving bodies like GPS Satellites are more difficult still. However angles of measurement from the Earths surface are used in all these forms of navigation. Some people will tell you that GPS is based upon the measurement of time and they are correct (once). By that I mean that if you know where a sate
