HEADERS_END

One Nautical Mile is defined as the distance covered by

one arc-minute on a Great Circle. This could be either

the equator, or a line of longitude.

That means there are 60*90 Nautical Miles from the North

Pole to the Equator (90 degrees of latitude, times 60

arc minutes per degree), so 5400NM is 10 million metres

(by the definition of the metre).

Hence the Nautical Mile is 1851.851... metres, and has

since been declared to be 1852 metres, or 6076 feet.

Close enough.

Because the Earth is not exactly a sphere, the distance

equating to one arc-minute varies according to where you

are. At the poles, where the surface of the Earth is closer

to the centre, it's about 6067 feet, while at the Equator

it's about 6087 feet. Thus practice intrudes on theory,

and things get messy.

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CategoryMaths