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A nautical mile is a unit of length used in air, marine, and space navigation, and for the definition of territorial waters. [2] [3] [4] Historically, it was defined as the meridian arc length corresponding to one minute ( 1 / 60 of a degree) of latitude at the equator, so that Earth's polar circumference is very near to 21,600 nautical miles (that is 60 minutes × 360 degrees).
A geographical mile is defined to be the length of one minute of arc along the equator (one equatorial minute of longitude) therefore a degree of longitude along the equator is exactly 60 geographical miles or 111.3 kilometers, as there are 60 minutes in a degree. The length of 1 minute of longitude along the equator is 1 geographical mile or 1 ...
A second of arc, arcsecond (abbreviated as arcsec), or arc second, denoted by the symbol ″, [2] is a unit of angular measurement equal to 1 / 60 of a minute of arc, 1 / 3600 of a degree, [1] 1 / 1 296 000 of a turn, and π / 648 000 (about 1 / 206 264.8 ) of a radian.
When each equatorial degree was divided into 18 leagues, the geographical mile was equal to 1 / 54 degree or about 2.06 kilometres (1.28 mi); when divided into 20 leagues, the geographical mile was equal to 1 / 60 degree, approximating the values provided above; and when divided into 25 leagues, the geographical mile was equal ...
A degree (in full, a degree of arc, arc degree, or arcdegree), usually denoted by ° (the degree symbol), is a measurement of a plane angle in which one full rotation is 360 degrees. [ 4 ] It is not an SI unit —the SI unit of angular measure is the radian —but it is mentioned in the SI brochure as an accepted unit . [ 5 ]
As one degree is 1 / 360 of a circle, one minute of arc is 1 / 21600 of a circle – such that the polar circumference of the Earth would be exactly 21,600 miles. Gunter used Snellius's circumference to define a nautical mile as 6,080 feet, the length of one minute of arc at 48 degrees latitude.
The equator is divided into 360 degrees of longitude, so each degree at the equator represents 111,319.5 metres (365,221 ft). As one moves away from the equator towards a pole, however, one degree of longitude is multiplied by the cosine of the latitude, decreasing the distance, approaching zero at the pole.
£10,000 (equivalent to £1.83 million in 2023 [10]) for a method that could determine longitude within 1 degree (equivalent to 60 nautical miles (110 km; 69 mi) at the equator). £15,000 (equivalent to £2.74 million in 2023 [10]) for a method that could determine longitude within 40 minutes.