Why is a nautical mile longer than a standard land mile?

Answer 1

Difference Between Nautical & Statute MNautical Mile: It is the length of an arc on a surface of the Earth that subtends an angle of 1 minute on the centre of curvature of that section of the Earth.

The Earth is not a perfect sphere. It is flatter at the poles and seems to bulge at the eqautor. This shape makes it an Oblate Spheroid.

So, the Nautical Mile is larger at the Poles than at the Equator. The exact length of a Nautical Mile at the Poles is 6107 feet, while at the Equator it is 6040 feet. (2009.08.10 I think the stated locations of the 6107 ft and 6040 ft are reversed. An angle of 1 minute is no different pointing at the poles than at the equator. The farther one moves away from the vertex, the longer the arc length gets and visa versa.) [The prior parenthetical "correction" is NOT correct! The original author is correct.What the reviewer did not calculate was the slight variance between minutes of latitude going from the equator to the poles. Why? It's about the Earth being an oblate spheroid and not a perfect sphere. One degree of latitude = 362775.7596463919 feet at the equator and 366449.1269711854 feet at the pole. Divide those numbers by 60, which is the number of minutes in a degree, and you'll get about 6046 feet to one minute of arc at the equator and 6107 feet to one minute of arc at the pole. The 6080 figure is about the average of those two numbers or, more precisely, about 6076.7 feet at 45 degrees of latitutde. A nautical mile is defined as equal to one minute of arc. - Richard M. Bash - January 21, 2010] However, for ease of understanding and for solving questions we take it as a round figure of 6080 feet in a Nautical Mile.

{Am sorry, will shortly try to create a link for the image,( or better still get my best friend to do it---he is a genius with this stuff) to demonstrate what i mean}

Statute Mile: It is an arbitrary unit of distance as decreed by a statute of Queen Elizabeth.

Thus, a Statute Mile has 5280 feet while the Nautical Mile has 6080 feet.

Answer 2

The international standard definition is: 1 nautical mile = 1,852 metres exactly.[1] The nautical mile was historically defined as a minute of arc along a meridian of the Earth, making a meridian exactly 180×60 = 10,800 historical nautical miles.[6] It can therefore be used for approximate measures on a meridian as change of latitude on a nautical chart. The originally intended definition of the metre as 10-7 of a half-meridian makes the mean historical nautical mile exactly (2×107)/10,800 = 1,851.851851… historical metres. Based on the current IUGG meridian of 20,003,931.4585 (standard) metres the mean historical nautical mile is 1,852.216 m.

Answer 3

they didnt have sign posts