Navigation: Distance in miles and nautical miles

For almost everything else the Metric system is the best system to use, it’s widely used in the world like the way English is understood.

The Metric system is extensively integrated into science and engineering.

However in Navigation based on extremely old standards (people have been making maps for as long as there have been kings) inherited from the Sumerian civilization.

When we talk about degrees° minutes’ and seconds”  they are commonly refereed to as degrees of an arc, minutes of an arc or seconds of an arc.

The basic idea is that 1 minute (of an arc) is 1 nautical mile.

1 minute of an arc = 1 nautical mile = 6076 feet = 1.15 statute miles  = 1.852 kilometers

1 second of an arc is therefore 101.2666 feet  = 101 + 4/15  feet =  101 feet 3.2 inches = 30.866 meters

Note the current standard American nautical mile is 6080.2 feet.

So because these standards are locked together an have huge historical legacy it worth learning them.

The idea that 1 minute of an arc is 1 nautical mile helps bring real world scale to something as abstract as 1/60 of 1 degree on a compass.

Calculation to show diameter of earth

Based on 180 degrees pole to pole : 1 minute of and arc  X 60  X 360 X nautical mile = circumference of earth

1* 60 * 360 = 21,600 nautical miles

circumference = π * D

circumference / π  =diameter of earth in nautical miles

21,600/ 3.14157 = 6875. 54 nautical miles

In kilometers:

6875.54 *1.852 km    =   12,733.5 km

accepted value, average earth diameter : 12,742 km

99.93% of the modern accepted value.

For example if you found a pirate treasure map, you can be sure its is distances are measured in nautical miles. Sadly even nautical miles had local variants due to local variants in what was a mile. Nautical mile are also 1% shorter at the poles as the earth is an oblate sphere ( a sphere with smaller diameter at the poles).


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