NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: The Nautical Mile and the arc minute
From: Gary LaPook
Date: 2015 Jun 5, 21:23 +0000
From: Frank Reed <NoReply_FrankReed@fer3.com>
To: garylapook@pacbell.net
Sent: Friday, June 5, 2015 1:36 PM
Subject: [NavList] Re: The Nautical Mile and the arc minute
From: Gary LaPook
Date: 2015 Jun 5, 21:23 +0000
Yep, 5,400 nautical miles from the equator to the north pole (90 degrees times 60 NM per degree = 5,400 NM) is the same as 10,000,000 meters (10,000 km), from the equator to the north pole, the original definition of the meter from the 18th century. So meters., 54 NM = 100 km and 1 km = 1852 meters exactly, by definition. (Close enough, 100,000 meters / 54 = 1851.851852.)
gl
From: Frank Reed <NoReply_FrankReed@fer3.com>
To: garylapook@pacbell.net
Sent: Friday, June 5, 2015 1:36 PM
Subject: [NavList] Re: The Nautical Mile and the arc minute
Bob, you wrote:
PS: I wrote that the "nautical mile is 'however long it needs to be' to match one minute of arc motion across the Earth's surface as measured from the center of the Earth." This definition was so "slick" that it also became the basis for linear measurement in the metric system. One kilometer was defined originally as 'however long it needs to be' such that 100 of them make up one grad of arc as measured from the center of the Earth (with 100 grads to a right angle). The metric system "borrowed" the concept of the sea mile for the original definition of the meter. And from that origin, we're still left with the 'fun fact' today that 54 nautical miles is almost exactly equal to 100 km (the very small difference arising from later re-definitions).
