Re: How fast is a knot, anyway

[John Brownlee <jonnie@chronic.lpl.arizona.edu>]

	I'd have to look at the surface model for the earth's surface, but
my guess is that the words we should be thinking of are 'oblate spheroid'. 
The nautical mile is originally a convenience unit, roughly equated to an
angular cartographic measurement. Because the Earth is not a perfect sphere
and the lat and long system (usually) is, some nonlinear departure towards
the poles would be necessary. I suspect one value is averaged over a
variety of latitudes, and the other is the cannonical "at-equator" one.
This is postulated because the 5 foot difference is about the same value as
the oblateness parameter for the Earth. 
	I'll double check and see how much horse-hockey is in the above
statement.

							John

John Brownlee
Lunar and Planetary Lab
University of Arizona
jonnie @ lpl . arizona . edu