Re: How fast is a knot, anyway

[Ray Keefer <Ray.Keefer@eng.Sun.COM>]

Hi,

Actually I think the 5 foot difference is due to the then existing
assumption of the circumference of the earth at the equator way back when
a knot was actually defined.

In other words, the knot was defined based on incorrect data, but good
enough for the accuracy of the day.

Regards,
Ray

> 	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
>