On 27 Aug 2003 20:30:05 GMT, (JJ Sinclair) wrote:

John Lee wrote.
Nowhere! However on the equator 1 second of longitude
equals 1 nautical mile


Hmmmm? When I went to navigation school, 1 degree of latitude anywhere in the
world and 1 degree of longitude (on the equator) was made up of 60 minutes and
each minute was 1 nautical mile. A second would be 6080 devided by 60 or 101
feet. Please don't tell me they have changed all that. I'm not talking about
the nit-pickers that want to say there is an + or - a foot or two in a nautical
mile, but I would like to believe we still have 360 degrees around the equator
and 90 degrees north and 90 degrees south latitude.
JJ Sinclair

Maybe Eratosthenes still thought the Earth was a near-perfect sphere,
when he made a fairly reasonable calculation of its diameter Maybe
Columbus wasn't even aware of the true shape of the poles.

But we've known about the flattening at the poles for about four
centuries at least, probably longer than nautical miles have existed.
Certainly since long before the French scientists in the 1790s
designed the meter to be 1/10000000 of the distance from the equator
to the North Pole.

We do, of course, have 360 degrees around the equator. When we agree
on a starting point (e.g., the point where it crosses the meridian
through Greenwich, England, the one most often used now), any
particular place will always be the same number of degrees from it.

We also have 90 degrees between the equator and either pole. The
equator is always 0 degrees and the poles 90 degrees. But in between,
there are at least three different ways of measuring latitude:
geocentric latitude (the angle formed at the center of the Earth),
geodetic latitude (the one normally used, the angle formed between the
line normal to the tangent of the ellipsoid and the axis of rotation),
and the angles used in the parametric formulas representing an
ellipse. These don't agree with each other at any place not on the
equator or the poles.

Gene Nygaard
http://ourworld.compuserve.com/homepages/Gene_Nygaard/