Calculating the circle distance at varying latititudes

Is there an expression out there for determining the distance around
the globe, at let's say the tropic of cancer and the tropic of
capricorn? I know that the radius of the earth is 6371 - is there
perhaps an expression which relates the circle distance at the tropic
of cancer/capricorn to the radius or even perhaps the GCD?

I am attempting to determine how the circle distances change as you
move from the equator to either of the poles.


thanks

On 23 Apr 2006 16:55:44 -0700, "den1s" wrote:

Is there an expression out there for determining the distance around
the globe, at let's say the tropic of cancer and the tropic of
capricorn? I know that the radius of the earth is 6371 - is there
perhaps an expression which relates the circle distance at the tropic
of cancer/capricorn to the radius or even perhaps the GCD?

I am attempting to determine how the circle distances change as you
move from the equator to either of the poles.

r times two pi times the cosine of the latitude.

Don

"Don Tuite" wrote in message
...
[...]
I am attempting to determine how the circle distances change as you
move from the equator to either of the poles.

r times two pi times the cosine of the latitude.

As a rough estimate, that's not bad. However, the Earth is not perfectly
spherical. It bulges out at the equator, and so you have to adjust r based
on latitude for that equation to come out right.

Pete

Approx. 13.5 mi difference between the polar and equatorial radii.
But it's not a perfect ellipsoid either so calculation for distance
around a particular latitude may not be so easy. So you may as well use
the equation for a sphere and carry a little extra gas.

This is somewhat interesting reading:
http://exchange.manifold.net/manifol..._Ellipsoid.htm

Tony P.

"Peter Duniho" wrote in message
...
"Don Tuite" wrote in message
...
[...]
I am attempting to determine how the circle distances change as you
move from the equator to either of the poles.

r times two pi times the cosine of the latitude.

As a rough estimate, that's not bad. However, the Earth is not perfectly
spherical. It bulges out at the equator, and so you have to adjust r
based on latitude for that equation to come out right.

Pete

Ahh yes shades of solid geometry, Caro High School, 1956...

denny

In a previous article, "den1s" said:
I am attempting to determine how the circle distances change as you
move from the equator to either of the poles.

Google up "Aviation Formulary". Very useful site.


--
Paul Tomblin http://xcski.com/blogs/pt/
Pascal - A programming language named after a man who would turn over in his
grave if he knew about it.