Calculating the circle distance at varying latititudes

[den1s]

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

[Don Tuite]

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

[Peter Duniho]

"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

[muff528]

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/manifold/manuals/5_userman/mfd50The_Earth_as_an_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
>

[Denny]

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

denny

[Paul Tomblin]

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.