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Subject: Re: earth radius
From: David Robinson <[log in to unmask]>
Reply-To:Geography <[log in to unmask]>
Date:Tue, 28 Jan 1997 02:12:46 GMT

text/plain (38 lines)

On 24 Jan 1997 06:41:49 GMT ,EE at University of South wrote:
Florida Subject: earth radius

> I need help finding the average (or approximate) radius of the earth
> near Florida. I know that the earth's mean  at the equator is 6.38X10^6
> and over the entire oblate sphere 6.37X10^6.

I'm not quite sure what you are asking. I assume you mean the true
radius through the central point of the globe, or do you mean the
radius of a slice through the Earth at the latitude of Florida?

If you mean the true radius it can be calculated from the formula for
the radius of an ellipse, given that the semi-polar radius is 6356.8km
and the equitorial radius is 6378.2km

Obviously if you want to be more accurate you need to consider the
height of a specific point above the original datum for the radius
calculations, which I assume was mean sealevel.

Since the difference between polar and equitorial radius is only 0.3
of one percent, do you really need to be more precise than the global
mean radius?  What are you doing that requires such accuracy?

If you want the radius of a slice at the latitude of Florida, just find
the distance between two lines of longitude at Florida's latitude,
multiply by 360 to give the circumference and deduce the radius from
that perhaps?

It's an intersting problem I've never really thought about before,
despite teaching geography for years.

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