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My conclusion from this is that a pear shaped earth has a negligible effect on
the accuracy of sight reduction.  It doesn't matter what distance you are from
the center of the earth (well there is an over-simplification) as long as the
horizon is also at the same level.  Since the horizon is likely to be only 4
to 10 nm away, this pear shape notion becomes moot because you and the horizon
are at the same height.

On Wed, 2 Oct 2002 16:28:29 +1000 Peter Fogg  wrote:

> David Weilacher wrote:
>
> > Can anyone give me a numerical representation
> of the shape of earth?  I'm
> > thinking something like the length of a line
> of latitude for each 10 degrees
> > north and south of the equator.
>
> I'm told that Meridional Distances do indicate
> this:
>
> 10 d lat  597.11
> 20        1194.58
> 30        1792.72
> 40        2391.75
> 50        2991.82
> 60        3592.91
> 70        4194.91
> 80        4797.59
> 90        5400.63
>
> so, if I've understood correctly, a degree at
> 10d of lat.is 59.71 nm, and a
> degree at 90d of lat. is 60.007 nm.
>



Dave Weilacher
.US Coast Guard licensed captain
.    #889968
.ASA certified sailing and celestial
.    navigation instructor #990800
.IBM AS400 RPG contract programmer

   

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