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From: Jim Thompson (no email)
Date: Sat Apr 02 2005 - 04:58:49 EST
I should let Frank or George explain this, but maybe if I take a stab then
I'll learn too.
The oblateness correction accounts for the distortion of the earth into an
oblate spheroid (spinning ellipse) from a true sphere (spinning circle),
caused by its spin around the polar axis. As a result, parallax in altitude
can vary by less than 20 seconds of arc between the spherical and oblate
spheroid models. This correcttion is not enough to worry about in most
practical CN, even for lunar distance sight reduction.
On page 280 of the Nautical Almanac (2004): "If an error of 0.2' is
significant (then the) expression for the parallax in altitude for the Moon
should include a small correction OB for the oblateness of the Earth...".
On http://www.clockwk.com/lunars/easylun.html
Frank wrote, "The method I've described here does not include a correction
for the oblateness of the Earth. This can be added easily but it's a fairly
minor issue."
On http://www.irbs.com/lists/navigation/0503/0048.html
Alex quoted Frank, "Earth's oblateness yields a slightly non-vertical
component to parallax..."
On http://www.irbs.com/lists/navigation/0210/0231.html
Herbert Prinz wrote, "...correction for oblateness of the earth amounting to
3" of arc..."
Jim Thompson
PLEASE NOTE NEW:
www.jimthompson.net
--------------------
Outgoing email scanned by Norton Antivirus
> -----Original Message-----
> From: Navigation Mailing List
> [mailto:]On Behalf Of Bill
> Sent: April 2, 2005 12:40 AM
> To:
> Subject: Lunars calculator
>
>
> Trying my hand at Lunars. In the results on the Frank/Centennia Software's
> calculation screen, there is an angle given above "Corrected for
> oblateness." I am unable to correlate that angle to anything I am aware of
> at this point in my journey.
>
> Any help in understanding its significance would be appreciated.
>
> Thanks
>
> Bill
>
>
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