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Subject: Re: Sextant Positions versus Map Datums?
From: Steven Wepster (wepster@XXX.XXX)
Date: Fri Jan 18 2002 - 07:27:31 EST
Dear Hal,
Do you have a page reference for this?
_Steven.
>According to Jean Meeus, Astronomical Algorithms, 2nd edition,
>astronomical observations (which are the basis for the Nautical
>Almanac) use the IAU 1976 ellipsoid (International Astronomical Union
>1976). Those values are
>
>a: 6378.14 km (the radius of the earth at the equator)
>f: 1/298.257 (flattening of the ellipsoid)
>
>b/a: 0.99664719 (ratio of polar radius to equatorial radius)
>
>b/a = 1-f
>
>e = sqrt(2f -f*f) = 0.08181922 (eccentricity of the meridian)
>
>I just took a look at the US Naval Observatory's NOVAS package source
>code, and they're using the same values (and to the same number of
>significant digits, to boot!)
>
>Sextant positions are referenced to the surface of this ellipsoid,
>not to a sphere.
>
>See also http://www.colorado.edu/geography/craft/notes/datum/datum.html
>
>
>Hal
>
>----
>Hal Mueller hal@XXX.XXX
>Mobile Geographics LLC http://www.mobilegeographics.com/
>8015 28th Ave NW
>Seattle, Washington (206) 297-9575
>98117 fax (206) 297-9576
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