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Subject: Re: M.O.O. Alternative table 1
From: Russell Sher (rsher@XXX.XXX)
Date: Wed Nov 28 2001 - 04:47:25 EST
Hi Eric - welcome to the list...
As far as the Alternative table 1 goes, I don't know of any gain in using
this for small boat navigation where (relative) ground speeds are minimal.
The tables were of course designed with aviators in mind. I have never heard
of (or read of) any emphasis on using them for marine navigation.
As far as your second question goes; Remember that the tables are simply
precomputed formulae.(where Hc and Zn are computed using Dr Lat, LHA and DEC
as arguments)
Volume 1 simply exploits the fact that the declinations of stars change very
little and so technically, there may be a slight loss of accuracy here
between extremes of a year. However there is the correctional table supplied
for this purpose.
Also, by dividing Volume 1 into north and south hemispheres the table will
of course give azimuth Zn, directly (as opposed to azimuth angle Z which
must be converted.)
But in any case Ho249 is not as accurate as Ho229 - note that in Ho249 the
azimuth angles and calculated altitudes do not give decimal point precision.
For small-boat navigation this is quite acceptable. This should further
suggest that there is not much gain in using Alt table 1. (perhaps other
opinions will prevail...!)
Volume 1 also forms a star identifier/locator by precomputing the Hc and Zn
of the body.
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