NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lunar Distances with Alex's SNO-T
From: Frank Reed CT
Date: 2006 Nov 5, 19:22 EST
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From: Frank Reed CT
Date: 2006 Nov 5, 19:22 EST
You wrote:
"I have seen "adjustments" to NA values of up to 0.1 min to
minimize
maximum error when using the given interpolation tables, but where
might the 0.3 min differences that Frank mentions be?"
maximum error when using the given interpolation tables, but where
might the 0.3 min differences that Frank mentions be?"
Just as one example, there's the Sun altitude corrections. One column
covers October to March, the other covers April to September. Because of this
organization, there is an artificial jump in the altitude correction of 0.3
minutes of arc going from March 31st to April 1st and September 30th to October
1st. This is no problem for standard line of position
navigation.
Also, according to section 24, "Main data" in the Explanation in the
Nautical Almanac, "the largest error that can occur in the GHA or Dec of any
body other than the Sun or Moon is less than 0.2'; it may reach 0.25' for the
GHA of the Sun and 0.3' for that of the Moon." I don't know why that is, but
I'll take their word for it. This is why you can't really trust the almanac data
100% of the time when doing lunars (I should add that most of the time, the
accuracy is good enough). But no problem-- anything tabulated in the Nautical
Almanac can be calculated at higher accuracy from scratch.
-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
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