NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Latitude by Lunar Distance
From: Peter Fogg
Date: 2006 Oct 9, 09:51 +1000
From: Peter Fogg
Date: 2006 Oct 9, 09:51 +1000
On 10/8/06, Frank wrote:
> ...you are apparently
> working only to the nearest 0.01 degrees. That's much too coarse. You
> should re-do the calculations working to the nearest 0.0001 degrees.
> Then differences of 0.1 minutes of arc are much more likely to be
> correct.
At Lat N38d, Lon W070d, on 11 Oct 2006 (All at sea)
GMT Body Azimuth Altitude
6h 36m Aldebaran 134.616d 62.060d
Moon(Centre) 110.677 67.341
Distance between bodies 11.412d
6h 39m Pollux 79.036d 34.175d
Moon(Centre) 111.618 67.882
Distance between bodies 38.476d
At Lat N41d, Lon W074d, on 11 Oct 2006 (Approx New York)
GMT Body Azimuth Altitude
6h 36m Aldebaran 132.171d 57.758d
Moon(Centre) 111.847 63.315
Distance between bodies 11.37d
6h 39m Pollux 78.781d 31.723d
Moon(Centre) 112.735 63.828
Distance between bodies 38.454d
The differences between these results and those sent
previously are negligible.
> Also, please note that the observed distances I quoted (and
> yes, they ARE correct) were distances from the Moon's limb to the star,
> not the Moon's center.
It seems that the centre of the moon is the relevant point of
reference, as James R. Van Zandt points out.
> Ah, but Peter, the difference in parallax IS due to a change in
> position. That's why this works. :-)
The correction for parallax is positive and that for refraction is
negative. There will be an infinite number of positions where the two
corrections can cancel one another, ie; the distances will be the
same.
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