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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Bowditch (2002) Table 17
From: Gary LaPook
Date: 2012 Apr 30, 23:06 -0700
From: Gary LaPook
Date: 2012 Apr 30, 23:06 -0700
Obviously the enter the table with "the height of eye of the observer in nautical miles;" is a typo. The reason you do not need to correct for dip in table 17 is that you are not measuring the height of an object using the visible horizon as the reference point as you would when measuring the altitude of a star. The height of eye is needed to determine the distance to the visible horizon so the angle below the horizon to the waterline of the object can be converted to the distance closer than the horizon can be determined and then tabulated as the distance from the observer. This is an interesting new table and was not in earlier editions of Bowditch.
The purpose of the dip short of the horizon table always eluded me since you need to know accurately the distance from you to the intervening shoreline which means that you had to know where you were and if you knew that then why are you taking celestial observations in the first place. But it does make sense for ships in convoy since a ship may be between you and the horizon on the azimuth of the star you are shooting and you can know the distance to the other ship accurately and measure the star from that ship's waterline even though you don't your location on the face of the globe. gl gl --- On Mon, 4/30/12, slk1000@aol.com <slk1000@aol.com> wrote:
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