NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: dip, dip short, distance off with buildings, etc.
From: Frank Reed CT
Date: 2006 Jan 11, 06:44 EST
From: Frank Reed CT
Date: 2006 Jan 11, 06:44 EST
Bill, you wrote: "To follow up on your use of a 0.15 constant (R/(1-.15) for calculating dip, short dip etc., one might question the entire system. " You bet. The entire system depends on a very specific choice for the value of terrestrial refraction. Don't get me wrong, the choice in Bowditch is certainly a good one "on average" --if you have to pick one value, you couldn't do much worse. But how much should a navigator trust those tables? This is the really interesting matter. If I look up a dip short value, or if I estimate a distance from Table XV, what kind of confidence can I have in the results? That "on average" choice in Bowditch could be very wrong in fairly common atmospheric conditions. There are coastal locations where significant temperature inversions occur each and every day, and these definitely have a big impact on the numbers in the tables. -FER 42.0N 87.7W, or 41.4N 72.1W. www.HistoricalAtlas.com/lunars
