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    Re: Summer reading
    From: Bob Goethe
    Date: 2016 Aug 30, 11:01 -0700

    Jackson, thank you for your book recommendations.  I have just requested two of them from my local library.

    I purchased a 1977 edition of Bowditch (actually, volume 1 is 1977 while the "matching" volume 2 was published in 1975) because https://www.starpath.com/resources2/sight_average.pdf by David Burch indicated that a "1977 or earlier" edition would have a better discussion of celestial sight averaging.  I read it through from cover to cover, and found it a delightful journey.

    I have also read the 2002 edition cover to cover, and my sense is that 1) Bowditch editors wanted to get the book down to one volume instead of two, and found that - in the GPS era - an easy step to take was to strip out a lot of the celestial material, and 2) Bowditch 2002 tells you all you need to DO celestial navigation, but does not spend as much time as it used to in telling you WHY you do those things.  The other thing that the 1977 edition has is a (to me, at least) fascinating chapter on sight reduction techniques as they have evolved over time.  That chapter is completely missing from the 2002 edition.

    One of the things I found striking in my 1977 was the dismissal of the noon sight.  "As accurate time became available at sea...the noon sight lost its importance....True, the solution of a meridian altitude is simple and quick, but this is more than offset by the need for determining the time at which to make the observation, the dislike of many mariners for having to make an observation at a predetermined time, the inconvenience sometimes experiened when local apparent noon occurs at a time when other activities conflict with observation, and the possibility of missing the observation because of overcase conditions.  The practice of observing a body when a line of position is desired, and solving those which happen to have a meridian angle of 0° or 180° in the same manner as other observations, is a growing practice that eliminates the need for remembering a separate procedure for bodies on the celestial meridain.   The modern navigator thinks primarily in terms of lines of position, reather than of latitude and longitude observations" (p. 560).

    This perspective, from the last pre-GPS-era Bowditch edition, seems significant to me, as it is based on input from a much larger number of working celestial navigators than exists in the world today.  Oddly enough, most of the celestial nav texts I have reviewed from the 21st century (including Bowditch 2002) suggest that the noon sight is more simple to do than a St. Hilaire line of position, with no appreciation for what the consensus of "modern navigators" was in 1977 regarding simplicity in celestial nav. 

    John Karl's book, Celestial Navigation in the GPS Age, is an exception here.  He seems more in sync with Bowditch 1977, and says regarding "special sights":  "The advantage of having good proficiency in one method might trump the advantages of these additional sights.... Additionally, I think there has been an irrelevant historical carryover on the importance of determining latitude rather than a regular LOP.  After all, a known latitude is just an east-west LOP.  [The real consideratioin is] the LOP crossing angle at noon relative to the morning and afternoon sun lines, used for running fixes" (p. 159).

    Bob

       
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