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    Re: Chauvenet's practical navigation experience
    From: Antoine Couëtte
    Date: 2010 Mar 15, 07:30 -0700

    Frank,


    Thank you very much for your in-depth and quite "convincing" story about William Chauvenet.

    I am a believer now :-)

    The - well established now - fact that Chauvenet had little practical experience at sea did not prevent him at all to become a "classical reference", not only inside the US NAVY as you rightly pointed it out by the end of your article, but also - as I would assume it - in the Royal Navy and in the English Speaking Community as well. Interestingly enough, my Navigation Teacher at the French Naval Academy highly regarded William Chauvenet.

    And, when I last met late Dr. Leroy E. Dogget, then Director of the US Nautical Almanac Office in the early 1980's, Dr. Dogget handed me a handwritten note which I just found again a few days ago stapled on the front page of my Copy of the 1981 Astronomcal Almanac. Dr Doggett had mentioned there and then a list of some very good Treaties of Astronomical Navigation in his viewpoint, showing as follows :

    - "A Manual of Spherical and Practical Astronomy" by William Chauvenet from the USA, and

    - "Textbook on Spherical Astronomy" by William M. Smart from the UK, and

    - (although not directly focused on Navigation), "Astronomie Générale" by André Danjon, former Director of the Paris Observatory. For some reason it seemed to be one of Dr. Doggett's favorite Treaties. I find the A. Danjon's compendium a "gold mine" as it complements both other Treaties very nicely. In particular it carries a lot of numerical examples which at times seem to lack in Smart's treaty (at least in my edition, sixth edition 1977 paperback). And in particular A. Danjon was the first Astronomer to give an accurate description and an exact formulation of the refraction induced parallax for close bodies, an effect which can exceed 1 arc second just for the Moon itself, and which can reach very much higher values for artificial satellites.

    This specific correction has been very accurately detailed and modelized - among others of course - for the GALILEO Navigation Satellites. Accordingly the quality of their satellites tracking and satellites trajectory modelling has been improved compared to the already impressively accurate NAVSTAR. This explains why in "absolute/free mode" - and to a lesser extent in the "augmented/differential mode" which is already "deadly accurate" with GPS NAVSTAR - the GALILEO Satellites Navigation System is expected to become even more accurate than GPS NVASTAR.

    Best Regards from

    Antoine M. "Kermit" Couëtte


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