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    Re: French Bureau of Longitude in 1885
    From: Antoine Couëtte
    Date: 2016 Oct 3, 22:38 -0700

    Dear Paul,

     

    By the way, Bureau des Longitudes has also highly contributed the new Fundamental Astronomy concepts which - as almost always now - came as a result of International Team Work: Rotating Originnon-Rotating OriginICRS, ITRS and so on ... well familiar to yourself and Astronomers worldwide now.

    Also, the only fully analytical and up to date Moon Theory currently available on the market is the Series of ELPxxxx theories (Ephémérides Lunaires Parisiennes) developed by Dr Jean Chapront and his Wife Dr Michelle Chapront-Touzé from a CNRS Unit (Centre National de Recherche Scienfiques) working closely and jointly with (and the premises of) Bureau des Longitudes on this project. During the 1970's-1980', ar least 3 International Teams (1 in Japan, 1 in the USA and 1 in France) were independently attempting to develop such new analytical theories of the Movement of Moon in order to take over the former Moon Theory by Ernest William Brown  (UK, 1919) subsequently improved by Wallace John Eckert  from IBM (ILE: Improved Lunar Ephemeris, 1954 USA).

    Very important to acknowledge here that Ernest Brown's achievement was amazing for its time (1919) since he was able to resolve and manually compute over 2,500 perturbations without any single reported error.

    It should be noticed that ILE is the first ever Moon "fully self contained" Theory - i.e. no additional corrective terms, whether "empirical" or other - which fully passes the 6" accuracy test on its results.

    Out of these 3 very solid International temas working in the mid 70's onto new Moon analytical Theories, only Jean and Michelle Chapront eventually fully completed their titanic work. In the same manner as Pierre Bretagnon, they also relied upon international contributions, either directly from the Moon Laser Radar Rangings results, or indirectly form JPL Planetary theories since they also used Pierre Bretagnon's theories VSOPxxxx which were already using with the best integration constants then available, namely the JPL ones.

    For example it can be estimated that Jean and Michelle Chapront's ELP-S2001b Theory is about 80 to 100 times more accurate than Ernest William Brown's Moon Theory over a much greater time span. One of these ELP theories, fitted to the most recent laser ranging data, is accurate to better than +/5 centimeters at least over +/-15 years around 2000.0 when compared to Bureau des Longitudes INPOP2013C or to the very best JPL last published numerical integration theories.

    Thank you very much to you, Paul, for your Warm Appraisal and very Kind Comments about recent and current French Contributions to Fundamental Astronomy.

    Best Friendly Regards,

    Kermit

       
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