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    Re: Semi-diameter in the Nautical Almanac
    From: Antoine Couëtte
    Date: 2009 Dec 15, 09:27 -0800

    IN reply to [NavList 11165]


    You are raising an excellent point.


    May I also raise a somewhat related topic concerning an other kind of height corrections ?

    It concerns the Moon Height corrections and the way they have been presented in - at least - the UK/US NAL and the French NAL.

    I have always experienced that Moon height correction tables are quite difficult to interpolate accurately to the nearest 0.1'. I thought that they certainly could be greatly improved in this area. I had done so in the past - in the mid 70's when in the Indian Ocean - but, since I now compute these corrections automatically, I unfortunately lost this my painstakingly manually computed and rearranged Moon tables. They took twice or three times as much space than the conventional ones printed in both NAL's, but with them I was able to achieve great improvements in getting the Moon heights corrections right almost every single time.

    Only some 10 years later with my HP41 Calculator could I get further confirmation of my own previous unability to consistently achieve excellent results through interpolation of our conventional Moon Height tables. To my great disbelief, between 20 and 25 % of my Moon Height corrections showed errors ranging between 0.5' and 1.5' while I had so many times attempted to "swift view interpolate" these tables. (As OOD's - except in isolated navigation areas - we could not devote too much of our attention to just ONE item).

    In our community - at least on our side of the Atlantic, and of course "south of the channel" should I add - many collegues did not like Moon LOP's very much. They kept considering them as rather unreliable. I had difficulties to reconcile this generally well accepted view point among us with the fact that Astronomers kept claiming that the Moon Position was known to an accuracy definitely better than the 0.1' accuracy we were trying to achieve in our height interpolations.

    Now, I know why many collegues and myself did not like Moon LOP's that much ! We all had difficulties in correctly/accurately interpolating our Moon Height corrections tables !

    Has some of us experienced the same situation ? Possibly this has been addressed here before, and if so, please let me know (I am still a newcomer among you).

    Thank you


    Antoine M. Cou�tte

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