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    Re: Daytime Venus Lunar
    From: Antoine Couëtte
    Date: 2012 Aug 13, 11:26 -0700

    Hello again from Mauritius !

    Your Venus Lunar is extremely interesting, Greg, because :

    - Venus is very close from the Moon. Accurately clearing such short distances can no longer be made through "classical" Tables, as it can be done only through Computers. Frank, be so kind as to correct me if I'm wrong. And,

    - Venus phase correction is significant in this example.

    IF NO PHASE CORRECTION, and if assuming that both position and UT are correct, I am computing that you "should" have observed a Sextant Distance of 2°05'980 - hence a difference of 0'18 with your records, Greg - and a cleared distance of 2°56'424. I observe a difference of 0'224 in the cleared distances between Frank's results and mine.

    IF PHASE CORRECTION TAKEN IN ACCOUNT IN THE COMPUTATION, and still assuming that both position and UT are "perfect", then you "should" have observed a sextant distance of 2°05'896 - hence a difference of 0'096 with your record, Greg - and a cleared distance of 2°56'342. I keep observing a still relatively important difference of 0'142 between Frank's results and mine as far as cleared distances are concerned (more on this further down).

    *******

    This is an opportunity to once again try to get more in-depth information from you Frank.

    On all the lunars I cross-checked against your own results, certainly well above 100 now, I always found differences in cleared distances less than 0'1, none reaching 0'14 and definitely none 0'2, EXCEPT for short distances (say below 7°) and/or involving planet phase correction.

    Through careful comparisons and especially devised examples, and although my Ephemeris software is a little less accurate than yours, Frank, I have come to the provisional conclusion that :
    - your computer does not perform phase correction, and
    - by internal nature of the algorithms you are using, there is a slight accuracy degradation (reaching at times up to 0'25 for occultations) in your own determination of Cleared distances, although you did start up with "perfect" Ephemeris data.

    I would certainly appreciate a lot if we could have third party confirmation on my assumptions here-above, through computations through different software. Paul, you should be able to tackle this one (with a zillion decimals). Thanks in advance.

    The interest of this Lunar is to try for me to better understand what's going on, no more and no less. It might definitely bring me an "Opportunity" ( ... trying to stay current on what's going on, which by the way is a superb achievement of NASA and allies) to improve my software. The only thing I am interested in is WHAT is the best result assuming that the Moon is perfectly spherical(whether we take or not Planet phase effect into account).

    And by the way, Greg, since you definitely observed the non-circular shape of Venus, does it make sense if I suspect that you did shoot for Venus Center of Light, in which case you again super duper aced it ? Even if you did shoot for Venus center, a 0'2 achievement is already an excellent milestone ... Well, we all know after all that you belong to the Ancient Order ...

    Best Friendly Regards to all

    Kermit


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