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    Re: Graphs of Lunar Distances.
    From: Antoine Couëtte
    Date: 2010 Nov 10, 03:08 -0800

    Dear Douglas,

    In further reference to your post [NavList # 14207]dtd 25 Oct 2010, with a partial quotation given in the bottom of this post, I have observed - exactly as Frank kept pointing out for your recent Lunars in both this current "Luni-Solar Distance" thread as well as in the previous one "Graphs of Lunar Distances" - that the quality of your own Lunar observations is significantly better than your own feeling derived from your own computation results.

    I personally rely on independent computations which over 95% of the time fully match Frank's INSTANTANEOUS ANGULAR results.

    As a note, my only caution here about Frank's computer - as I just explained in NavList [#14316] to which Frank will likely reply - is that in some very special and infrequent cases the PUBLISHED RATIO between distance error increment and the corresponding longitude error increment seems to be way off reality.

    But, as regards INTANTANEOUS POSITIONAL RESULTS (and NOT THEIR TRENDS as kindly "challenged" in NavList [#14316]) I have many times observed that Frank's Computer is definitely "battle tested". There remain subtle differences between our computations results - with certainly the biggest one (and still mysterious to me) being the way Frank deals with the planets semi-diameters. But, other than this minor point, I can definitely confirm Frank's claims for quality of computational results regarding traditional Lunars. One day in a near future I am hoping to test his computer even on the (delicate) field of the Lunar occultations which are a limit case for Lunars with distance to limb equal to zero.

    Back to your example quoted here-under, with an observation time of 23h05m02.0s UT, your observation processed through Frank's computer gives the following results : Error in Lunar 0.4' , Approximate error in Longitude 0°13'2. This is exactly Frank's remark in his post [NavList#14231] dtd 27 October 2010, (last note in the bottom)

    Since your position is fully known and from your quoted Lunar distance of 72d17.3m (far limb), I have derived on my own a UT time of 23h16m09.8s . When processed through Frank's Computer this result is graded as : Error in Lunar 0.0', Approximate Error i Longitude 0°01'4. Once again our computations results fully agree to the accuracy of 6 arc seconds (or actually better as most often).

    We should therefore consider that your observation is 1min24.4 seconds off, which transletes into 0.4 arc minute observational error by Frank's published results (or 0.49 arc minute observational error according to my results).

    In this specific case I would also highly question your results derived from Oliv Soft Tables which yield an Observed UT time equalt to QUOTE 23hr-13'-36".6 UNQUOTE. As we can see, this result shows up in the opposite direction of Franks's results. As a check, and if you enter your Lunar Distance with a resulting observation time of 23h13m36.6s, Frank's computer rating now becomes : Error in Lunar 1.1' Approximate Errror in Longitude 31.6 min.

    So, there must probably remain a bug somewhere in your Lunar computational clearing process.

    To recap, Frank's repeated comments about the quality of your Lunars is fully right : they are definitely BETTER than what you have computed up until now.

    Best Friendly Regards


    Antoine M. "Kermit" Couëtte

    HEREUNDER IS A QUOTATION from your your referenced 25 Oct 2010 post [NavList#14207]

    I have just been outside and taken a Moon/Jupiter Distance.
    Perfect conditions. Bright clear sky; Moon and Jupiter beaming like lighthouse lights.
    Here is my latest effort and the latest results for a typical 'single-shot' sight. It is not bad but still not brilliant in my opinion.


    Lunar / Jupiter Observation

    Observer's position:
    Lat: North 50deg-49.910
    Long: West 000deg-51.300

    Monday 25th.X.2010.
    All times GMT. (UTC)

    MOON/JUPITER. (Jupiter to far limb)

    Time of observation = 23hr-15'-02" GMT
    Moon/Jupiter observed distance by Frieberger Sextant x4 (I think) telescope.
    = 72deg-17'.3
    minus SemiDiam 15'.36
    gives apparent Lunar distance = 72deg-01'.94

    Moon true alt (from ICE) 48deg-03'.7
    plus refn 0'.9
    minus Par-in-Alt 39'.1
    gives 'observed' Moon alt = 47deg-26'.5

    Jupiter true alt (from ICE) = 30deg-58'.0
    plus refn 1'.7
    gives 'observed' alt = 30deg-59'.7

    The Cleared Lunar Distance calculated is = 71.749551deg
    = 71deg-44'.873
    which comparing and interpolating with the Oliv Soft tables gives
    time= 23hr-13'-36".6

    An error of 1min-24".4 in time, equiv to 3/4 of a minute of arc.
    One of my better ones! I must be getting better at it.

    Douglas Denny.
    Chichester. England.

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