NavList:

Feb 12, 2010

Dear Paul, Dear Frank, and Dear "M. Waldenland",

Back to NavList for me … in order to comment some of the results and data lately exchanged together on Lunars and more especially on the Lunar Occultation examples, including an 19 Oct 1997 Aldebaran Lunar Occultation example by Jean Meeus and our now familiar 1903 March, 03 Occultation example of the star Kap Cnc published by FN Captain Arago.

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First of all, I wish to again thank you Frank for your most interesting insights on how the Moon Limb apparent shape can now be fully taken in account for accurate Lunars/Lunar Occultations reductions (this was your Post # 11804 dated 06 Feb 2010).

It is extremely interesting to know that the Moon limb "exact apparent shape" can be up to one arc-second away from its "average (circular) value" as seen from the Earth.

And just as a reminder, this concept of the "Moon limb shape accurate determination" is not taken in account in the ensuing discussion and comments.

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Then I wish to thank you "M. Waldenland" for the last results you sent to me on this Immersion / Emersion example as seen from Brest, Province of Britain in the Country of France. For each case you gave me results computed by two types of software. These results agree to within 2 seconds of time.

Thank you also for your own newly computed ALDEBARAN CASE results given in your post # 12133 dated Mar 2, 19:41

Your Immersion time is UT=7h44m48s and your Emersion Time is UT=09h02m51s, while

for this example, - in NavList # 12012 dated 23 Feb 2010 - Paul published his results as 07h44m48.2s and 09h02m51.3 s, and

the results I published for this same example are 07h44m47.3s and 09h02m51.2s

We all are within less than one second of time apart … Isn't that GREAT !!!

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And last - but not least - I would like to thank you Paul for your very useful Information about retrieving the Star Catalog sources (namely the SIMBAD CATALOG) and about the Precession and Nutation theories you are using for your computation (this was your post # 12020 dated Feb 24, 2010).

Thank you also for the numerical results you also solved and indicated in your post # 12012 dated Feb 23, 2010.

This has enabled me to quickly identify why for the Arago's case my position for Kap Cnc was about 1 arc second away from yours, while on the other hand we are in such a good agreement for the Aldebaran case.

The reason was not - as I had earlier suspected - my own use of Precession series different from the now official 2006 IAU Precession series. It was a much simpler reason. When including Aldebaran in my ROM Navigation Stars list, I did very carefully verify - and more than once ! - all its numerical data. Since Kap Cnc is not - what a surprise ! - in this list, I had incorrectly typed in RAM its proper motion in R.A.

So, with now the same ICRS 2000.0 values as yours, I do get the exact same values as the ones you mentioned in your post # 12020, to within better than 1/100 arcsecond. Sight of relief now !!! :-)

Therefore I have computed again this occultation with "our" Kap Cnc apparent Coordinates, and I am now getting the following results : Immersion at UT1=22h43m36.8s (your results : 22h43m36.7s) and Emersion at UT1=23h59m36.1s (you quoted 22h59m36.0s). I think that I can now fully rest in peace !

And by the way, thanks to your precious and courteous information, I am also using now the IAU2006 Precession Series (P03 from Mrs Nicole Capitaine). My last issue of the CONNAISSANCE DES TEMPS dates back from 2005 and my last one of the ASTRONOMICAL ALMANAC dates back from … 1992. I should buy both current issues of each, just to keep myself informed of their latest changes in presentation and content.

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Thank you again to all of you for your Kind Attention and help

Antoine M. "Kermit" Couëtte

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