NavList:

Geoffrey,

I DO agree to your peaceful and (hopefully) Peace bringing tone of your last post.

Thank you very much to you, because I think that at times we lack Peace Bringers here.

Everything would certainly be better if these past recent 'hard exchanges' could become definitely closed. They first and essentially brought (personal) sorrow to (many) interested readers - to say the least - as they might have been felt as totally undeserved on and from either side.

They also probably might start preventing some (or even "more" ?) of us from further contributing, should they not cease now, which would be a real pity for us all.

So, let us "erase" off our minds, souls and even hearts - if achievable - these just recently written hard exchanges, whether due to "strong" language in reply to "teasing" languague then perceived as "provoking".

Let us consider that they have not been written at all.

Agree everyone ?

*******

Most importantly, I would take this chance here to congratulate Henry for his so impressive CelNav experience ... Did you happen to know, Henry, QMCS Stevens who was your alter ego I think on USS John F. Kennedy (height of eye : 117 ft !!! ) and with whom I shot quite a few stars back in ... 1986 ?

Since some of us would be delighted to know your past navigation experiences, I would be very interested to know, Henry, your own view point on the following :

- During my nine and half (full) years at sea, first as a Ship conning officer mostly in the Indian Ocean with then CelNav as part of my everyday routine duties, and then as an Aircraft Carrier pilot - where I informally shot as many evening fixes as I could when not in night flight - I have kept in my personal archives some 400+ observations out of a grand total probably close to 2000 (less or more), i.e. only some 40 times !!! less than your own experience ....

- In the recent years, when reprocessing with modern software all my previous observations (1972-1980) which I had to perform through tables then - at least for the height reductions part of them - I discovered that a significant number (close to one fourth) of my Moon height reductions were "off" by up to 5.0 !!!! arc minutes, with an average error value somewhere close to 1.0 arc minute. Certainly this was due to inexperience, inattention or simply fatigue (sextant value erroneous reading or copying/writing ??? ) ... I have eventually come to the conclusion that the Moon Parallax Tabular corrections were often quite difficult for me to adequately perform at all times, because very often I had not performed them correctly, which in turned had forced me to reject a number of my Moon Observed heights which actually were quite correct then, as I could discover only years later.

This is a subject that I have evoked in a post a few months ago, probably (slightly??/definitely!!!) off topic then.

Is it something you did experience yourself, Henry, or did other NavList Members experience the same results ?

Since the mid 1950's, we know that ALL Moon apparent coordinates published in the NAL are accurate to all their published figures.

(One systematic exception though that I know of, since I happened to discover it by chance, simply through systematically crosschecking my software values against published values. It concerns the French Nautical Almanac Moon Coordinates published for the year 1980 in which they forgot to take the deltaT value in account. They simply made all calculations with delta=0, vs. deltaT=51 seconds or so for that time. So all its published Moon Greenwhich Hour Angles are systematically off by 0.4' and its published Declinations by up to 0.2' when close to zero, i.e. for the highest values of the Declination hourly variation. When, back in 1985, I face to face reported this error to the Bureau des Longitudes, the long life Lady Astronomer then in charge checked it at once through comparing the published values for 31 Dec 1979 24h and for 01 Jan 1980 00h. She acknowledged this past error, and then immediately had this superb, extraordinary and magnificent reply which I will never ever forget : "Vous savez, Monsieur, IL NOUS FAUT TOUJOURS GARDER BEAUCOUP D'HUMILITE DANS NOTRE TRAVAIL" / "You know, Sir, IN OUR JOB WE MUST ALWAYS STAY HUMBLE". And they accordingly fully revised their procedures although this error had apparently happened only once, 6 or 7 years earlier.

So the Moon coordinates accuracy can (almost) no longer be put up to question here and now.

But I had always heard - in both the French Military Navy and the French Commercial Navy - that Moonshots just simply did/(do) not work OK and were/(are) not quite reliable ... certainly not as much as the Sun, Planets or star shots.

Would this not be simply an effect of the actual difficulties of correctly performing at all times, JUST FROM LOOKING UP the Moon Height Correction tables - i.e. without additionnal paper/pencil computations - the generally quite important Moon parallax correction ?

This also brings up another point here. Any significant improvement in Celnav requires automatic data transmission from Sextant and Chronometer to computers/calculators. This would be a safe way to increase observations reliability.

Any feedback from your past experience here, Henry, would be very much appreciated.

Thank you very much for your Kind Attention, and

Best Regards

Antoine M. "Kermit" Couëtte
CDR (FN) Ret.

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