NavList:

Sometime in 2009 (which post ??? I just cannot dig it up) Frank you mentioned a lunar example which I had earlier found here: http://gallica.bnf.fr/ark:/12148/bpt6k948062 (still available there ?)

Frank you certainly had a good look at it because as I recall you mentioned it as worth of interest ... and it actually is !!!

The Lunar method given by Captain Arago is quite similar to a method which he quotes as being then used to reduce occultations. Instead of reducing the observed sextant distance between limbs into a gecocentric Centers distance, Arago first only and simply reduces the sextant distance into the topocentric apparent distance between refracted centers. And then from CT (Connaissance des Temps) he works "backwards" - as we would say - starting from its published (geocentric) equatorial coordinates into "CT derived" topocentric apparent distances between centers at two times (hopefully supposed to be) around the observation time. To this effect he has published lengthy Tables to have all "refracted parallax" corrections completed. By comparison between these two "CT derived" values and the one "sextant observed" values (hopefully somewhere in between) he then very classically (simple "proportion rule") gets his chronometer righted as they all needed to.

It is an interesting approach for which he claims an excellent suitability for even the smallest Limb distances, in order to remedy to a then known weakness of some of the more "classical" methods.

... Well ! since I am of of his very late successors - we probably joined the French Naval Academy about one century apart - I am to say that it is a quite clever method. I still doubt whether it was actually used on board since just a few years later (@ 1905) all Lunar distances were dropped in the CT.

One question though : are short limb distances still a limitation nowadays with the powerful computation software available on line ? For example, in your Lunar on-line computer Frank or for other on-line Lunar computers you might know of ?

Sorry Frank, to react so late to your "bell ringing" to catch up our attention.

Best Regards to all and Happy New Year (in France, it is permitted to wish "Happy New Year" as late as the 31 st of January ...)

Antoine M. "Kermit" Couëtte

PS : This is my very first posting with your new NavList server. Your "spelling tool" is just GREAT. CONGRATULATIONS

Maybe this time this New Server will be super efficient to prevent the Internet - of course I mean the Internet itself and by no means myself - from inserting spelling errors in my post just AFTER I proofread it and hit the SEND button. :-))
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