NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Antoine Couëtte
Date: 2012 Jul 23, 15:40 -0700
Dear Don,
Thank you for your last contribution on the ship's journal of the Adventure. It certainly clears up many points and enables reconciling a number of initially different viewpoints between us. Your information about their usage of the dates is a KEY and crucial element, a subject about which I already had received meanwhile a nice, kind and independent private confirmation from Douglas Denny. Thanks to you also Douglas.
As it now appears, the expression "In Ohamaneno harbor in Ulietea. Lat. 16 45 1/2 S." should not be interpreted literally. If at the time of this morning Lunar the ship was in fact 4 or 5 miles west of the western shore of Ulietea - a reason why they subsequently had to warp the ship against/into the likely prevailing easterly/southeasterly winds - then taking reliable Sun and Moon heights must have been fully practicable. In other words, from such a position west of Ulietea the horizon should have been well clear of land obstructions for both the Sun and the Moon. It certainly holds true for Lady Moon who was definitely hanging then west of their apparent South Western tip of Bola Bola. It was also true for the Sun (it had too, anyway, Alex, no ?). I am therefore suggesting a position near S16°45'and W151°35' - just 5 miles off the harbor -from which the horizon below the Moon was well clear of any land obstruction, and the horizon below the Sun was also clear of all land obstructions, since from such position and at a time close to 17h05m GMT, the Sun was hanging in the (narrow) gap between RAIATEA and TAHAA.
Any best guess ?
I just need to rework this Lunar from this newly guessed "probable position" near S16°45'and W151°35', but no time now.
Then, your remarks solve it all, Don.
*******
As a provisional conclusion, could we not say that :
- From fixed points, they apparently were already able to determine their Latitude with an incredible accuracy (much better than 0.5' to say the least, and I almost dare stating *** to within 0'1 ***). For Ohamaneno harbor, their latitude determination seems accurate to 0'05/3" ! This was achieved most probably as the result of a good number of averaged Sun observations. The Sun Declination was already known, predicted and published to an accuracy of 6" to 12" at that time. This certainly speaks strongly in favor of the kind of accuracy - the same 6" to 12 " with multiple averaged observations !!! - they were already able to achieve when observing heights with their best Lunar Distance Sextants, which they most certainly were using also for their Latitudes determinations.
- Their Longitude determination was accurate to about 10 NM and probably better than 15 NM, which boils down to a 30" accuracy on Lunar Distances, should they have had "perfect" Lunar Tables and computation tools, which still was not the actual case, and
- too bad that this specific Lunar apparently was NOT taken from a fully known position. This could have enabled us many more interesting findings.
Then, LAST BUT NOT LEAST, an obvious and immediate question : Any published Cook's Lunar anywhere from a land place which can be (fully and firmly) established to-day ? Anyone knows ??? ... so that I can start playing the very same game again ... :-))
Thanks to all, our current conclusions achieved through nice team-work seem to bring quite reasonable and acceptable responses and answers to all the points I raised a week ago. Thanks again
Kermit
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