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Brad M., you wrote:
"Here is a clear case of occultations in use at sea.  While his use of the 
small telescope may bring the claim that the occulatation was not at sea, the 
short answer is that the Endurance was trapped in the ice during this time.  
The position within the Weddell Sea, albeit it frozen in the pack ice, still 
qualifies as "at sea"!"

Ha! Yeah, that's funny. :-) I don't think too many mariners stuck in place in 
pack ice would call themselves 'at sea' but technically they are. Some of 
those 19th century whalers might have found themselves in the same 
circumstances, but I haven't seen any cases of occultations observed on 
ordinary commercial vessels.

Explorers and scientific expeditions, incidentally, are exactly the sort of 
people who would have used occultations since they are likely to carry good 
telescopes, likely to include people with astronomical observation and 
calculation skills on their teams, and likely to be able to set up good 
observing sites on solid ground (or solid ice!). If you're interested in this 
particular case, you could probably find out the reduction method that was 
used either by digging around in the original documents or you might be able 
to make a very good educated guess by researching the background of 
Shackleton's astronomer.

Occultations could also be used by a modern "navigator" (I use the term in 
quotes simply because most people would be doing this for the fun of it or 
perhaps to win points in a sailing race rather than for navigation in the 
literal sense). You could use a few occultations to check a chronometer, as 
they did historically. Or... you could also use a couple of occultations at 
known GMT to get a real position fix. This is fundamentally the same problem 
as the "position fix by lunar distances" that Dave and Andres and I (and a 
few others --sorry if I've left anyone out who is enthusiastic about this 
method) have been talking about for a couple of years. In fact, for a 
land-based observer, it could yield a very accurate fix, comparable to a 
standard celestial fix. Since decent models of the lunar limb are available, 
and better ones should become available very soon, the reduction can be much 
more accurate than it was historically. How good would your position fix be 
if you could time and reduce occultations with an error on the order of half 
a second or better? A big advantage of this method is that you don't need a 
visible horizon or a sextant. An ordinary spotting scope would probably 
suffice. On the other hand, unless you're prepared for some really laborious 
paper work, it also calls for a computing device of some sort. This method 
would be largely useless "at sea" unless you have some sort of stabilization 
system or perhaps a digital camera recording continuously. And needless to 
say, it would only work now and then, when the Moon is well-placed for 
observing and when there happen to be stars conveniently placed for 
occultation observations.

-FER
www.HistoricalAtlas.com/lunars


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