NavList:

Frank and Dave, thank you both for your observations and pointers to information. I've looked at both the downloaded Brunnow Spherical Trig and Chauvenet* (found in Buchanan's Eclipses). There's obviously a lot more to this than I thought! It seems my intuition was wrong and to solve the problem I need either an iterative method or a third piece of information in addition to Latitude and time (the original appeal was to find longitude with just an Almamac and stopwatch since Latitude can be readily found). On the other hand I've found that Occultations are a fascinating field of study.... so much to learn so little time. I'm not sure what I'll do with with this but it's so interesting just to explore it all. Both these books, especially Brunnow, invite a thorough read in due course. It's probably only through Navlist that I could get useful help in undersytanding the issue rather than just suggestions to download the software that does the job.

* Also the Explanatory Supplement to the Astronomical Almanac would seem to be a very useful reference although, sadly, I can't find a free downloadable copy .

Thanks for your help.

Regards

Bob