NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Early lunars
From: George Huxtable
Date: 2010 Mar 19, 20:34 -0000
From: George Huxtable
Date: 2010 Mar 19, 20:34 -0000
I doubt if Apache Runner will find any pre-1500 material on lunars, though the idea of using the Moon for such a purpose was certainly around in the mid 16th century, as the attached illustrations from Peter Apian show. Indeed, I've read that Ptolemy estimated the longitude span of the Mediterreanean by reports of time-of-night of lunar eclipses from distant observers, though I can't quote chapter and verse. I doubt if Columbus deduced anything worthwhile about his position from an observed lunar eclipse Another who was supposed to have used an eclipse in that way was Vespucchi, but I don't think it's been well authenticated. It wasn't until about 1700 that predictions of the Moon's position became good enough to provide much more than the crudest estimate of longitude. It was better if an observation could be compared with a simultaneous observation of the Moon at the navigator's home port, rather than a prediction, such as James managed in Canada (on land) in 1632. But then, that was only useful after-the-event, for geography rather than navigation. The first practical use of the Moon for sea longitude was by Halley in 1699-1700. I haven't come across John Kirtland Wright, or the paper that's referred to, and would like to discover a bit more. George. contact George Huxtable, at george@hux.me.uk or at +44 1865 820222 (from UK, 01865 820222) or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK. ----- Original Message ----- From: "Apache Runner"To: Sent: Friday, March 19, 2010 5:33 PM Subject: [NavList] Re:Sobel and Longitude. was:: Re: David Thomson and his lunar tables | Perhaps the definition of a conscientious navigator is one who would take a | lunar when the opportunity arose? | | I'm trying to track some pre-1500 material on lunars. There's a paper by | John Kirtland Wright who found some sources as far back as the middle ages | where the authors speculate on what are effectively lunars - I can give you | the source. Then, there are the accounts of Columbus using lunar eclipses | to try to measure longitudes - the most famous being the St. Ann's Bay | episode. | | In that era, I think the best one could do would be a crude timing of | eclipses using hour glasses and extract a time relative to sunrise/sunset or | some other easy event. If there's any material on pre 1500 mentions of | lunars, I'd be grateful to hear it. I only have the Wright article and the | Columbus stories (via Samuel Eliot Morrison's biography). | | | | On Fri, Mar 19, 2010 at 11:40 AM, Ken Muldrew wrote: | | > On 18 Mar 2010 at 23:38, George Huxtable wrote: | > | > > But in the | > > lunar era, a conscientious navigator would take a lunar when | > > the opportunity arose, when the Moon was visible in a clear sky. It was | > > part of the "professional pride" that Henry has referred to. | > | > George, | > Do you have any historical evidence to support this claim? Although | > instructors of navigation may have wished for such zeal in their students, | > without historical evidence, such as logbooks, one should be skeptical. | > The logbooks that Frank has studied, and written about here, provide a | > different view of how navigators depended on lunars in that era. It may be | > that his sources (primarily American whalers) have a bias toward a certain | > type of navigator, but anyone proposing that hypothesis is obligated to | > provide some evidence to support it. Frank's historical evidence from | > primary sources has to be considered a trump card in this debate until | > such time as other sources can be shown to contradict, or at least temper, | > his conclusions. | > | > Ken Muldrew. | > | > | > | > |