NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lunars
From: Frank Reed
Date: 2007 Sep 24, 00:18 -0400
From: Frank Reed
Date: 2007 Sep 24, 00:18 -0400
Hi John, you wrote: "Some of you may want to check out my new book, Celestial Navigation in the GPS Age, available from, www.celestaire.com or www.paracay.com . Among other things, it discusses lunar sights using only the same old understandable basics of CN, without using tables or approximations -- just a hand calculator and the Almanac." John, I got a look at your book a while back. It's very nice, but I wouldn't think the chapter on lunars would be a really critical reason for anyone to buy it. It's very good, of course, and for someone who's never heard of lunars, it would be an eye-opener. But there's so much other stuff in the book, and maybe you would like to describe it for the group?? Just in general terms: what's the book's goal, intended audience, any special point of view?, maybe a short list of topics covered, topics not covered? For those of you who attended the Celestial Navigation Weekend at Mystic Seaport in June, 2006, you probably met John Karl. He's that guy from Wisconsin (hope I got that right) who was quite interested in Herbert Prinz's explanation of solving the standard spherical triangle using a diagram (a flat, 2d diagram, that is). And you asked: "BTW, in the book I make the observation that the sun-moon distance changes about one minute of arc per two minutes of time. So to do better than finding UT to with one minute requires some pretty adroit observing. And if the LD distance were accurate to one minute of arc, the longitude would be accurate to only about 30'. Doesn't this explain why the famous British Parliament Prize was for determining longitude better than 30' of arc?? " Nope. Just a coincidence. The prize rules were set in 1714. That's even before the invention of the reflecting octant, which soon led to the sextant. In 1714, it was still harder to imagine measuring the lunar distance at a sufficiently accurate level for determining a useful longitude. Typical latitude measurements using the non-reflecting instruments of that era were known to be accurate to roughly +/-10 minutes of arc --sometimes better, sometimes worse. -FER --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to NavList@fer3.com To , send email to NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---