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John Karl has written-

"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."

Well, that's interesting news. It's a long time since a book has appeared
that treats lunars seriously. I hope some listmember will purchase a copy on
our behalf and provide us with a review of it.

However, it's a bit sad to read, from the author of a work that deals with
lunars, that-

"I haven't checked the Nav List for some time.... Now I see some discussion
on Lunar Distance Tables this month."

Well, discussion on various aspects of lunars has been occurring, frequently
if sporadically, for a long time, on this list and on its predecessor. It's
one of its main topics. Somehow I doubt if lunars get discussed in such
width or depth elsewhere.

John Karl's name is new to me, as a contributor to this list. I hope he will
continue to contribute, and we can learn from each other.

"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'."

John, those facts are well-known to those of us who discuss lunars on this
list; indeed, they underlie most of the discussion on lunars, to the extent
that they are often left unstated.

"Doesn't this explain why the  famous British Parliament Prize was for
determining longitude better than 30' of arc?? "

The problem, in those days, wasn't confined to the observing. It was the
total error, in predicting where the Moon should be in the sky, measuring
where it is in the sky, and calculating out all those corrections, that had
to kept within 1', to achieve an accuracy in longitude of 30'. At the time
the longitude prize was claimed, the predictions were to no better than
about half a minute. That left only half a minute allowable accuracy, in
observation + correction. A difficult task indeed, with the instruments of
the day- and even now!

George.

contact George Huxtable at george@huxtable.u-net.com
or at +44 1865 820222 (from UK, 01865 820222)
or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.


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