NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: No Lunars Era
From: Frank Reed CT
Date: 2004 Dec 6, 20:33 EST
But I would like to address your points one by one.
From: Frank Reed CT
Date: 2004 Dec 6, 20:33 EST
Alex E wrote:
"I am saying (answering the question why there was no "Lunar era") that
there was no "Lunars era" in history of navigation because"...
I think you may be jumping too quickly to an answer. We've got to
establish the facts on the ground first...
But I would like to address your points one by one.
You said:
"a) accuracy is too low"
Thirty to sixty minutes in longitude is an enormous improvement over pure
dead reckoning on a long ocean voyage. But did average navigators understand the
concept of error bars? I don't think so. I don't think practicing scientists in
this era even had a good handle on the issue.
"b) reduction is too hard."
This wasn't true. The math was tedious; it wasn't hard. But there WAS an
associated expense. You had to study this stuff, or hire someone who had studied
it.
"c) a better method (chronometer) became available at almost the same
time."
In the logbooks, longitude by chronometer takes over starting c.1835 (to
reiterate, that's for American commercial vessels). Lunars were available
starting in 1769. That's over SIXTY YEARS --a very long lag. Lunars definitely
were used in this earlier period but they were not used the way that some modern
navigation enthusiasts imagine. They were not ever a primary method of
determining longitude at sea except for a very few, like Bowditch. Instead, just
as they were an occasional check on the "longitude by chronometer" in 1850,
lunars in 1800 were an occasional check on the "longitude by DR".
Something to consider: Longitude by dead reckoning does work. A good 19th
century navigator could probably count on it up to perhaps five miles a day
average error. Since this is a random error most of the time, the cumulative
error would be about 5miles*sqrt(days). After 14 days, this would amount to
about 19 miles expected error in longitude. That's just barely enough to be
detectable by a lunar observation. So perhaps the "once every two weeks" pattern
for taking lunars was all that was required and a completely practical solution
to the problem. Of course, if the dead reckoning is going wrong because of a
steady current instead of random error, the difference in longitude could be
much greater in the same period of time...
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
[ ] Mystic, Connecticut
[X] Chicago, Illinois