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From: Frank Reed (no email)
Date: Mon May 16 2005 - 23:25:14 EDT
Gordon T, you wrote:
"It would seem to me that by 1855, having the correct time via
accurate chronometers was not really much of an issue, if you
could afford a good one. I think that doing Lunar Distances at sea
was not that common."
That's true. The 1850s were the closing days in the use of lunars at sea.
There were many nautical astronomy experts on-shore who advocated them, but in
practice, by this date, they were rare. Why was that? I brought this issue up
because PART of the reason was the inaccuracy of the almanac data.
And:
"They may have been done on land or in port for getting time in
isolated places"
Lunars were used at sea as a check on the longitude on a fairly regular
basis from the origin of the Nautical Almanac through the 1850s. In the period up
to about 1835, they were a check on the dead reackoning longitude. In the
period from about 1835 to about 1855, they were a check on the chronometer
longitude. As I've written before on the list, they were never (or only rarely)
considered a "primary" means of getting longitude. There was no "lunars era"
before the "chronometer era", no period when navigators did lunars every day
in the same way that they used chronometers in later years. But this should
not be taken to mean that lunars were some unwieldy exotic thing never
practiced by real men at sea. Far from it. There is ample evidence in the logbooks
that have survived from the period. Many ordinary navigators practiced lunars
and checked their longitudes with them on a fairly regular basis. For lunars,
this "regular basis" meant several times a month. This is hard data. We don't
have to speculate because the navigators wrote it all down.
And wrote:
"but I think the Noon Sun Sight ruled, and maybe
still does. It is the easiest to do, and requires the least
calculations."
The noon sun sight is and was irrelevant to the issue of lunars since lunars
were sights for determining longitude. With a chronometer, and a graphed set
of sights around LAN, you can get longitude (with some important caveats)
but without a chronometer, the Noon sight is useless for longitude.
And:
"I don't think that 30 seconds difference would be that big of
a deal between the British and American Almanacs"
Actually it was a HUGE deal, and the release of the American almanac spurred
the Europeans to improve theirs.
You wrote:
"LD's seem to me to be very hard to do right and accurate, especially on
board a ship."
You've been exposed to the mythology that developed during the long death of
lunars from the 1850s through the early 20th century. You should really try
some lunars, and find out for yourself whether they're difficult. They're
challenging, yes, but not really much more difficult than any accurate celestial
sight. Despite the moaning and groaning from many modern would-be historians
of lunars, these observations did not require three observers, they did not
require four hours to clear, and they did not require expert knowledge of
nautical astronomy. Ordinary navigators regularly determined their longitudes to
the nearest half degree or so. They did it with ten or twenty minutes of
observation and about twenty minutes of math work, and yes, they did it at sea.
And you noted in a ps:
"The British, and rightly so, complained bitterly about us
"up starts" ripping them off, with copyright violations. We copied
without regard, by reprinting tons of British
books and documents. It was kind of a sore in their side."
That was true fifty years earlier but not by 1855. The American almanac,
when it was released in 1852 (with data for the year 1855) was the best in the
world.
And:
"The British Navy, in spite of America's victories in Revolutionary War
and in the War of 1812, was still the best in the world and we knew it."
Very true, but navies are only one side of maritime history. The American
commercial fleet in the mid-19th century was enormous. By the 1840s, the
eastern Pacific Ocean was virtually an American lake. But not because of the US
Navy --rather because of the American whaling fleet. Hawaii is a US state today,
and not an offspring of the British Empire, because of this history.
-FER
42.0N 87.7W, or 41.4N 72.1W.
www.HistoricalAtlas.com/lunars
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