NavList:

   

Reply

Henry wrote-

      "I have completed downloading and chronologically arranging by
intended year of use copies of The American Ephemeris and Nautical Almanac
for the years 1855 through 1920, all inclusive. Anyone desiring a copy of
this publication for any year within the range indicated may email me off
list and I shall be pleased to forward the same - each file running between
about 20 and 30 MB. I am currently working on a similar downloading of the
British counterpart to the American and have completed about 60 downloads,
commencing with 1767.

      I fully realize that these pubs are generally available on the
internet, however, have found them to be inconsistently or even erroneously
identified, generally by year of publication as opposed to year of intended
of use. When working with old texts or logbooks, I now have the relevant
Almanac immediately at hand - it works for me."

      ============

      Bravo, Henry! That's quite an undertaking. Especially if Henry is
offering to be some sort of distributor of such Almanac information, which,
as he says, is by no means simple to access.

      I am specially interested in these words-
      "I am currently working on a similar downloading of the British
counterpart to the American and have completed about 60 downloads,
commencing with 1767."

      First, a bit of a quibble, in my usual vein. Isn't it a bit
Americo-centric to refer to the British almanac as "the British counterpart
to the American...", when it preceded it by many years, and the American
version commences life by wholesale copying from the British?

      But, more seriously, if Henry's project has taken him far enough, I
would welcome copies of any relevant Almanacs he can provide covering the
years 1803 and 1804, the first two years of the Lewis and Clark journey
across America, some aspects of which I have studied in detail.

      ==============

      And Frank added-

      "I've been assembling a table of the typical error (s.d.) of the
published lunar distances compared to their known values from modern
ephemerides. What I have is mostly sufficient for that but I'm particularly
interested in the changes through 1820. "

      That, too, seems a worthwhile project, and many of us would be
interested in its results.

      I wonder, however, if a simpler analysis would provide useful
information. Printed errors in lunar distance involve errors in the
following-

      1. The predicted position (in celestial lat and long) of the Moon, at
Greenwich noon and midnight.
      2. The predicted position (in celestial lat and long) of the Sun or
star (or, later, planet).
      3. Interpolating those predictions to a Greenwich time, at 3-hour
intervals (by a 4-point non-linear fit, for the Moon).
      4. Calculating a great-circle angle between them.
      5. Any subsequent blunders in transcribing or typesetting that were
not picked out in time for an erratum slip.

      It seems likely to me that the overall error will be dominated
completely by item 1, compared to which the others are all negligible. I
don't KNOW if that's the case, however, and have made no efforts to test
it.

      Right from 1767, the predicted ecliptic latitude and longitude of the
Moon, at Greenwich noon and midnight, were tabulated; given, somewhat
optimistically, to the nearest arc-second.

      It strikes me that if those predictions were collected, over a long
period, and compared with modern Moon predictions, the differences could be
very informative, especially when plotted in terms of the Moon's  phase,
declination, and nodal cycles. I have never got involved in such a study,
partly because of the difficulties, in the past, of collecting that Almanac
information (and partly, I admit, due to a certain natural indolence). I
don't know if anyone has made such a study, but haven't heard of it.

      I understand that the Moon predictions in the American almanac became
more accurate on account of their earlier adoption of Brown's lunar theory.
It would be interesting to see how that worked out in practice.

      Greenwich astronomers, as I understand, from time to time, analysed
past lunar predictions by comparison with their recorded observations of
the same meridian passage, but I've never seen the results of any such
study or even discovered a reference to it. If anyone knows of such
reports, I would be most interested.

      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: "hch" 
To: 
Sent: Thursday, November 25, 2010 3:42 AM
Subject: [NavList] Nautical Almanacs


| To all,
|
| I have completed downloading and chronologically arranging by intended
year of use copies of The American Ephemeris and Nautical Almanac for the
years 1855 through 1920, all inclusive. Anyone desiring a copy of this
publication for any year within the range indicated may email me off list
and I shall be pleased to forward the same - each file running between
about 20 and 30 MB. I am currently working on a similar downloading of the
British counterpart to the American and have completed about 60 downloads,
commencing with 1767.
|
| I fully realize that these pubs are generally available on the internet,
however, have found them to be inconsistently or even erroneously
identified, generally by year of publication as opposed to year of intended
of use. When working with old texts or logbooks, I now have the relevant
Almanac immediately at hand - it works for me.
|
| Regards,
|
| Henry
|
|
|
|
|

   

Reply