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Frank wrote: No. That is not true. You can ignore earth flattening and the
cost in the
position fix will be trivial. It is a MINOR matter...

Yes I agree that it is so in most practical cases. On the other hand, if you
would like to do an exact reproduction of the old method , as I have tried
to do, the problem with earth oblateness should not be ignored.

Frank wrote: And further, I would note that the approach you are taking on
this 'earth
> flattening' correction is the long way around. Have you read Chauvenet?

I don't know Chauvenet. Can you enlight me please.

I have started looking at your LD prediction program and, in due time, I
will run my test cases in your model to compare. It should be rather
interesting because I think I have arather good precision in my way to
calculate.

Kent N

----- Original Message -----
From: 
To: 
Sent: Sunday, July 06, 2008 11:31 AM
Subject: [NavList 5709] Re: Lunar trouble, need help


>
> Kent, you wrote:
> "My sources are navigation textbooks from 1795, 1796, 1842, 1845, 1853,
> 1873
> and 1896. I have also taken alook into Bowditch 1834."
>
> Ok. That helps me to understand where you're coming from.
>
> And you added:
> "What you find in textbooks are good examples which can be used for
> testing
> and "validation" of your model. That was the very reason for using
> textbooks. It is very rare that you find errors in good texybooks."
>
> Yes. I agree. These textbooks and navigation manuals often provide good
> examples. However, it is CRITICAL that you recognize that these are school
> books written on shore. They tell us about navigational education, but the
> relationship to navigational practice is ambiguous at best. If you want to
> learn about actual navigational practice, you have to dig through primary
> source materials: logbooks, journals, and the scrap paper of traditional
> navigation.
>
> And you wrote:
> "You may have a point that the focus were on "small things""
>
> Also bear in mind that these books were written in a period of fierce
> commercial competition. These navigation textbooks were marketed, peddled,
> "sold" by their publishers. And they exaggerated the importance of small
> details to sell more books.
>
> And you wrote:
> "however I don't agree with you concerning a exclusion of correction for
> earth flatness. One of the real challenges with LD's is to get corrections
> for earth flatness correct."
>
> No. That is not true. You can ignore earth flattening and the cost in the
> position fix will be trivial. It is a MINOR matter. On average, you can
> expect a longitude by lunars to be offset by about ONE nautical mile if
> earth flattening is ignored and around FIVE nautical miles at the high
> maximum (which is very rare). Nautical astronomers did, of course, spend a
> lot of time worrying about this small matter, but it was wasted time.
>
> And further, I would note that the approach you are taking on this 'earth
> flattening' correction is the long way around. Have you read Chauvenet?
> George Huxtable is also taking the long way around; the correction for
> oblateness is not that difficult if you really feel a need to include it.
> Have you tried the calculator on my web site:
> www.HistoricalAtlas.com/lunars
> ? You can optionally turn off the correction for oblateness and see very
> quickly how small it actually is.
>
> By the way, you asked whether "oblateness" would be the better term in
> English. It's 'technical language', so the community who would use the
> expression is rather small, but yes, generally, you would say 'oblateness'
> in English rather than 'earth flattening'. Nonetheless, I want to say that
> you have been very clear in your wording, and I don't think that there has
> been any confusion.
>
> I noted that Moon-Sun lunars were the most common. You replied:
> "I think the explanation is simple. It is much easier to find the local
> time
> using the sun than with any other celestial object. You don't need to
> calculate the long way with Aries, RA etc."
>
> Yes. I agree. I think that's most of it. There are some other smaller
> reasons. At a practical level, many people seem to agree that it's an
> easier
> observation visually (when the Sun is used). And of course, there's no
> identification issue. We today are accustomed to the idea that celestial
> navigators know the stars and can identify them all, but this was
> apparently
> not the case 150-200 years ago. It was a rare navigator who could find the
> lunars stars...
>
> I wrote: "Watches were not the issue. Plenty of good watches were widely
> available in the period."
> And you replied: "This view is not consistent with advices found in the
> earlier references above."
>
> Yes. And that is a typical textbook bias. The textbooks were generally
> written by mathematicians and theoreticians. They tended not to be
> practical
> individuals. They didn't like solutions involving mechanical devices. But
> pocket watches were widely available, at least to ships' officers, even at
> the beginning of the EIGHTEENTH century. By the 19th century, they were so
> common that it wasn't even necessary to refer to them. Watches were
> ubiquitous.
>
> -FER
>
>
> >
>



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