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Old 21-04-2015, 18:53   #61
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Re: Help with (fictional) celestial navigation

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Originally Posted by jheldatksuedu View Post
using the earth's moon for navigation on mars would be ridiculous,....
Yup. It'd be called "Earth" and be an oblong dot. We don't see mars as a disc from here.

Using either of Mars's moons would be tough too, as they whizz around the planet licketly split.

I like the concept alot. The fact that celestial has been out of favor for hundreds of years and the kids figure it out is neat. Quite Heinleinesque.
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Old 21-04-2015, 19:01   #62
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Re: Help with (fictional) celestial navigation

I think I agree with Wotname and The Penguin. I have a vague memory in school of learning the exact lesson Wotname described regarding deduced reckoning.

Like my Astro, my chartwork terminology and labeling has been poorly exercised for many years.

I can dock the heck out of a ship though, that knowledge is doing just fine.

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Old 21-04-2015, 22:02   #63
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Re: Help with (fictional) celestial navigation

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Originally Posted by El Pinguino View Post
and I just did a google search for ded' reckoning...plenty of sites say that is the correct and original form.... such as The Straight Dope: Is "dead reckoning" short for "deduced reckoning"?
And of course if you found it on the internet then it must be correct. After the internet always has correct information.

I confess I was always in the camp that believes the term derived from deduced and over time the abbreviation ded became dead.

But then when I did a google search I find this article. The Straight Dope: Is "dead reckoning" short for "deduced reckoning"? It documents the spelling "dead" back to 1708.
Of all the dictionaries I checked that gave an etymology, the American Heritage Dictionary is most amenable to the "deduced" theory, saying "Possibly alteration of ded. abbr. of deduced." "Possibly" is the kindest treatment this theory is given in any dictionary I could find. The Encarta World English Dictionary says "probably from dead 'absolute' or 'exact,' although 'dead' may be by folk etymology from ded., a shortening of deduce or deduction." The Dictionary of Misinformation says of the "deduced" theory, "There is no evidence for such a belief." The Oxford English Dictionary says that the term is from the adjective "dead" and doesn't deign to even discuss the supposed derivation from "deduced". The Oxford Dictionary of English Etymology provides the final nail in the coffin: "a proposed etym. ded., for deduced, has no justification."

These sources agree on the derivation from the adjective "dead" but differ on what "dead" is supposed to mean in this context. One theory, supported by the OED, is that it's dead in the sense "complete(ly)" or "absolute(ly)," also found in "dead wrong," "dead ahead," "dead last," etc. The idea seems to be that the dead-reckoning position is one based completely on reckoning (calculation) and not at all on observation of landmarks. Others hold that "dead" means "unmoving," as in "dead in the water." The idea here is that dead reckoning is calculated with respect to an object (like the log) that is dead in the water (not moving with respect to the surface of the water). Yet another theory is that it comes from "dead seas" (supposed to mean "unknown seas"), where dead reckoning would be an important tool.

In the earliest dictionary entry I could find for the term (1708, Dictionarium Anglo-Britannicum), it is spelled "Dead-reckoning" (with the hyphen, but without any mention of "deduced"). It seems that the "dead" spelling is older than "ded." by more than three centuries.

And then there is this book from 1867, a very interesting read for many reasons. For one how some nautical terminology has changed and some has not. Since the Brits do seem to be sticklers for details and "proper" English I would put some credence to their spelling of the term as dead reckoning. Front page and xcerpts copied below.
http://www.gutenberg.org/files/26000...-h/26000-h.htm



THE
SAILOR'S WORD-BOOK:


AN ALPHABETICAL DIGEST
OF
NAUTICAL TERMS,
INCLUDING SOME MORE ESPECIALLY MILITARY AND SCIENTIFIC, BUT USEFUL TO SEAMEN;
AS WELL AS ARCHAISMS OF EARLY VOYAGERS, ETC.
BY THE LATE
ADMIRAL W. H. SMYTH,
K.S.F., D.C.L., &c.


REVISED FOR THE PRESS BY
VICE-ADMIRAL SIR E. BELCHER,
K.C.B., &c. &c.



LONDON:
BLACKIE AND SON, PATERNOSTER ROW;
AND GLASGOW AND EDINBURGH.
1867.


DEAD-RECKONING. The estimation of the ship's place without any observation of the heavenly bodies; it is discovered from the distance she has run by the log, and the courses steered by the compass, then rectifying these data by the usual allowance for current, lee-way, &c., according to the ship's known trim. This reckoning, however, should be corrected by astronomical observations of the sun, moon, and stars, whenever available, proving the importance of practical astronomy.
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Old 21-04-2015, 22:58   #64
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Re: Help with (fictional) celestial navigation

Having found it on the internet is just as good as having found it in a book shop.. most of the non sense on the 'net has come from books......
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Old 21-04-2015, 23:04   #65
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Re: Help with (fictional) celestial navigation

If you just need your protagonist to be in the wrong place, the simplest explanation is that he's doing the celestial navigation correctly, but his time is wrong. This would produce a consistent error east or west every time even when doing everything correctly.

He can discover the time problem by referencing a better time, or by sighting against a landmark with a known position on the chart.
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Old 22-04-2015, 00:59   #66
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Re: Help with (fictional) celestial navigation

Mars...yes, but wouldn't they need an almanac and tables developed for Mars rather than Earth? And the odds are, none will be developed for Mars because the technology is already so out of use. Even if their stolen rover somehow was equipped with a sextant, or even if they kludged one together with more accuracy than, say, the type of instruments Columbus used to take a basic height of the sun.


I'd have to take a double dose of "willing suspension of disbelief" to think that 100 years from now, navigation satellites would still be relied upon, yet unable to withstand solar flares. But I'm a hard audience.(G)
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Old 22-04-2015, 10:47   #67
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Re: Help with (fictional) celestial navigation

dead vs ded

My copy (1976) of Oxfords Companion to Ships and the Sea gives the correct spelling as "Dead Reckoning".

It notes that the usage of "dead" goes back at least 400 years (cira 15XX). It noted that there were some who promoted "ded" as the original spelling as shorthand for deduced but found this to be unlikely as that deduced was not commonly used in the English language at that time. And especially not used in navigation at that time.

Further it states that sailors of the time referred to uncharted waters as 'dead" waters and that it was likely that during times where due to overcast etc the sun and other references were not visible (the times that dead reckoning was used) sailors would sail into "dead" waters as well. Thus Dead reckoning.

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Old 22-04-2015, 11:09   #68
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Re: Help with (fictional) celestial navigation

"dead" water probably correct as source. Never saw "ded (deduced) reckoning" since first sailing intro at age 5 (1936). Father was USNA, surely would have known correct term. In fact, since then this is the first mention of ded I have ever seen.
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Old 22-04-2015, 14:05   #69
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Re: Help with (fictional) celestial navigation

Given the levels of literacy 400 years ago 'dead' was probably how the scholars of Oxford or where-ever decided it should be spelt. In use by common sailor-men it was probably spoken as 'ded' or in certain parts.... 'dud' .... or maybe even 'deed'.

Getting back to Mars.... there will be no point in knowing where you are unless you have a chart showing where everything else , or at least where your destination is....
Likewise on earth.... no point in knowing where you are to three decimal places . Try giving some bloke in the Simpson Desert his lat / long and telling him to find his was home without a map.
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Old 22-04-2015, 14:20   #70
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Re: Help with (fictional) celestial navigation

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Originally Posted by El Pinguino View Post
Given the levels of literacy 400 years ago 'dead' was probably how the scholars of Oxford or where-ever decided it should be spelt. In use by common sailor-men it was probably spoken as 'ded' or in certain parts.... 'dud' .... or maybe even 'deed'.

Getting back to Mars.... there will be no point in knowing where you are unless you have a chart showing where everything else , or at least where your destination is....
Likewise on earth.... no point in knowing where you are to three decimal places . Try giving some bloke in the Simpson Desert his lat / long and telling him to find his was home without a map.
The chart is on their smart-phone of the age. Also a star chart and camera that can map their position....
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Old 22-04-2015, 14:49   #71
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Re: Help with (fictional) celestial navigation

You want to shoot as many stars as you can get. The more LOP's you get the better. Why?...because it gets you a more accurate average. You weight the lines that you think are the most accurate and throw out or weight less heavily the lines that you believe are less accurate. This is one of those situations where navigation becomes more of an art than a science. You base your position on an estimate of what in your experience is most likely to be closest to your actual position at that time.

Two LOP's does not mean that you were where they intersect....it's most likely a worse fix than if you had shot five stars.
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Old 22-04-2015, 14:50   #72
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Re: Help with (fictional) celestial navigation

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Originally Posted by El Pinguino View Post
Given the levels of literacy 400 years ago 'dead' was probably how the scholars of Oxford or where-ever decided it should be spelt. In use by common sailor-men it was probably spoken as 'ded' or in certain parts.... 'dud' .... or maybe even 'deed'.
Pronunciation certainly was odd compared to the written word in them olden days. Gunul for gunwale, foc'sl for forecastle, woostersheer for Worchestershire. People sure did talk funny.
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Old 23-04-2015, 14:11   #73
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Re: Help with (fictional) celestial navigation

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"dead" water probably correct as source. Never saw "ded (deduced) reckoning" since first sailing intro at age 5 (1936). Father was USNA, surely would have known correct term. In fact, since then this is the first mention of ded I have ever seen.
Doesn't Chapmans &/or Duttons mention "ded" from "deduced?"
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Old 23-04-2015, 14:29   #74
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Re: Help with (fictional) celestial navigation

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Doesn't Chapmans &/or Duttons mention "ded" from "deduced?"
Looked in my most recent edition of Chapman and saw no mention deduced in the chapter on dead reckoning.

Don't have a copy of Duttons at the house. Checked The Mariner's Dictionary by Bradford and no mention there either.

I still think that the fact that the 1867 British book The Sailor's Work Book doesn't mention deduced a significant bit of evidence against.
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Old 23-04-2015, 14:40   #75
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Re: Help with (fictional) celestial navigation

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"dead" water probably correct as source. Never saw "ded (deduced) reckoning" since first sailing intro at age 5 (1936). Father was USNA, surely would have known correct term. In fact, since then this is the first mention of ded I have ever seen.
I can think of a number of sailing terms that also use dead.

Dead ahead or astern
Dead slow
Dead light
Deadeye
Deadrise

Surely at least some of these derive from some common use of the word dead.
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