A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Brad Morris
Date: 2012 Jul 12, 16:22 -0700
Interesting point. Dropped into a featureless environment without last known position. Without Almanac. Without instruments.
First to find the hemisphere N or S. Tricky only below the 23rd parallel, easy above. Whilst facing the meridian of the sun, the sun rises in the east and sets in the west, so in southerly latitudes, the sun rises on your right hand and sets on your left. Opposite in the northern latitudes.
These directions swap when below the 23rd parallel, leaving some uncertainty, but at least you are warm! So above 23 and up to 90, you know your hemisphere. Mighty cold at the pole, you may be motivated!
Next determine the latitude from the elevation of the sun at meridian passage and the declination of the sun. Assumes you know the day of the year, not prohibited in the definition. Make a protractor, you didn't bring it. Or fudge on the word instrument and bring your astrolabe.
Still lost, but heading in the right direction!
My copy of Duttons (Academy textbook) offers a few salient points. (1) NEVER abandon the ship's sextant. (2) WRITE DOWN the last known position (3) try to hack any available watch to the ships chronometer. (4) Bring navigation almanac & other associated information.
To which I might add, your EPIRB, with gps, homing beacon for localization by helo & parajumper, satellite uplink to the US Coast Guard Rescue channel, water immersion instant on and, I dare say, a fully charged battery! That's just a 'touch' better than Atkinson's Epitome and perhaps a pinch more than a 2102D (look for my electronic version, the 2102E, in the archives) and still blows the doors off the sextant.
yup, that'll do!
Dead reckoning etc are certainly valid methods of navigation. What I had in mind at my writing was a method if dropped into an unknown land and unknown initial position, one would need some external source such as an almanac. In that sense a lunar is a black box because one needs the almanac to get time and then position.South pacific navigators have been memorizing data and sailing without instrument a long time. But it is really a form of dead reckoning with lines of travel based on the parallel tracks of stares, as an example. If they were dropped in without an initial fix... They would be in the words of Dannial Boon "I've never been lost but I was a bit bewildered for a few days once"By the way in 1988 I crossed the pond from NY to France with the Electronics in "lock up". I wasn't brave enough (stupid enough) to leave them behind but was interested to feel the uncertainty.
Thomas A. Sult, MDSent from iPhone
On Jul 12, 2012, at 17:20, Brad Morris <firstname.lastname@example.org> wrote:
*amplitude of the sunOn Jul 12, 2012 6:07 PM, "Brad Morris" <email@example.com> wrote:
You wrote:" There is no navigation system that is derivable from first principles on board the boat"
1) A system of navigation does not have to derive correct fixes, it just is a system.
2) At "first principals", you may have me, but I selected solar elevation at meridian passage and the compass. You may have others.
I have on my book shelf "Atkinson's Epitome of Navigation", published in 1753. Not a reprint, mind you, but a survivor! Atkinson provides a system of navigation, using the first principals detailed above. It was the system used by Her Majesty's Ships, up until the time of Nevil Maskelyne and John Harrison, so I think this qualifies. For example "Variation of the Compass by an Altitude" (of the sun) is covered.
You then wrote" Perhaps best stated as there is no fix method that is internal to the boat."
BradOn Jul 12, 2012 4:41 PM, "Thomas Sult" <firstname.lastname@example.org> wrote:Perhaps best stated as there is no fix method that is internal to the boat.
Thomas A. Sult, MDSent from iPhone
On Jul 12, 2012, at 15:17, Brad Morris <email@example.com> wrote:
Sailing a latitude line to cross an ocean is one.
If utmost accuracy is not important, then dead reckoning is another, as was done for 100's of years before lunars and chronometers.
BradOn Jul 12, 2012 4:10 PM, "Thomas Sult" <firstname.lastname@example.org> wrote:The almanac is no less a black box. So even a lunar is a black box. There is no navigation system that is derivable from first principles on board the boat.
Thomas A. Sult, MDSent from iPhone
On Jul 12, 2012, at 15:03, Frank Reed <FrankReed@HistoricalAtlas.com> wrote:
Alan, you wrote:
"I'm simply taking as correct, the numbers produced by a "black box", which more often than not are correct"
You were talking about a GPS receiver, but you have also just described a nineteenth century chronometer! Seriously, while celestial certainly has a lot of that "do-it-yourself feeling", and that's a big part of why we enjoy it, it is also in many ways a "black box" activity. A fair case could be made that the chronometer is the earliest example of a black box. It has no "user-serviceable" parts and no means of testing it (on its own) to determine whether it is behaving properly. It normally shows no visible signs of failure. Yet these "black boxes" have been essential to celestial navigation two hundred years. In the earliest period, this was seen as a near-fatal flaw in the concept of the chronometer. A chronometer was seen as worthless without lunars for testing, and some argued, with some reason, that this implied that chronometers were little more than a luxury. As the nineteenth century progressed, the simple method of polling was developed: carry several chronometers and let them vote. It's still used with mission-critical black box systems. To put it in the same terms as some recent comments on GPS, "the best backup for a chronometer is another chronometer".
It's also worth remembering that the astronomical data published in the various nautical almanacs is simply handed down to us from the clouds. The Nautical Almanac is also a "black box". Few practicing navigators have had any means to judge whether the data on refraction and other altitude corrections, let alone the ephemeris data themselves are correct.
Incidentally, in the last 18th century through the first half of the 19th century (with rapidly decreasing frequency), navigators could use "lunars" as a completely independent check on chronometers. Yet they found them difficult to trust. I have speculated recently that this was, in part, because lunars were not a "black box" calculation. When you as sole navigator can see all your work laid out before you, and when you know that you have made various conscious choices of clearing methods to use and details to include or exclude, there is much more room for self-doubt. On some early ships with enough competent navigators aboard, the "polling method" used later for chronometers could also be applied to lunars: have three junior officers each independently work and clear their lunars and treat each of them as "black boxes". Majority rules, simple as that.
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