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Reilly
Mountain climber
The Other Monrovia- CA
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Jan 28, 2019 - 08:30am PT
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Somewhat interesting but it seems like an expensive effort just for some photos.
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Reilly
Mountain climber
The Other Monrovia- CA
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Jan 28, 2019 - 09:11am PT
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That far south solar sextant shots are harder to achieve accuracy although the ship wasn’t rocking and he might have also done a lunar shot so the position could well be quite good, at least as good as his chronometer(s) were.
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Mighty Hiker
climber
Outside the Asylum
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Topic Author's Reply - Jan 28, 2019 - 09:17am PT
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The location where Endurance sank is known exactly, from a long series of observations taken by Worsley (and others) while she was beset, and just before she sank. They were surveying from a solid platform on the ice. She may of course have skewed as she sank, and so be a short distance away.
68°39'30.0" South and 52°26'30.0" West when she sank. Seems pretty exact.
https://weddellseaexpedition.org/news/weddell-sea-expedition-moves-on-to-endurance-wreck-site/
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Reilly
Mountain climber
The Other Monrovia- CA
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Jan 28, 2019 - 09:27am PT
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The chronometers are the issue most likely.
“ Accuracies of less than 10 nautical miles (19 km) error in position are difficult to achieve using the "longitude by chronometer" method.” 🤓
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Mighty Hiker
climber
Outside the Asylum
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Topic Author's Reply - Jan 28, 2019 - 09:32am PT
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For a single observation, seems reasonable. For a series of observations taken over the year that Endurance was beset before she sank, probably using several chronometers, you'd think it would average out.
Perhaps Guido is around and can comment? He's a naughtycal fellow.
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Reilly
Mountain climber
The Other Monrovia- CA
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Jan 28, 2019 - 09:45am PT
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I suspect an accuracy within a mile or so is reasonable to assume. I would think they have
side-scanning sonar to make it even easier.
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Lorenzo
Trad climber
Portland Oregon
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Jan 28, 2019 - 09:57am PT
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A description of Worseleys’s trust in the chronometer: ( only one is mentioned)
First. He guided the crew of the Dudley Docker to Elephant Island ( 20 miles across) exactly where he calculated. Though they lost sight of each other, all three boats landed on the same beach.
Upon leaving the Island in the James Caird,
There was no margin for error as the James Caird would sail into the South Atlantic if he missed the island; this would mean almost certain death for those in the lifeboat but also those remaining on Elephant Island. Fortuitously, the weather was fine on the day of departure from the island and this allowed Worsley to obtain a sun sighting to ensure that his chronometer was rated.
He was only able to take a few sightings on the way to SGeorgia and warned Shackleton that he expected accuracy of only 10 miles, so they aimed for S. Georgia’s West side .
On 8 May, through mists and squalls, the crew sighted South Georgia's Cape Demidov, precisely in line with the course calculated by Worsley.
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Reilly
Mountain climber
The Other Monrovia- CA
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Jan 28, 2019 - 10:06am PT
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THE OG chronometer...
Back then a commoner would be lucky to earn £50/ year!
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Lorenzo
Trad climber
Portland Oregon
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Jan 28, 2019 - 10:12am PT
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And a description of the fate of the chronometer on the James Caird.
The chronometer and a small watch were bequeathed to SPRI in 1943 by
F.A. Worsley, with the information recorded in the accession register
that they were used for navigation during the voyage of the lifeboat
James Caird from Elephant Island to South Georgia. Frank Worsley
recorded that "this chronometer, an excellent one of Smith's, was the
sole survivor, in good working order, of the twenty-four with which we
set out in the Endurance."
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Reilly
Mountain climber
The Other Monrovia- CA
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Jan 28, 2019 - 10:14am PT
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24? Not taking any chances, were they? Well, with navigation anyway.
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Lorenzo
Trad climber
Portland Oregon
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Jan 28, 2019 - 10:19am PT
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They also had the pocket watch :-)
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Lorenzo
Trad climber
Portland Oregon
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Jan 28, 2019 - 10:25am PT
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the whole navigation kit on the James Caird.
I can’t tell if the sextant has an artificial horizon.
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Reilly
Mountain climber
The Other Monrovia- CA
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Jan 28, 2019 - 10:34am PT
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Hmmm. Headed to Cambridge in May. Might have to make time for the Scott Polar Research Institute! Thanks!
I can almost guarantee that an artificial horizon was not even an option back then.
They are virtually useless at sea. Of course, frozen into the ice they would be useful
but the sextant would have had to have been custom made. Not saying that wasn’t a
possibility but not very likely IMHO, especially seeing as how they are still very rare.
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Lorenzo
Trad climber
Portland Oregon
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Jan 28, 2019 - 12:34pm PT
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Artificial horizons came into use by 1907, so they would have been cutting edge for Shackleton’s expedition. It’s not out of the question that an expedition with 24 chronometers might have one. The admiralty had been looking for on for 100 years previous.
https://www.scientificamerican.com/article/an-artificial-horizon-for-sextants/
And you are right, it would have been very difficult to steady the horizon bubble at sea, but we are talking Worseley. The method used was to judge the ends of oscillation of the bubble.
And I had mentioned it because they did take observations on the pack ice and it would have been useful there, and a sketchy sight at sea might have been better than trying to guesstimate a foggy horizon in large long period waves.
If there is one on that sextant I don’t see it .
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Toker Villain
Big Wall climber
Toquerville, Utah
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Jan 28, 2019 - 12:38pm PT
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I was blown away by the exhibit at the Field Museum where a life sized reproduction of the James Caird was surround by screens depicting rough seas.
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Reilly
Mountain climber
The Other Monrovia- CA
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Jan 28, 2019 - 12:47pm PT
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I doubt he took all 24 chronos on the Caird so the ones with the artificial horizon would have been dead weight. I guess back then they must have been made for landlubber surveying and such, eh? As an aside, those guys back then were pretty amazing with their dead reckoning when there was no horizon, or anything celestial, factoring log ‘heaving’, currents, and leeway. Well towards the end of the 1800’s many merchant captains got by on rudimentary celestial skills. Of course, if they got within 10-20 miles they were likely to make a good landfall as long as their lookout could see.
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Lorenzo
Trad climber
Portland Oregon
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Jan 28, 2019 - 12:48pm PT
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As an interesting side note, the impact crater exactly at the South Pole of the moon is named Shackleton.
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Reilly
Mountain climber
The Other Monrovia- CA
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Jan 28, 2019 - 12:51pm PT
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And another coinkidink is that the 2024 total eclipse path will pass right down Main St of the tiny town in Ohio where John Glenn grew up!
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