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» Online Classroom   » Celestial Navigation   » Public Discussion of Cel Nav   » 9.5 and 9.6 : In the mountains?

Author Topic: 9.5 and 9.6 : In the mountains?
Michael Donatz

 - posted November 28, 2020 09:01 AM      Profile for Michael Donatz           Edit/Delete Post 
It appears that the DR coordinates for the moon and sun fixes are in the Oregon Cascades: https://www.google.com/maps/place/44°58'00.0%22N+122°24'00.0%22W/@44.8447378,-122.9098458,9.73z/data=!4m5!3m4!1s0x0:0x0!8m2!3d44.9666667!4d-122.4

I'm working the problem like I'm not several thousand feet underneath rock, but maybe I'm mistaken?

I checked the errata at https://www.starpath.com/celnavbook/errata.htm and didn't find anything about the given DR coordinates.

From: New York City
David Burch

 - posted November 28, 2020 10:54 AM      Profile for David Burch           Edit/Delete Post 
Thanks very much for pointing this out. It is in the errata now.

This is one of the beauties of celestial navigation. It can be done on land or sea. Famous documented examples are from Lewis and Clark, Perry at the North Pole, and Morton Stanley's 700-mile search for Dr Livingston in Africa. Starpath served as a consultant on the navigation of that venture shown on the History Channel.

You can think of this Moon-Sun running fix from chapter 9 as carried out in a Toyota Land Cruiser using a bubble sextant as an artificial horizon. To see the actual track this expedition might have followed download this kml file and drop it on Google earth, and then zoom in. (I believe this requires Google Earth Desktop. It seems they removed this option from Google Earth Web.)

But with that said, this should have been noted as a hypothetical example. The dip correction would have to be adjusted to 0.0 for the bubble data and the HE does not matter. I will see if we can rewrite that to cover these matters... and make an errata. In short, the data are just fine and the location is no problem, but the dip should not be there.

Thanks again. For now, just pretend this was all water.

From: Starpath, Seattle, WA
David Burch

 - posted November 28, 2020 12:57 PM      Profile for David Burch           Edit/Delete Post 
To make the errata, we note that the precise CMG between the two points is 337T and the distance is 26.7 nmi. The time run is 1105 - 750 = 3h 15m = 3.25h, or 26.7/3.25 = 8.2 kts.

Both C and S are close enough to the ones in the existing exercise (335, 7.8)to just leave these unchanged.

Thus to fix this exercise, we need to add a note about bubble sextant use, then set HE = 0, reduce the Hs of each sight by 3.9' (to remove the dip correction), and then the answer will be the same.

Thus the new 9.6 Moon #2 Hs is = 51º 21.3' and new 9.6 Sun #8 Hs sun = 51º 49.7'

Summary: we can pretend this is all water and work the sights as presented, or we can make the above changes and work this as a Toyota Land Cruiser fix — which is, of course, a figure of speech in deference to this venerable vehicle. You could also carry out this fix with a sextant in your backpack on a good electric scooter.


In Passing: the Toyota Land Cruiser is the most sought after vehicle in the deserts of Africa and the Australian Outback. The Long Term Almanac that we publish was computed and written by Dr. Geoffrey Kolbe, a British engineer and navigator, who has spent extensive time on desert expeditions in Libya and Egypt, all navigated with celestial navigation. Some of his work was presented in fiction form (under a pseudonym) as a Kindle adventure novel, War Gold wherein a Toyota Land Cruiser played a key role in the outcome of this thriller. If you read Kindle books, as a navigator, you will especially enjoy this book.

From: Starpath, Seattle, WA

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