NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Emergency Navigation
From: Lu Abel
Date: 2012 Jul 13, 21:52 -0700
From: Lu Abel
Date: 2012 Jul 13, 21:52 -0700
Brad:
I must respectfully disagree. If I plant a stick in the ground and are willing to measure its shadow for a full year (or at least from one solstice to the other), I can indeed deduce my latitude. If I want to do it in less time (say in just a day or in a week) I must have a declination table and an idea of what date it is. While the latter was not necessarily forbidden by the statement of the problem, the former certainly is.
I had originally wondered if I could have applied the Rule of Twelfths to approximating the sun's declination for any particular date, but it turns out that the curve of the sun's declination is NOT a sine wave (nice explanation in Wikipedia)
Lu
From: Brad Morris <bradley.r.morris@gmail.com>
To: NavList@fer3.com
Sent: Friday, July 13, 2012 4:58 PM
Subject: [NavList] Re: Emergency Navigation
Hi LuA stick in the ground, a little trigonometry and some patience will get you the degree of latitude. The ancients had it and used it to effect. You acknowledge this yourself when you state that the Portuguese mounted shore parties. Of course, possible at sea only on a stable platform or a calm day.As I noted before, the hemisphere is easy above 23 degrees of latitude. Its the hemisphere below 23 degrees of latitude thats hard, particularly as you approach the equator. Throw in the sun's declination and the degree of uncertainty rises.As we approach the poles, the sun skims the horizon, at times without a readily apparent meridian culmination. The hemisphere would be apparent but not the degree of latitude.I therefore agree, "easy latitude" is indeed relative. But it can be done, without instruments or almanacs to a 'reasonable' level of precision.Kind Regards
BradOn Jul 13, 2012 7:41 PM, "Lu Abel" <luabel@ymail.com> wrote:I think "finding latitude is easy" is very relative. If you have a sextant (but I think the original statement of the challenge said "no instruments") and you're in the Northern Hemisphere, it's easy to take a Polaris shot. How about if you're in the southern hemisphere? As I recollect, one of the triumphs of the early Portuguese explorers working their way down the coast of Africa was their shore-side support team producing a table of the Sun's declination right before the equator was crossed and it became the only practical way to find latitude..
From: Brad Morris <bradley.r.morris@gmail.com>
To: NavList@fer3.com
Sent: Friday, July 13, 2012 1:14 PM
Subject: [NavList] Re: Emergency Navigation
Finding the latitude: easy.
Finding the longitude: fairly hard and in these exercises so far, involves memorization.
Asking somebody where you are: Simple and effective!Certainly better than +/-90 latitude and +/-180 longitude.Best Regards
Brad