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, 22:01 -0700
From: Lu Abel
Date: 2012 Jul 13, 22:01 -0700
Brad:
My choice of words may not have been entirely clear, but when I spoke of tables of the sun's declination being produced for Portuguese mariners, I was not implying that they landed shore parties and measured their latitude by staying ashore long enough to determine it by a half-year or longer's measurement of the sun's shadow.
Rather, I was thinking of the men of learning back in Portugal that produced a table of the sun's declination. Whether this was in Prince Henry's supposed center of navigational studies or somewhere else, I believe that there is well-documented evidence that the Portuguese were the first to produce declination tables decades if
not a half-century before Columbus.
True declination tables would also enable ships' captains to determine their longitude while at sea, using whatever pre-sextant instruments were part of their kit -- backstaffs or whatever.
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
