NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Pointers
From: Frank Reed CT
Date: 2004 Oct 9, 17:28 EDT
From: Frank Reed CT
Date: 2004 Oct 9, 17:28 EDT
Alex E wrote:
"I just read a funny paper:
Joel Brenner, Determination of latitude in an emergency,
American Math. Monthly, 51, N 6 (1944) 343-244.
The author recommends a method of determination of latitude
without almanach, without any tables, using only a sextant
and Polaris (and the "Pointers")."
This general type of "lifeboat" latitude was widely known. Mixter's "Primer of Navigation" (1940), which should be in any navigation enthusiast's library, has in section 2706:
"if adrift in a small boat without an almanac, a thoughtful navigator can estimate the Polaris correction closely enough to give latitude within an error of 20' or less."
Mixter goes on to describe the star epsilon Cassiopeiae at the end of the "W" of Cassiopeia and notes that this star "always indicates the LHA of Polaris". So by eyeballing the LHA of epsilon Cass, you are getting the LHA of Polaris directly. Due to precession, this is no longer strictly true, but it's still close enough to win a bet. Nobody uses this stuff for "lifeboat navigation" anymore but it might come up as a navigational "challenge" or game of some sort.
The Pointers (alpha and beta UMa) work in the same way if you remember an extra angular correction, but it's just as easy to find epsilon Cass and then the correction is nearly zero. Today, in 2004, you'll get very slightly better results by noting that Kochab (beta UMi) is almost exactly on the opposite side of the North Celestial Pole from Polaris. They all work well enough. In a real world game, you would be unlikely to find any difference from using any of these.
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
"I just read a funny paper:
Joel Brenner, Determination of latitude in an emergency,
American Math. Monthly, 51, N 6 (1944) 343-244.
The author recommends a method of determination of latitude
without almanach, without any tables, using only a sextant
and Polaris (and the "Pointers")."
This general type of "lifeboat" latitude was widely known. Mixter's "Primer of Navigation" (1940), which should be in any navigation enthusiast's library, has in section 2706:
"if adrift in a small boat without an almanac, a thoughtful navigator can estimate the Polaris correction closely enough to give latitude within an error of 20' or less."
Mixter goes on to describe the star epsilon Cassiopeiae at the end of the "W" of Cassiopeia and notes that this star "always indicates the LHA of Polaris". So by eyeballing the LHA of epsilon Cass, you are getting the LHA of Polaris directly. Due to precession, this is no longer strictly true, but it's still close enough to win a bet. Nobody uses this stuff for "lifeboat navigation" anymore but it might come up as a navigational "challenge" or game of some sort.
The Pointers (alpha and beta UMa) work in the same way if you remember an extra angular correction, but it's just as easy to find epsilon Cass and then the correction is nearly zero. Today, in 2004, you'll get very slightly better results by noting that Kochab (beta UMi) is almost exactly on the opposite side of the North Celestial Pole from Polaris. They all work well enough. In a real world game, you would be unlikely to find any difference from using any of these.
Frank R
[ ] Mystic, Connecticut
[X] Chicago, Illinois
