NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Finding latitude by length of day
From: John Huth
Date: 2009 Dec 6, 10:32 -0500
From: John Huth
Date: 2009 Dec 6, 10:32 -0500
Gary -
Thanks for scanning that and sending it around. I've been wanting to get a copy of The Raft Book for some time, but have only seen expensive and worn copies on EBay
I've been curious about the practical use of this technique for some time. Two things came to mind:
1.) How well does it work? Rather than use a table, I just calculated the function and made an exel spread sheet. I tried this once on Oct. 6th and was out by 300 miles in my latitude. Gatty's comment that you can't use it +/- 10 days around the equinoxes doesn't really convey the uncertainty - it's best around the solstices and the precision deteriorates as you get close to the equinoxes by quite some amount.
2.) Does anyone/has anyone ever used this? I haven't found any instance of this being used in modern times as an emergency means of finding latitude. The best example was the Greek and Arab classification of climes or climates, which are zones of latitude that are identified by the length of day at the summer solstice. This made me wonder how they measured the length of day - klepsidra? sun dial? hour glass?
Thanks for sending that around.
John H.
--
NavList message boards: www.fer3.com/arc
Or post by email to: NavList@fer3.com
To , email NavList+@fer3.com
Thanks for scanning that and sending it around. I've been wanting to get a copy of The Raft Book for some time, but have only seen expensive and worn copies on EBay
I've been curious about the practical use of this technique for some time. Two things came to mind:
1.) How well does it work? Rather than use a table, I just calculated the function and made an exel spread sheet. I tried this once on Oct. 6th and was out by 300 miles in my latitude. Gatty's comment that you can't use it +/- 10 days around the equinoxes doesn't really convey the uncertainty - it's best around the solstices and the precision deteriorates as you get close to the equinoxes by quite some amount.
2.) Does anyone/has anyone ever used this? I haven't found any instance of this being used in modern times as an emergency means of finding latitude. The best example was the Greek and Arab classification of climes or climates, which are zones of latitude that are identified by the length of day at the summer solstice. This made me wonder how they measured the length of day - klepsidra? sun dial? hour glass?
Thanks for sending that around.
John H.
On Sun, Dec 6, 2009 at 4:59 AM, <glapook@pacbell.net> wrote:
This topic has come up from time to time. To further this discussion I am attaching excerpts from two references. First, AFM 64-5, "Survival." This manual contains a nomogram for this determination. Second, excerpts from Gatty's "Raft Book." There is a detailed table on the back of his world map for this computation. There are also instructions for making a "bow" to use in measuring altitudes. Both of these books also contain methods for determining longitude by timing sunrise.
gl
Linked File: https://www.NavList.net/imgx/f2-AFM-64-5.pdf
Linked File: https://www.NavList.net/imgx/f1-Raft-Book.pdf
--
NavList message boards: www.fer3.com/arc
Or post by email to: NavList@fer3.com
To , email NavList+@fer3.com
--
NavList message boards: www.fer3.com/arc
Or post by email to: NavList@fer3.com
To , email NavList+@fer3.com
