# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Help for beginner
From: Gary LaPook
Date: 2015 Dec 21, 07:39 +0000
I just measured the distance from my ass to my eye (sitting down), two feet, four inches, 2.3 feet. Since the distance to the horizon is (close enough for government work) the square root of the height of your eye above the surface of the water I would only need a lake 1.5 nautical miles across
to use the water surface horizon for celestial observations if i sit down right on the water's edge. So, it doesn't need to be a big lake.

gl

To: garylapook---.net
Sent: Sunday, December 20, 2015 11:30 PM
Subject: [NavList] Re: Help for beginner

First a correction to some wording of your questions.
Position is a two dimensional concept on the surface of the earth so one piece of data, a sight, will never determine your position.  A meridian transit sight only gives latitude but not longitude.
The beauty of and importance of the MT sight is that the math to extract the latitude information is substantially simpler than a sight taken at other times, but a sight taken at any time is equally effective t determining your position.  One sight removes the uncertainty from two dimensions to one.  At the end of the sight you know you are a line not a surface.
Now for how to practice taking sights.  You have to have a horizon or substitute, artificial horizon obviously won't work for a body too high in the sky.  Absent a natural horizon, ie one where you don't see the other shore or one where the water excedes of several miles then you can use a smaller body of water and a dip corrected for the shortness of the distance to the waters edge, you need to investigate dip short corrections.  I have successfully done this with a pond as small as 100 yards across.  It helps if you reduce the height to eye by lying on the ground or in Alabama in the summer time I would think about submerging yourself up to you neck.
Dave

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