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Mr Boersma,

I am getting an experiment of my own under way. I myself don't sail but live a 
few minutes away from a sea-level view of sunset, not sunrise, but that I 
have all year round. I could drive out to Cape Aghulas, about 200 miles away, 
then wait for "perfect" or excellent conditions. From there I have a view of 
both sunrise and sunset more or less at any time of the year between August 
and May. I am making rough estimates of the sun's declinations. Weather 
conditions are another matter, but clear skies are "common". I don't know 
what the coast line is like there, whether I would be making my observations 
from a beach or from the top of a cliff. If not at sea-level, I could use two 
level, vertical boards and an improvised right angle to find observed 
altitude zero which needs to be further adjusted for refraction. Of course, I 
could stay right here where I lack a view of sunrise and use a shadow stick 
(a trusty kebab skewer) and the equation of time to get noon (using knowledge 
of my longitude would be cheating) and then multiply the time from noon to 
sunset by two to get the length of day. W

Christian Scheele
Cape Town



----- Original Message -----
From: "mike boersma" 
To: NavList@fer3.com
Sent: Thursday, January 28, 2010 1:30:46 AM GMT +02:00 Harare / Pretoria
Subject: [NavList] Re: Impressed with the Raft Book



Mr. Scheele 

As cloudy and cold as it has been here in Western Michigan, I instead used 
data from the US Naval Observatory for my local area as the time for the 
sunrise, sunset, and length of day. 

I compared this data to the data in Gatty's charts. 

I will repeat the experiment again when it is warmer without using the USNO 
data to see how things work in real life. 
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