NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Jack Aubrey's fixing of longitude
From: Geoffrey Kolbe
Date: 2011 Jun 21, 06:14 +0100
From: Geoffrey Kolbe
Date: 2011 Jun 21, 06:14 +0100
At 23:54 20/06/2011, Albert wrote: >Well, I still remember the explanation Jack gave me about the >procedure for the intended observation... > >The idea was to determine the exact local time for the moon set. >Previously - and using the data contained in the Nautical Almanac - >he had calculated the local time of this event for the estimated >island position. > >The difference between the estimated and the actual moon-set local >time was then used to lay down the island. The exact local time of >this observation was determined with the aid of the chronometers >(good enough for the short time period since noon). > >"Two seven four" was the azimuth of the moon when her lower lobe >touched the horizon. This fits very well with the described >situation (Venus above the moon). Using moon-set to find time is a laudable idea - but if I were doing it, I would find the highest hill and perch myself on top of that. Even doing the observation from the ship's tops would have been better than the shore. Finding the height of the hill above sea level would be needed of course, but that would not have been difficult. And why would the azimuth have been so important for a timing observation? I am afraid I don't see that. Geoffrey Kolbe