NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Fix by equal altitude sights around local apparent noon
From: Geoffrey Kolbe
Date: 2009 Oct 13, 21:35 +0100
From: Geoffrey Kolbe
Date: 2009 Oct 13, 21:35 +0100
In [NavList 10109) John Huth wrote >For my class, I made a rudimentary quadrant, where the angular scale >came from successively bisecting angles to get 64 divisions. I'm >not claiming great accuracy with this, perhaps 30 arc-minutes at >best. I measured the sun's altitude multiple times when it was >rising, during meridian passage (for latitude) and then when it was >setting. In terms of getting the LAN, the midpoint of the rising >curve and the setting curve turned out to be reasonably accurate, >given how rudimentary my quadrant was. I got to within 20 >arc-minutes of my longitude (which might not sound like anything >great to people accustomed to sextants). > >Obviously this doesn't work for a moving vessel, but I found it >interesting that a crude instrument, coupled with a watch could do a >reasonable job in determining longitude. > > John Huth It may be of interest that the method of equal altitudes is probably the most precise method of determining a position using a "portable" optical device. The device - called a precision astrolabe in Europe and an 'equiangulator' in the United States - is quite simple. A telescope, a beam splitter and a pool of mercury. By noting the elapsed time between the moments when the reflected and direct image of a given celestial object were seen to coincide in the eyepiece, it was possible to determine position to great accuracy See, for example, http://www.aggregat456.com/2006/07/geodet.html for more information. Geoffrey Kolbe --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList+@fer3.com -~----------~----~----~----~------~----~------~--~---