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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Making an artificial horizon, and leveling thereof
From: Geoffrey Kolbe
Date: 2011 Jan 26, 06:10 +0000
From: Geoffrey Kolbe
Date: 2011 Jan 26, 06:10 +0000
At 04:56 26/01/2011, you wrote: >Gary: > >In answer to your question, the usual, so far as I know, way. Zero >the micrometer, I'm using an Astra 111B sextant. Then zero the index arm. > >Re the AH shots listed, I focoused the sextant scope on the roof >lines of small buildings, private residences, within 1/4 mile of >where I stood, beyond that proceeding as sextant instructions I've >seen say, adjusting the micrometer till I got an "unbroken horizon >line", that being the aforementioned roof line. Read the error off >the micrometer, subtracting for "on the arc", adding for "off the arc". The index mirror and the horizon mirror on the sextant are separated in height by about two inches. 1/4 mile is 440 yards, so there will be a parallax error of around half a minute in your IE determination, which is quite significant. Sextant altitudes of celestial bodies will end up being around half a minute higher than they should be. Geoffrey Kolbe
