NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Unrealistic expectations
From: Geoffrey Kolbe
Date: 2013 Oct 12, 21:03 +0100
Ah, you have misunderstood me.
Since you are timing the moment when the cross hairs are tangential to the trailing edge of the sun to determine its azimuth, you doubtless adding the semi-diameter of the sun to your measured azimuth to get the azimuth of the sun.
However, the only circumstance when your cross hairs are are tangential to the sun at a point where a horizontal line through that point will also go through the centre of the sun, is when the sun is on the horizon. At all other altitudes, the cross hairs of your theodolite will tangential to the sun such that a line joining that point to the centre of the sun will not be horizontal. There will therefore be a larger azimuth correction to make to account for the semi-diameter of the sun.
The formula for this correction is in the paper I cited earlier....
Geoffrey Kolbe
From: Geoffrey Kolbe
Date: 2013 Oct 12, 21:03 +0100
On 12/10/2013 13:52, Richard Gaarden
wrote:
When I set up the Multiyear Interactive Computer Almanac on my computer the elevation of the viewing site was included.
Ah, you have misunderstood me.
Since you are timing the moment when the cross hairs are tangential to the trailing edge of the sun to determine its azimuth, you doubtless adding the semi-diameter of the sun to your measured azimuth to get the azimuth of the sun.
However, the only circumstance when your cross hairs are are tangential to the sun at a point where a horizontal line through that point will also go through the centre of the sun, is when the sun is on the horizon. At all other altitudes, the cross hairs of your theodolite will tangential to the sun such that a line joining that point to the centre of the sun will not be horizontal. There will therefore be a larger azimuth correction to make to account for the semi-diameter of the sun.
The formula for this correction is in the paper I cited earlier....
Geoffrey Kolbe
