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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Shadow sights for longitude
From: David Fleming
Date: 2018 Jan 13, 10:47 -0800
From: David Fleming
Date: 2018 Jan 13, 10:47 -0800
PeterM
I had not heard of shadow sharpeners but I believe you are right. It seems that they are again a pinhole camera that allows you to image the edge of the shadow producer!
DavidP
I'm imagining that the precision of the length measurements remain constant. That is, if the best I can do is 1 mm out of 10cm scale then if I make
a larger instrument that I'll be limited to the same precision or 1cm out of 1 meter, or...
DaveF
On Sat, Jan 13, 2018 at 7:23 AM, David Pike <NoReply_DavidPike@fer3.com> wrote:
David Fleming wrote: Increaseing shadow length will not improve the accuracy. As has been noted the accuracy is limited by the sun not being a point source of light.
I think we’re talking about two different error sources here. There’re the difficulties caused by the Sun not being a point source of light and also the difficulties in measuring the base and the perpendicular of our triangle accurately, even if the Sun was a point source. Size won’t improve the former although it might make that difficulty more obvious, but it can improve the latter. DaveP
