NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: shadow stick trivia question
From: John Huth
Date: 2009 Oct 16, 07:15 -0400
From: John Huth
Date: 2009 Oct 16, 07:15 -0400
Frank -
You're right. I realized the error I had in visualizing it. A straight line will have a shadow on the equinox that's due east/west. It's tough to visualize because at the moment of sunrise/sunset, the length of the shadow is infinite, so it's really a limit. I really need to go calculate this. Just for fun, I found the following applet:
http://www.ies.co.jp/math/java/conics/hidokei/hidokei2.html
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You're right. I realized the error I had in visualizing it. A straight line will have a shadow on the equinox that's due east/west. It's tough to visualize because at the moment of sunrise/sunset, the length of the shadow is infinite, so it's really a limit. I really need to go calculate this. Just for fun, I found the following applet:
http://www.ies.co.jp/math/java/conics/hidokei/hidokei2.html
On Thu, Oct 15, 2009 at 9:34 PM, <frankreed@historicalatlas.com> wrote:
Well, I'm never 100% sure, but I think that's right. The cone collapses to a plane for a great circle... a plane intersecting another plane (the local ground) yields a straight line.
-FER
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