A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Adrian F
Date: 2021 Jun 1, 05:12 -0700
You said : "If the gnomon (the stick) is at 51.2°N (at the latitude equal to star's declination) the shadow will draw the staight East-West line".
I'm afraid I'm having a little difficulty in seeing that. A shadow staying on the straight East-West line seems to imply the star staying at a constant azimuth of 90° or 270°. Taking the latitude of the stick to be the same as the declination of Vega (38.8°), it seems to me that Vega's azimuth from the stick will vary from 37° (when it rises) to 90°, then from 270° to 323° (when it sets). Or am I missing something ?
Thank you for your helpful description of the conic sections as the gnomon moves southwards from the pole, and my apologies if I'm misunderstanding what you were describing regarding a straight line.