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Plotting the ecliptic on 2102-D star finder
From: Denis A
Date: 2026 Jan 18, 09:13 -0800
From: Denis A
Date: 2026 Jan 18, 09:13 -0800
Hi,
It is inaccurate to say that the ecliptic is projected onto a circle at the base of the 2102D. The base of the 2102D is not a projection of the sky, such as an astrolabe with a stereographic projection. It simply places the stars on lines of isodeclination, shifting the negative declinations by 90°. Since the ecliptic is not an isodeclination circle, it cannot be represented by a circle, as are the tropics, for example. The proof of this is that the points of intersection between your circle and the celestial equator (the equinoxes) are not aligned with the vernal point Aries. Your point-by-point plotting method was correct, and in this case the equinoxes were correctly positioned.
