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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2025 Mar 28, 13:24 -0700
Bela Kovacs,
You wrote:
"I am trying to understand why the Sun has an ecliptic latitude. Is it some kind of parallax?"
That's how I always understood it, but such a tiny effect might have some further complexity.
I grabbed the Sun's daily geocentric ecliptic latitude for three years from the JPL Horizons app and graphed it. See below. There is a pattern that looks reasonable, oscillating up and down with a range of just about one second of arc, and yet there is a funny wobble to it. Why is that? Maybe the clean symmetry in the remainder of the period is actually unusual, and there is normally a secondary wobble that is here only apparent for a few months (?). I haven't looked into it further...
Naturally, something as small as this has no navigational significance, but it's interesting nonetheless.
Frank Reed
