A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Shoemaker
Date: 2019 Feb 22, 07:59 -0800
I thought I understood star motions – my thinking was that they are basically motionless, compared to each other, in our sky, except for long term motions such as axial precession and proper motion. After working with some Polaris sights and looking at SHA and declination for Polaris for different months, I noticed that there appears to be annual oscillations with the SHA and declination of Polaris, that are somewhat out of phase with each other. I graphed the changes using data from https://aa.usno.navy.mil/data/docs/geocentric.php - Apparent Geocentric - and it seemed to verify the annual oscillations. My earlier thinking was that any changes in SHA and Dec of any star would be constant in either a positive or negative direction throughout the year, such as changes from proper motion. I know these small changes aren’t enough to be of concern in celestial navigation, a few seconds of arc, but I am wondering - Is Polaris close enough to Earth that our planet’s annual motions around the sun cause annual, cyclical changes to the SHA and Declination of Polaris ?