A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2016 Sep 27, 08:48 -0700
Herbert Prinz, you wrote:
"Other than aberration and parallax, which Frank already covered, only proper motion of the stars will affect their relative positions. The effect can actually be greater than that of parallax, but as far as I am aware, it concerns only one navigational star: Alpha Centauri. An almanac that is 20 years old will show a position that is wrong by a little more than a minute of arc. "
Don't forget Arcturus! :)
These changes figure into the popular H.O. 249 volume 1 (or Pub. 249). Aberration is ignored in 249 because it follows an annual cycle and is not significant for the level of accuracy promised by those tables. Precession and proper motion are cumulative on a time scale of decades and centuries so they have to be added into the five-year updates of the tables.
Back to aberration, I wrote all about aberration and sextant observations on New Year's Eve 2004, nearly twelve long years ago. Read here: