NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2022 Feb 22, 11:45 -0800
Not exactly celestial navigation, but of peripheral interest, I hope.
The offficial IAU boundaries of the constellations were established in epoch 1925 coordinates. These boundaries have precessed and continue to precess. Mostly, this is good thing because they generally track the stars. Polaris will remain in the constellation Ursa Minor for a very long time (until it glides out under the power of its own proper motion). But the constellation boundaries were composed of meridians of right ascension (RA, or 360°-SHA) and arcs of small circles of declination. These now look a bit odd since they no longer line up with the modern coordinate grids. In the image below we can see the boundary of Ursa Minor, near Polaris, is a circular arc, but it's centered on the "wrong" pole. The coordinates have precessed nearly 50 minutes of arc in the time since the constellation boundaries were formally defined.
Frank Reed
