A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2020 Sep 15, 12:22 -0700
Bob Goethe, you asked:
"can you explain the color coding of the black vs. the blue or green fonts for stars?"
Yes. Fortunately I saved a couple of copies of output from their web app, including the documentation, just before they shut down last year. I was, in fact, planning ahead for this eventuality. I had to read about the color-coding myself to remember how it worked.
- Blue: Stars listed as "selected stars" in Pub.249 v.1 (and also Gacrux *). This is a subset of the 57 standard navigational stars. They are highlighted in blue only when their altitudes are greater than 15° and less than 65°.
- Green: Polaris and GHA Aries. Polaris is always an oddball in lists of navigation stars. It's not one of the 57, which is why some of us refer to the "57+1" nav stars.
- Black: The remaining navigational stars.
- Red: Solar System objects: Sun, Moon, and planets.
* Why Gacrux? It's not one of the selected stars. I suspect that this is an old bug in the USNO software. They probably used a "search in string" method to decide if a star was one of the selected stars. The brighter star Acrux is one of the selected stars. But its name is found inside Gacrux. Hence, bug. Yet another reason why Gacrux is a stupid name!