A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2016 Feb 21, 15:23 -0800
Now and then we discuss using the planet Mercury for celestial navigation. It's rare when it's available and other brighter objects aren't more convenient, but it's one of these things that we try when we have run out of other challenges. But where can we get GHA and Dec, or better yet calculated altitude and azimuth for Mercury? In addition to various astronomical options (not navigation-related), as it turns out, it's been hidden in plain sight for years. You go to the usual USNO web app here and enter your data. Here's the usual output page for a location near me on February 1, 2016 before dawn. It shows data for the Sun, Moon, navigational stars and planets, but no Mercury. As I noted in a message yesterday, you can edit the URL (the web address) to get at some hidden data. In this case, change the value of "qqo" to "mercury" --even "qqo=me" is sufficient-- and there it is: celestial navigation data for the planet Mercury, direct from the US Naval Observatory.
This process of editing the URL may not be familiar. I have created a simple entry form that does the work:
http://www.fer3.com/arc/USNO-data-NavList.html. This is just knocked together. If there's interest, I'll clean it up and add more capabilities (e.g., multiple dates, formatted output, raw output, etc.). Note that the data is still direct from the USNO web app.