Star catalogue is missing 21 of the 57 common navigational stars

[paulross]

The missing stars, by 'common' name, are: Acamar, Acrux, Adhara, Alkaid, Alpheratz, Ankaa, Atria, Avior, Diphda, Eltanin, Formalhaut, Gacrux, Gienah, Hadar, Menkent, Miaplacidus, Mirfak, Rigil Kentaurus, Sabik, Suhail, Zubenelgenubi.

There is some differences between these 'common' names (found in Nautical Almanacs and named by the IAU-CSN) and formal star catalogues. For example:

• Almanac/IAU-CSN name 'Eltanin' is formally known as 'Gamma Draconis' in the catalogue.
• Almanac/IAU-CSN name 'Hadar' is formally known as 'Beta Centauri' in the catalogue.
• Almanac/IAU-CSN name 'Rigil Kentaurus' is formally known as 'Alpha Centauri A' in the catalogue.

Sources:

Star names: "IAU Catalog of Star Names (IAU-CSN)": https://www.iau.org/science/scientific_bodies/working_groups/280/ Which links to: http://www.pas.rochester.edu/~emamajek/WGSN/IAU-CSN.txt

Star names and navigation data: Her Majesty's Nautical Almanac Office Publications ('Almanac'):

• NP314-18 "The Nautical Almanac" (2017).
• DP330 "NavPac and Compact Data" (2015).
• NP303 (AP3270) "Rapid Sight Reduction Tables for Navigation" (2012).

Star astronomical data ('the catalogue'): https://heasarc.gsfc.nasa.gov/cgi-bin/W3Browse/w3hdprods.pl

[brandon-rhodes]

Thanks for the contribution — and, wow, you even added tests! I'm not sure how soon a new PyEphem will be released, since at the moment I'm focusing on Skyfield, but I'm happy to see this code landed either way!