IAU Recommendations

Recommendations for the IAU (International Astronomical Union)


The IAU is the international body responsible for nomenclature for celestial bodies: stars, planets, comets, galaxies etc. On the matter of bright star designations, it defers to history (e.g. Greek letter, Roman letter and numerical designations allocated by Bayer, Flamsteed, Lacaille, Baily, Gould and others), but this is problematic as there is much inconsistency, with designations being added, removed or modified according to the whims of creators of individual catalogues. Errors made by these compilers have often gone uncontested down to the current time.

For example, the use of both lower case roman and greek letters has generated much confusion over similar-looking letters, and puiblications such as catalogues and atlases have had numerous errors in them. The latest edition of the Bright Star Catalogue has eliminated all roman letters, surely an overkill, as no replacement designations have been supplied (many brights stars being reduced to catalogue numbers), and many roman letters are unambiguous and could easily be retained.

While many have followed this lead, designations of many other stars have 'disappeared' because the star doesn't happen to be included in the Bright Star Catalogue (which is not exhaustive). But atlas publishers, such as Sky & Telescope, have gone their own way, as well they might, because it's surely only academics that are satisfied with long and cumbersome designations, and atlas pages with many unnamed (& large) dots. However, in attempting to clear up previous confusion over some designations, they have merely deleted anything that had a whiff of contention, whether or not the truth of the matter is available or not (e.g. 1 Sgr or 11 Sgr preceding 12 Sgr: due to Flamsteeds error, it is 1, not 11. Newest atlases pretend it is unnumbered).

So everyone is making unilateral (though well-intentioned) and contradictory decisions, meaning that we are no closer to resolving this issue. The IAU must take control.


I am therefore developing the following recommendations in parallel with an extension of the Bright Star Catalogue (5th edition, preliminary version) that is commonly used. They are listed in order of decreasing priority (in my own judgement, based on the greatest need, and how contentious each item is). While the overriding methodology has been to preserve existing designations as far as possible, I recognise that some changes are contentious. However, if the IAU can deal with the Pluto problem, I'm convinced that it can deal with the current problem. Astronomy is a science with a loyal following of amateurs: it behoves us, in the 21st century, to get our house in order for the benefit of all concerned.
Firstly, two important proposals not pertinent to bright stars:

  1. No uniform nomenclature has yet been adopted for near stars, an area of research that is only going to become more important in the future. The IAU should adopt a nomenclature N , somewhat akin to the number of Variable stars. So the closest few stars to Earth become: N0, N1 Centauri A-C, N1 Oph, N1 Leo . . . with the numeral increasing with each instance within each constellation. Appoint a suitable team or body to oversee these designations, both the initial seeding of stars with reliable parallaxes (taking my Near Star Catalogue as a starting point) according to increasing distance, and thereafter adding new entries without regard to order (no decimals please!) I have expanded on this at http://uranometria.blogspot.com/p/near-star-catalogue.html
  2. Numerous double star catalogues are referred to in literature, and all I ask is that where a double star designation (Struve, Dunlop etc) is introduced, it become customary according to IAU guidelines to provide an alternative, non-double designation, also (e.g. a letter or number if available like 61 Cygni, or otherwise HD or other catalogue number).
As pertaining to bright stars:

  1. Define (once and for all) the designations for all stars with Greek letters, Flamsteed numbers, and Upper-case Roman letters (which are less prone to confusion that lower-case ones) according to previous practice. Restore those designations that have sometimes been omitted for fainter stars (c.f. my EBSC, in preparation, and Morton Wagman's book, Lost Stars. A wide, maximal strategy should be adopted, making corrections to confused designations (c.f. Wagman), and in the rare case where two competing and equally-valid designations exist in the literature (most often, the numbering order of Bayer letters like pi1, pi2 etc), make a decision that best matches historical practice or parallel examples so that we will all stick to it, forever.
  2. Ratify the use of Gould numbers, where available, for stars south of +10 degrees declination. The Southern sky is bereft of Flamsteed numbers, and many bright stars can only otherwise be referred to by reference to a catalogue. Some Gould numbers are still in use (e.g. 82 G. Eridani), and now that the entire catalogue is available at http://www.uranometriaargentina.com/ and at Vizier, this is a change easily adopted, with great benefits. I have included Gould numbers in both the NSC and EBSC catalogues I have compiled.
  3. Define greek letters to constellations where, due to historical accident, a proper allocation has not occured. For example in Leo Minor, Baily stated his intention to allocate letters to all stars brighter than 4.5V. Not only was this too stingy incomparison to others such as Bayer and Gould, he made a mistake and only included Beta, where Alpha and Gamma (at least) should surely have been defined. He made the same mistake in Monoceros, but because that constellation fell within Gould's purview, he made corrections there. We surely shouldn't have to put up with what amounts to an error, editorial or otherwise.
  4. For discussion: Transform or rename lower case letter designations to upper-case ones from A-Q. This range is enough for most constellations: there will be some losses in some large Southern constellations, which will be offset by the use of Gould numbers. This is a compromise between removing all letter designations, and retaining those that are easily confused with the greek ones.
Many opinions there, some controvertial...but what do you think?


  1. I agree. It would be nice to have some of these things settled once and for all. I hope some real thought is put to it before it becomes permanent though.

  2. Anonymous24 May, 2012

    Ditto, I likewise agree. Put some thought to this and make a final decision. Richard, I think you have come up with an excellent solution here.

    I don't know what it is about scientists that they should put such a low priority for making a decision on something like this. Sure they get along fine with their 5, 6, 7 digit catalog numbers for what they are doing, but come on, we aren't going to like it. It is likely they don't even see a problem here at all, but it does matter to us amateurs!

    (I often think it is too bad that they have stewardship over it when they seem to care so little.)

  3. Anonymous24 May, 2012

    This is cool. I really like the idea of numbering outward in order of distance. Great idea. This kinda assumes that all the stars are bright enough that we can see them, though. How would we handle new dim systems as they are discovered, like brown dwarfs, that might show up closer in?