Specifications concerning designations for astronomical radiation sources outside the solar system

How to refer to a source or designate a new one from the Working Group Designations of IAU Commission B2


  1. General Recommendations All object listings should always contain, next to a principal designation, a second designation or positional information.
  2. Case of existing designations
  3. Creation of new designations
  4. Advice on designations
  5. Further information

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          Specifications concerning designations                 
    for astronomical radiation sources outside the solar system
| |

Short title:  IAU Recommendations for Nomenclature 
Key words:    Designations IAU 

         (version 2008 November 26)

A look at the current literature reveals that unclear, ambiguous or confusing designations of astronomical sources of radiation are too often encountered. Therefore, all contributors to databases, and authors of papers, catalogs and surveys, are urged to adhere to the following set of specifications (developed and endorsed by the International Astronomical Union); otherwise, significant data may be irretrievably lost.

1. General recommendations

All source listings should always contain positional information and/or a second designation next to a principal designation in order to avoid ambiguities that can arise with a single designation.

2. Case of existing designations

3. Creation of new designations

The designation of an astronomical source should consist of the following parts :


Note that the ^ is used here to denote a blank. It is used for emphasis in showing where spaces occur in a designation. (Users are expected to use an actual blank and not this character.) Parentheses are required if a specifier is included. Acronym and sequence are essential, specifier is optional; the number of blanks may be larger in machine-readable files to right justify numerical or tabular data.

The following examples illustrate the recommended form of astronomical designations :


3.1 Acronym

The acronym (earlier called origin) is a code (i.e., alphanumerical string of characters) that specifies the catalog or collection of sources. It may be constructed from catalog names (e.g., NGC, BD), the names of authors (RCW), instruments or observatories used for large surveys (VLA, IRAS, 3C, 51W), etc – see helpful hints on creating acronyms.

The following rules apply to the construction of new acronyms:

3.2 Sequence

The sequence (or numbering) is an alphanumeric string of characters, normally only numerical, that uniquely determines the source within a catalog or collection. It may be a sequence number within a catalog (e. g., HD^224801), a combination of fields, or it may be based on coordinates. The way the sequence is constructed is called the format of the sequence; the symbols used are summarized in the Inventory of the Formats, a document which also includes examples of use and misuse.

3.2.1 Use of coordinates

Coordinate-based designations are just ``names'' and should have enough significant figures to unambiguously identify the sources. It is expected that precise coordinates will be provided in the paper (e.g., in a table), accompanied by any needed explanations and other relevant information.

If coordinates in any form are used to encode a source of radiation, a set of rules applies, which we will illustrate with a source, namely the QSO with coordinates:

   (J2000.0)  00h51m09.38s  –42° 26' 33.8''
   (B1950.0)  00h48m48.97s  –42° 42' 52.1''

3.3 Specifier

The specifier is optional and allows one to indicate other source parameters. However, they are not required syntax and are enclosed in parentheses.

3.4 Punctuation and special characters

If the designation requires the use of punctuation or special characters, the recommendations are the following :

If, at some stage, subcomponents or multiplicity of sources is recognized, the current practice is to name the subcomponents with letters or numerals such as W 51 A. Alternatively the subcomponent receives a standard designation which may be added to the sequence of the parent source with a colon; e.g., ABELL^1644:[D80]^053    where D80 refers to Dressler's catalog of morphological types in 55 rich clusters of galaxies