Astronomical nomenclature has been a continuing problem, and the IAU has prepared recommendations. Foremost among them is that pre-existing designations should not be changed. New designations, on the other hand, should follow certain rules. "How to refer to a source or designate a new one" can be found at, more complete recommendations are at, and the nomenclature dictionary is at For new large surveys, it is possible to pre-register an acronym with the IAU; a submittal form may be found at

The following was largely written by Mr. Marion Schmitz and Dr. Helene Dickel ( Dr. Dickel ( is the US contact for advice concerning nomenclature. She has been most willing to help authors who have questions or problems. I encourage authors who have concerns about nomenclature to discuss them with me or with Dr. Dickel (or with their own contact in the case of foreign authors).

There are three classes of object nomenclature: I) an archival name, II) a common usage name, and III) a nickname.

Class I names have the requirement that they must be unique through all wavelengths and disciplines. These are what NED and SIMBAD require in order to maintain non-ambiguous entries in the data bases. If (when) the journals start providing hot-links between the electronic text and the databases, they, too, will need to use this class. We are not there yet, but Class I names should be used unless the Class II designation is overwhelmingly familiar.

Class II names are those which are most often encountered in the literature and comprise the bulk of the situations about which Data Centers are asked. These are generally short, easily recognized names which may or may not be unique but are unambiguous to experts in the field within the context of the article. For example, the Lynds Dark Nebulae have a Class I acronym of `LDN', but `L' is an acceptable Class II acronym in most cases. Please be careful with Class II acronyms, howver: `N' is not an acceptable Class II abbreviation for `NGC'. Use the Class I acronym unless there is no reasonable possibility of misunderstanding.

Class III names (``nicknames'') are those that are severely abbreviated and are used to save space (in the article) or time (in a presentation). There is often duplication in these names compared to other usage at other times. An example might be an IRAS source designated by the RA portion of the name but missing the `IRAS' acronym and the declination. Nicknames are acceptable but only if specifically introduced and defined within each individual article. They are not acceptable as a primary object designation.

The basic designation consists of an acronym and a sequence such as NGC 6334 or PSR J1302-6350. Hyphens in source designations are to be avoided, subject to the rule that pre-existing designations are not changed. `-' should be reserved for the minus sign as much as possible. It should never be used to designate a range of specifiers. Use the `/' or unambiguous words instead (e.g., ``the five sources HH 29 to 33'').

Parenthesis `()' are used for additional optional specifiers: Sometimes a velocity is needed to unambiguously identify two close sources. Such a ``specifier'' could be enclosed in parenthesis, e.g. H2O G123.4+57.6 (VLSR=-185km/s). Other optional specifiers may just give cross-identifications with an `=' if they are identical sources. If there is no `=', then it means that the new source is associated with or in the general area of the object given within the parentheses. An example is AC 211 which is identical to an X-ray source and is associated with the globular cluster M 15. It could be designated AC 211 or alternatively as AC 211 (=1E 2127+119; M 15)

The `/' separates a list of specifiers. For example, `HH 29/33' means the two objects HH 29 and HH 33. To give a list of multiple objects, list their specifiers individually or use unambiguous descriptive text as above.

Colons `:' are used in the designations of spatial subcomponents of a source. Old designations for subcomponents usually just added a letter or numerals, e.g. NGC 6334 A or occasionally a cardinal direction e.g. NGC 6334 North. This was adequate when few subcomponents of a source were known, but it breaks down if there are many subcomponents or surveys at many wavelengths (e.g., radio, IR, x-ray, masers, etc.) where sources may not coincide. Currently the recommended method for designating subcomponents is to give the designation of the parent source followed by a `:' and then the designation of the subcomponent. It is recommended that the acronym used for the subcomponent be comprised of the initials of the authors rather than the object type unless it is a large comprehensive compilation. This helps avoid duplication and confusion and allows an easier trace to the reference. Suppose two new OH masers were detected in the DR 21 star-forming region by Smith, Mathis, and Osker, then they might be designated as DR 21:SMO 1 and DR 21:SMO 2. Unknown to them, Austin, Carls, and Trend might have simultaneously detected the 2nd of these plus two different OH masers and named them DR 21:ACT 1, DR 21:ACT 2, and DR 21:ACT 3. Confusion was averted by both groups not naming them DR 21:OH 1, DR 21:OH 2, etc. However, centralized, large compilations such as the updated catalogues of Planetary Nebulae, HH objects, etc. are encouraged. Therefore one could imagine an update of the OH survey (Turner 1979); such a revised catalog with designations OH would cross reference the earlier SMO and ACT OH detections.

If non-standard or unfamiliar designations are used, a reference to the original source of the designation should be given.