IAU nomenclature

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IAU Nomenclature



This term refers to the system of lunar nomenclature recommended by the IAU. By international agreement this is the single system of naming lunar features to which all astronomers, amateur and professional, world-wide, are expected to adhere. Names and changes to names are proposed from various sources; but, until very recently, the actual nomenclature could be modified only by resolution of the IAU General Assembly, which meets every three years.

The current system of lunar nomenclature segregates the features into 18 categories drawn from a larger list whose definitions can be found on an IAU page or in the present glossary. The IAU website, hosted by the United States Geological Service, is the official IAU list and replaces the 1994/1995 printed Gazetteer of Planetary Nomenclature, which is rather rare, out-dated, and no longer in print.

At present, there are reportedly 8,962 approved lunar names in the IAU's online database. Including discontinued names, the total is well over 9,000. 1,906 of these are "primary" named features. The remainder are "satellite features".

Most of the 18 categories into which lunar features are segregated in the IAU Gazetteer are related to IAU-approved Latin feature type prefixes or suffixes. According to rules laid down in 1976 (IAU Transactions XVIB, p. 330, Items 5 & 6) only 14 Latin terms are approved for use on the Moon. Two of these -- Palus and Oceanus -- are retained for historical reasons; and another two -- Planum and Tholus are theoretically avaliable but have never been used. The prefix Planitia was also used once, but does not appear in the 1976 list. Craters -- by far the most numerous category of IAU-named features -- do not use Latin prefixes or suffixes.

Additional Information

The IAU system of lunar names is not a fixed one, but rather an evolving one that has changed many times in the past (not always for the best) and will continue to change in the future.


The impetus to standardize the international lunar nomenclature can be traced back to the complaints of British astronomer S. A. Saunder beginning in about 1905, and eventually presented to the General Assembly of the International Association of Academies (a short-lived precursor of the IAU) in 1907. In response, a committee, largely under the leadership of H. H. Turner of Oxford University, was appointed to solicit suggestions for improvement; and Saunder and the German astronomer Franz were asked to cooperate in the production of a map. Saunder, with the help of Turner’s assistant Mary Blagg, also produced a Collated List of Lunar Formations, published in 1913. The list, compiled by Blagg, compared how each significant feature had been named in the maps of Neison, Schmidt and Beer and Mädler.

The Beginnings

Following the founding of the IAU in 1919, the work of Turner’s international committee was taken over by the newly created IAU Commission 17 (Lunar Nomenclature), of which Turner was again President. Blagg annotated the maps, which had been completed by 1922, with the numbers from the Collated List. With the assistance of Karl Müller, Blagg was commissioned to select a single name for each of these and indicate its position on a series of maps. This work was not actually completed until 1935 with the publication of Blagg and Müller's Named Lunar Formations, the first officially adopted system of IAU lunar nomenclature. The system adopted included a number of names that had not been used by Neison, Schmidt or Beer and Mädler, and hence had not appeared in the 1913 Collated List. The system adopted in 1935 included 681 primary names and more than 5400 subsidiary features (designated by a primary name and a Greek or Roman letter or numeral).

Although printed copies of Blagg and Müller are extremely rare, what is substantially their proposed list can be viewed on-line as the index to the Lunar Topographic Maps on the LPI website. The small notations "CL. No." at the head of every entry are the references to Blagg's Collated List as expanded in Blagg and Müller. With the adoption of Blagg and Müller, the IAU approved a system in which major craters were given names, smaller craters nearby given Roman letter designations, isolated elevated features given a name (usually of a nearby crater) followed by Greek letter, and what are now called "rima" (rilles) being given names followed by Roman Numerals.

With the publication of Blagg and Müller, any further duties related to lunar nomenclature were transferred to Commission 16.

The Middle Phase

With the exception of the feature Deslandres being added at the 1942 IAU meeting, essentially no changes were made to the system for more than 25 years. But various lunar scientists were at work on their own improved lists, most notably Gerard Kuiper, who was, at times, President of Commission 16, and whose own project to develop a System of Lunar Craters began at Yerkes Observatory in 1958. This was completed in 1966, under Kuiper's direction, by D.W.G. Arthur and colleagues at Kuiper's newly created Lunar and Planetary Laboratory. The System of Lunar Craters was essentially a refinement of Blagg and Müller with far more precise maps and an extension of the names into the libration zones. Two semi-independent efforts were going on at the same time: the preparation of the Rectified Lunar Atlas (also at the LPL), and the LAC series lunar charts (prepared for NASA by the DMA). This work was generally endorsed by the IAU, with a list of changes presented by Arthur in 1964 being formally approved. However, some of the later developments at the LPL, such as the system of lettered crater designations for the Moon’s farside, formally proposed by Whitaker in NASA RP-1097 seems definitely to have not been approved until the 2006 General Assembly (see Recent Developments).

Like Blagg and Müller, printed copies of the System of Lunar Craters are extremely rare, but the 44 sectional maps which were part of it can be viewed on-line as part of an amateur lunar domes project. The Rectified Lunar Atlas is also somewhat rare, but the LAC charts are freely available to all on the LPI website.

The Space-based Phase

In the early to middle 1960’s space-based images of the Moon’s farside first became available, and the IAU assumed the responsibility of establishing a system of nomenclature for it, as well as for the many features beyond the limit of earth-based telescopic observation that the satellites were revealing. An initial list of 18 farside names, approved in 1961, proved somewhat premature, and the positions and descriptions of several of those features had to be later corrected. Serious efforts to manage the farside were deferred until 1967, with a final list of 513 new names being adopted in 1970.

No system of subsidiary features to go with the new farside names was proposed, and indeed the problem of naming very small features produced considerably more controversy. As a solution, Commission 17 decided in 1973 to drop all the Greek-lettered peaks of the existing nomenclature, and gradually replace the lettered craters and numbered rilles with individual names, which could be extended to the smallest features. At the same time, the nomenclature duties of Commission 17 were passed to a new Working Group for Planetary System Nomenclature (WGPSN).

In the next few years the WGPSN recommended approval of much of the new nomenclature that had been introduced on NASA’s LTO and Topophotomap map series, as well as many of the previously unofficial Apollo landing site feature names. Many of the names introduced in this way did not fit the traditional pattern, including many extremely small features given male and female first names.

Although NASA refrained from using lettered crater designations on its DMA-produced maps for several years in the early 1970's it is not entirely clear from the record that the IAU ever actually disallowed the use of lettered names, as has been frequently claimed. On the contrary, it seems to have advocated the use of a dual system in which both names would be used as already lettered craters were gradually assigned names of their own, and previously unnamed features were named (a process that has never been completed).

Interest in lunar nomenclature, and the pace of adding new names to the Moon, waned as the WGPSN became preoccupied with assigning names to the increasing number of features being revealed on the surfaces of other planets and their satellites. Earlier promises to publish comprehensive lists of the approved nomenclature do not seem to have been met.

The Planetary Gazetteer Phase

Among the resolutions proposed by the WGPSN in 1976 (IAU Transactions XVIB) was the plan to publish a comprehensive list of planetary nomenclature related resolutions and all then-current IAU-approved names, to be followed by supplementary volumes detailing the changes approved at each subsequent General Assembly meeting. According to Whitaker (p. 186), work on this was begun almost at once by the Astrogeology Branch of the United States Geological Survey (USGS), but nothing appeared until 1995 when US Government Printing Office issued (for NASA and the USGS) Gazetteer of Planetary Nomenclature 1994 (also known as USGS Bulletin 2129). The fact that NASA and the USGS "may be willing to undertake regular publication of a Gazetteer of Planetary Nomenclature under the auspices of the WGPSN" had been reported in IAU Transactions XXIIA (1993), and the WGPSN recommended to the Executive Committee, at that time, that such a Gazetteer might be regarded as the official documentation of IAU-planetary nomenclature, in place of that published (in scattered places) in the IAU Transactions. The fate of that recommendation does not seem to have been recorded. The completion of an initial Gazetteer, accurate through 1994 (the one mentioned by Whitaker), and prepared "in cooperation with WGPSN" was announced in IAU Transactions XXIIIB (1997). Whether this is precisely the publication envisioned in 1976 is unclear, for it was soon converted to an on-line electronic version, and the promised triennial printed supplements were never issued. The WGPSN's 1993 recommendation that the Gazetteer replace the IAU's traditional system of publishing new names in the Transactions may not have been approved, for as late as 1999 (IAU Transactions XXIVA), the WSPSN's report mentions that the electronic Gazetteer was a "very useful' compilation of current IAU nomenclature, but that it "does not make the printing of new, approved nomenclature in the IAU Transactions superfluous."

Despite the implication of Whitaker's remark, there were several printed versions of the Gazetteer issued before the "official" one of 1994/5. Between 1976 and 1995, the the WGPSN prepared for NASA what are apparently several semi-official preliminary versions of the final Gazetteer mentioned in the 1997 IAU Transactions. These appeared as USGS "Open File Report" (#84-692), the earliest copies of which were called the Annual Gazetteer of Planetary Nomenclature. Whitaker himself, according to a message from Jennifer Blue, owns three copies: a 1984 preliminary edition, a 1986 edition with a "first version" of the Introduction, and another 1986 edition with a second version of the Introduction. The USGS in Flagstaff owns several copies, all of which, according to Jennifer, are dated 1986 on the title pages. What seems to be a more widely-distributed version (at least one that appears in many college catalogs), and usually reported as being on microform, is dated 1989. That version is now available on-line, although a special reader (much like the Adobe Acrobat Reader) is required to view it. The introductory text gives some flavor of the original intentions of the computer file and the personnel involved in creating it. Oddly, despite the date, the 1989 edition does not include the seven Challenger astronaut names, preliminarily added in 1987, and approved by the General Assembly in 1988. There is also a copy of the much expanded introductory text from a 1991 printing (or computer printout?) on the LPI website, including a discussion of the rules and guidelines then in effect for the naming of planetary surface features.

The 1989 release of the Gazetteer has a very close resemblance to the current on-line computer database, but does not conform precisely to the guidelines for a Gazetteer announced in 1976. For example, it states that the computer file would be updated annually, and that a formal illustrated version would be published only once every six years. The Introduction also indicates that this was intended to be not only a list of all IAU-approved names, but also of names appearing on "published maps" (by which seems to be meant those published by the DMA, the USGS and comparable agencies in the Soviet Union), which would presumably be given a provisional status pending approval by the IAU. IAU-approved names are distinguished from non-IAU-approved ones by an Approval Status field, essentially identical (as are all the other fields) to that in the modern Gazetteer .

The positions and diameters of many lunar features given in the Open File Report differ from the previous IAU data as published in Blagg and Müller and the System of Lunar Craters, but unfortunately the Introduction fails to explain where the new data came from. The Introduction also includes a number of intriguing remarks such as "Most Lunar albedo features have been given formal names. The exception is Reiner Gamma, an enigmatic feature. The next version of the gazetteer will include all albedo names, including Reiner Gamma." (later editions of the Gazetteer did not list any additional lunar albedo features, and it is not known what these formal names may have been).

Although the Gazetteer was released by the USGS, Whitaker states in his introduction to NASA RP-1097 that the lunar section was actually prepared by the Center for Earth and Planetary Sciences at the U.S. National Air and Space Museum under the direction of Farouk El-Baz, a prominent selenographer (who is thanked in the Acknowledgments section of the Open File Report for developing the first computerized list of lunar feature names). Because the IAU had announced in 1973 its intention to replace lettered lunar crater names with individual names, the printed Gazetteer did not list any of the lettered designations previously recorded in the System of Lunar Craters, nor any of the new lettered designations assigned by Whitaker to craters on the farside. According to Whitaker, this decision caused concern at NASA, and prompted the somewhat parallel production of RP-1097 as a more complete list of the then-current lunar nomenclature (both IAU-approved and non-IAU approved). Whitaker also claims that many errors that had been corrected in the proofs of Gazetteer of Planetary Nomenclature 1994 reappeared in the final version issued in 1995. In any event, the two lists, despite their supposedly parallel development, are not always consistent as to the positions and diameters of lunar features.

The 1994/1995 printed Gazetteer of Planetary Nomenclature seems to have been fairly widely distributed, however it rapidly became out-of-date. Fortunately modern computer technology has, as mentioned above, allowed it to be replaced by an on-line version hosted for the IAU by the USGS. Despite initial concerns about an electronic database replacing changes announced in the Transactions, the IAU-USGS website has become the last word not only on lunar nomenclature, but also with regard to named surface features on all solar system bodies for which imagery is available.


Crater Representation


Crater Barchart

Left: Crater representation of those listed on the USGS Gazateer of Planetary Nonmenclature - in kilometric increments (not including lettered craters).
Right: A simple bar chart of the above-mentioned named craters. - JohnMoore2

Recent Developments

Until recently, names proposed by the WGPSN, and published in the on-line Gazetteer, were considered provisional (unofficial) until they had been formally approved at one of the triennial (every three years) meetings of the IAU General Assembly. At a recent meeting, a resolution was apparently passed instituting a new approval policy. According to this policy a vote by the General Assembly is no longer required for approval of a new name. Names published at the request of the WGPSN in the on-line Gazetteer are now instantly official, but may be withdrawn if an objection is raised within the first three months. In general, as seems to have been the case for the last several years, approved name changes seem no longer to be published in the IAU Transactions except in summary form.

The second biggest change since the inception of the IAU Gazetteer of Planetary Nomenclature has been the re-adoption of the lettered craters, or "satellite features", as they are called at the 2006 General Assembly. This was the result of several years of lobbying by Jennifer Blue of the USGS and Jonathan McDowell of the Harvard-Smithsonian Center for Astrophysics, who had electronically transcribed the 1982 NASA Reference Publication 1097, which contained a complete listing of all features on the Moon regarded as "official" by NASA in about 1981. Unlike the System of Lunar Craters or the earlier NASA SP-241, RP-1097 did not contain listings of the Greek-lettered peaks or the Roman-numeraled rilles. Those features are no longer part of the official system.

A 2009 presentation (PDF) identifies a seven-member Lunar Task Group which currently processes name requests and submits them to the WGPSN for approval and publication in the Gazetteer. A need for many new names is anticipated in connection with the recent resurgence of lunar exploration. According to this report, as of December 2008, "the lunar name bank [from which most new names are drawn] currently includes more than 250 names of prominent individuals, including 45 names of Nobel prize winners." The status of the naming of lunar craters is summarized (without further explanation) in the following table:

Crater Diameter (km)
Named Craters
Unnamed Craters
21 – 40
41 - 80

The category "Unnamed craters" appears to include craters named as satellite features (lettered craters), as well as craters that actually lack names. Judging from recent performance, in the future unnamed craters will be assigned individual names rather than letters associating them with existing craters, and the presentation mentions that some current letter designations may be replaced with new non-lettered names.

IAU Name Change Chronology

For a list of changes to the IAU nomenclature, and the years in which they were made see the IAU Names Chronology page.


The IAU nomenclature is often criticized as being arbitrary, illogical and inconsistent. In large part this results from many small and seemingly insignificant features having names, while many larger and more obvious ones do not. As explained by Whitaker, the original dichotomy resulted from the catalog of Blagg and Müller including both the major features that had been historically named and the much smaller features used in the control networks of Franz and Saunder (mostly given lettered names). This resulted in a large middle range of unnamed features. This dichotomy was exaggerated still further by approval, mostly in 1976, of Landing Site Names and (inadvertently?) many of the Minor Feature names that had been used on the extremely high resolution Topophotomaps that had been prepared for NASA from Apollo photos by the DMA. Because lettered feature names were not allowed at that time, this gave full independent name status to many extremely small features for no reason other than that they happened to fall in one of the few areas mapped at this resolution and to have caught the fancy of the mapmaker. It appears that the mapmakers thought these names might be helpful when using the map, but did not intend for them to become part of the official nomenclature.

An additional criticism, which may or may not be true, is that in the original scheme names were assigned in such a way that the parent of a satellite feature could be easily and unambiguously identified by placing its letter designation on the side of that feature facing the parent. As lettered craters were subsequently given names, and some of them satellites of their own, this system (if it ever existed) has certainly been broken.

[Placing letters on the side of a designated crater in line with the feature it is named after was introduced in the map of Beer and Mädler and explicitly described in their accompanying book. This system was used relatively consistently for 135 years, including in the System of Lunar Craters in the 1960s, after which time lunar nomenclature administratively fell into the hands of people who did not understand its history and practical use. - tychocrater Dec 20, 2008]

Finally, some users feel that the Latinization of names such as “Vallis Schröteri” for “Schröter’s Valley,” introduced in the 1960’s, is an unnecessary obfuscation. Others refuse to accept such IAU-endorsed changes as the 2000 renaming of the traditional “Walter” to Walther and the use of the original name for a new crater Walter.


The bulk of this article has been pieced together based on the writings of Ewen Whitaker, the DMA-produced reference material in the Maps Catalog on the LPI website, and, where possible, direct reference to the IAU Transactions. There seems, at times to have been a considerable amount of friction between the various parties involved -- the IAU, the LPL, the DMA, the USGS, and NASA (not to mention non-US parties, such as the Russians who had strongly different views about the proper naming of the Moon’s farside). Many of these parties are very critical of the decisions made by the others, and hold them responsible for the shortcomings of the present system. The author has attempted to create as balanced an overview as possible, but because of his lack of direct knowledge of these matters (and the necessity of viewing the subject as filtered through the eyes of those who participated in them), some of the statements and chronology may be incorrect. Hopefully others will correct them. - JimMosher

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