SLC Nomenclature

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Note: since this page was written, the full text from the publications for Quadrants 1 and 2 has become available on-line. See the System of Lunar Craters page.

The System of Lunar Craters was the first exhaustive modern catalog of craters, being based on diameter measures made on sheets from Kuiper’s Photographic Lunar Atlas. I was one of only two measuring assistants who co-authored all four parts of the catalog. Working under D.W.G. Arthur, and in close association with E.A. Whitaker, we examined over 11,000 craters. We had the advantage of access to the best lunar photographs available as well as rectified images of the limb regions that were later published as the Rectified Lunar Atlas.

Because The System of Lunar Craters catalog is not readily available (although until recently the maps were as Lunar Quadrant Maps from Sky and Telescope) I have entered the parts of each of the four catalog sections that deal with nomenclature. Although there were various coauthors of the System, the text was written by Dai Arthur, in consultation with Ewen Whitaker. Here is the largest description of our System nomenclature policies from our Quadrant I catalog, the rest will follow soon. Happy history!

[As of December 2008, I have not yet added the nomenclature text from the other quadrants! - tychocrater Dec 20, 2008 ]

The System of Lunar Craters - Quadrant I

Arthur, Agnieray, Horvath, Wood and Chapman
Communications of the Lunar and Planetary Laboratory #30, 1963.

7: The Nomenclature

(p. 74-75)
Contemporary lunar nomenclature descends from the maps of Riccioli and Mädler. Riccioli innovated the convention of naming the more prominent lunar craters after famous philosophers, scientists, and explorers, while Beer and Mädler applied this to a scheme in which smaller craters are lettered and associated with nearby named objects. Thus, Plato A would be a crater not far from the crater Plato.

For compactness of medium- and small-scale lunar maps, only the letter is entered on the map and the prefixing name is understood. Thus, in the example mentioned, only the letter A is shown and the prefix Plato is understood. Clearly, some further convention is necessary to distinguish between objects with the same letter but different prefixes. This convention also was laid down by Beer and Mädler, but it is not well understood, or ignored by some contemporary lunar cartographers. It may be useful to restate it here, since its neglect causes confusion. When a lettered formation is associated with a named formation, the letter is placed against that side of the formation which is nearest to the named formation. Thus, for Plato A, the A is placed against the side of the crater which is nearest to Plato.

The scheme of Beer and Mädler was not long left in peace. Neison, Schmidt and a succession of British selenographers published maps in which new new names were introduced and the original conventions were either disregarded or mutilated. Unfortunately, there was no uniformity in the additions and alterations so that in time many craters accumulated several different designations. This chaotic situation should have been brought to an end with the publication in 1935 of Blagg and Müller’s Named Lunar Formations, consisting of a catalog and a map. The work was performed at the request of Commission 16 of the International Astronomical Union and the resulting publications were given due authority by the IAU in 1932.

Unfortunately, the Blagg and Müller scheme did not achieve wide usage or acceptance among those who were then active in selenography. This may have been due to the rather limited distribution of the publications, but also may have resulted from the rather illegible nature of the outer sheets of the map. Indeed, for the limb regions, the Blagg and Müller scheme is frequently defective and erroneous, since their map does not correspond to what can be seen on modern lunar photographs. In fact, it was based in part on photographic materials which would now be regarded as inadequate.

Even if the defects of the Blagg and Müller scheme are ignored, there are other factors present which make a revised scheme an urgent necessity. All the major maps of the past were drawn on the orthographic projection in which limb regions are strongly compressed by foreshortening. Today, new maps are being published in conformal (isomorphic) or near-conformal projections in which there is no foreshortening, each object being shown in horizontal plan. Furthermore, these new maps are the results of intense and careful surveys of a type never achieved before. Thus the new maps show numerous small features well, which were drawn with doubt and generalization on the older maps.

The changes in the new maps (namely, new projections, increased density of detail, and larger scales) all have important implications for the nomenclature. Associations which were valid for the orthographic projection break down in the new maps, since craters which formerly appeared reasonably close together may actually be widely separated. Thus it is often no longer appropriate to letter craters as has been done before. The conformal projections also frequently create wide lacunae in the network of name in the limb regions.

In addition to all this, Blagg and Müller’s scheme contains craters which do not exist, crater with two designations, craters with identical designations, illogical situations in which objects are associated with named craters which lie beyond other named craters, and similar defects.

It would be relatively easy to start afresh and create a new nomenclature which would be logical, consistent, and unambiguous. However, the demands of tradition and continuity cannot be ignored. A completely new scheme would render almost useless much of the selenographic literature of the past. Therefore, the nomenclature of this catalog is merely an augmented and amended form of that of Blagg and Müller. The emphasis is on addition rather than alteration and the catalog contains designations for numerous objects which were formerly anonymous.

Changes have been made, but only of necessity. In particular, the number of new names has been kept to a minimum. These are limited to the limb regions in which the removal of foreshortening in the new maps creates illogical situations in the existing scheme. The new names for Quadrant I are:
  • Banachiewicz, T. - Polish astronomer;
  • Dubiago, D. I. - Russian astronomer;
  • Belkovich, I.V. - : Russian selenodestist;
  • Hayn, F. - German selenodetist;
  • Nansen, F. - Norwegian polar explorer.

The first four of these were astronomers closely connected with the development of selenodesy, perhaps the most demanding and difficult of the lunar sciences; the firth was a polar explorer of considerable fame whose name is thus appropriate for an object not far from the lunar north pole.

The task of clarifying, correcting, and amplifying the nomenclature has not been a light one. Often the intentions of Blagg and Müller are so obscure that to arrive at a decision it has been found necessary to refer to the works of Mädler, Lohrmann, Schmidt, and others. In some cases in the limb regions Blagg and Müller misidentified the crater named by one of these authorities, but occasionally they appear to have made a better choice. In such cases we have retained their identifications even though they are incorrect historically.

Errors and defects of the Blagg and Müller scheme necessitate certain alterations in the designations. Frequently we have been obliged to change the designations of craters, by changing either the letter or name prefix. It seemed best to retain the letter whenever possible and in almost all cases we have been able to do this.

The emphasis in this catalog and the accompanying map is on the craters. Nevertheless, attention has been given to the 1961 resolutions of the International Astronomical Union. The principal recommendations are the latinization of some generic terms, e.g.,

  • rima for rille;
  • rupes for fault or wall;
  • vallis for valley;
  • mons for mount;
  • montes for mountains.

The latinization of some of the proper names introduces problems for which there are no entirely satisfactory solutions. If the rules are applied strictly, the resultant designations are often so unfamiliar as to cause confusion and to court rejection. Hence some names have not been correctly Latinized while others have been left in their original form. Generally speaking, Montes is used for all mountain chains and is followed by a Latin noun in the nominative case. A few exceptions are allowed even in this in order to follow traditions when this is strong and consistent. Mons is used for single mountain masses which are individually named. There is one exception to this: Mont Blanc is a well known terrestrial peak with a lunar counterpart. The Latinized form of this name is Mons Candidus which is so unfamiliar as to be unsuitable. Nor is the hybrid form Mons Blanc any better. In this one case we have retained the original form as there is a strong terrestrial association which should not be destroyed. Similar difficulties arise with other names of northern European origin. In general we have used hybrid forms for these.

Following Blagg and Müller, craters are indicated by Roman upper-case letters while Greek lower-case characters are used for elevations. The maps of this catalog show two changes. In the first place we have added considerably to the number of designated craters and freely used double letters, such as AB, AC, BF, etc. Secondly, we have considerably reduced the use of Greek letters. Blagg and Müller followed Mädler and Schmidt in applying designations to elevations when when they were merely the east and west walls of craters. There seems to be no real need for this and we have restricted the use of Greek letters to isolated peaks and masses which appear to be useful as landmarks. In areas which are relatively empty except for isolated peaks, we have added some Greek letters in order to provide additional landmarks.

Certain conventions have been followed in order to simplify matters for the users of the maps. Firstly, a designation is always taken to apply to a specific object and never to a group. In cases such as Anaximander, where the designation formerly applied to a group of confluent craters, one crater has been selected to retain the original name while the remaining objects receive fresh designations.

Secondly, we have avoided lacing a named object within another, since this must lead to confusion in the lettered objects. However, there are at least three such cases where frequent past usage justifies their retention: Horrocks within Hipparchus, Hell within Deslandres, and Fabricius within Janssen.

Thirdly, the convention has been laid down that the straight line joining a named object to the lettered objects associated with it should never cross the corresponding lines for another named feature. This convention was violated in places by Blagg and Müller and the result is extremely confusing to the user of their map.

14: Contemporary Literature

(p. 77)

The only other works of importance relating to lunar nomenclature are the lunar charts of the Aeronautical Chart and Information Center of the U.S. Air Force and the Rectified Lunar Atlas now being prepared for publication under the direction of Dr. G.P. Kuiper.

The A.C.I.C. charts at 1:1,000,000 are probably the most complete and detailed lunar maps ever published. These are the result of both telescopic and photographic interpretation by full-time specialists. As a result of the close cooperation between A.C.I.C and LPL, the nomenclature of this catalog is identical with that of the A.C.I.C. charts. The nomenclature overlays for their charts are prepared in manuscript at LPL [by Chuck Wood] so that there is little possibility of discrepancies between the publications of the two organizations or of a recurrence of the chaotic situations which have plagued the subject in the past.

However, there are minor differences which should be noted. Up to the present the A.C.I.C. maps do not carry any indications of the designations of the elevations; that is, no Greek letters are shown. Furthermore, in places the A.C.I.C. maps may indicate double-lettered craters by the combinations Ab, Ac, Ga, whereas we would indicate them by AB, AC, GA. This difference I trivial and cannot confuse.

The Rectified Lunar Atlas places special emphasis on the libratory zones. These contain numerous large craters which if it would not be appropriate to designate by mere letters when useful photographs are obtained by extra-terrestrial stations. Unfortunately the work on the present catalog was already well advanced before the nomenclature scheme for libratory zones came under consideration. Hence certain craters which are designated by letters in this catalog have received names in the Rectified Lunar Atlas. These two sets of designations may for the present be regarded as alternatives, the one suitable for orthographic maps in mean libration, the other more suitable for maps which will undoubtedly be be produced in the future. For the first lunar quadrant the alternatives are:
  • Gioja A = Byrd;
  • Gioja B = Peary;
  • Alhazen F = Cannon;
  • Plutarch A = Hubble;
  • Euctemon J = de Sitter.

Ambiguities of this type will not arise in the remaining three quadrants. It remains to say that these new names are tentative and are being submitted to Commission 16 of the International Astronomical Union for approval.

- tychocrater Jul 29, 2007