Galileo’s impression was that the dark, flat areas on the moon were seas, real watery oceans, and that the bright and rougher regions densely studded with craters were continents. These maria (Latin for “seas”) were named primarily after states of mind or conditions of nature: Mare Frigoris (the Sea of Cold), Lacus Somniorum (the Lake of Dreams), Mare Crisium (the Sea of Crises), Sinus Iridum (the Bay of Rainbows), Mare Serenitatis (the Sea of Serenity), Oceanus Procellarum (the Ocean of Storms), Mare Nubium (the Sea of Clouds), Mare Fecunditatis (the Sea of Fertility), Sinus Aestuum (the Bay of Billows), Mare Imbrium (the Sea of Rains) and Mare Tranquillitatis (the Sea of Tranquillity)-a poetic and evocative collection of place names, particularly for so inhospitable an environment as the Moon. Unfortunately, the lunar maria are bone-dry, and samples returned from them by the U.S. Apollo and Soviet Luna missions imply that never in their past were they filled with water. There never were seas, bays, lakes or rainbows on the Moon. These names have survived to the present. The first spacecraft to return data from the surface of the Moon, Luna 2, touched down in Mare Imbrium; and the first human beings to make landfall on our natural satellite, the astronauts of Apollo 11, did so, ten years later, in Mare Tranquillitatis. I think Galileo would have been surprised and pleased.
Despite Hevelius’ misgivings, the lunar craters were named after scientists and philosophers by Giovanni Battista Riccioli in a 1651 publication, Almagestum Novum. The title of the book means “The New Almagest,” the old Almagest having been the life’s work of Ptolemy. (“Almagest,” a modest title, means “The Greatest” in Arabic.) Riccioli simply published a map on which he placed his personal preferences for crater names, and the precedent and many of his choices have been followed without question ever since. Riccioli’s book came out nine years after the death of Galileo, and there has certainly been adequate opportunity to rename craters later. Nevertheless, astronomers have retained this embarrassingly ungenerous recognition of Galileo. Twice as large as crater Galileo is one called Hell after the Jesuit father Maximilian Hell.
One of the most striking of the lunar craters is Clavius, 142 miles in diameter and the site of a fictional lunar base in the movie 2001: A Space Odyssey. Clavius is the Latinized name of Christoffel Schlüssel (= “key” in German = Clavius), another member of the Jesuit order, and a supporter of Ptolemy. Galileo engaged in a protracted controversy on the priority of discovery and the nature of sunspots with yet another Jesuit priest, Christopher Scheiner, which developed into a bitter personal antagonism and which is thought by many historians of science to have contributed to the house arrest of Galileo, the proscription of his books, and his confession, extracted under threat of torture by the Inquisition, that his previous Copernican writings were heretical and that Earth did not move. Scheiner is commemorated by a lunar crater 70 miles across. And Hevelius, who objected altogether to the naming of lunar features after people, has a handsome crater named after himself.
Riccioli gave the names Tycho, Kepler and, interestingly, Copernicus to three of the most prominent craters on the Moon. Riccioli himself and his student Grimaldi received large craters at the limb, or edge, of the moon, Riccioli’s being 106 miles across. Another prominent crater is named Alphonsus after Alphonso X of Castile, a thirteenth-century Spanish monarch who had commented, after witnessing the complexity of the Ptolemaic system, that had he been present at the Creation, he could have given God some useful suggestions on ordering the universe. (It is amusing to imagine Alphonso X’s response were he to learn that seven hundred years later a nation across the Western ocean would send an engine called Ranger 9 to the Moon, automatically producing images of the lunar surface as it descended, until finally it crashed in a pre-existing depression named, after His Castilian Majesty, Alphonsus.) A somewhat less prominent crater is named after Fabricius, the Latinized name of David Goldschmidt, who in 1596 discovered that the star Mira varied periodically in brightness, striking another blow against the view championed by Aristotle and supported by the Church that the heavens were unchanging.
Thus the prejudice against Galileo in seventeenth-century Italy did not, in the naming of lunar features, carry over as a completely consistent bias in favor of Church fathers and Church doctrines on matters astronomical. Of the approximately seven thousand designated lunar formations it is difficult to extract any consistent pattern. There are craters named after political figures who had little direct or apparent connection with astronomy, such as Julius Caesar and Kaiser Wilhelm I, and after individuals of heroic obscurity: for example, crater Wurzelbaur (50 miles in diameter) and crater Billy (31 miles in diameter). Most of the designations of small lunar craters are derived from large and nearby craters, as, for example, near the crater Mösting are the smaller craters Mösting A, Mösting B, Mösting C, and so on. A wise prohibition against naming craters after living individuals has been breached only occasionally, as in assigning a few quite small craters to American astronauts of the Apollo lunar missions, and by a curious symmetry in the age of détente, to Soviet cosmonauts who remained behind in Earth orbit.
In this century an attempt has been made to name, consistently and coherently, surface features and other celestial objects by giving this function to special commissions of the International Astronomical Union (IAU), the organization of all professional astronomers on the planet Earth. A previously unnamed bay of one of the lunar “seas,” examined in detail by the American Ranger spacecraft, was officially designated Mare Cognitum (the Known Sea). It is a name not so much of quiet satisfaction as of jubilation. IAU deliberations have not always been easy. For example, when the first-somewhat indistinct-photographs of the far side of the Moon were returned by the historically important Luna 3 mission, the Soviet discoverers wished to name a long, bright marking on their photographs “The Soviet Mountains.” Since there is no major terrestrial mountain range of this name, the suggestion was in conflict with the Hevelius convention. It was accepted, nevertheless, in homage to the remarkable feat of Luna 3. Unfortunately, subsequent data suggest that the Soviet Mountains are not mountains at all.
In a related instance, Soviet delegates proposed naming one of the two maria on the lunar far side (both very small compared with those on the near side) Mare Moscoviense (the Sea of Moscow). But Western astronomers objected that this again departed from tradition because Moscow was neither a condition of nature nor a state of mind. It was pointed out in response that the most recent namings of lunar maria-those on the limbs, which are difficult to make out with ground-based telescopes-have not quite followed this convention either: as Mare Marginis (the Marginal Sea), Mare Orientale (the Eastern Sea) and Mare Smythii (the Smyth Sea). Perfect consistency having already been breached, the issue was decided in favor of the Soviet proposal. At an IAU meeting in Berkeley, California, in 1961, it was officially ruled by Audouin Dollfus of France that Moscow is a state of mind.