Early Theories and Questions. about the Moon

If you have binoculars of ten power or even less, you can go out in your backyard on any clear night when the Moon is up—best perhaps at a quarter – moon phase, not a full moon—and become a lunar scientist. Brace yourself against a solid support so your hands are steady and focus on the line that separates the illuminated part of the Moon from the dark portion. Near this line the Sun casts the longest shadows, and you can see the greatest topographic detail. The technical term for this line is the lunar terminator, but you needn’t know this to start your studies. Your ten-power binoculars are about half as powerful as the telescope constructed by Galileo Galilei, who early in the seven­teenth century first began to study the Moon with more than the naked eye.

What will you see? Depending on where the line between the bright and dark portions falls on the particular night, you will probably see, just as Galileo did in 1609—to his amazement—some large and small circular craters, perhaps some mountains, and some apparently smooth areas that are known as maria, or seas. In 1963, some 350 years after Galileo made his first observations, the craters were the most controversial of all lunar features, sparking the most heated debates. What was their origin? Were they the remains of volcanoes? Were they caused by impacts like those that left similar craters on Earth? Were they the result of some combination of processes or the product of unknown forces? The lunar maria were also controversial; they were generally interpreted as lava flows. But how were they formed, and how did they spread over such a vast area? How were the mountains formed? Their very existence provoked debates about the internal structure of the Moon and its evolution.

The major, fundamental lunar questions being debated by planetary scien­tists when the Apollo program began can be quickly summarized: How old is the Moon, how was it formed, and what is its composition? Finding the answers was the driving force behind the desire to carry out a host of experiments on the Apollo missions. And a large science payload would be needed to resolve these difficult questions. The answers to some of them would come in part from samples collected on the Apollo landings, and in turn the samples would tell us a lot about the origin of the craters. If the Apollo missions landed at interesting points on the Moon and included various geophysical experiments along with geologic traverses, these mysteries might be resolved. From the answers we anticipated understanding Earth better, especially its early history. When I joined NASA in 1963 my knowledge of the Moon and of the ongoing debates was close to zero. I quickly resolved to fill this void and began to study the literature.

As soon as I returned to the United States from Colombia, I went to the local library and bookstores to find books to increase my meager knowledge. To my surprise, there were very few. And in recalling my undergraduate and graduate studies in the earth sciences, I could not remember that any attention had been paid to the Moon or the Earth-Moon system. The first book I bought was The Measure of the Moon, by Ralph B. Baldwin.1 It turned out to be a fortuitous choice. Not only had Baldwin done a comprehensive survey of the literature (the specialized literature was much more extensive than that found in general bookstores), he had organized the existing knowledge and theories and pre­sented them in a readable fashion. His opening sentence was prophetic: ‘‘Every investigation of the Moon raises more problems than it solves.’’ During the next five or six years I would find myself immersed in these problems and dealing daily with the various protagonists cited in the research. I later learned that I was in good company by being impressed by Baldwin’s work; Harold Urey, a Nobel laureate in chemistry, had become fascinated by the Moon’s many myste­ries after reading Baldwin’s earlier book, The Face of the Moon, and had put forth his own theories on how the Moon formed.

My first impression that there was little source material quickly changed. Baldwin’s references were extensive, too many—in light of my new duties—for more than a cursory review. I settled on purchasing a few texts to read in their entirety and keep available as a small reference library. In addition to Baldwin I read The Moon, by Zdenak Kopal and Zdenka Mikhalov; Structure of the Moon’s Surface by Gilbert Fielder; Harold Urey’s The Planets and several of his articles

and reports; Gerard P. Kuiper’s ‘‘On the Origin of Lunar Surface Features’’; and an article by my old mines professor L. W. LeRoy, ‘‘Lunar Features and Lunar Problems.’’2

Perhaps most interesting of all, I discovered that most of the leading figures in lunar and planetary science, including Urey, Kuiper, Fielder, Kopal, and Baldwin, were active and accessible. In addition, some of the younger lions, such as Shoemaker, Frank Press at Lamont-Doherty, Jack Green at North American Aviation, John O’Keefe at the Goddard Space Flight Center, and Carl Sagan of Cornell University, were already involved in NASA programs.

The origin and age of the Moon had intrigued astronomers and Earth scientists for many centuries, with theories proposed based on a minimum of hard data. By the early 1960s existing theories had become more sophisticated, supported by ever increasing observational data and, soon, by returns from several of NASA’s unmanned programs. Three theories on the Moon’s origin held sway: (1) the Moon and the Earth had formed more or less simultaneously from the same primordial cloud of debris surrounding the Sun; (2) the Moon had been separated from the Earth either through tidal movements or by the impact of another body (some would split this into two theories); and (3) the Moon had formed elsewhere in the solar system, and in its orbit around the Sun it had been captured by the Earth’s gravitational field in an early close encoun­ter. Based on the information then available, each of these theories could be supported or argued against depending on one’s point of view and which data one considered most critical. The date when any of these events took place was also conjectural, but it was generally believed that the Moon had become Earth’s companion early in the formation of the solar system, some 4.5 to 5 billion years ago.

Certain information was well documented. The Moon’s physical dimensions and mass, its distance from Earth, and several other properties were known rather precisely. Unlike Earth’s, the Moon’s magnetic field, if any, was thought to be weak; its mass and volume translated to a body less dense than Earth, probably without an iron core or at best with a very small core. It had no discernible atmosphere. We knew that the Moon was locked into a slowly expanding orbit that allowed only one side to face Earth. The Moon’s farside or back side (not ‘‘dark side’’ as so many ill-informed writers call it, since it is lit by the Sun in the same manner as the side facing Earth) was a total mystery; was it the same as what we could see or very different? This lack of information had made the Moon’s farside the playground of science fiction writers for many years. One could imagine all sorts of strange things back there, including alien colonies.3

Probably the most contentious issue was the origin of lunar craters. Were they formed by some internal process like volcanism or by the impacts of small to large bodies like meteorites? The literature was full of this particular contro­versy, and the debate—at times vitriolic—went on at all lunar symposia. Each side had its champions, although it appeared that the “impactors” were begin­ning to win the day. Any of the three lunar origin theories could accommodate either an impact or a volcanic explanation, but the subsequent history or postorigin modification of the Moon’s surface would be entirely different de­pending on which crater theory proved correct. If the craters were volcanic, then the Moon’s interior had been molten after its formation and we could expect to find many Earthlike conditions. If the craters were caused by impacts, then the Moon’s evolution might have been very different from Earth’s, even though most students believed that impacts were common in Earth’s early history. Complicating this debate, we could observe other features on the Moon such as sinuous, riverlike rills and odd-shaped depressions that did not con­form to the contours expected of impact craters. What was the Moon trying to tell us? Had there once been water on the Moon? Had a combination of pro­cesses taken place? Were they still taking place?

A primary scientific justification for studying the Moon, with either manned or unmanned spacecraft, was to help us unravel Earth’s early history. A new term had been coined for such study, ‘‘comparative planetology,’’ and we used it frequently in our briefings both inside and outside NASA. Comparative plan­etology means studying the planets by comparing what can be observed or measured on one with similar characteristics on another; through this back – and-forth association we would increase our overall understanding of all the planets. We believed that applying this technique to the Earth-Moon system would be especially fruitful. In all the solar system, our Moon is the largest relative to the size of the planet it orbits—in essence we are a two-planet sys­tem. By studying the Moon we believed we would learn much about Earth. When the Apollo project began many basic questions concerning our home planet were unanswered, and many were similar to those we were asking about the Moon. How was it formed, and how had it changed during its early evolu­tion? What is the thick zone just beneath Earth’s crust—the mantle—made of?

How does the mantle influence or produce the energy that moves large sections of Earth’s surface?4

Earth’s surface is a dynamic place. Mountains rise and are eroded away, sea basins and lakes fill and dry up, and continents move vast distances, a process called “continental drift.’’ The record can be deciphered by earth scientists in the rocks of Earth’s crust. But our understanding becomes sketchier and more uncertain as we go back in time toward Earth’s earliest history. That part is obscured, hidden, or even destroyed by the very processes mentioned above. The oldest Earth rocks that have been positively dated, from northern Canada, are approximately 4 billion years old. The oldest piece of the solar system dated thus far is the Allende meteorite, calculated to be almost 4.6 billion years old, supporting the earlier theories that the solar system might be 5 billion years old. These dates, however, leave a gap of almost a billion years from the oldest dated Earth rocks to the solar system’s birth. This billion-year gap continues to be an enticing field for speculation and investigation.

Returning now to the three theories of lunar origin: What were their im­plications for Apollo? Could we expect to shed light on these riddles or perhaps even solve them? If either of the first two was correct—if the Earth and the Moon formed simultaneously and close together or if the Moon broke off from Earth, then one would expect the rock types or minerals we would find on the Moon to be similar to those on Earth. If the third theory was correct, that the Moon formed somewhere else in the solar system and was later captured by Earth, then we might find different rock types and minerals on the Moon, perhaps similar to some of the more exotic meteorites that have been recovered at various places on Earth. Regardless of the ultimate answer, we were confident we would be able to date the rocks and get a handle on a pressing question: When was the Moon formed? Some believed the Moon’s surface was ancient, that all the features we observed had formed early in its history and had changed little since then. Confirming this would be exciting; the Moon, as many were fond of saying, could act as a Rosetta Stone in deciphering the birth of the Earth and the solar system!

Harold Urey at the University of California, San Diego, was a strong propo­nent of the third theory. He believed the Moon had been formed through the accretion of planetesimals (large pieces of the primordial cloud from which the Sun and eventually the whole solar system evolved) and that this happened some 4.5 billion years ago. If true, it was an ancient and unchanged body and worthy of careful study. The Moon has an irregular shape (it is not a perfect spheroid but has slight polar flattening and an Earth-facing equatorial bulge), and it wobbles on its axis. Urey argued that the Moon had never been com­pletely molten or these irregularities would not have survived. According to his calculations, the Moon had formed as a somewhat cold body—those who said the maria were lava flows erupting from a molten interior were wrong. The maria, he believed, were the result of large-scale melting caused by the impact of large bodies, such as the one that had formed Mare Imbrium, and the maria material might have been the melted remains of carbonaceous chondrites, an unusual type of meteorite occasionally found on Earth. Urey was looking for­ward with great anticipation to obtaining lunar samples, especially from the maria (they should not be Earthlike lava), to prove his theory.

Urey’s reputation as a Nobel laureate was important in legitimizing our lunar studies. When he spoke, everyone listened. Although he had many differ­ences with other lunar scholars, sometimes he agreed with them. He agreed, for instance, that most craters were certainly of impact origin and that much of the lunar topography was shaped by ejecta from the impacts. He did not think there had been much volcanism on the Moon, but he accepted the observations of some volcanolike features. In a letter to Jay Holmes at NASA headquarters in January 1964 Urey said: ‘‘I am sure that only the most experienced hard rock geologist could possibly do anything about the subject satisfactorily. I urge strongly that all astronauts be well trained hard rock geologists. The Apollo project is being severely criticized by outstanding people, and I believe that if we do not at least [do] the very best that we can to solve important scientific problems that this criticism may well swell to a very great chorus.’’5 Urey’s suggestion on astronaut training was one of the first shots in a long campaign that led to the scientist-astronaut selections discussed in later chapters. Regard­less of his opinions, his presence at any lunar symposium guaranteed vigorous debate and lots of publicity, a commodity we eagerly sought as we struggled to make NASA management recognize how important the Moon would be in resolving issues of such magnitude.

Another vigorous debater was Thomas Gold, a professor at Cornell Univer­sity who had made his early reputation in astronomy. In recent years he had focused on problems related to the Moon. Tommy Gold was to prove a thorn in our sides with his strange theories, seldom supported by anyone else in the scientific community. His most controversial one, first proposed in 1955, was that the lunar surface was covered by a layer of fine particles eroded from the lunar highlands, perhaps several kilometers thick, that could move across the lunar surface and fill in depressions.6

He sought to prove this contention with photographs showing that most lunar features had a smooth appearance and many craters seemed to be filled rather uniformly with some material. He generally discounted the idea that this fill might have been molten material like lava or ejecta from impacts. Radar studies of the Moon tended to support his thesis that the uppermost soil layer was fine grained and of low density, but how thick this layer might be and what area it covered could not be resolved from the radar data.7 Other interpreta­tions were also possible.

The character of the lunar soil, especially its topmost layer, was of course a great concern, since it would directly affect the design of the lunar module (LM) and the astronauts’ ability to land and move around on the surface. Not much was known about how soils and fine-grained material would behave in the high vacuum found on the Moon. Several government and private labora­tories had done experiments to examine this question. Bruce Hapke at Cornell University, for example, had shown that fine particles deposited in a vacuum tended to stick together loosely, forming what he called ‘‘fairy castle’’ structures, or soils with low bearing strength.8 This could be seen as substantiating Gold’s contention of a low density lunar surface.

Before the return of pictures from Ranger, and later the Surveyor and Lunar Orbiter missions, photographs of the Moon had come from telescopic images, with a resolution of at best a thousand feet. Under such low resolution, every feature on the Moon appeared somewhat smooth. This problem did not deter Gold. Even after we received the higher resolution Ranger, Surveyor, and Lunar Orbiter photos, he continued to predict that when the lunar module attempted to land it would sink out of sight in his electrostatically levitated dust. At this early stage such predictions alarmed NASA’s engineers, for it was difficult to prove him wrong.

Fortunately questions of this type—though not so outrageous—had been anticipated, and the Surveyor spacecraft were designed to answer them. Sur­veyor did prove Gold wrong, which he accepted grudgingly, continuing to maintain that some areas of the Moon were covered with fluffy dust. He clearly enjoyed being the center of controversy, and after Surveyor’s deflator he came up with another whopper: the lunar dust would be pyrophoric. When the astronauts landed and opened their LM hatch, the oxygen released from the cabin would combine with the soil and cause an explosion. His reasoning was that the lunar surface, exposed for eons to the bombardment of the solar wind, had become oxygen deficient and would undergo an explosive oxidation when exposed to the LM atmosphere. This prediction also worried the engineers, and it would not be possible to prove or disprove it with any projects in the pipeline before the actual landing.

The school of volcanic crater supporters started strongly and slowly declined in influence as more and more observational and experimental data became available. But in 1963 and 1964 they still made a good case for their views. The leaders of this school were Gerard Kuiper, at that time director of the Lunar and Planetary Laboratory in Tucson, John O’Keefe at Goddard Space Flight Center (GSFC), and North American Aviation’s Jack Green. Each of these advocates had a somewhat different interpretation of what was observed on the Moon. Both Kuiper and O’Keefe admitted that impacts had played a role in the Moon’s evolution, but they still thought volcanism was the major explanation of its present surface formations. Kuiper had been an early student of the Moon. Ignoring Urey’s counterarguments, he believed the original substance that came together to form the Moon contained enough radioactive material to eventually raise the interior temperature and melt the entire Moon. In his model this had occurred some 4.5 billion years ago, forming the maria and filling the larger craters, all subsequently modified by meteoroids.

Green, however, took a hard-line approach. Essentially all features on the Moon could be, and should be, explained by volcanic processes. Jack was a colorful figure, never taken aback by criticism, and a good debater. You could count on him to enliven any lunar symposium. His forte was showing side-by­side photographs of terrestrial and lunar features that looked almost identical. The terrestrial features, of course, were always volcanic in origin.

The impact school was led by Gene Shoemaker and his United States Geo­logical Survey (USGS) followers. Gene had been influenced by an earlier and revered USGS chief geologist, Grove K. Gilbert, who in 1893 published a paper concluding that the Moon’s craters were probably of impact origin.9 Gene had carefully studied Meteor Crater in Arizona, just east of his new Flagstaff offices, as well as several other craters of known impact origin in other parts of the world. Robert Bryson, from NASA headquarters, had funded Gene to develop a detailed report of his findings that would combine his earlier studies and field observations at Meteor Crater. By 1964 Gene’s studies had been completed for some time, but he had not finished the written report. This was a sore point with Bob because so little had been published on the geology and mechanics of impact craters, and Gene’s work was intended to fill this void. He had published a short report on his work in 1963, but the full report was still in draft form.10

Bob, a former USGS geologist, had great insight into what it would take to convince the scientific community that important information could come from lunar studies. In addition to Gene’s work, Bob funded some of the studies of Ed Chao at USGS, who in 1960 discovered coesite in the shocked debris from Meteor Crater, a type of silica that forms only under extremely high pressure. Before Chao’s discovery, coesite had been made in the laboratory but had never been found in nature. This mineral is now a key fingerprint for identifying impact craters. Soon after this discovery Chao found stishovite, another form of high pressure silica, in rocks ejected from Meteor Crater-further confirma­tion that an impact of enormous energy had created the crater. Chao was later detailed to NASA as Apollo science work expanded, and we worked together under Will Foster. Bryson also funded the telescopic mapping of the Moon, initially through Robert Hackman at USGS. These maps laid the groundwork for all the subsequent lunar geological interpretations used during the Apollo landings and the planning that preceded them.

Despite the annoyance at NASA headquarters about the Meteor Crater re­port, Gene was a walking encyclopedia concerning what happens when a rela­tively small meteorite hits a solid object like Earth. (The iron meteorite named the Canyon Diablo that blasted the four-thousand-foot-diameter Meteor Cra­ter probably weighed about seven thousand tons.) He extrapolated these results to the larger lunar craters that must have been formed by even larger bodies. He was joined in this knowledge by experimenters such as Donald Gault at the NASA Ames Research Center and others who had conducted small hyper­velocity, laboratory-scale impact studies. In addition to making direct field observations on Earth, Gene and his staff, following Bob Hackman’s lead, had spent considerable time mapping the Moon using several large telescopes. Ap­plying standard terrestrial geological interpretations to these eyeball studies, they had become convinced that the Moon was pockmarked with impact cra­ters. Shoemaker was sure that almost all lunar craters had been formed by this mechanism, not through volcanism.

In a trip report of a visit to Menlo Park in May 1963, Bob Fudali described his conversations with Henry Moore, Dick Eggelton, Donald Wilhelms, Harold Masursky, and Michael Carr of USGS.11 After spending many hours drawing geological maps of the Moon based on telescopic observations, the USGS geolo­gists believed that, despite the high density of impact craters, there was substan­tial evidence of volcanic activity on the Moon, somewhat at variance with Shoemaker’s views. They also believed there was evidence that the maria were covered with extrusive igneous material, and they were convinced that tektites (rounded glassy bodies probably of meteoritic origin found at several places on Earth) originated on the Moon, thus supporting O’Keefe’s theories. Because of the chemical composition of the tektites, this meant that at least some parts of the Moon were ‘‘granitic,’’ which in turn meant that at some point in its evolu­tion the Moon had undergone differentiation in the presence of water. One could then conclude that the Moon was at least somewhat like Earth.

In addition to these major theories and vigorous debates, several related questions had puzzled lunar scientists for many years. Answers were especially important to the new breed of comparative planetologists, for they hoped the answers would shed new light on similar questions about Earth’s evolution.

During its early formation, Earth went through partial melting and differen­tiation. As the material that was to make up the bulk of Earth’s mass accumu­lated, the heavier material sank to the center, forming a core. Each layer above the core was of decreasing density, and the lightest materials formed the crust. Although we do not completely understand these various deep materials that form the bulk of Earth’s interior, we can infer and calculate what they are. Based on this knowledge, we have reconstructed the processes that formed them. As an example, we know that Earth’s continents are relatively light material ‘‘float­ing’’ on denser underlying rock. We also know that through geologic time there has been a constant churning of the upper layers and that Earth’s surface today looks very different than it did, say, 3 billion years ago. Although we say we know these things, they are really just theories based on observable field data and hypothetical calculations. It would be reassuring if we could find other examples of these processes or similar ones elsewhere in the solar system. What better place to look than the Moon, our closest neighbor?

Had the Moon undergone differentiation in its early history? Telescopes showed mountains on the Moon. They were generally lighter in color than the lowland maria and thus probably different in composition. Were the moun­tains less dense, as terrestrial mountains are less dense, on average, than Earth’s crust and upper mantle? If you believed that tektites came from the Moon, differentiation was a given, with less dense material occurring at the surface. Did the Moon have a core? The tiny but measurable magnetic field (averaging five gammas and believed to be due primarily to the interaction of the Moon with the solar wind) and overall lower density seemed to negate a lunarwide field, but we had not been able to make close-up measurements. Perhaps there were weak, relict local magnetic fields that would be evidence of early core formation. Why did the nearside and farside of the Moon look different? This question became more important when we received Lunar Orbiter pictures of the Moon’s farside with much higher resolution than those returned by Lunik 3 and the full extent of these differences became known. Did Earth-Moon tidal effects account for these differences, or was it some other factor?

Whether water ever existed on the Moon was another important question. Because the Moon has no discernible atmosphere (it was estimated to be equiv­alent to Earth’s atmosphere at altitudes above six hundred miles, appropriately an exosphere),12 water probably would not be found on the lunar surface under any conditions, but it might still exist belowground. Some proposed that it might be found in permanently shadowed craters near the lunar poles. Urey in 1952 and Kenneth Watson, Bruce Murray, and Harrison Brown in 1961 pro­vided an analytical basis for such predictions. The latter authors concluded, ‘‘In any event, local concentrations of ice on the moon would appear to be well within the realm of possibility. Unfortunately, if it exists, it will be found in shaded areas, and attempts to determine whether it is present must await the time when suitable instruments can be placed in those areas.’’13 Some thirty-five years later the Clementine and Lunar Prospector missions seem to support their analysis, though it is probably safe to say the authors had not imagined that ice would be detected by instruments in lunar orbit; such a possibility was beyond their dreams in the early 1950s.

On Earth, water is needed to form granites, so if granites existed on the Moon, then water must have been present in its early history. If water could be found on the Moon it would greatly simplify our plans for post-Apollo manned exploration. Its presence in an easily recoverable form would reduce the potable water we would have to transport to the Moon, and water could be used as a source of oxygen for manned habitats. Far-out planners even envisioned mak­ing rocket fuel by separating the hydrogen and oxygen. The questions posed by present-day space planners or raised by the information gained from the Clem­entine and Lunar Prospector missions thus are not new but were on our minds thirty years earlier.

Would we find any evidence of life forms, however primitive, in the samples brought back to Earth? This outcome was considered unlikely but not impossi­ble. For this reason the samples and the astronauts would be quarantined on their return lest they carry some deadly virus or pathogen to which we poor earthlings would have no immunity. Any evidence of life would be astounding and would require rethinking how life formed on Earth.

All the questions above, and their answers, were important both to NASA (especially my office) and to the scientific community in general. Our post – Apollo mission strategies were based on attempting to find answers, which in turn would help us plan our programs for Venus, Mars, and beyond, using the Moon as a staging point for these more difficult missions. And there was still the link to understanding Earth.14

All these theories, questions, and debates could be resolved by a relatively small suite of activities and experiments. The trick would be to design them so they could be carried on the missions and deployed by the astronauts. The astronauts would have to sample the rocks and soil at their landing sites over as large an area as possible and bring the samples back to Earth for analysis and reconstruction of their geological context. Also, to complete the picture they would need to carry certain geophysical instruments to collect data pertaining to the Moon’s subsurface or other environmental conditions. In the introduc­tion to his book, Baldwin had stated: ‘‘It is beyond hope that we shall ever have a complete and definitive answer to all lunar problems.’’ Finally he had predicted: ‘‘Landing on the moon and analyzing its materials will help greatly but will raise more problems than are solved.’’15 These predictions echoed concerns raised in his first chapter. We hoped that our plans for extensive manned lunar explora­tion would go a long way toward changing his mind on both of them.

After becoming reasonably familiar with the current state of knowledge about the Moon, I started making some personal observations. I got permission from Tom Evans to contract with the Astronomy Department at the University of Virginia for time on their large (twenty-six-inch refractor) telescope so some of us on the NASA headquarters staff could travel to Charlottesville and make our own close-up studies. Laurence Fredrick, director of the Leander McCor­mick Observatory, was a gracious host for those of us that took advantage of the opportunity. This telescope, almost a twin to the famous Naval Observatory telescope in Washington, D. C., where some of the first lunar studies had taken place in the nineteenth century, including those by Gilbert, was the one USGS used in 1961 to begin the detailed mapping of the Moon funded by Bob Bryson. Because this work had recently been transferred to the Lick Observatory in California and a new observatory near Flagstaff, observing time was available. The Virginia telescope was an ideal instrument for casual Moon viewing be­cause with easily mastered techniques it provided a resolution of a few thou­sand feet for lunar surface features. Charlottesville was only a two-hour drive from Washington, so we could leave the office immediately after work, stop for a quick dinner, set up the telescope in plenty of time for a few hours of viewing, and still get home shortly after midnight.

A twenty-six-inch-refractor telescope is a very large piece of equipment. The telescope with its mount weighed some eight tons. A rotating dome with sliding doors covered the telescope, and housed within the dome were the electronics and motors that allowed one to point and track the telescope. Under Larry Fredrick’s tutelage, I became adept at operating the instrument, and after a few nights’ practice I was able to observe by myself. As one might expect, viewing was ideal on clear nights, and the winter months were best of all because cold, stable air reduces atmospheric disturbances. But even on exceptionally clear nights there was always a shimmering distortion caused by Earth’s atmosphere, making it appear that heat waves were rising from the Moon and tending to obscure features under high magnification. I spent many a cold night studying the Moon’s surface, following the terminator as it slowly moved across the face of the Moon revealing the surface detail. When the Sun’s angle was correct I could compare my observations with the first USGS lunar maps of the Coper­nicus and Kepler regions to understand how this latest attempt to map the Moon geologically was carried out and why the USGS mappers were identifying certain types of surface features as discrete geological formations. The subtlety of most of these features was evident, and I came to appreciate how an earth – bound geologist’s imagination might become a dominant factor in drawing a geological map of the Moon with the enormous disadvantage of never having set foot on the surface.

Another compelling reason for spending time observing the Moon was the recent spate of reports by reputable astronomers about transient phenomena on the lunar surface. In 1958 a sensational announcement had been made by Soviet astronomer Nikolai Kozyrev, who claimed he had recorded spectra of a transient event on the Moon near the central peak of the crater Alphonsus. Other observers soon reported color changes and similar events at other lunar features, the most exciting being at the crater Aristarchus.

Excerpts from the report written by James Greenacre, employed at that time by the U. S. Air Force Lunar Mapping Program at Lowell Observatory near Flagstaff, Arizona, tell his exciting story of what he observed one night at Aristarchus.

Early in the evening of October 29, 1963, Mr. Edward Barr and I had started our regular lunar observations. . . . When I started to observe at 1830 MST. . .

I concentrated on the Cobra Head of Schroeter’s Valley. . . . at 1850 MST I noticed a reddish-orange color over the dome-like structure on the southwest side of the Cobra Head. Almost simultaneously I observed a small spot of the same color on a hilltop across the valley. Within two minutes these colors had become quite brilliant and had considerable sparkle. I immediately called Mr. Barr to share this observation with me. His first impression of the color was a dark orange. No other color spots were noted until 1855 MST when I ob­served an elongated streaked pink color along the southwest rim of Aristar­chus. . . . at approximately 1900 MST I noticed the spots of color at the Cobra Head and on the hill across the valley had changed to a light ruby red. . . . I had the impression that I was looking into a large polished gem ruby but could not see through it. Mr. Barr’s impression of the color at this time was that it was a little more dense than I had described it. . . . By 1905 MST it was apparent that the color was fading.16

Greenacre and Barr did not advance any theories on what may have caused the colors they observed, but in a contemporaneous report John Hall, director of the Lowell Observatory, vouched for the authenticity of the sighting. He called Greenacre ‘‘a very cautious observer’’ and noted that Greenacre’s boss, William Cannell, ‘‘stated that he could not recall that Greenacre had ever plotted a lunar feature which was not later confirmed by another observer.’’17

Thus was reported the first sighting of a lunar transient event, confirmed by two observers and, most important, made by highly qualified personnel. A second sighting by Barr and Greenacre, at the same location, was recorded one lunar month later on November 27, 1963.18 This observation also was con­firmed by Hall and by Fred Dungan, a scientific illustrator on the staff and a qualified telescopic observer. This color feature was reported to be somewhat larger than the one observed in October. It seemed beyond a doubt that some­thing was going on near Aristarchus, since other observers before and after Greenacre and Barr recorded similar activity in the vicinity.

Aristarchus is the brightest feature on the Moon’s nearside. This fact, along with the odd shapes of nearby features, suggested that it was of ‘‘recent’’ vol­canic origin. (Recent is a subjective term, since no one could then be sure of the relative ages of any lunar features, and the absolute times when they were formed were even larger unknowns.) By USGS’s reckoning brightness equated to ‘‘young,’’ and these color changes could mean that volcanic processes were still taking place on the Moon. This was an exciting prospect for those of us deciding what experiments to perform on the Moon. Thus, every night that I spent at the telescope I devoted some time to looking at Aristarchus, hoping I would see one of these ‘‘eruptions.’’ I never did.

After setting up the contract at the University of Virginia, I contacted an astronomer friend at the NASA Goddard Space Flight Center, Winifred C. ‘‘Wini’’ Cameron, suggesting we start a nationwide network of amateur and professional astronomers to maintain a continuous Moon watch for transient phenomena. Wini was already studying the origin of lunar features and was working with John O’Keefe at GSFC, so this activity fit neatly with her ongoing work. The idea was to publicize a telephone number where people could call in their observations. The person manning the hot line would then contact other observers to try to confirm the sighting. In spite of the acknowledged profes­sionalism of some who had made sightings, many in the small lunar commu­nity were skeptical about such events, so we needed to get independent confir­mation. We activated the network under Wini’s direction in 1965. She went on to study, extensively, lunar transient phenomena and began a program called Moon Blink that developed instrumentation specifically designed to measure and record such transient events.

Lunar transient events had been reported long before the start of the Apollo program, but as might be expected, Apollo aroused great interest in the Moon in amateur and professional astronomers alike. Many more reports of various types of sightings such as color changes, obscurations, and sudden bright spots were made after Apollo Moon landings became the centerpiece of NASA’s space program.19 Up until this time, however, except for Greenacre’s sighting, confir­mation had never been possible; subsequently there was independent confirma­tion of several events.

In 1967, after careful analysis of Lunar Orbiter У high resolution photo­graphs of the region of Aristarchus, scientists at the Lunar and Planetary Labo­ratory at the University of Arizona discovered some interesting features at the location of Greenacre’s color sightings. They reported that in Schroeters Valley, near the crater named the Cobra Head, they observed a volcanic-looking cone with flow features on its flanks, and that the crater Aristarchus showed evidence of volcanic activity.20 These discoveries suggested that Greenacre was observing the effects of ongoing lunar eruptions.

The information gained later during Project Apollo and from follow-on studies makes it seem likely that some type of gaseous emission or other surface changes did take place during this time. Some of the color changes reported may have been imagined or caused by terrestrial atmospheric distortion that fooled the observers, but some were almost certainly real events. Astronauts’ observations pertaining to lunar transient phenomena are discussed further in chapter 13. For more on the subject, see selected works by Cameron.21