We turn to the moon figuratively to inspire and imagine. Someday we may return literally to expand our horizons. In this painting astronauts survey a lunar landscape from a rock outcrop. Painting © William K. Hartmann, at Planetary Science Institute, Tucson.
Like any classic work of art, the moon means different things to different people. For millennia, humans have used its omnipresent face as a canvas for storytelling. Today, we see Earth’s faithful satellite in everything from the children’s book “Goodnight Moon” to the gallery of images collected by NASA’s Lunar Reconnaissance Orbiter (LRO).
Even the scientists who study the moon’s craters and ridges have found themselves occasionally inspired by new perspectives in the same way that ancient storytellers discovered new ways of telling familiar stories.
One of those scientists is William Hartmann, a planetary scientist with the Planetary Science Institute. When President Kennedy said, “We choose to go to the moon,” in the 1960s, many scientists quickly began studying the finer details of the lunar surface, Hartmann said in a telephone interview in October 2014. They needed to discover where humans could land safely and the locations of soils and rocks that astronauts should retrieve for further study on earth.
To begin answering these questions, Hartmann – at the time a graduate student assistant – helped to map the edges, called limb regions, of the moon. We see only the sides of those regions when we look at the moon from earth in the same way that we see only the front side of a stem when looking at a pumpkin. For a clear depiction of the shapes of lunar features in the limb regions, Gerard Kuiper, Hartmann’s professor, set up a matte white, 3-foot diameter hemisphere. They would project the best available photos of the moon onto the hemisphere, and then Hartmann would re-photograph the projected images straight on, as if he were hovering overhead.
All was proceeding as science normally does until one day in 1962 when Hartmann stood back from his lunar sphere and saw something unexpected. “It was a real Eureka moment,” he recalls.
Projected on the sphere, along the edge of the visible surface, Hartmann saw concentric rings of mountain ridges. They curved around the edge of a basin of dark lava called the Orientale mare. Never before had anyone comprehended the ring phenomenon. The angled light of the sun made it evident in the photo, by creating shadows behind the curve of peaks. Hartmann saw the mountains in a new way when he imagined that ridges on the dark side of the moon completed a 1,000-kilometer wide bull’s eye ring structure.
“I immediately realized this was the key to all the other mare basin structures, where (as with Imbrium and Nectaris, for example) segments of arcs could be seen around them.” Hartman said by email.
Discovery photo of the Orientale multi-ring basin, 1962. Only the eastern portion of the ring arcs is visible because the central and western portions of the basin lie on the far side of the moon. Sunlight streams from the right, throwing the far side of the basin into shadow at left. (University of Arizona, Lunar and Planetary Lab; photo courtesy of William K. Hartmann.)
Once seen, the concentric rings became so obvious that Hartmann could set a compass to trace a curve of mountains at the edge of a different mare, and then swing the compass to find other, less-obvious peaks along the circle, he said. Kuiper allowed Hartmann’s name to appear as first author on the paper they wrote about the discovery of the multi-ring basins, impact structures much larger than ordinary craters. But they had to wait five years before real, closeup, overhead photos of the entire Orientale Basin confirmed Hartmann’s imagined view of the entire structure.
The LRO satellite has sent images of the moon back to earth since 2009. A computer-generated, color-coded image completes the view of the rings Hartmann discovered, including the half that lay on the dark side of the moon, before seen only in his imagination.
Modern laser altimeter map of the Orientale multi-ring basin. Red = highest elevations; blue = lowest elevations. Only the eastern third (right) of the basin structure is visible from Earth. The western 2/3 (left) lie on the moon’s far side but were mapped here by the Lunar Reconnaissance Orbiter. (NASA, Lunar Reconnaissance Orbiter Laser Altimeter image.)
Hartmann said he thought a lot about his discovery. At the time, Gestalt psychology had gained popularity, with the concept that an overall pattern could arise from seemingly independent observations. So while other scientists often got lost in the details, Hartmann reminded himself to step back more often and look at the big picture.
For Hartmann, the moon is not only an imagination-spurring subject of research. The lunar landscape also inspires his paintings. In one he imagined himself standing in the Orientale basin, facing east from within the ring structure. Earth would be low on the horizon, he said, as we sometimes see the harvest moon edge up over the mountains.
Imaginary view from within the Orientale ring structure, looking east toward one of the ring-cliffs, with Earth visible in the sky. In this view, the sun behind us lights the cliff in the distance and bluish Earth-light illuminates the foreground. (Acrylic painting © William K. Hartmann, Planetary Science Institute, Tucson.)
While Hartmann continues his research, he adds to his portfolio of images. His moon, as art, simultaneously records and encourages exploration.
This early Hartmann painting pictures a future lunar base, with an array of solar panels, in the region of the Orientale basin. An eclipse of the sun by Earth scatters reddish light through Earths atmospher, as during sunse t on Earth. The light casts a coppery glow on the moon, as is also seen from Earth during an eclipse of the moon. Painting © William K. Hartmann, at Planetary Science Institute, Tucson.
Hartmann’s 1983 painting, On the Floor of Lunar Crater Tycho, invites comparison with an LRO image of the same crater, one of the most recent large impact craters on the moon. Hartmann populated his painting with explorers and showed the human scale of lunar structures and the color of lunar rock. Perhaps his most difficult task was to imagine a horizontal view.
Tycho is one of the youngest large impact craters on the moon, with an extremely rugged flor and bright rays of debries easily visible from earth. Here astronauts pick their way through the rubble to collect fresh lunar samples. Painting © William K. Har
NASA nominated five of the most stunning LRO images to appear as the cover shot for the LRO gallery. A view of Tycho crater won, shown from overhead as opposed to Hartmann’s horizontal view. The formation remains familiar to many backyard astronomers, yet in both of these images it appears anew from a closer perspective.
Tyco Central Peak Spectacular NASA/GSFC/ASU
Hartmann’s and the LRO’s images may differ in perspective, design, and color, yet each depicts the moon not only as science, but also as art.