| The Magazine of the CALIFORNIA ACADEMY OF SCIENCES |
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feature Hanna's Heavens From the Roof Prism Gang to the Theater of the Stars
The dimming of the house lights at the Morrison Planetarium inspires a kind of out-of-body experience. In an instant, viewers are transported from the crowded hallways of an urban science museum to the darkened serenity of a country night. The Milky Way arcs overhead in a subtle wash of stars, while the planets and constellations glow with striking familiarity across the vault of the sky. The view is so realistic that it takes even jaded modern viewers a few moments to remember where they are. In 1952, when the Morrison first opened, the sight was a revelation. The man largely responsible for bringing the night sky indoors was Academy curator of paleontology and diatom specialist G Dallas Hanna. Though neither an astronomer, a Swiss optician, nor a machinist, Hanna parlayed a practical knowledge of microscopes into a wartime workshop that culminated in the design and construction of one of the world’s most famous planetarium projectors. The fact that Hanna’s first name was simply the letter “G” only hints at the character of a man who was…different. Born in Arkansas in 1887, Hanna—or “Doc,” as he was generally known—graduated from the University of Kansas in 1911. He worked briefly for Alaska’s Bureau of Fisheries, making the 1,000-mile trip from Bristol Bay to Iditarod and back by dogsled. In 1918, he earned a PhD from George Washington University in St. Louis. Hanna came to the Academy as a researcher in 1919 and immediately established the Academy’s diatom collection. At a time when specialized scientific equipment was difficult to find, he learned to grind his own microscope lenses and machine his own instruments. With these tools, he became a leader in the field of diatom biostratigraphy. Oil companies would send him samples of diatom-rich rock and soil from all over the world in hopes that Hanna could divine their potential for oil exploration. Though he specialized in fossil shells, Hanna became an expert in a dizzying range of subjects. Among his 450 publications were articles covering the ancient amphibians of Illinois, whale fossils, scientific illustration, nudibranch preservation, the birds of San Francisco’s Golden Gate Park, and the repair of binoculars. And during his later years, he would develop a three-color printing process at which he and his wife Margaret spent long hours making color plates for Academy publications. But it took a World War to propel Hanna into the business of making a planetarium. In 1937, Nazi troop movements in Europe made the outbreak of war appear imminent. When that happened, the high-quality optics the U.S. military normally bought from Germany would no longer be available. Without ship’s binoculars or submarine periscopes, fighting a lengthy war would be next to impossible. Hanna and other optical craftsmen scattered throughout the United States were notified that their skills would be needed to produce replacement parts—specifically, roof prisms. These special prisms were a crucial component of periscopes, range finders, and anti-aircraft gunsights, and their exacting fabrication required specialists. Hanna and the others in the group, organized primarily by Albert Ingalls, an editor with Scientific American, called themselves the “Roof Prism Gang.” Over the course of the war, these volunteers would painstakingly craft 28,360 of the precious prisms. With the help of Academy instrument-maker Albert S. (“Jimmy”) Getten, Hanna transformed the Academy’s North American Hall into an optical fabrication shop. Hanna himself had already made 165 roof prisms when the U.S. Navy charged the Academy group with a new task: the reconditioning of used optics and, later, binocular repairs. The Navy wanted an optical facility located in a West Coast port so they wouldn’t have to ship everything across the country by train. The high quality of work being done at the Academy made the arrangement a perfect match. Meanwhile, other Academy staff pitched in as time allowed. The size of the optical staff—all trained by Hanna—eventually grew to 50, some of whom worked full time on the project. Curator of Herpetology Joseph Slevin, a veteran of World War I, shipped all his type specimens inland for safety and closed his department to become a foreman in the optical shop. W.M. Chapman, Curator of Fishes, put in time repairing binoculars, and the Steinhart Aquarium’s operating engineer, Benjamin Culleton, contributed several hours a day after work. But the skill needed to grind glass wasn’t as easily learned as binocular repair, and Hanna obviously couldn’t do it all himself. It was Albert Ingalls who suggested enlisting local astronomy buffs for help. Because premade telescopes were so expensive, these hobbyists ground their own precisely-curved mirrors and custom-built their telescopes. If there was one thing these men knew as well as they knew the stars, it was optics and glass-working techniques. Between 1942 and 1946, Academy staff manufactured 10,000 optical parts and repaired 6,000 pairs of binoculars. While grinding glass, Hanna and Ingalls forged friendships with the astronomers. And all these men could talk about were the “planetariums” that could so realistically simulate the night sky. Though invented in Germany in 1923, there weren’t that many around yet. The first in the United States, located in Chicago, opened in 1930, and by the outbreak of World War II, there were still only five large planetaria in the country. The telescope-makers insisted that San Francisco deserved one, too. However, at war’s end, the area of Germany where the Zeiss factory was located came under Russian control. The postwar chill in diplomatic relations meant that buying a star projector—at least from Zeiss—was out of the question. Nevertheless, interest in building a planetarium in San Francisco lingered. In 1948, funding finally materialized in the form of separate financial offers from C.M. Goethe, a longtime Academy member and supporter, and Edward Hohfeld. Hohfeld was the executor of the estate of May Treat Morrison. She had wanted to build a memorial to her late husband, prominent San Francisco attorney Alexander F. Morrison, and Hohfeld was authorized to offer the Academy $200,000 to build a planetarium bearing his name. Along with some additional fundraising, the bequest paid for both the planetarium theater and the building to house it. But the most important element of the planetarium—the star projector—remained out of reach. With the experience they had gained during the war, the Academy’s instrument makers were confident they could handle the job themselves. The trustees hired Russell Porter, who had been instrumental in the design and installation of the 200-inch Hale Telescope on Palomar Mountain, to make sure the Roof Prism Gang was up to the task. After interviewing Academy personnel and reviewing their plans, he convinced the Trustees that the optical team could build a star projector comparable to or even better than a Zeiss by themselves. Hanna led the project. They began by studying pictures of the Zeiss projector at the Griffith Observatory planetarium in Los Angeles. It was shaped like an old-fashioned dumbbell, with two spheres, or “starballs,” to project stars at the ends. Cagelike assemblies between the starballs simulated the Sun, Moon, and planets. The starballs consisted of 32 lens assemblies, each of which projected a portion of the sky. When fitted together like the pieces of a giant jigsaw puzzle, the device could reproduce the entire sky. Because the projector was to be made from cast iron, the Zeiss design would put too much stress on the cages. The projector’s special type of cast iron (mehanite) would have made the starballs at the ends too heavy for the flimsy planet cages to support. So Hanna and Getten reversed the arrangement. They decided to place the massive starballs closer to the center and the two planet cages at the ends. This redistributed the machine’s mass, making the whole instrument much easier to rotate. Smaller, quieter motors could be used to simulate the slow east-to-west movement of the sky. Another major difference was in the way the stars themselves were simulated. In the Zeiss projector, light from lamps at the center of each starball shone through thin sheets of metal, called “starplates,” that had tiny, carefully-positioned holes drilled into them. When focused with lenses onto the dome, dots of light replicated the appearance of the constellations. But upon close examination, these artificial stars were not entirely convincing. The Zeiss stars had a discernable roundness that, because of their enormous distances from Earth, real stars lack when observed with the naked eye. Real stars also vary in brightness from one another. In a planetarium sky, however, all of the stars have the same brightness per unit of area, since they’re all created by a single light source. To make these differences apparent, the stars are shown in a range of sizes. The brighter the star, the larger the drill hole—and the more noticeable, therefore, its round shape becomes. Hanna developed a clever method to sidestep the round star problem. Within the optical path of each of the Morrison projector’s 32 star cells is a flat lens surface. This is where the slide is located in a typical slide projector. Hanna decided to use this surface as the starplate itself. But instead of drilling circular holes into the metal plates, he hit on the idea of using carborundum grains to depict the irregular outlines of the stars. Hanna realized that sand-like particles of carborundum—an abrasive grit commonly used to polish lenses—could be placed onto this flat lens surface. Different-sized particles could represent the different star brightnesses. Frances Greeby, one of Hanna’s optical workers, spent six months hand-placing thousands of carborundum grains onto the 32 condenser flats. Hanna built her a special microscope to help with the task. The instrument allowed Greeby to position the grains at the correct coordinates. Staff astronomer Leon Salanave worked out the positional corrections necessary because the star projector lamps were not at the precise center of the planetarium dome. Otherwise, the projectors would have distorted some of the constellations. After the grains were in place, the condenser surface was coated with an opaque layer of vaporized aluminum—the same process used to produce mirrors for reflecting telescopes. When the grains were brushed off, each left a clear hole in the coating through which light could shine. The result: projected stars with the irregular outlines of carborundum grains. Against the backdrop of the planetarium dome, the stars had a pointlike appearance, creating a more natural-looking sky. Another important consideration was the number of stars to be projected. On a clear night, the unaided human eye can see about 5,000 stars. By comparison, the Zeiss instrument projected 8,900 stars. Hanna made the decision to limit the number of stars projected by the Morrison machine to 3,800. Fewer stars certainly made the job much easier for Greeby, but still produced a familiar night sky. Reading the notes Hanna made during the projector’s construction is revealing. For example, before deciding on carborundum particles, he experimented with using the microscopic objects of his vocation, diatoms. Nor was the design of the projector always clear cut. A letter suggests that as late as 1950—two years before its debut—the final configuration of the star projector had not yet been decided. The machine’s shape evolved from a single sphere to the classic Zeiss dumbbell and eventually to the final design. During the construction, Hanna admitted later, certain component drawings weren’t made until after the parts had been assembled; in the fever to build the projector, more than a few parts had been crafted on the fly. When the Morrison star projector was unveiled on November 8, 1952, it was heralded as far superior to the German model. It reproduced the night sky more faithfully than any planetarium had before. Wagner Schlesinger, then the director of Chicago’s Adler Planetarium (the country’s first planetarium) declared the Morrison projector the best in the world, and the realism of its sky the best he’d ever seen. Coronet magazine declared, “They Out-Zeissed Zeiss!” So successful was the Morrison star projector that it caught the eye of Japanese optical manufacturer Seizo Goto during a trip to the United States in 1958. Goto specialized in astronomical instruments and had decided to branch out to include planetarium projectors. Seeing the advantages of the Morrison machine over the German-made Zeiss, Goto decided to emulate it. For several decades afterward, much of Goto’s planetarium line consisted of strangely familiar-looking “Morrison-style” projectors. Although the design of its largest instruments has since changed, Goto’s smaller projectors still use the basic Morrison configuration, with star spheres near the center and planets at the ends. Hanna continued working at the Academy until his sudden death due to a heart attack in 1970. The Morrison Planetarium’s star projector—the only such instrument of its kind—was just one of his many accomplishments, though perhaps the only one that many casual visitors to the Academy have had the opportunity to see. It has been operated continuously for 51 years, a term of service far longer than that of most other star projectors. Soon to be retired, the projector has stood as a historic tribute to the skill, dedication, and dogged “can-do” spirit of its builders—a handful of amateur optical workers led by the “Renaissance Man of Natural History.” Bing F. Quock is Assistant Chair of the Morrison Planetarium in San Francisco. |
