Moving Heaven and Earth

By Lawrence Biemiller

Boulder, Colo. -- Among human conceits, replicating the vastness and beauty of the night sky indoors deserves special mention. There's something peerlessly audacious about trying to recreate, even rival, the majesty of a starry night, the pale wandering path of the Milky Way, the half-perceived color of a planet bright at sunset. Not to mention that doing so involves mathematical problems worthy of Ptolemy, the great astronomer, and mechanical challenges that would have befuddled da Vinci.

But man's audacity is the last thing on the minds of the second graders squirming in their seats this morning beneath the white dome of the Fiske Planetarium here on the University of Colorado's campus. They have come for a show called "Kids in Space," in which one Capt. Ann Dromeda tours the solar system with a crew of, well, kids. The show relies on a high-quality audio track and countless slides that slip into place in front of the lenses of the planetarium's 75 carousel projectors, arrayed just out of sight at the base of the dome. And like every planetarium show here, even those for seething rows of 7-year-olds, this one has its moment of awe.

As the light dims and the dome vanishes into blackness, the star projector rises from its well in the middle of the room, and stars appear everywhere -- some 6,700 of them, more than you would almost ever see naturally. The star projector, which resembles a satellite studded with lenses, is rotating slowly in midair. Above it the Moon rises hastily and planets hurry across the ecliptic; time has been collapsed so that days pass like minutes. For a few moments, awe silences the second graders.

The Fiske Planetarium, opened in 1975 at a cost of about $1.8-million, is said to be the largest between Chicago and Los Angeles, and it is one of the largest on a university campus anywhere. It seats more than 200 under a dome with a diameter of 65 feet. Operators can summon more than 100 special effects, many from homemade devices. A laser projector is one of the newest and most popular features.

The star of the show, however, is the one-ton Zeiss Model VI star projector. Made by the German company Carl Zeiss, which built the first successful star projector in 1923, the Model VI represented the state of the art when it was new. The star field it projects is "exceptionally realistic," says Bob Stoller, a 23-year Fiske veteran who is the projector's caretaker and the planetarium's operations manager.

Although its purpose is to project stars, the Model VI is essentially "a mechanical analog computer," he says proudly. The daily rising and setting of the Sun and the Moon, the change in the height of each above the horizon through the seasons, the motions of the other planets relative to Earth through the centuries -- all those are built into the star projector's gearing. Any time the star projector's Sun rises, it does so precisely as it would on a given date in a given location. Essentially, the Model VI is a time machine whose gears can accurately track centuries' worth of the movement of astronomical bodies relative to Earth. "You can go back hundreds of years and get the eclipses right," Mr. Stoller says.

Even more remarkable is that the Model VI is designed to show the solar system not as it actually is -- nine planets in fairly simple orbits around the Sun -- but as it appears from Earth. That is a far more complicated undertaking because Earth is not orbiting the Sun at a speed synchronized with those of the other planets. And because those planets all move in roughly the same plane, we see their orbits edge-on. When, from our vantage point, a planet loops back on the far side of its orbit, it appears to be moving backward against the fixed background of stars. That phenomenon, called retrograde motion, is difficult enough to understand -- it gave Ptolemy no end of trouble -- let alone build into gears.

The star projector "is an amazing piece of machinery," says Andrew Hamilton, an associate professor of astronomy. Even though it is almost 30 years old, he says, the Model VI "produces beautiful, high-resolution stars, and it has a superb black level." The blackness of the star field's background is a serious issue for new digital-projection systems that are being sold for planetariums, he says, because those systems can't yet match the rich, velvety night of the Model VI. So Mr. Hamilton says the Model VI should be augmented by a digital "all sky" projection system that would replace many of the slide projectors. The university's astronomy department is considering upgrades for the planetarium, he says.

The Model VI, nicknamed "Fritz," has been upgraded in some respects over the years, and Mr. Stoller maintains it lovingly. He thoroughly cleans and lubricates the projector annually, and he's skilled enough to make other repairs as they become necessary. But the Model VI is showing its age. The gears in its Moon projector, for instance, are just about worn out. "I have to adjust it once a month," Mr. Stoller says, adding that the projector is "an electromechanical system with late-'60s electronics."

Mr. Stoller says new star projectors rely on computers, not complex trains of gears, to place the Sun and the planets where they belong in the night sky. New projectors also use fiber optics to create the images of stars. A separate fiber, colored as appropriate, projects each star. The Model VI, by comparison, projects stars by focusing light from 1,000-watt mercury bulbs onto glass plates into which the stars are etched. Its stars are all the same color, except for a prominent few that are projected separately.

Even so, the star projector ranks as a triumph of mechanical achievement. The same cannot be said of the planetarium's other projection equipment, however. The carousel slide projectors, for instance, use overlapping images to create landscapes around the dome's base -- suburban backyards, Italian towns, Martian vistas (the projectors are aimed 22 degrees to the left to avoid illuminating the Model VI). The slides, which must be distorted so they will look right on the concave dome, include some hand-painted scenes and some worked up from photographs of gravel or the sculpting foam used by model-railroad enthusiasts. Although many of the scenes are skillfully rendered, the sky above them is so realistic that they appear slightly amateurish in comparison. And while the special-effects projectors, many created by Mr. Stoller in the planetarium's workshop, are cleverly contrived -- a piece of melted plastic over a lens gives the effect of clouds, for instance -- they can't help seeming like crude stagecraft beside the splendid star projector itself.

Nonetheless, the slides and special effects play important roles. The planetarium is largely self-sustaining, and to pay the bills Mr. Stoller and his staff have no choice but to offer the paying public what it wants to see -- which is more than just stars and planets. Between 25,000 and 30,000 people a year come for a variety of shows: lectures on the Colorado skies and astronomical phenomena, instructional shows for school groups, shows with Halloween and Christmas themes, even laser shows based on music by U2, the Red Hot Chili Peppers, and Depeche Mode.

Of course, astronomy classes use the planetarium as well. "Virtually everyone who teaches an intro-level class uses it at some time," says John T. Stocke, a professor of astronomy, after the regular Thursday meeting of his course on how different cultures have viewed the heavens. "This was one of the few places I could give such a course," he says. "The intricacies of the motions of the sky cause students some difficulty. That's what I use the planetarium for."

Mr. Stoller and Francisco Salas, the program supervisor, are the planetarium's only full-time staff members. The planetarium also has several part-time employees and undergraduates to help with office work, ushering, and running shows. The shows, which can involve as many as 3,500 cues in an hourlong production, are controlled largely by a computer, but the students also field a wide range of astronomy questions, deal with sticking slide carousels, and operate the Model VI.

And it is a marvelous thing, the Model VI. Mr. Stoller is happy to show it off, along with effects like a solar flare, a spinning Earth, and a supernova. Standing at the control board, he switches on a recording of American Indian flute players and starts the planets in motion. The Moon races across the dome, and then the Sun, with the stars still brilliant behind it and the Milky Way spectacular against the blackness. He points out shooting stars and constellations -- Cygnus, the swan; Orion, the hunter with the three-starred belt. Spring becomes summer, with planets scurrying high overhead, and then fall. In the darkness the star projector rotates slowly, silently, hardly seeming audacious at all.

Copyright © 2003 by The Chronicle of Higher Education. Published January 24, 2003.