The Earth and Moon 


Music of the Hemispheres by Peter Carrington 

     The line of eight-year olds stretched across the lobby like some multi-colored snake. Shepherded by parents trying to maintain some minimum din, they filed and bustled into the planetarium. 

     With everyone seated, the dome, which was now the sky, was dimmed until the first stars came out of the background. In the cacophony of high voices could be heard the words Orion and Mars. Excitement was high and quiet was a long time coming. 

     "Does anyone notice anything different about the Sky Theater?" queried David Batch, Director of the MSU Planetarium. 

     "The projector is gone," came a hundred replies and yells. 

     A feature of all classic planetarium shows besides the stars, planets, and processions, is always that fantastic projector, looking like a self-propelled beam of Erector Set with spheres at each end. Now, at the MSU Abrams Planetarium, that is gone. 

     It has been replaced by the Digistar planetarium projection system, no ordinary projector by any means. It looks like a 4' x 3' x 3' credenza with a polished hemisphere on the top surface. But what it can project on the dome of a planetarium is a world away from the old but elegant planetarium machine. 

     When Abrams Planetarium opened in 1963 it was heralded with fanfare as the most advanced computer assisted planetarium in the world. Astronomy magazines even implied that you could simulate the appearance of the stars from anywhere in the solar system. Now this was more or less true, but only because solar system-scale distances are so small compared to stellar distances. Even viewing from Pluto, the most distant of planets, would not shift the stars' relative positions perceptibly. Besides, all the stars are rigidly built into the spherical surfaces of the classical planetarium projector, making stars fixed in relative position. 

     The Digistar is literally a sophisticated video system projected on the dome. The stars are produced from a digital database which has three-dimensional coordinates for all stars within 200 parsecs (625 light-years) of Earth. This makes it possible to simulate a space voyage of hundreds of light-years, showing a faithful representation of shifting parallax arrangements and stars drifting past the spacecraft. Stars are still points of white light. This is not Hollywood. As one approaches the stars Antares, it doesn't become a giant red ball of granular gas columns and prominences. This sort of thing will have to wait for future advances in memory storage, digital image compression, and projectable color phosphors. The trip is impressive without it. 

     The central projector is only the centerpiece of an overall remodeling. Director Batch describes what a visitor sees in the theater now. "It will look the same except that the room may seem a bit smaller to people. We've taken the outside wall -- the dome stayed exactly the same size -- and pushed it in about five feet. The reason for that is to do what many other modern planetariums have done. That is to have an area called the projection cove. That's where the projectors are stacked. It circles the theater so that you can aim projectors at any spot on the dome, whereas before we were limited to placing them toward the back of the room, where we had to put our equipment. Now we can put projectors anywhere. We can also use many more than we could have before. To accommodate the wall being moved in, we have taken out a number of seats. 

     "It held about 250 people before. That turns out to be an enormous number for our size dome. In fact, I don't know of any fifty-foot planetarium built recently, that has that many seats. Modern ones being built now have about 150 seats, in a fifty-foot theater. That's what we have now. 

     "The current philosophy in building planetarium seating is to have comfortable, good line-of-sight seats, as opposed to having lots of seats. In the old days there was more of a pack-em-in type style. In truth there were very few programs that would sell-out. So a 150 seats will be adequate for our area." 

     "When people walk in, it will look smaller, I think, but they'll be more impressed with what they will be able to see and how they will be able to see. The sky will seem the same size or maybe even a little bigger because with the walls closer the sky will seem a little bit larger by comparison." 

     "The one thing they'll probably notice right off the bat, is that that big old hunk of a projector will not be there any more. In some sense, that will be a disappointment. I too enjoyed looking at the machine..." 

     "There were only eight of that model projector ever built. And there haven't been any others built in quite a number of years. 

     "This particular model had some drawbacks to it. Most of those eight have already been replaced. We were the very first, actually the prototype of that machine." 

     The Digistar system is produced by the Evans and Sutherland company, based in Salt Lake City, Utah. Their primary products have dealt in computer simulations, especially aircraft simulations. Evidently, an amateur astronomer employee with an interest in planetariums got permission to develop a planetarium projector, the prototype of which the company then committed to. 

     Not only did it sell, but Batch reports, "The last six or seven large planetariums purchased in the US have all been of this type." 

     "This technology, at the moment, still is growing. It looks like the interest is there for long-term growth because Evans and Sutherland has done some administrative reorganization. They've created a new division called Education and Entertainment and Digistar is the first product in that area, whereas before the company was mostly defense oriented." 

     As the children shifted in their seats, the lines formed connecting the stars of the constellations. The children's excited yells punctuating the presentation. 

     "Now we are going to head out into space," promised Director Batch, "a few hundred light-years, as though we were traveling towards another star." 

     Suddenly stars whisked past. The illusion of travel seemed to point toward a particular star. Except for the fact that your chair was still firmly bolted to the floor, it was almost like motion. 

     For a half-second the whispering ceased, then pandemonium broke out with yells of "Wow," and "Did you see that?" 

     But this is by no means all the Digistar is good for. "For any image which consisting of dots and lines, the Digistar can draw and project it onto this hemispherical screen." Batch continues, "It doesn't have to be a sky any longer. In fact one of the things that's creating a lot of interest is three dimensional modeling of molecules.  It's better than a flat screen because you actually feel as though you are inside of the object. We hope that other  departments on campus will find uses for this that we haven't thought of yet. 

      Of course running the planetarium from a computer keyboard is nothing like the traditional controls, and Batch and his staff have their work cut out. 

     "This really is a completely different approach. Although many of the concepts we presented with the old projector we can also present with this one. The actual physical manipulation to get the projector to do those things, is so different that it's going to take a lot of retraining. 

     "Now we're on a keyboard. We're typing in commands that Evans and Sutherland wrote to make this thing do specific things." 

     Another advantage of this system is the ability to share elaborate productions graphics and effects with others.  Batch anticipates that will greatly enrich the visual repertoire. 

     "In fact, part of the remodeling we have done is to become more standard, to match up more closely with planetariums which are being built nowadays so that we can more easily exchange programming and other visuals. We will be using a battery of carousel-type projectors as well as a video projector or two. We will have the standard, what we call panorama projection system used to set a scene. This gives you a horizon scene. There is a new technique, that we have never had the technology to use, which has caught on in more modern planetariums called all-sky projection where you use six projectors, each one making a pie-shaped or wedge-shaped image to create a color image that completely fills the dome. Anything you can get photographed in color or however, can be projected. 

     "The beauty from our standpoint, because we have such a small staff, is that we can purchase, or borrow, or swap things with other folks because we are all completely compatible; whereas now we don't have that ability. Basically, in days past, we had to tailor-make everything to fit our circumstances. We were one of a kind, in terms of special effects." 

     The Digistar has revolutionized the sky shows, but the mission of the Abrams Planetarium, in Director Batch's words, remains the same. "Pretty much, although broadening the way we go about it. I think of the projector as being only part of the mission. It is certainly one of the most obvious parts. The physical facility is part of what we do. We think of ourselves as an astronomy and space science resource center. And one way to fulfill that mission, is through programming. That part of it won't change." The nationally famous monthly Sky Calendar and all the interpretive science programs continue full speed. 

     And what of that marvelous old projector machine? 

     "We hope eventually, to take that machine and put it on display in the lobby, so everyone will still get a chance to see it."

Photo credit: The Earth and Moon by the Galileo Spacecraft in 1990