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Stellar Cartography: The Amazing Tech of Modern Planetariums

By Matthew Braga

How today's planetariums let viewers swim through the universe.

In 1913, astronomer Max Wolf had a modest proposal – one that called for a device capable of projecting the positions and movements of celestial bodies in the night sky. He brought the proposal to Oskar von Miller, founder of the Deutsches Museum in Munich. And because projection required knowledge of lenses and light, von Miller approached the famed German optics manufacturer Carl Zeiss.

It took scientists, engineers and draftsmen five years of trial and error before they had an instrument that could project complex astronomical principles on the ceiling of a darkened room, and five more to complete the device. But in 1923 – ten years after Wolf's proposal – the optomechanical Zeiss Model I star projector was unveiled.

"Never before was an instrument created which is so instructive as this," wrote the Swedish astronomer Elis Strömgren, the year of its release – a nod to the Model I's ability to project various sized points of light from the center of a hemispherical dome, thus creating the illusion of orbiting planets and stars. "The planetarium is school, theater, and cinema in one classroom under the eternal dome of the sky."

That basic concept proved so effective that modernized Zeiss projectors are now still in use. Mark R. Chartrand, the former chairman of the American Museum of Natural History's Hayden Planetarium in New York City, credited the company with spawning an entire industry. And yet, it's an industry that Wolf and von Miller would scarcely recognize today.

The Morrison Planetarium in San Francisco.

Which isn't to say that's a bad thing. Like most industries, planetariums have undergone a digital renaissance of sorts. Over the past 15 years, those still using Zeiss, or Zeiss-like optomechanical projectors, have retrofitted and revamped their facilities with the addition of digital projection. But there’s more to it than that; there's also the hardware, software and architectural considerations required to construct and maintain a modern planetarium dome too.

In 2000, the Hayden Planetarium was one of the first to make this conversion. The museum worked with then-nascent digital immersive dome company Global Immersion to install multiple CRT projectors around the circumference of the dome, and used specialized supercomputing clusters from Sun Microsystems and Silicon Graphics to handle the complex tasks of video playback and real-time 3D simulation.

Beth Nicholas, the company’s marketing manager, estimates that there are now about 3,500 digital planetariums worldwide. Most of them, however, are quite small, measuring up to 12 meters in diameter (which includes many of the portable domes that are deployed for travelling exhibits and events). It's only when you go beyond 18 meters that you get into the better known and more expensive dome theaters – the type most often found in educational institutions, science centers and museums.

"They tend to be the ones that really go for the big buck," she explains, which can easily cost millions of dollars. "Very high performance and very state of the art display systems, service systems, production suites, render farms, integrated telescope and observatory systems.”

Image Credit: Carl Zeiss

Last summer, for example, Global Immersion worked with the Adler Planetarium in Chicago to unveil the world's highest-resolution digital planetarium theater – a 75-foot dome with twenty 2K projectors, that produce a combined image measuring approximately 8000 by 8000 pixels in size. The Wall Street Journal reported Adler’s Grainger Sky Theater revamp required $14-million USD in fundraising.

Smaller installations can be done with as little as two projectors, placed in the center of the dome, similar to the position of a traditional Zeiss star ball (the tradeoffs being a loss of resolution and image fidelity). But on a screen of the Adler’s size, resolution is important – and the planetarium's previous system, which only projected an image totaling 2K in resolution, had its shortcomings.

"We have a model of a globular cluster, and they all kind of looked the same,” explained Mark SubbaRao, Ph.D, an astronomer and director of the Space Visualization Laboratory at the Adler, who worked on the Sloan Digital Sky Survey for ten years. But at a higher resolution, "you're able to resolve more and more of those stars.”

Combining the output of twenty projectors, however, is no small feat. It takes a dedicated computer for each projector to perform the geometric corrections required to compensate for the curved surface of the dome. Also, this distortion means that projection channels must be overlapped, and pixels inevitably lost. For those of you that have already done the math, this explains why twenty 2K projectors only produce a combined image resolution of 8K.

It’s also crucial that the output from each of those projectors be kept in perfect sync. A typical planetarium show is usually sliced into parts and distributed to each projector before it is played.

“If one slice is behind the other you'll see that very obviously on the screen,” explained Martin Howe, Global Immersion’s CEO. “So a lot of high-speed technology is used to synchronize these different computer servers across the cluster."

The Adler actually has two of these clusters, consisting of twenty Windows PCs – one for production, and one for development – each running high-end NVIDIA Quadro GPUs. Combined, one cluster is capable of playing full-resolution 8K video content at 60fps, uncompressed, in perfect sync.

Some of that content comes from Evans & Sutherland, another immersive dome theater company. You might not recognize the name, but they’re responsible for creating the Kobayashi Maru simulation in the popular 1982 Star Trek film "The Wrath of Khan."

With the ability to weave narratives and feature characters on-screen many modern productions have begun to resemble movies or short films, but purposefully created to take full-advantage of the dome.

Evans & Sutherland is now a big producer of full-dome astronomy films – including Secret Lives of Stars, narrated by Patrick Stewart, and Robot Explorers 3D. However, the company also acts as a distributor of films produced by museums themselves.

The planetarium industry is unique in this way; Journey to the Stars, which is narrated by Whoopi Goldberg, was produced by the American Museum of Natural History, while a separate Adler production was made featuring Sesame Street’s Big Bird. It’s not often you find traditional theaters producing their own content, after all – but then again, most theaters don’t staff experts in astronomical science either.

What’s most interesting about some of Evans & Sutherland’s films, however, is that, while many feature astronomical concepts, their gaze isn’t always fixed entirely upon the sky. With the ability to weave narratives and feature characters on-screen – as is the case in Robot Explorers 3D – many modern productions have begun to resemble movies or short films, but purposefully created to take full-advantage of the dome. An increasing number of films, such as those about climate change or the ocean, may not even feature the sky at all.

“It's really a new medium,” said Michael Daut, the company’s director of show production and marketing. “We like to say it's the closest thing we have to the holodeck."

However – at least where astronomy is concerned – a more apt comparison might also be Star Trek: Generations’ stellar cartography lab. In the film, this was an expansive, curved room upon which Captain Jean-Luc Picard and the android Data could gaze out upon an interactive simulation of the stars, planets and nebulae beyond.

As it turns out, there’s a piece of software called Uniview that works very similarly. It’s an interactive 3D simulation of the universe, a viewer first conceived of in 2003 to interpret astronomical datasets from the Hayden planetarium (it has since grown to accept regularly updated datasets on everything from cloud conditions to high-resolution imagery of the moon, thanks to the likes of NASA, NOAA, and many more). Users can fly around the universe in real-time, on a scale that ranges from the smallest mountains on Earth, all the way to the immense afterglow of the Big Bang.

A good example of Uniview in action is the 2009 film “The Known Universe.” Produced at the American Museum of Natural History’s Hayden Planetarium, the film moves from the Himalayas to the distant reaches of space, displaying satellite orbits and constellations along the way.

“We can visit Mars and we can see the Curiosity rover just as it landed with a full-dome panorama,” explained Daniel Arnberg, an astronomer with SCISS, the company behind Uniview, and graduate from Sweden’s Uppsala University. “Those kind of things simply wouldn't be possible ten years ago – or five years ago, even.”

There are now competing products, including Evans & Sutherland’s own DigiStar system, Microsoft’s Worldwide Telescope and Sky-Skan’s DigitalSky. But at the Adler planetarium, Dr. SubbaRao has been producing live shows with Uniview that complement the facilities pre-rendered video offerings. His most recent show, “Welcome to The Universe,” took six months to write, edit and script, and was finally release in late May.

Though the show has scripted elements, it’s easy for Dr. SubbaRao to take control and fly to objects suggested by members of the audience – making it especially useful as an interactive teaching tool.

“For example we have a little thing about the Earth in my show, and we just started talking about a volcano that went off in Russia that happened [in October],” he explains. “And you can't do that if you render it out as movie."

In fact, just over a decade ago, this sort of thing wouldn’t have even been possible at all. There would be basic projection, sure, and in some cases overheard slides, but nothing quite nearly as in-depth. And while all that technology makes the modern planetarium much different than the early domes of old – more theater and cinema than Strömgren could have ever imagined – they still remain, as he wrote then, “one classroom under the eternal dome of the sky.”