How to Design a Planetarium

Planetariums are truly amazing immersive environments. As dome theaters, they stimulate human perception in a way that no other architecture can. We hear a lot about the immersive experience of virtual reality, but the planetarium remains the most famously communal of virtual spaces — the immersive environment where we gather to learn and be transported to galaxies “far, far away.

”Planetarium design is also mathematically challenging, both from an architectural and audiovisual perspective. For decades, planetarium technology was really no more sophisticated than a pinhole projector. Set the spherical projector, or “star ball,” in the middle of an in-the-round audience and the night sky could be cast on the dome above. This worked well for depicting the night sky as it appears to an Earthbound observer.

To create a full-color spherical experience of the cosmos from variable viewpoints, however, required computational power and Computer-Aided Design (CAD). In 1997, Myles Gordon, Vice President of Education at the American Museum of Natural History, and Carter Emmart, Director of Astrovisualization, changed the planetarium industry when they decided they wanted their digitalized scientific information to be incorporated into a digital projector. I was privileged to be a consultant to AMNH as they went through the process of redesigning the Hayden Planetarium. Digital technology offered the opportunity to bring the audience and dome closer together to journey through a dynamic simulation of the Cosmos. The human eye has a field-of-view of about 190 degrees horizontal and 120 degrees vertical. The redesigned Hayden Planetarium at AMNH is 360 degrees by 160 degrees. It has been called the largest virtual reality simulator in the world.

Designing from the Inside Out

Designing immersive audiovisual technology is about developing an experience from the viewer’s head out. An architect is designing from the building in. When designers plan immersive theaters, they think in terms of geometrical shapes and spaces: a sphere in a sphere, a sphere in a cube, a leaning toroid in a cube, and so on. The more complex the geometry, of course, the more challenging the integration of the technology, the airflow, the seating, the exit and entrances. You’re usually dealing with a section of a sphere within a square envelope, so you end up with little corners into which you must package equipment. That’s why it’s so important for the architects and engineers to work hand-in-hand on these projects, building a model together.

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How to Design a Planetarium? These are the Essential Elements.

For a fully immersive experience, we have to establish a set of principles that start from the audience’s point of view and lay out the space in regards to entrance location, exit, tilt, and where you’re going to put the equipment for least amount of visual disruption. Every theater tells a different story. You can’t just ask, “What tilt angle is the most successful?” You have to do a whole set of work to come up with the optimum shape, tilt, and dimension in relation to the content that will be shown and the space that will contain it. Some planetarium design elements include:

Acoustics and Lighting

Spherical spaces produce what’s called the dome effect. A dome is a reflector that’s spherical; it focuses light like a headlight. This holds true for sound, too. A sound picked up in one part of a dome can be heard in a focused way in another part. That’s why we use a perforated aluminum screen with acoustic material behind it so that the audio coming into the dome is not refocused back out somewhere else. You still get seat-to-seat transfer, where you can hear a conversation from the other end of the planetarium, which can be compensated for somewhat by specifying the right acoustic mass for interior finishes, especially upholstery.

The other thing is that light gets picked up and gives a “glow” to the dome. Green is especially bad because of where it is on the color spectrum, and of course exit signs are usually green. That’s why we try to position exit signs away from the lip of the screen, and why we try and use red signs and not green if acceptable to local code. When you’re packaging the theater it's imperative to think about these elements.

Fire Sprinklers

Sprinkler placement is another challenge with planetarium design. Code usually requires overhead sprinklers, but if you had sprinklers poking through the screen you’d ruin the effect. Combine this with requirements for the distance of sprinklers to occupants, and you have a challenge. At the California Academy of Science Morrison Planetarium, we coordinated with the fire consultant to specify sprinklers with jetting that can propel water far enough to reach audience members.

Air

Air movement in dome theaters is an issue because, as with sprinklers, you can’t place ventilation grilles in the middle of the screen, and letting air move through a perforated screen stains the screen over time. It is especially important, however, to achieve airflow in an immersive theater because it helps dull motion conflict. When you’re on a train and the train next to you starts moving you get motion conflict. This is why people can feel a little queasy in an immersive environment. There’s a curve of response where if you cool people it lessens the queasiness. If you sit on a tarmac on an airplane, you’ll hear the air conditioning turn on just before takeoff. That’s to make the passengers feel less queasy. Theme parks use this technique on rides, too.We work with a mechanical/electrical engineer to design airflow that rolls over people’s heads for the most comfortable experience. If you’re doing an immersive VR experience for corporate environment this will be equally important.

Dome Tilt

Older planetariums were modeled on the “celestial sphere,” mimicking the night sky. This meant they were level in relation to the audience.in order for there to be a wide enough field of view, there had to be a 6- to 8-foot height between the audience’s head and the edge of the dome screen. The audience felt like they were looking into something, breaking the illusion of total immersion.

I came into planetarium design after working on helicopter simulators, which have a very different point of view. In a helicopter simulation, the pilot sits and looks forward into a tilted hemisphere that represents the horizon. The field of view fills the pilot’s vision, resulting in near total immersion. With digital audiovisual technology, planetariums have moved toward a tilt that brings the horizon and audience closer together.When we designed the California Academy’s Morrison Planetarium, we wove the screen, the architecture, and the technology more tightly together than ever before. The audience is seated at a 30-degree angle, facing a 165-degree dome screen (see section plan). That’s why it’s regarded as one of the most immersive experiences in the world.

There is a place in the universe of immersive environments for both virtual reality headsets and planetariums. An immersive space is about shared experiences. You can truly collimate so you feel depth and distance. You’re unencumbered, so it’s a more natural experience. But if you want to look at the engineering of a space in detail, a headset is great for that. We're on the cusp of an incredible melding of technology and built environments, both from design and experience viewpoints, that will take us to places we can't imagine.