How a full-dome planetarium projection actually works

Most visitors walk into the Astro Haven dome, look up at the curved ceiling, and assume there is one very powerful projector somewhere in the middle. There is not. The system is more interesting than that, and understanding it makes the experience a bit different the second time you visit.

The dome is not a flat screen bent into a curve ¶

A standard cinema screen is flat, and the projector throws a rectangular image at it. A planetarium dome is a hemisphere, and the image has to fill it without distortion. That requires a completely different approach to both the projection hardware and the software that generates the content.

The dome at Astro Haven is 12 metres in diameter and tilted at 15 degrees from vertical. The tilt means the audience can sit in reclining seats and look up at the centre of the dome without craning their necks. It also means the geometry of the projection is slightly asymmetric, which the software has to compensate for in real time.

Fisheye lenses and the projector stack ¶

The projection system uses a cluster of high-resolution projectors, each fitted with a fisheye lens. Each projector covers a portion of the dome, and the images are blended at the edges so the joins are invisible. The fisheye lens introduces a specific kind of barrel distortion, and the software pre-distorts the image in the opposite direction so that when it hits the curved surface it looks correct.

The upgrade we completed in early 2024 moved the system to 8K total resolution across the dome. That sounds like a marketing number, but it has a practical effect: star fields look like star fields rather than grids of bright squares. The difference is most obvious in the Milky Way sequences, where the density of stars is high enough that lower-resolution systems start to show their pixel structure.

Real-time rendering versus pre-rendered video ¶

Some planetarium shows are pre-rendered video files, played back like a film. Ours are rendered in real time by a software system that holds a database of several hundred million stars, all the known solar system objects, and a set of galaxy and nebula models. The presenter controls the view live during the show, which is why they can stop, zoom in on a specific crater on Mars, or jump to a different part of the sky if someone asks a question.

Real-time rendering means the show is never exactly the same twice. It also means the system can show the sky as it actually appears tonight, from this location, at this time. That is what makes the Night Sky Tonight sessions work: the dome is showing you the real sky, just without the clouds and the light pollution.

The sound system ¶

The dome has a 7.1 surround sound system with speakers positioned around the perimeter and a subwoofer under the floor. For the space sequences this matters more than you might expect: the low-frequency rumble during a rocket launch sequence is not decoration, it is part of how the scale registers. The hearing loop runs off the same audio feed and covers the full seating area.

If you want to see the projection room after a show, ask the presenter. We do not always have time, but when we do it is worth a look.