The dome is the single most permanent decision in a planetarium project. Projectors, software and seats can all be replaced over the life of the theatre, but the dome screen and the building around it are there to stay.

Three choices define it: the diameter, the tilt and the seating layout. Together they decide how many people the theatre holds, what kind of shows work best, and which projection system it needs.

Dome diameter

The diameter sets the seat count and the overall sense of scale.

  • Small domes suit classrooms and teaching labs. They are affordable, easy to fit into existing buildings and ideal for interactive lessons with one class at a time.
  • Medium domes are the most common choice for schools, universities and regional science centres, balancing capacity with running cost.
  • Large domes are built for public theatres and flagship science centres that need to seat a few hundred visitors per show.

A larger dome is not automatically better. It needs brighter projection, more powerful audio and a taller building, and every one of those adds to both capital and running costs. Size the dome to your expected visitor numbers and the number of shows you can realistically run each day.

Horizontal or tilted?

Horizontal domes

In a horizontal dome the spring line is level and the seats face the centre or recline towards the zenith. Every visitor sees the sky the same way, just as they would outdoors.

Horizontal domes are the classic choice for astronomy education and live sky shows, and they work especially well with optomechanical star projectors placed in the centre of the room.

Tilted domes

In a tilted dome the screen is angled forward, typically by somewhere between 10 and 30 degrees, and the seating is raked so everyone faces the same direction.

Tilted domes give a stronger feeling of immersion and are well suited to cinematic fulldome films. The trade-off is that the sky appears tilted relative to the real horizon, which some astronomy educators find less natural for teaching.

Seating layouts

The seating layout follows from the tilt.

  • Concentric seating surrounds a central projector and suits horizontal domes. It feels communal and works well for presenter-led shows.
  • Unidirectional seating faces one way under a tilted dome, like a cinema. It gives the best view of fulldome films and makes it easier to place a presenter at the front.

Comfort matters more than in most venues, because visitors look up for the whole show. Reclining seats with good head support make a real difference to how a show is remembered.

How the dome shapes the projection system

Once diameter and tilt are known, the projection system can be specified:

  • Brightness and resolution must scale with the dome size. A large dome needs more projectors, or brighter ones, to keep the image sharp edge to edge.
  • Projector placement depends on the seating. A central star projector suits concentric seating; edge-mounted digital projectors suit both.
  • Screen coating affects contrast. Lower-gain coatings reduce light bouncing across the dome, which keeps dark scenes and star fields crisp.

This is why the dome and the projection design should be considered together from the start rather than one after the other.

Practical checks before you commit

Before finalising the dome specification, check:

  1. Ceiling height and structure – can the building take the dome and its suspension?
  2. Sight lines – does every seat see the main action without turning awkwardly?
  3. Accessibility – are wheelchair positions well placed, not pushed to the edge?
  4. Acoustics – is the dome perforated and is there space behind it for speakers and acoustic treatment?
  5. Maintenance access – can technicians reach the projectors and the screen safely?

Frequently asked questions

Is a tilted dome better than a horizontal dome?

Neither is better in general. Horizontal domes suit astronomy teaching and live sky shows; tilted domes suit immersive films. Choose based on the programme you plan to run.

Can an existing dome be re-used in an upgrade?

Often, yes. If the screen is in good condition, it can be cleaned or recoated and paired with a new projection system. See Upgrading an Existing Planetarium.

Does the dome size affect running costs?

Yes. Larger domes need more projection, more energy and more maintenance. Factor this into your budget alongside the capital cost.

Need help choosing?

We help clients match the dome to their audience, site and projection system. Discuss your project with our engineers.