The most striking feature of most planetaria is their large dome shaped projection screens onto which scenes of stars, planets and other celestial objects can be made to appear and move realistically to simulate the complex 'motions of the heavens'. These domes can be anything from 3-30m in diameter, accommodating from 1 to 500 people.

Traditionally, planetaria domes were mounted horizontally, matching the natural horizon of the real night sky. However, because that configuration requires highly inclined chairs for comfortable viewing "straight up", increasingly domes are being built tilted from the horizontal by between 5 and 30 degrees to provide greater comfort. Tilted domes tend to create a favoured 'sweet spot' for optimum viewing, centrally about a third of the way up the dome from the lowest point. For this reason, titled domes generally have seating arranged 'stadium-style' in rows as opposed to the traditional epicentric/circular arrangement of seating common in horizontal domes.

The celestial scenes on the dome can be created using a wide variety of technologies, ranging from precision-engineered 'star balls' that combine optical and electro-mechanical technology, through slide projector, video and digital projector systems. Whatever technologies are used, the objective is to link them together to provide an accurate relative motion of the sky. Typical systems can be can be set to display the sky at any point in time, past or present, and often to show the night sky as it would appear from any point of latitude on earth.

Since the early 1990s, fully featured 3-D digital planetaria have added an extra degree of freedom to a presenter giving a show because they allow simulation of the view from any point in space, not just the earth-bound view with which we are most familiar and to which traditional 'star-ball' planetarium technology is limited. This new virtual reality-capability to travel through the universe provides important educational benefits because it conveys the fact that space has depth powerfully, helping audiences to leave behind the ancient misconception that the stars are stuck on the inside of a giant celestial sphere and instead to understand the true layout of the solar system and beyond.