A planetarium is a facility with a specialized theater in which representations of the solar system, galaxy, or universe can be projected. With the use of a hemispheric screen and a specialized projector, a planetarium can surround viewers with a glimpse into the night sky. Planetariums of varying sizes can be found all over the world, and they are popular destinations for people of all ages. Chances are high that there is a planetarium somewhere near you; to find one, you can search for “planetarium” and your area in your favorite search engine.
The roots of the planetarium are quite ancient, and the term was actually originally used to refer to a model of various celestial bodies, also known as an orrery. People used a wide variety of techniques to create projections and representations of the night sky for study and education, but the Zeiss firm is usually credited with the development of the modern planetarium, in the early 1920s. Zeiss developed the projector technology necessary to project onto a half-dome, and it was the major producer of planetarium equipment well through the 1960s.
Some people use the term “planetarium” to refer specifically to the projection equipment used in a planetarium. This equipment must be capable of projecting images smoothly across an entire dome, and since most planetariums have animated demonstrations, it must also be capable of movement. Modern projectors often rely heavily on lasers to keep their images crisp and clean; lasers can also be used to highlight specific features of interest in the demonstration.
Many planetariums have reclined seating, so that viewers can see the entire display without contorting themselves. Depending on the facility, the presentation may be brief or lengthy, with a wide variety of sound effects and narration styles. One of the most common uses of a planetarium is to highlight the constellations so that people can learn more about the night sky as seen from earth.
In addition to a central theater, most modern planetariums also have a variety of science and space related diversions for their audiences. While waiting to see a show, people can experiment with various physical demonstrations, look at models, charts, and other informational displays, and talk with planetarium guides. It is also common for a planetarium to have a regular theater to show educational footage or footage from space which might be of particular interest.