A planetarium is a theater where you can look at images of planets, stars, and other celestial bodies on the dome-shaped ceiling. Planetariums host school field trips by day, and can even host Pink Floyd laser light rock shows by night.

Use the noun planetarium for the projector that shines light onto the surface of the building's dome, recreating solar systems and constellations — and also for the building itself, where such a show is put on. Because planetarium is a Modern Latin word (from the roots planeta, or "planet," and -arium, "a place for,"), its plural can be either planetariums or planetaria.

Definitions of planetarium
  1. noun
    an apparatus or model for representing the solar systems
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    planetarium consisting of an apparatus that illustrates the relative positions and motions of bodies in the solar system by rotation and revolution of balls moved by wheelwork; sometimes incorporated in a clock
    type of:
    model, simulation
    a representation of something (sometimes on a smaller scale)
  2. noun
    an optical device for projecting images of celestial bodies and other astronomical phenomena onto the inner surface of a hemispherical dome
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    type of:
    optical device
    a device for producing or controlling light
  3. noun
    a building housing an instrument for projecting the positions of the planets onto a domed ceiling
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    type of:
    building, edifice
    a structure that has a roof and walls and stands more or less permanently in one place
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