planetarium

American  

[plan-i-tair-ee-uhm] / ˌplæn ɪˈtɛər i əm /

noun

planetariums, plural planetaria plural

1. an apparatus or model representing the planetary system.

2. a device that produces a representation of the heavens by the use of a number of moving projectors.

3. the building or room in which such a device is housed.

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planetarium British  

/ ˌplænɪˈtɛərɪəm /

noun

1. an instrument for simulating the apparent motions of the sun, moon, and planets against a background of stars by projecting images of these bodies onto the inside of a domed ceiling

2. a building in which such an instrument is housed

3. a model of the solar system, sometimes mechanized to show the relative motions of the planets

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Other Word Forms

Inflected Forms

noun

• planetaria
  plural
• planetariums
  plural

Etymology

Origin of planetarium

1765–75; < New Latin, noun use of neuter of Latin planētārius planetary; cf. -arium

Explanation

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.

Example Sentences

The Adler Planetarium is $25, while the Art Institute of Chicago is $32.

From The Wall Street Journal • Apr. 16, 2026

The PhD students are based at the Armagh Observatory and Planetarium and so their watch party is a little different as it will involve state-of-the-art telescopes.

From BBC • Apr. 1, 2026

New York City’s Hayden Planetarium was named for a banker, Charles Hayden, who funded its creation, and passed away two years after it opened.

From Slate • Dec. 20, 2025

Ytasha Womack, a screenwriter on “Niyah and the Multiverse,” currently playing at the Adler Planetarium in Chicago, is the author of numerous works including “Black Panther: A Cultural Exploration.”

From New York Times • Mar. 16, 2024

“Why must she use this sort of envelope?” he asked angrily, studying the little circle of a Planetarium Station, New York, postmark on the thick tan paper.

From "A Confederacy of Dunces" by John Kennedy Toole