planetarium

noun

plan·​e·​tar·​i·​um ˌpla-nə-ˈter-ē-əm 

plural planetariums or planetaria ˌpla-nə-ˈter-ē-ə 

1

: a model or representation of the solar system

2

a

: an optical device for projecting various celestial images and effects

b

: a building or room housing such a projector

Examples of planetarium in a Sentence

Recent Examples on the Web

Hyperia can livestream observations and beam images to planetariums, classrooms, or theaters. —New Atlas, 26 Jan. 2026

Stroll beneath a towering rainforest dome, marvel at coral reef aquariums, and journey through the cosmos in the planetarium’s sweeping dome. —Lewis Nunn, Forbes.com, 22 Jan. 2026

The planetarium, located in the Jenks High School Math and Science building, includes a 50-foot-high SciDome, classes and talks on astronomy and individual telescopes. —Isa Almeida, Oklahoman, 15 Jan. 2026

Construction has already begun on an expansion, with the work slated to include a state-of-the-art digital planetarium and event venue for speaking engagements and workshops. —Lauren Breedlove, Travel + Leisure, 10 Jan. 2026

Word History

First Known Use

1860, in the meaning defined at sense 1

Rhymes for planetarium

• honorarium
• sanitarium
• aquarium
• herbarium
• ovarium
• puparium
• samarium
• zoarium
• armamentarium
• cerium

Kids Definition

planetarium

noun

plan·​e·​tar·​i·​um ˌplan-ə-ˈter-ē-əm 

plural planetariums or planetaria -ē-ə 

1

: a device that projects images of heavenly bodies on a ceiling shaped like a dome

2

: a building or room housing a planetarium