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

Venus and Jupiter should also be visible, said Scott Kardel, associate professor of astronomy and the assistant planetarium director at Palomar College. —Maura Fox, San Diego Union-Tribune, 13 Apr. 2026

Inside the University of Texas at Arlington planetarium, students and space enthusiasts gathered to witness the next chapter in lunar exploration. —Erin Jones, CBS News, 2 Apr. 2026

For museum and planetarium, the cost is $5 per person. —Susan McDonald, The Providence Journal, 26 Mar. 2026

Also in Arizona, the International Dark Sky Discovery Center in Fountain Hills is slated to open mid-year as the world’s first visitor center dedicated to dark skies, with an observatory, planetarium, and research facilities. —Megan Eaves, Outside, 16 Mar. 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