1. a building or room with a domed ceiling that shows images of stars, planets, and other celestial objects
2. a device that projects images of celestial objects onto a dome or ceiling

Examples

• The school took a field trip to the planetarium to learn about constellations.
• The planetarium show explained how the solar system formed.
• Children watched in amazement as stars appeared on the planetarium’s dome.
• The museum’s new planetarium can seat 200 visitors.
• They installed a digital planetarium projector last year.
• The planetarium director gave a lecture about black holes.