ˌplanəˈta(a)rēəm, -ter-, -tār- noun
( plural planetariums -mz ; or planetar·ia -ēə)
Etymology: planet + -arium
1.
a. : orrery 1
b. : a model representing the solar system
2.
a. : an optical device designed to project (as on a domed ceiling) various celestial images and effects (as the appearance of the nighttime sky) at a specific time and place
b. : a building or room housing such a device