plan·e·tar·i·um 
(plăn′ĭ-târē-əm)
(plăn′ĭ-târē-əm)n. pl. plan·e·tar·i·ums or plan·e·tar·i·a (-ē-ə)
1. An apparatus or model representing the solar system.
2.
a. An optical device for projecting images of celestial bodies and other astronomical phenomena onto the inner surface of a hemispherical dome.
b. A building or room containing a planetarium, with seats for an audience.