means A domed theater where projectors cast a simulated night sky onto the ceiling, recreating stars, planets, and their movements for an audience below.

from From the Latin 'planeta' (wandering star) — itself borrowed from Greek 'planḗtēs,' a wanderer, because the planets visibly roamed against the fixed stars — paired with the Latin suffix '-arium,' which marks a place where something is kept or housed, as in 'aquarium' or 'herbarium.' So the word literally promises a place that holds the wanderers, a coinage of the modern scientific age when projection technology finally made an indoor heaven possible.