Lower Intermediate - Galileo's theory
During the dark ages there were a few great men that were silenced because of their scientific views that eventually proved to be correct. We discuss the theory of one of those men in today's lesson which is full of useful vocabulary around astronomy.
A planetarium is a model of the solar system, sometimes mechanized to show the relative motions of the planets, and I doubt whether "qubba samaawiyya" can denote this kind of model. The literal translation of "qubba samaawiyya" is "heavenly vault", and "heavenly vault" is probably what is meant here. "Heavenly vault" is a very common English expression which has literal equivalents in languages like French and German.
I would say "it does not hang from a heavenly vault". The simple verb form ("does not hang") would be appropriate here. The progressive form ("is not hanging") would refer to something temporary (e.g. "He was hanging from the balcony when the firemen arrived.").