Omega Mysterium was a moon which, along with Falkus and Flidor, orbited Skaro. (AUDIO: Davros, Innocence, Purity)
During Davros' youth, both it and Falkus could be seen clearly from his stepfather Colonel Nasgard's house on Drammankin Lake. Elsewhere on Skaro, they were obscured by the high levels of radiation in the atmosphere. (AUDIO: Innocence)