Looking through the new books selection at the library, I recently selected MURDER SHE WROTE: THE QUEEN'S JEWELS by Jessica Fletcher and Donald Bain.
Much of the action takes place on the Queen Mary 2. I was surprised to find that that cruise ship has a planetarium. It must be a very large one as three hundred participants are there for the talks given by the main character. The projector is (apparently) used for atmosphere as stars are reflected from the blade of the knife.
Googling "Queen Mary" and planetarium, I find that ship does have a planetarium.