Its all Latin and Greek to me. The most commonly mispronounced constellation I've heard is Pleiades. My father corrected me on this one; he studied Latin and Greek. After I looked it up, I realised it's one of those English vs US things.
US: /ˈpliː.ədiːz/ PLEE-ə-deez or sometimes /ˈpleɪ.ədiːz/ PLAY-ə-deez
UK: /ˈplaɪ.ədiːz/ PLYE-ə-deez
Guess it comes down to personal preference, but I still reckon the English are correct, after all it is their language, despite what the Americans think. How can you have US English?