False constellations
Famous astrophysicist Neil DeGrasse Tyson found this specific plot hole. After seeing the movie, he brought up the fact that, given their position, the constellations we see in the movie do not match what the Titanic passengers would have seen in real life.
He then gave Cameron the right version to fix this error before the 3D version of the film was released, though we doubt many people were aware of it at the time.
