Constellations that are not accurate
Neil DeGrasse Tyson, a well-known astrophysicist, identified this plot hole. Following his viewing of the film, he noted that the constellations depicted in the film are not compatible with what the passengers on the Titanic would have seen in real life, given their vantage point. He then sent Cameron the proper version before releasing the 3D version of the film to repair the error — though we doubt many people were aware of it in the first place.
