It took James Cameron 60 weeks to prepare Titanic for its rerelease, but apart from remastering the original at 4k resolution and converting it to stereoscopic 3D, nothing about the movie has really changed.
Well, almost nothing.
According to Cameron: "Neil deGrasse Tyson sent me quite a snarky email saying that, at that time of year [April 15, at 4:20 am], in that position in the Atlantic in 1912, when Rose is lying on the piece of driftwood and staring up at the stars, that is not the star field she would have seen."
"And with my reputation as a perfectionist, I should have known that and I should have put the right star field in. So I said ‘All right, send me the right stars for that exact time and I'll put it in the movie.'"
So Tyson did just that, and Cameron re-shot the scene. According to the Telegraph, it is the only major technical change in the film's re-release.