I suspect it is to do with the stitching of various images together. As the Earth is in the way if you try to take a picture of the universe from one point, the

I suspect it is to do with the stitching of various images together. As the Earth is in the way if you try to take a picture of the universe from one point, they would have had to stitch multiple images together taken from either side of the Earth. You sometimes get a similar effect when you stitch together spherical photos and then rotate the view to a slightly odd angle relative to the original shots.