Here's how it is: The Earth from TBP got used up, so I built a new one.
Anyway, the old Earth skybox (which was privateered from TBP - can't remember who its original creator was) had a lot of flaws. Basically it was just an image/render of Earth that was plastered on a very, very large plane on the skybox, and the apparent diameter of the planet was grossly larger than what the actual surface features visible suggested.
For those interested in the geometric problem, basically the issue was that as you view a sphere from a distance you see very much of the surface facing you, but when you get closer, the amount of surface visible will drastically decrease while the apparent diameter approaches 90 degrees asymptotically as the view angle tangents the planet's surface, defining the visible circular area of the surface...
However, as the new skybox was basically purpose-built for a single scene in AoA - namely the Lucifer cutscene - it needed to match the apparent diameter of the old skybox Earth for cinematic purposes.
As a result, I was required to position the camera close (too close in my opinion) to the surface so that the planet would correctly fill the required amount of apparent diameter out of the 3D scene.
Now, this would not have actually been an issue since technically NASA's Blue Marble textures stretch all the way to insane 86400x43200 resolution. This would have been more than sufficient to offer 1:1 or lesser scaling factor on the visible portion of the surface, which is always desireable in renders like this (results in crisp, sharp rendered image). However, software and hardware limitations forced me to only use puny 21600x10800 resolution textures on the planet, and this of course reduced the quality of the final skybox renders.
Fortunately, in it's intended use in AoA, the camera never really looks very much at the area immediately below the camera, which is worst affected by texture stretching. As a result I and the rest of the team deemed the quality of the skybox sufficient for its intended use, although I have to agree that it is barely passable for other uses.
Ideally I would have mapped the planet sphere so that it would be divided into eight sections, each using a single 21600^2 texture as required. Unfortunately, my practical skills with Blender are not so hot and I don't know if there's a feature to simply do this or if it requires UVmapping, which I know even less of.
In fact, I'm going to post a request for an icosphere model with subdivision 5 or greater mapped in a described fashion.
Anyway, now you know the most likely reason as to why the AoA Earth skybox has sort of blurry textures on some parts.
