The Morning After: Rockets' Red Glare

So the thing I was skeptical about before watching Discovery's When We Left Earth in HD was: why exactly would old film benefit from high definition? Grainy footage is grainy footage, right? But comparing it with the standard-def version I screened, there does seem to be a difference: HD can't make blurry footage crisp, but HDTV (and, presumably, whatever remastering magic Discovery worked) does make the colors pop, and turns graininess into texture. (I remember having the same reaction to the old surfing footage in the gorgeous John from Cincinnati credits.) Everything bursts from the screen: the tail plumes, the explosions, even Gus Grissom's nipples. In HD or SD, what did you think?