Well, actually, over the distance to the sun, which is important when dealing with optical considerations, its probably insane. Theoretically, it might be considered infinite, but I'm sure there are some molecules floating around over there. Not sure what sokarul is saying though...seriously, the math works...
Although, again, for those who don't like reading back in the page, its the IOR which matters for optical considerations, which changes from 1 to 1.0002, which is completely negligible as in most cases as the angular change is completely beyond our ability to detect, as infinitely more things come into effect, like the humidity, and etc.