This is my favorite Clarke story. The short story version may be a little bit "better" technically, but the long version is overflowing with ideas -- maybe too many for a single story, but I guess that's how I like my SF.The moon, the invaders, the two civilizations: Clarke was one of the best at taking science to a place where it functioned like myth. Clarke's third law notwithstanding, the way advanced technologies ARE distinguishable from magic is that they are based on as yet undiscovered natural laws, not on supernatural agency. But maybe that's just hair-splitting, based on a misunderstanding of what's natural and what's super...