"During the years of Captain Kirk's Enterprise 4% of the galaxy has been charted -- not explored -- since exploration would have required visits to all the approximately 11,000,000,000 stars and planetary systems in that 4% of the galaxy. By the time of our 24th century stories, only 19% of it has been charted. If only one of a million of the stars in the galaxy has worlds and if only one of out of a million of these worlds were capable of supporting life, and if only one out of a million were capable of supporting life, and if only one out of a million of those bore intelligent life, there would still be millions of inhabited worlds for us to visit."