The universe is a place of wide extremes: light, dark… wet, dry… air, vacuum… hungry, fed. Human life tends to flourish in the balance. We feel most comfortable in places that are not too hot or too cold, not too light or too dark — in other words, places that are “just right.” Most of our planet fits that description. As long as you stay away from the South Pole and don’t fall into a volcano, Earth is a pretty comfortable world. But now that humans are venturing into space — not as visitors, but as homesteaders — finding the right balance is more of a challenge.