The scale of things is hard to grasp. The distance from Earth to the Moon — some four hundred thousand kilometers — is the shortest cosmic scale of any significance, but one that already stretches the imagination. The Apollo astronauts took three days to traverse that distance; a span that light, the fastest thing in the cosmos, takes a little over a second to cover.
Things quickly get worse. We can have little hope of really appreciating the distance to the Sun — one hundred and fifty million kilometers, eight light-minutes — or that to the orbit of Neptune — four point four billion kilometers. These are numbers and distances beyond human reckoning, relics of a cosmos so vast that our presence here quickly pales into an alarming insignificance.