The earth upon which we live is only one of many worlds that whirl
through space. If we are to understand our own world, we must first
learn something about the worlds in the skies. These bodies are arranged
in groups, or systems, sweeping through circuits that baffle
measurement; and such is the magnitude of the boundless space they
occupy that our entire solar system is only a point in comparison. To
this vast expanse of worlds, and systems and space we give the general
name _Universe_.