How does gravity, the weakest of the fundamental forces, control the universe of planets, stars, and galaxies? It really boils down to the enormous mass contained in astronomical objects. I will describe some important effects of gravity, ranging from the orbits of asteroids, to the interactions of galaxies, to the fate of the universe itself. I will also illustrate how gravity can be used as a tool that enables astronomers to detect, among other things, planets outside the solar system, black holes, and dark matter.