An orbital resonance occurs when two bodies orbiting the Sun exert a regular, periodic gravitational influence on one other, caused by their orbital periods being related by a ratio of small integers, such as 3:1, 5:2, 7:3, 2:1 and so on. In an orbital resonance of an asteroid with the giant planet Jupiter, there is a regular periodic perturbation of the smaller body caused by the gravitational attraction to Jupiter. Over the course of several billion years, the cumulative effect of this perturbation ejects the asteroid into a nonresonant orbit. This gives rise to depleted regions in the asteroid belt, known as Kirkwood gaps. In this Demonstration, the formation of the principal Kirkwood gaps is simulated as the time slider is moved over a multi-billion year (Gyr) range.