| commensurability |
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The property shared by two orbits - either actual orbits or ones that are theoretically possible - that the period of revolution in one is equal to or a simple fraction of the period in the other. Many such commensurabilities are observed between the orbits of the planets, their natural satellites and the asteroids. For example, the Trojan asteroids share the orbit of Jupiter (1:1), and the periods of Jupiter and Saturn are in the ratio 2:5. Commensurabilities arise from the long-term resonance effects that the gravitational interactions between the objects have on their orbits. Commensurabilities also occur between rotational and orbital motion. See also: synchronous rotation. |