柯克伍德空隙（Kirkwood gap）是分布在小行星主带之内的空隙，半长轴（或相当于轨道周期）如右图所见，是位在与木星产生轨道共振的地点上。

举例说，只有少数的小行星在轨道长半径为2.5AU之处，相当于轨道周期3.95年，是木星轨道周期的三分之一（因此称为1：3轨道共振）。其它轨道共振的位置都在周期与木星成简单数值比的位置上，这些微弱的共振只会导致小行星的离散，直方图中的突出通常都肇因于小行星家族的出现。

这些空隙是丹尼尔·柯克伍德在1857年首先注意到的，他也正确的解释了空隙是来自于木星的轨道共振。

A Kirkwood gap is a gap or dip in the distribution of the semi-major axes (or equivalently of the orbital periods) of the orbits of main-belt asteroids. They correspond to the locations of orbital resonances with Jupiter.

For example, there are very few asteroids with semimajor axis near 2.50 AU, period 3.95 years, which would make three orbits for each orbit of Jupiter (hence, called the 3:1 orbital resonance). Other orbital resonances correspond to orbital periods whose lengths are simple fractions of Jupiter's. The weaker resonances lead only to a depletion of asteroids, while spikes in the histogram are often due to the presence of a prominent asteroid family.