  We describe a novel method of tracking the rotational motion of clusters of
colloidal particles. Our method utilizes rigid body transfor- mations to
determine the rotations of a cluster and extends conventional proven particle
tracking techniques in a simple way, thus facilitating the study of rotational
dynamics in systems containing or composed of colloidal clusters. We test our
method by measuring dynamical properties of simulated Brownian clusters under
conditions relevant to microscopy experiments. We then use the technique to
track and describe the motions of a real colloidal cluster imaged with confocal
microscopy.
