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The small moon Janus overtakes the larger moon Rhea in a dance played out before Saturn and its rings.

Observations of mutual moon-crossing events like this one, in which one moon passes close to or in front of another, help scientists refine their understanding of the orbits of Saturn's moons. This movie is a concatenation of 12 still images taken over a span of 24 minutes. The images were reprojected to a uniform view and computer interpolation was used to smooth the moons' motions between the frames. ...