Cassini captured the images for this mosaic on 12 December 2011. The five images used in this mosaic were taken sequentially, and the background moons shifted positions between frames; this composition does not actually reflect a confluence of moons that happened at one distinct moment in time. From left to right, the ringmoons are Prometheus, Epimetheus, and Pandora.
Dione, Prometheus, and Epimetheus are all in the positions they occupied at 13:02 UTC; Pandora is positioned near where it was nine minutes later, at 13:11 UTC. Otherwise, Pandora would have been out of the frame.
NASA / JPL / Dave Seal (Solar System Simulator)
Cassini, Rhea, and Dione during Rhea/Dione mutual event observation
Solar System Simulator diagram of Cassini, Rhea, and Dione during Rhea/Dione mutual event observation