The massive compact star cluster in NGC 3603. The image is a colour composite of observations using the WFPC2 filters F547M (1997) and F555W (2007) (blue), F675W (green) and F814W (red). The field of view is about 20 arcsec across. The boxes show a zoomed view of three foreground stars with a particularly high apparent speed relative to the cluster members. Other fast-moving stars can be spotted by closer examination of the two pictures. Most of the cluster stars move by less than 1/10 of a pixel over the 10-year period, which is not discernible by eye.