  We report on the results of a time-series photometric survey of M50 (NGC
2323), a ~130 Myr open cluster, carried out using the CTIO 4m Blanco telescope
and Mosaic-II detector as part of the Monitor project. Rotation periods were
derived for 812 candidate cluster members over the mass range 0.2 <~ M/Msol <~
1.1. The rotation period distributions show a clear mass-dependent morphology,
statistically indistinguishable from those in NGC 2516 and M35 taken from the
literature. Due to the availability of data from three observing runs separated
by ~10 and 1 month timescales, we are able to demonstrate clear evidence for
evolution of the photometric amplitudes, and hence spot patterns, over the 10
month gap, although we are not able to constrain the timescales for these
effects in detail due to limitations imposed by the large gaps in our sampling,
preventing use of the phase information.
