  The advent of JWST (the James Webb Space Telescope) now allows entire star
cluster populations to be imaged in galaxies at cosmologically significant
redshifts, bringing with it the need to apply K-corrections to their magnitudes
and colour indices. Since the stellar populations within star clusters can be
well approximated by a single age and metallicity, their spectral energy
distributions are very different from those of galaxies or supernovae, and
their K-corrections behave differently. We derive the photometric K-corrections
versus redshift for model star clusters that cover a wide range of ages and
metallicities, illustrating the results particularly for the broadband filters
on the HST/ACS and the JWST/NIRCam cameras that are most commonly being used
for imaging of populations of star clusters in distant galaxies. In an
Appendix, we introduce a simple webtool called RESCUER that can generate
K-values for any user-defined combination of cluster properties.

Astrophysics of Galaxies;Cosmology and Nongalactic Astrophysics;Instrumentation and Methods for Astrophysics