  Stars are powerful sources for weakly interacting particles that are produced
by nuclear or plasma processes in their hot interior. These fluxes can be used
for direct measurements (e.g. solar or supernova neutrinos) or the
back-reaction on the star can be used to derive limits on new particles. We
discuss two examples of current interest, the search for solar axions by the
CAST experiment at CERN and stellar-evolution limits on the size of putative
large extra dimensions.
