We study the radiation emitted by a cavity moving in vacuum. We give a
quantitative estimate of the photon production inside the cavity as w
ell as of the photon flux radiated from the cavity. A resonance enhanc
ement occurs not only when the cavity length is modulated but also for
a global oscillation of the cavity. For a high finesse cavity the emi
tted radiation surpasses radiation from a single mirror by orders of m
agnitude.