  We calculate the transition radiation process $\nu \to \nu \gamma$ at an
interface of two media. The neutrinos are taken to be with only standard-model
couplings. The medium fulfills the dual purpose of inducing an effective
neutrino-photon vertex and of modifying the photon dispersion relation. The
transition radiation occurs when at least one of those quantities have
different values in different media. The neutrino mass is ignored due to its
negligible contribution. We present a result for the probability of the
transition radiation which is both accurate and analytic. For $E_\nu =1$ MeV
neutrino crossing polyethylene-vacuum interface the transition radiation
probability is about $10^{-39}$ and the energy intensity is about $10^{-34}$
eV. At the surface of the neutron stars the transition radiation probability
may be $\sim 10^{-20}$. Our result on three orders of magnitude is larger than
the results of previous calculations.
