  Directional dark matter detectors will be able to record the recoil momentum
spectrum of nuclei hit by dark matter WIMPs. We show that the recoil momentum
spectrum is the Radon transform of the WIMP velocity distribution. This allows
us to obtain analytic expressions for the recoil spectra of a variety of
velocity distributions. We comment on the possibility of inverting the recoil
momentum spectrum and obtaining the three-dimensional WIMP velocity
distribution from data.
