Pyrometric measurements of single-shock-compressed liquid deuterium reveal that shock front temperatures T increase from 0.47 to 4.4 eV as the pressure P increases from 31 to 230 GPa. Where deuterium becomes both conducting and highly compressible, 30< or =P< or =50 GPa, T is lower than most models predict and T<<T(Fermi), proving that deuterium is a degenerate Fermi-liquid metal. At P>50 Gpa, where the optical reflectivity is saturated, there is an increase in the rate that T increases with P.