Determining the melting temperature of iron at the Earth's inner and outer boundary near 3 Mbar is an important problem in geophysics. A knowledge of the pressure, volume, temperature, and internal energy of solid and molten iron at megabar pressures and several thousand degrees provides a critical constraint for modeling the Earth's core. An optical method measuring the thermal radiation from the thin metal film deposited on an optically transparent window material is described. Issues which need to be addressed to obtain accurate thermodynamic shock temperatures of metals from the thermal radiation measured are discussed. These issues include characteristics of metal films, thermal conduction occurring at the metal/window interface, optical and thermal properties of metal and window material, and characteristics of the radiation measured. ¿ American Geophysical Union 1990