Until the landing of the Surveyor 1 spacecraft on the moon, it had been inferred from earth-based optical, thermal, radio, and radar observations that the surface f the moon consisted of material of low-bulk density (less than 1 g/cm^3) and high porosity. Recently, a change in this belief, at least with respect to the optical data, has occurred, although a low density continues to be postulated on the basis of radiometric data.