Isaak's work in resonant-scattering spectroscopy observations of the Sun directly led to the first detection (1979) of the Solar five-minute oscillations as a global phenomenon, directly leading to the science of Helioseismology - the study of the solar interior by analysis of the properties of these oscillations. Isaak led the High Resolution Optical Spectroscopy (HiROS) Group at the University of Birmingham, establishing the six-site global BiSON network for helioseismic observations. In many ways ahead of his time, Isaak also devoted efforts to observation of these 'solar like' observations in other stars, a science now known as Asteroseismology.