Afterwards,   Spiegel's work focused on models of the solar cycle and radiative processes in hot stars. He authored or co-authored more than 100 papers involving collaborations with over 60 individuals; these papers have been cited well in excess of 3000 times.
Spiegel's subsequent work was centered on solar cycle models and radiative processes in hot stars. He wrote or co-wrote numerous papers involving collaborations with over 60 individuals, which were cited well beyond 3000 times.