Herman Zanstra (November 3 1894 – October 2 1972) was a Dutch astronomer.
He did undergraduate studies at the Delft Institute of Technology in the Netherlands. He then earned a Ph.D. in mathematics at the University of Minnesota at Minneapolis in 1923 with a dissertation entitled A Study of Relative Motion in Connection with Classical Mechanics. As a postdoc at Caltech he wrote a famous paper, An Application of the Quantum Theory to the Luminosity of Diffuse Nebulae, which for the first time provided a quantitative method (the "Zanstra method ") for understanding the luminosity of nebulas and comets.
After teaching briefly at the University of Washington he went to London and eventually to the University of Amsterdam. World War II left him stranded in South Africa, and he therefore took up a teaching position in Durban, but returned to Europe after the war.
He won the Gold Medal of the Royal Astronomical Society in 1961.
A crater on the Moon is named after him.
