Herman Zanstra (November 3, 1894, Schoterland – October 2, 1972, Haarlem) was a Dutch astronomer.
While working in Delft for four years, the last two as a high school teacher, he wrote a highly theoretical and mathematical paper on relative motion which he sent to William Francis Gray Swann.
Swann, then offered him to earn a Ph.D. degree in theoretical physics with him at the University of Minnesota at Minneapolis, which he did in two years time by expanding on his paper (dissertation: A Study of Relative Motion in Connection with Classical Mechanics, 1923).
Here 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.
In 1949 he became member of the Royal Netherlands Academy of Arts and Sciences.