Minnaert obtained a PhD in biology at
Ghent University in 1914. Later he obtained also a PhD in physics from
Utrecht University, under the supervision of
Leonard Ornstein. He was a supporter of the
Flemish movement during World War I and endorsed the replacement of French by Dutch during the
German occupation of Belgium. He worked as "lector fysica" at the new Flemish University of Ghent, which was made possible by the support of the German occupation forces, and was viewed as connivance with the enemy by the reestablished Belgian authorities. Because of this, he was sentenced after the war in absence to 15 years of forced labor. However, Minnaert had anticipated this outcome by fleeing Belgium in time. In 1918, he found a position at Utrecht University in the Netherlands, initially to do
photometric research. In
Utrecht, he became interested in astronomy, and he became a pioneer of solar research. He specialized in
spectroscopy and the study of
stellar atmospheres and invented the spectroscopic
curve of growth. Minnaert was also interested in
bubbles and musical nature of the sounds made by running water. In 1933 he published a solution for the
acoustic resonance frequency of a single bubble in water, the so-called
Minnaert resonance. In 1937, he was appointed director of the stellar observatory
Sonnenborgh in Utrecht and full professor in astronomy at the university. In 1940, he published his famous
Utrecht Atlas of the solar spectrum. In 1941, he invented the
Minnaert function, which is used in optical measurements of celestial bodies. During the German occupation of the Netherlands in World War II, he was imprisoned in
Kamp Sint-Michielsgestel by the Germans because of his left-wing, anti-
fascist sympathies. During his incarceration, he taught physics and astronomy to his fellow prisoners. After the War, he was one of the founders of the
Mathematisch Centrum in Amsterdam. Minnaert was elected to the
American Academy of Arts and Sciences in 1959. In 1946 he became member of the
Royal Netherlands Academy of Arts and Sciences. He became a member of the United States
National Academy of Sciences in 1964 and the
American Philosophical Society in 1969. == Publications==