Marcel Minnaert

Marcel Gilles Jozef Minnaert (12 February 1893 – 26 October 1970) was a Dutch astronomer of Belgian origin. He was born in Bruges and died in Utrecht.

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.

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