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. He is notable for his contributions to astronomy and physics and for a popular book on meteorological optics: "Light and colour in the open air", first published in English in 1940. Biography. 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 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. In 1946 he became member of the Royal Netherlands Academy of Arts and Sciences. Publications. One of his interests was the effects of the atmosphere on light and images. His classic book on  this subject, the first part of a trilogy, was originally published in Dutch in 1937 as: Honors. Awards Named after him