Background

Marcel Minnaert was born on February 12, 1893, in Bruges, Belgium to the family of Josephus Ludovicus Minnaert and Josephina Philippina van Overberge. His parents were teachers at normal schools and many of his other relatives were involved in teaching, which background undoubtedly determined his later interest in science and education. Both parents were liberal and interested in Flemish causes. In 1902 the family moved to Ghent, where Jozef Minnaert died that same year.

Education

Minnaert went to secondary school (Athenaeum) in Ghent and had a workshop and laboratory. In 1910 he entered the University of Ghent to study natural sciences, with biology as his main subject, but he also took examinations in subjects such as the history of art. He received his doctorate in 1914 on a dissertation entitled Contributions a la photobiologie quantita. At that time the University of Ghent, although situated in the heart of the Dutch-speaking part of Belgium, used French as the language of instruction, as did the other universities and most of the secondary schools in Flemish Belgium. Minnaert, who gradually realized that the linguistic problem was also a social problem related to the underdeveloped status of Flanders, joined associations of Flemish students and intellectuals who sought political equality and, later, relative independence (federalism) for both parts of Belgium. They also wished to convert the University of Ghent to the Dutch language. During the German occupation of Belgium in World War I, the latter goal was attained. The urgent need for teachers at the new Flemish university induced Minnaert to go to Leiden in 1915-1916 to study physics.

At the end of the war those who had cooperated in the linguistic reform of the University of Ghent were accused of collaboration with the Germans, and many received long prison sentences. In order to escape that fate, Minnaert moved to Utrecht, to which place he was attracted by the technique of objective photometry, then being developed at its physics laboratory by W. H. Julius, Ornsiein, and Moll. He readily understood the importance of the technique because of his previous experience in photobiology, in which specialty the lack of quantitative measures was deeply felt. The director, W. H. Julius, had just set up a solar spectrograph - at that time the third in the world - intending to apply spectrophotometric techniques to the solar spectrum. Minnaert became interested in this work, and after Julius’ death in 1924 he assumed the main responsibility for solar research at Utrecht. In 1925 he defended - cum laude - another thesis, this time in physics: “Onregelmatige straalkromming”(“Irregular Refraction of Light”).

Career

After Minnaert's return to Ghent after Leiden in 1916, he was named an associate professor of physics and remained in that post until 1918. After that, he had to leave for Utrecht due to political reasons.

Because of his prior work on photobiology, Minnaert was interested in the developing field of solar photometry, which was being developed by Pannekoek at Amsterdam and Julius at Utrecht. Julius appointed him observer at the University of Utrecht's Physics Laboratory, where he had recently installed a solar spectrograph for doing spectrophotometric research on the Sun's spectrum. Upon Julius's death, in 1924, Minnaert was put in charge of solar research at Utrecht. Minnaert took part in a number of solar-eclipse expeditions and became known especially for his work during the eclipse of 1927 in Lapland, during which photometric work was first done on the flash spectrum. His research was focused especially on the origin of Fraunhofer lines. In 1933 Minnaert was naturalized, and in 1937 he became director of the Utrecht Observatory and professor of astronomy. In that year he declined the offer of a professorship at the University of Chicago and the Yerkes Observatory. His photometric work on the Sun culminated in the Photometric Atlas of the Solar Spectrum, published in 1940, which has remained a standard source. As a result of his increasing international reputation, Minnaert became active in the International Astronomical Union and served as a chairman of its commission on the Sun and on the exchange of astronomers. In the last few years of his life, he was very active in an international group purchasing books for the University of Hanoi, North Vietnam.

Achievements

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  Marcel Minnaert pioneered in solar spectrophotometry and showed how such a technique could reveal much about the structure of the Sun’s outer layers. In 1947 he received the gold medal of the Royal Astronomical Society and in 1951 that of the Astronomical Society of the Pacific (Bruce Medal). He held honorary doctorates from the universities of Heidelberg, Moscow, and Nice. Asteroid 1670 Minnaert, crater Minnaert on the Moon, Minnaert building of the Uithof campus of Utrecht University, Minnaert function, and Minnaert resonance were all given name to honor Marcel Minnaert.

Works

More photos

• book

  • The Nature of Light and Colour in the Open Air

    (Rainbows, mirages, multiple moons, black snow, colored sh...)

    1954
  • Light and Color in the Outdoors

    (All of science springs from the observation of nature. In...)

    1993
  • De natuurkunde van 't vrije veld 1941
  • Practical Work in Elementary Astronomy 1969

Politics

Since his early years, Minnaert had been active in Flemish causes, and during his university years, he worked actively to turn the University of Ghent into a Dutch-speaking university. At the beginning of the First World War, he was part of a small group of Flemish-minded intellectuals who began publishing De Bestuurlijke Sclwiding, in which they militated for an administrative partition of Belgium between a French-speaking Walloon, and a Dutch-speaking Flemish part. Within the various groups to which he belonged, Minnaert always cautioned against too strong an orientation to Germany and advocated, rather, close contacts with the Netherlands. Wlien, in 1915-1916 he spent a year at Leiden to improve his knowledge of mathematics and physics, in the hospitality circle around Ehrenfest, he came into contact with Dirk Stiiiik and D. Coster, convinced socialists who introduced Minnaert to Marxism. Under the German occupation, he was given a teaching appointment in physics al the now Dutchspeaking University of Ghent, and he introduced innovations in teaching. But as the Allied troops moved north and the German troops retreated, in 1918, the Flemish movement disintegrated and Minnaert and his mother fled to the Netherlands.

Minnaert had strong left-wing sympathies but was too committed to science to link himself to any political party. Yet his political ideas were sufficiently known to the Germans for him to be imprisoned in 1942-1944.

Views

Minnaert developed the concepts “equivalent width” and “curve of growth”; the theory of weak lines was carried further; and the intensity measurements of sunspots made possible the physical interpretation of these phenomena. This work, performed in the physics laboratory at Utrecht, culminated in 1940 in Photometric Atlas of the Solar Spectrum (in collaboration with Houtgast and Mulders), which is still a standard reference.

Minnaert was an enthusiastic defender of Esperanto - attracted by the simplicity and regularity of this artificial language which, he felt, could be of great importance for both scientific and social communication.

Minnaert had a strong interest in humanity and its problems. Philosophically Minnaert defended determinism.

Membership

Minnaert was a member of the Royal Netherlands Academy of Arts and Sciences, of the Royal Academy of Science, Letters and Fine Arts of Belgium, of the Royal Society of Arts and Sciences of Uppsala, and of the Instituto de Coimbra; and associate of the Royal Astronomical Society of London. He also was a member of the American Academy of Arts and Sciences, the German Academy of Sciences Leopoldina, and of the National Academy of Sciences.

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  Royal Netherlands Academy of Arts and Sciences , Netherlands

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  Royal Academy of Science, Letters and Fine Arts of Belgium , Belgium

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  Royal Astronomical Society of London , United Kingdom

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  American Academy of Arts and Sciences , United States

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  German Academy of Sciences Leopoldina , Germany

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  National Academy of Sciences , United States

• Royal Society of Arts and Sciences of Uppsala , Sweden

• Instituto de Coimbra , Portugal

Personality

Minnaert spoke ten languages fluently and could read in even more. He loved music and painting and cultivated both actively. He was admired and loved by his friends, students, and co-workers, and respected by those who did not agree with his social or political ideas. He also was a vegetarian.

Interests

• music, painting, languages, Esperanto

• Philosophers & Thinkers

  Karl Marx

Connections

In 1928 Minnaert married Maria Boergonje Coelingh, who defended her thesis in physics in 1938. They had two sons Koenraad and Boudewijn.

Father:

Josephus Ludovicus Minnaert

Mother:

Josephina Philippina van Overberge

Wife:

Maria Boergonje Coelingh

Son:

Koenraad Minnaert

Son:

Boudewijn Minnaert

Doctoral advisor:

Leonard Ornstein

Doctoral student:

Hendrik Christoffel van de Hulst

References

• Dictionary of Scientific Biography: Volumes 9 & 10
  1981
• Marcel Minnaert, Astrofysicus 1893-1970: De Rok Van Het Universum
  2003
• The Rise of Radio Astronomy in the Netherlands: The People and the Politics
  2016