Marcel Gilles Jozef Minnaert (12 February 1893 – 26 October 1970) was a Dutch

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, natural satellite, moons, comets and galaxy, g ...

Belgian Belgian may refer to: * Something of, or related to, Belgium * Belgians, people from Belgium or of Belgian descent * Languages of Belgium, languages spoken in Belgium, such as Dutch, French, and German *Ancient Belgian language, an extinct languag ...

origin. He was born in

Bruges Bruges ( , nl, Brugge ) is the capital and largest City status in Belgium, city of the Provinces of Belgium, province of West Flanders in the Flemish Region of Belgium, in the northwest of the country, and the sixth-largest city of the countr ...

and died in

Utrecht Utrecht ( , , ) is the List of cities in the Netherlands by province, fourth-largest city and a List of municipalities of the Netherlands, municipality of the Netherlands, capital and most populous city of the Provinces of the Netherlands, pro ...

. He is notable for his contributions to

astronomy Astronomy () is a natural science that studies astronomical object, celestial objects and phenomena. It uses mathematics, physics, and chemistry in order to explain their origin and chronology of the Universe, evolution. Objects of interest ...

and

physics Physics is the natural science that studies matter, its fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge which r ...

and for a popular book on

meteorological optics Atmospheric optics is "the study of the optical characteristics of the atmosphere or products of atmospheric processes .... ncludingtemporal and spatial resolutions beyond those discernible with the naked eye". Meteorological optics is "that par ...

: ''Light and colour in the open air'', first published in English in 1940.

Biography

Minnaert obtained a PhD in

biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...

Ghent University Ghent University ( nl, Universiteit Gent, abbreviated as UGent) is a public research university located in Ghent, Belgium. Established before the state of Belgium itself, the university was founded by the Dutch King William I in 1817, when the ...

in 1914. Later he obtained also a PhD in

from

Utrecht University Utrecht University (UU; nl, Universiteit Utrecht, formerly ''Rijksuniversiteit Utrecht'') is a public research university in Utrecht, Netherlands. Established , it is one of the oldest universities in the Netherlands. In 2018, it had an enrollme ...

, under the supervision of

Leonard Ornstein Leonard Salomon Ornstein (November 12, 1880 in Nijmegen, the Netherlands – May 20, 1941 in Utrecht, the Netherlands) was a Dutch physicist. Biography Ornstein studied theoretical physics with Hendrik Antoon Lorentz at University of Lei ...

. He was a supporter of the

Flemish movement The Flemish Movement ( nl, Vlaamse Beweging) is an umbrella term which encompasses various political groups in the Belgian region of Flanders and, less commonly, in French Flanders. Ideologically, it encompasses groups which have sought to promo ...

during

World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...

and endorsed the replacement of French by

Dutch Dutch commonly refers to: * Something of, from, or related to the Netherlands * Dutch people () * Dutch language () Dutch may also refer to: Places * Dutch, West Virginia, a community in the United States * Pennsylvania Dutch Country People E ...

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 ) , anthem = ( en, "William of Nassau") , image_map = , map_caption = , subdivision_type = Sovereign state , subdivision_name = Kingdom of the Netherlands , established_title = Before independence , established_date = Spanish Netherl ...

, initially to do photometric research. In

, he became interested in

, and he became a pioneer of solar research. He specialized in

spectroscopy Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. Matter wa ...

and the study of

stellar atmosphere The stellar atmosphere is the outer region of the volume of a star, lying above the stellar core, radiation zone and convection zone. Overview The stellar atmosphere is divided into several regions of distinct character: * The photosphere, whi ...

s and invented the spectroscopic

curve of growth In astronomy, the curve of growth describes the equivalent width of a spectral line A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow freque ...

. 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 Resonance describes the phenomenon of increased amplitude that occurs when the frequency of an applied periodic force (or a Fourier component of it) is equal or close to a natural frequency of the system on which it acts. When an oscillat ...

of a single bubble in water, the so-called

Minnaert resonance The Minnaert resonance is a phenomenon associated with a gas bubble pulsating at its natural frequency in a liquid, neglecting the effects of surface tension and viscous attenuation. It is the frequency of the sound made by a drop of water from a ta ...

. 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 The Minnaert function is a photometric function used to interpret astronomical observations and remote sensing data for the Earth. It was named after the astronomer Marcel Minnaert. This function expresses the radiance factor (RADF) as a function ...

, which is used in optical measurements of celestial bodies. During the German occupation of the Netherlands in

World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...

, he was imprisoned by the Germans because of his left-wing, anti-

fascist Fascism is a far-right, Authoritarianism, authoritarian, ultranationalism, ultra-nationalist political Political ideology, ideology and Political movement, movement,: "extreme militaristic nationalism, contempt for electoral democracy and pol ...

sympathies. During his incarceration, he taught

and astronomy to his fellow prisoners. After the War, he was one of the founders of the

Mathematisch Centrum The (abbr. CWI; English: "National Research Institute for Mathematics and Computer Science") is a research centre in the field of mathematics and theoretical computer science. It is part of the institutes organization of the Dutch Research Cou ...

in Amsterdam. Minnaert was elected to the

American Academy of Arts and Sciences The American Academy of Arts and Sciences (abbreviation: AAA&S) is one of the oldest learned societies in the United States. It was founded in 1780 during the American Revolution by John Adams, John Hancock, James Bowdoin, Andrew Oliver, and ...

in 1959. In 1946 he became member of the

Royal Netherlands Academy of Arts and Sciences The Royal Netherlands Academy of Arts and Sciences ( nl, Koninklijke Nederlandse Akademie van Wetenschappen, abbreviated: KNAW) is an organization dedicated to the advancement of science and literature in the Netherlands. The academy is housed ...

. He became a member of the United States

National Academy of Sciences The National Academy of Sciences (NAS) is a United States nonprofit, non-governmental organization. NAS is part of the National Academies of Sciences, Engineering, and Medicine, along with the National Academy of Engineering (NAE) and the Nati ...

in 1964 and the

American Philosophical Society The American Philosophical Society (APS), founded in 1743 in Philadelphia, is a scholarly organization that promotes knowledge in the sciences and humanities through research, professional meetings, publications, library resources, and communit ...

in 1969.

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: *''De natuurkunde van 't vrije veld. Licht en kleur in het landschap''. It was released in English translation as: *''Light and colour in the open air'' (H. M. Kremer-Priest, Trans.). London: G. Bell and Sons. An edition of this book was reprinted in 1954, as a Dover reprint: *''The Nature of Light and Color in the Open Air'', Dover, 1954, and in a new translation with color photographs as: *''Light and Color in the Outdoors'', Springer, 1993, , , .

Honors

Awards *

Gold Medal of the Royal Astronomical Society The Gold Medal of the Royal Astronomical Society is the highest award given by the Royal Astronomical Society (RAS). The RAS Council have "complete freedom as to the grounds on which it is awarded" and it can be awarded for any reason. Past awar ...

(1947) *

Bruce Medal The Catherine Wolfe Bruce Gold Medal is awarded every year by the Astronomical Society of the Pacific for outstanding lifetime contributions to astronomy. It is named after Catherine Wolfe Bruce, an American patroness of astronomy, and was fi ...

(1951) Named after him *

Asteroid An asteroid is a minor planet of the inner Solar System. Sizes and shapes of asteroids vary significantly, ranging from 1-meter rocks to a dwarf planet almost 1000 km in diameter; they are rocky, metallic or icy bodies with no atmosphere. ...

1670 Minnaert *

Minnaert (crater) Minnaert is a large lunar impact crater that is located on the far side of the Moon, deep in the southern hemisphere. It is partly overlain along the southeastern side by the larger and younger crater Antoniadi. To the west-northwest lies Lyma ...

on the

Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...

Minnaert building
of the

Uithof Utrecht Science Park (also known as De Uithof) is a science park and neighbourhood in Utrecht, Netherlands. It is located to the east of the city. It is the largest campus of Utrecht University. Apart from the faculties of Law, Humanities and Univer ...

campus of

References

* Molenaar, Leo. ''De rok van het universum: Marcel Minnaert, astrofysicus 1893–1970'' Balans, Amsterdam, 2003

n Dutch N, or n, is the fourteenth letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''en'' (pronounced ), plural ''ens''. History ...

External links

Biography by Leo Molenaar

* Curve of growth
Astrowww.phys.uvic.ca
{{DEFAULTSORT:Minnaert, Marcel 1893 births 1970 deaths Belgian emigrants to the Netherlands 20th-century Dutch astronomers Foreign associates of the National Academy of Sciences Ghent University alumni Members of the Royal Netherlands Academy of Arts and Sciences Scientists from Bruges Recipients of the Gold Medal of the Royal Astronomical Society Science teachers Utrecht University faculty Members of the American Philosophical Society