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Louis George Henyey

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Louis George Henyey (February 3 1910February 18 1970) was an American astronomer.

When Louis Henyey suffered a stroke and died on February 18, 1970, the astronomy department lost its most respected senior member. He left a gap in our research and teaching program which we have not yet completely filled.


Louis Henyey was born in McKees Rocks, Pennsylvania on February 3, 1910, the son of Bela and Mary Henyey, both native Hungarians. Little is known of his parents; his biography gives his father's occupation as a moulder. A graduate from West High School in Cleveland in 1927, he went to Case School of Applied Science, where he earned a B.S. in 1932 and a M.S. a year later. After further graduate studies at the Yerkes Observatory, he received his Ph.D. at the University of Chicago in 1937.

His parents, Albert and Mary Henyey, were immigrants from Hungary. Louis George Henyey married Elizabeth Rose Belak, born in Budapest, on April 28, 1934; they had three children: Thomas Louis, Francis Stephen, and Elizabeth Maryrose.

His undergrad (1932) and masters (1933) were from the Case School of Applied Science.[1] In Yerkes Observatory of the University of Chicago he earned his doctorate in 1937, with a mathematical thesis on the topic of reflection nebulae. In 1947 he accepted a position as assistant professor in the Department of Astronomy at the University of California, Berkeley, and in 1954 he was promoted to professor. At Berkeley he became head of his own research group in the field of stellar evolution and supervised and collaborated with numerous graduate students, postdoctoral fellows, and scientific visitors. He died unexpectedly of a cerebral hemorrhage on February 18, 1970.

Early Years at UC Berkeley and Yerkes

When he arrived here from the Yerkes Observatory in 1947, the department was quite small, with five faculty members and a dozen or so graduate students. It was coasting on prestige earned for it by the monumental pioneering researches of Armin O. Leuschner, Tracy Crawford, and their colleagues in the fundamental field of stellar positions. The tradition was being carried on ably by Sturla Einarsson, but the department was badly in need of revitalization and modernization. The appointment of Louis Henyey was the important first step. His research and instruction in stellar structure and evolution influenced graduate students for twenty years and set the stage for an increasing emphasis on astrophysics and stellar astronomy. It was largely his presence and influence that persuaded Otto Struve to move to Berkeley in 1950. Through the efforts of Henyey and Struve, by the end of the 50s the faculty had doubled in size and the graduate student body had quadrupled.

He stayed on at the Yerkes Observatory, first as an instructor, then as assistant professor, working during the World War II years under an Office of Scientific Research and Development contract designing and constructing optical instruments. As part of this work, in collaboration with Jesse Greenstein, he designed and constructed a novel wide-angle camera that was later applied to the study of interstellar matter along the Milky Way. He stayed at Yerkes after the war until, as noted above, he accepted appointment at Berkeley in 1947.


Stellar Evolution

In his early days Louis Henyey was principally interested in the study of physical processes taking place in the diffuse nebulosities strewn between stars in the Galaxy. Several research papers appeared in the Astrophysical Journal covering various aspects of this very difficult problem. They included discussion of the mechanism of reflection of starlight from neighboring stars, the resulting color of reflection nebulae, and the way in which these nebulous clouds dimmed and reddened the light of background stars. His interest in the physics of very diffuse gases even led him into investigations of the spectra of comets. Soon after he moved to Berkeley, however, he became interested in the rapidly developing field of stellar structure and evolution. He quickly established himself as an internationally recognized pioneer in the theoretical study of the internal structure of stars and their probable evolution, particularly in their early stages of development as they approach that condition permitting energy production via thermonuclear processes involving hydrogen conversion to helium. He developed elegant computational procedures for calculating the internal structure of stars that soon became generally known as "the Henyey method." These interests obviously paralleled closely those of theorists at the Livermore Radiation Laboratory, and as a result he became a consultant at Livermore and collaborated with the laboratory staff on a number of papers on stellar structure which appeared in the Astrophysical Journal in the 1950s. This collaboration was augmented by a steady stream of graduate students and postdoctoral scholars attracted to Berkeley by his presence. Many of these graduate students are now at universities and other institutions in this country and abroad, further extending the application of methods learned under his guidance.


The application of Henyey's methods to stellar structure required the accessibility of large electronic computers. His earliest studies made extensive use of the computational facilities available at Livermore. It soon became evident to Henyey and Struve that future progress in this and other areas of astronomical research would be immeasurably aided by the existence of an appropriately powerful facility on the Berkeley campus. They became active supporters of a plan to enlarge a small computational facility already in existence in engineering. These efforts soon resulted in the establishment of the Computer Center, located first in Cory Hall, then in the basement of Campbell Hall, and finally in Evans. Henyey became in 1958 the first director of the Computer Center and was able during his tenure to initiate an expansion into the facility that we all enjoy today. When Struve took a leave of absence in 1959 to serve as director of the National Radio Astronomy Laboratory, Henyey replaced him as chairman of the Astronomy Department, a position that he held for five years. He, however, maintained his interest in the Computer Center, serving on its advisory committee until 1968.

Henyey's activities on behalf of the growing astronomy department far transcended his support of computational facilities. Radio astronomy was developing rapidly into a major field of research in this country and abroad, and it became evident early in the 1950s that our graduate student instructional capabilities would be greatly enhanced by the creation of a radio astronomy laboratory. Henyey enthusiastically and effectively supported this endeavor, which eventually culminated in the establishment of a radio astronomy observing site at Hat Creek in northern California. For several years, from 1961 to 1965, he helped to guide the development of instrumentation and research programs of the Radio Astronomy Laboratory through service on the laboratory's advisory committee.

Astronomy Department Growth Under Henyey

As the Department of Astronomy increased in size, it rapidly outgrew its traditional site near the campus North Gate. A new building was authorized to occupy a site south of the Mining Circle to be occupied by astronomy, mathematics, and statistics. As our representative in the committee planning this new building, Henyey was largely responsible for its final form. As a further outgrowth of the move to larger quarters, it was obvious that any optical observational facilities would have to be located largely off campus, as far as possible from bay fog and lights, yet close enough so that graduate-student observing would not interfere with campus instruction. Henyey undertook the burdensome task of searching for a suitable site in the East Bay hills. Largely at his recommendation, Leuschner Observatory was located on the Russell property some ten miles east of the campus. He was instrumental in securing National Science Foundation support, supervised the planning of the new building and facilities, and drew up the specifications of a new 30-inch reflecting telescope to occupy one of two domes (the other houses our older 20-inch telescope that was moved from North Gate).

Renown and Students

Henyey's influence was felt in the growing astronomy department in many, more subtle ways. His courses in astrophysics, stellar structure and evolution were generally regarded by the graduate students as the most difficult and comprehensive that we offered. His insistence on a thorough grounding in fundamental physical processes affected, and significantly upgraded, all instruction in the department.

Henyey's research accomplishments earned him a solid and growing reputation in this country and abroad. In 1948 he was elected a Fellow of the Royal Astronomical Society. He served as president of the Astronomical Society of the Pacific from 1965 to 1967, and was elected to the National Academy of Sciences in 1970.

The bare recital of accomplishments does not do justice to Louis Henyey as a man. For over twenty years students fortunate enough to earn their doctorates under him knew him as an exciting taskmaster, expecting and getting their best. At the same time they came to recognize that he was deeply interested in their individual welfare. Frequently, seminars were held in his home so that he could get to know them better. He would agonize even more than they did as they struggled through a difficult aspect of a dissertation. On occasion, he quietly forfeited the usual principal investigator's summer stipend on his National Science Foundation research grants in order that some student be adequately supported financially. Those students who knew him best always claimed that the "Henyey method" referred to earlier really had nothing to do with a computational technique but rather referred to the personal attention and sense of mutual involvement in a community research adventure that pervaded his groups of students down through the years. He would treat them as colleagues in their extensive group discussions, and as a result they all worked their heads off.

Family Life

Louis Henyey was equally devoted to his family and to his home, located high in the El Cerrito hills overlooking San Francisco Bay. He is survived by two sons, Thomas Louis and Francis Stephen, and a daughter, Elizabeth Maryrose. A fond mental picture survives from the days when his two sons were preschoolers, during a summer at the McDonald Observatory in the Davis Mountains in west Texas; during a community picnic he spent hours wading with them in a mountain stream, patiently searching for small fish and crayfish, and carefully answering all their eager questions. The large garden surrounding his home was a constant delight. He gathered and planted desert plants and flowers, and late in his life was experimenting with growing tuberous begonias. An avid music lover, he displayed a surprisingly intimate knowledge of musical structure and harmony.

The memory of Louis Henyey is still vivid among his colleagues, the astronomical community at large, his former students, and legions of friends. He is sorely missed.


He is best known for his two major scientific contributions in the field of stellar structure and evolution. First, he developed a method for automatic solution of the equations of stellar evolution, suitable for electronic computers and applicable to a wide range of physical conditions and phases in the lifetime of a star. Second, he made new calculation of the evolution of stars during their early history when gravitational contraction provides the main energy source, and during the transition phase when nuclear energy takes over from the gravitational source. His work on the diffusion of the light in galaxies resulted in what is referred to as the Henyey-Greenstein phase function,[2][3] first proposed in a paper he authored.[4] This scattering model has found use in other scientific disciplines.[5]

The crater Henyey on the Moon is named after him, as is the asteroid called 1365 Henyey.[6]


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