Born Litomysl (Czech Republic), 4 April 1914
Died Manchester, England, 23 June 1993
Czech-American-English astronomer Zdeněk Kopal is most often associated with studies of close binaries and their implications for the interior physics of stars and kinds of systems observed. A youthful enthusiastic amateur astronomer Kopal joined the Czech Astronomical Society in 1929 and became chair of its section on variable stars in 1931. He received a PhD summa cum laude in physics and mathematics at the Charles University of Prague (by then part of Czechoslovakia) in 1937; studied under Arthur Eddington in Cambridge, England, in 1938; and took an appointment at Harlow Shapley ’s Harvard College Observatory at the end of that year. Kopal quickly became an American citizen and worked on ballistics for the United States Navy at the Massachusetts Institute of Technology during World War II, as well as contributing to the mathematics needed for the first generation of computers. In 1951 he became professor and founding chair of the Astronomy Department at the University of Manchester, retiring in 1981 but remaining an active professor emeritus for the rest of his life. His daughter Zdenka married a British astronomer.
Kopal’s PhD dissertation already focused on the development of numerical methods for study of close pairs of stars, for instance, decomposition of the light curve into Fourier components, and he continued this work in Cambridge, England, and Cambridge, Massachusetts, USA. An early result was that the density distribution of stars must be far more centrally condensed than modelers had supposed for the rotation of the line of apsides of binary orbits to be as slow as it is. Thomas Cowling was able to show with Ludwig Biermann that Kopal had made a serious error in neglecting the tidal distortion of the shapes of stars, which puts them very nearly into equilibrium, so that they drag on each other very little. With this correction, apsidal motion and other probes of stellar interiors gave concordant results. At Manchester, Kopal produced his classic text, Close Binary Systems (1959), in which he summarized the state of the subject just before a three-pronged assault on binary evolution with transfer of material between the stars began in Europe. It is no coincidence that one of the three groups, under Miroslav Plavec, was working at the Astronomical Institute of the Czechoslovak Academy of Sciences, and Kopal maintained close contact with the Czech astronomical community thereafter.
The concept of mass transfer in binaries can be traced back to Gerard Kuiper in 1935, and Kopal 20 years later drew the critical distinction among detached systems (both stars smaller than their Roche lobes), semidetached systems (one star filling its lobe and transferring material to the other), and contact systems, where both stars fill their lobes and material can move back and forth.
With the advent of the space age, Kopal became fascinated by the idea of landing people on the Moon. Realizing that very good Moon maps would be needed, he obtained sponsorship from the United States Air Force to obtain a large number of very high-resolution images from the high-altitude observatory at Pic du Midi in the French Pyrenees. The funding was lavish by British standards of the time and enabled Kopal to bring students to Manchester from all over the Middle East. Many of them returned to their home countries to begin astronomy programs there, and the legacy can still be discerned in the relatively large number of papers from these countries published in one of the journals Kopal founded.
By 1962, Kopal recognized that the assortment of journals then being published did not really provide an adequate home for the rapidly increasing literature on solar system physics and astronomy. He therefore became the founding editor of Icarus, published by Academic Press, but turned the editorship over to others (initially Carl Sagan) in 1969. His second foray into publishing came with the recognition that there was also no journal focusing on results obtained from space by scientists in all the countries that hoped to pursue space programs. Thus came into being Astrophysics and Space Science, a Reidel journal for which Kopal remained an editor until his death, when it was taken over by his younger colleague at Manchester, John Dyson. Kopal usually maintained a friendly relationship with his authors, sometimes handwriting letters of acceptance. He remained active in space-based research throughout the remainder of his career, writing shortly before his death, for instance, on the shape of the nucleus of comet 1P/Halley as revealed in photographs by the Giotto mission.
Kopal served as an officer of the Royal Astronomical Society and in commissions of the International Astronomical Union. He was elected an honorary member of the Czech Astronomical Society in 1967, and minor planet (2628) is named Kopal. Kopal was the author of several popular books as well as many technical publications.