Obituary: Professor Zdenek Kopal

Zdenek Kopal, astronomer: born Litomysl 4 April 1914; Professor of Astronomy, Manchester University 1951-81, (Emeritus) 1981-93; married 1938 Alena Muldner (three daughters); died Wilmslow, Cheshire 23 June 1993.

ZDENEK KOPAL, the former Professor of Astronomy at Manchester University, made crucial discoveries in astrophysics, in particular in the study of the development of closely neighbouring stars, known as close binaries.

In many ways Kopal's life exemplified this century's upheavals, both in politics and in astronomy. He was born in the Austrian Empire, before the foundation of Czechoslovakia, and he was educated at Prague University, before modern astrophysics had taken hold. One of his teachers at Prague was the celebrated astronomer E. Finlay Freundlich, who made it his life's work to verify the predictions of Einstein's General Relativity, notably the deflection of starlight by the sun. Kopal had the same attitude to scientific questions: take nothing for granted if you cannot verify it. This philosophy stood him in good stead.

In 1938 Kopal worked with AS Eddington in Cambridge, and in the same year moved to the United States and held various appointments at Harvard and MIT. This time was crucial in his development as a scientist: for his wartime work he needed to be able to follow the propagation of shock waves in situations of military importance, and this task caused him to perfect his numerical skills. His book on Numerical Analysis, published in 1955, later became a classic of its kind.

Kopal was most at home with scientific questions that were clearly defined and amenable to mathematical treatment. At first it might appear that the study of close binaries was just of this kind. Take two nearby stars, calculate how much light each emits and then work out what the observer will record when one of the stars eclipses the other. But then other questions arise: how much of its partner's light is reflected and how much is absorbed by each of the stars, how does this affect their appearance?

There was considerable urgency in treating this range of problems. The climax of this research was reached in the 1950s, just when Kopal was at the height of his powers, and when he had taken up his professorship in Astronomy at Manchester University. The phrase that Kopal himself used was that eclipsing binaries provided the 'royal road' to an understanding of the structure and evolution of stars. At the time this was perfectly true, for no one then had any conception of the extent to which advances in theoretical astrophysics and in computational methods would change our understanding. So the best way of probing the inside of the star was to watch the perturbation caused by a nearby companion.

After a while it became clear that this programme would never work, because in a real sense there is something very special about close binaries. The discovery was made by Kopal himself; I got the impression that he did so much against his will and so he deserves twice the credit. To my mind it ranks with the most important developments in astrophysics of the 20th century, along with pulsars, quasars and gravitational lenses. What Kopal realised was that close binaries apparently defied the general rule that massive stars evolve faster than less massive stars. He produced incontrovertible evidence of many pairs where the lighter star had the larger radius and therefore would be deemed to be more evolved.

The solution to the puzzle was soon found: the presence of such a close companion caused the more evolved star to spill over its material, which would then fall on to its companion, and increase its mass. These close binaries now provide the explanation for many phenomena such as cataclysmic novae and X-ray binaries. Kopal, the classical astronomer, had become the founding father of some real gee-whizz astrophysics.

Of course Kopal made many other contributions: in the years before the Apollo programme he organised a comprehensive effort funded by the USAF to map the Moon from the Earth, he established a lively school of disciples in Manchester where he taught students from all over the world the mysteries of his craft. In 1962 he became the founder and first editor of the journal Icarus and in 1969 he founded an independent journal, Astrophysics and Space Science, a kind of Virgin Atlantic opposed to the (almost) monopoly of the big boys, like Astrophysical Journal. Later he founded the Moon journal, now expanded into Earth, Moon and Planets, and every year or two he would bring out another book on some astronomical topic, written in his inimitable style.

But the event which defined the man took place in Prague, in 1967, when his second daughter, Zdenka, got married. The wedding took place just after the 13th General Assembly of the International Astronomical Union. Many of his colleagues came to the ceremony, and to the splendid reception held later in the Czech pavilion, that had been repatriated from the World Fair in Brussels. But for the wedding itself Kopal had managed to persuade the authorities to reopen the cathedral in Prague Castle, and it was one of the most moving events imaginable. It seemed as if the population of the town took the opportunity to attend an act of worship in their cathedral which had been out of action for so long. It was a sign that the Czech population could not be held down for ever.

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