Spitzer was educated at Phillips Academy, in Andover, Maryland and at Yale University. He spent his first graduate year in Britain, as a Henry Fellow at Cambridge University. He records that the informal evening seminars given in Trinity College by S. Chandrasekhar were one major reason for his decision to work in astrophysics. Spitzer wrote his doctoral thesis at Princeton University with Henry Norris Russell as his adviser. His first position, as instructor in physics and astronomy at Yale from 1939, was interrupted by four years of war work at Columbia University, devoted largely to research in underwater sound.
His calibre was recognised in his appointment soon after as Russell's successor as Director of the Princeton University Observatory, a post he held from 1947 until his retirement. He and his colleague Martin Schwarzschild, whom he persuaded to join him, together built up a strong graduate teaching and research programme primarily in theoretical astrophysics, but with considerable emphasis on observational astronomy also.
In an autobiographical essay "Dreams, Stars and Electrons" - first published in the Annual Review of Astronomy and Astrophysics in 1989 and also the title of a volume of his selected writings, published this year - Spitzer gives as one of his long-term goals the wish to understand the formation of stars from the interstellar gas in our own and in other galaxies.
Over the decades, he and his collaborators studied in detail the physics of the interstellar gas and the associated dust and of the magnetic field permeating the gas. Of particular interest is the study of the tendency of dust grains to be aligned by the magnetic field, with an effect on starlight that was the first clue to the existence of a sizeable galactic magnetic field. He summarised his own work and that of others in a valuable text, Physical Processes in the Interstellar Medium (1978).
Already in 1946, Spitzer had written a paper pointing out the great advantages for astronomy of observations made from an orbiting space telescope, both through extending the accessible parts of the electromagnetic spectrum, and avoiding the inevitable distortions caused by the earth's atmosphere. The 1957 launch of the first Soviet sputnik gave an enormous impetus to the US space programme. With a contract from Nasa, a group of Princeton scientists under Spitzer's chairmanship explored both the possibilities of research on interstellar matter, through observation in the ultra-violet, and the engineering requirements for an astronomical satellite. Spitzer wrote that perhaps the high-point of his career was the day in 1972 when the ultra-violet spectrometer in the orbiting Copernicus satellite was switched on and immediately began operating as planned, so opening up a new chapter in the study of the interstellar gas. In its nine years of operation, the instrument yielded much information of major importance, confirming the theoretical prediction of giant clouds of molecular hydrogen, discovering regions in the galactic disk with a million-degree temperature and measuring the ratio of deuterium (an isotope of hydrogen) to normal hydrogen, of crucial importance for the Big Bang cosmological model.
But Spitzer's vision had already gone further; he dreamed of a general purpose telescope with a mirror in the three- metre class. Even after the doubts and hesitation of other astronomers had been assuaged, much diplomatic skill was needed before the go-ahead from Congress for the Hubble Space Telescope was gained in 1977. Spitzer was able to keep an eye on its subsequent development through his chairmanship of the overseeing committee of the Space Telescope Institute Council from 1981 until 1990, and took an active role in the telescope's refurbishment. He was delighted with the high quality material on the interstellar medium being fed back, and in fact was analysing data right up to his sudden and unexpected death. Spitzer's long-term aim - a proper understanding of star formation, with its consequences for galactic evolution and cosmology - will surely come through a judicious combination of physical and dynamical theory with detailed observational material from the space telescopes of today and of the future.
Spitzer's studies on interstellar matter inevitably led to his probing the general properties of fully or partially ionized gases that carry the currents maintaining the galactic magnetic field. The theory of encounters between charged particles is quite similar to the analogous theory for gravitating bodies, such as stars and gas clouds. Spitzer and collaborators showed how energy interchange between stars in a globular cluster leads to the evolution of the cluster through slow but steady escape of the high-velocity stars, while simultaneously the more massive stars tend to sink towards the centre, a process that can lead to the collapse of the cloud core, perhaps to form a black hole. This whole area is treated with characteristic lucidity in another monograph, Dynamical Evolution of Globular Clusters (1987).
Another major problem to which Spitzer devoted much thought from early on is the search for an unlimited supply of cheap energy. In 1951, he persuaded the US Atomic Energy Commission to back the study of controlled thermonuclear fusion in hot, magnetically confined ionized gas ("plasma"). He had worked out a magnetic configuration - "the Stellarator concept" - which he hoped would effectively confine the gas long enough for hydrogen to fuse into helium, as occurs in stellar interiors. Project Matterhorn, which was carried out between 1953 and 1961, and evolved into the Princeton Plasma Physics Laboratory, became a world leader in this area, and a worthy competitor to the UK Atomic Energy Authority's Harwell and Culham laboratories.
Spitzer's shrewd comments in Nature magazine on the 1959 Harwell "zeta" experiments are well remembered. He was also quick to recognise the advantages of the Russian "tokamak" alternative. Princeton developed one of the world's most successful machines, making a step-by-step approach to the "break even" conditions, at which fusion energy output begins to exceed the driving energy. Spitzer must have been saddened in his last days, knowing that Congress had taken the prima facie short-sighted step of cutting off the funds needed for the next stage, shutting down the machine permanently as from this week. However, the physics and astrophysics worlds have as a permanent legacy the beautifully succinct tract Physics of Fully Ionized Gases (1956), based on material prepared for the original Princeton research group, from which generations have learned the essentials of plasma physics.
Lyman Spitzer was both an outstanding scientist and a warm and lovable human being, with wide interests outside his specialities. The atmosphere in the Observatory under the joint leadership with Martin Schwarzschild combined high academic standards and enthusiasm with a courtesy that made work there a particular pleasure. He and his splendid wife Doreen were perfect hosts to the many visitors of all generations to Princeton.
Lyman Spitzer, physicist and astronomer: born Toledo, Ohio 26 June 1914; Instructor in Physics and Astronomy, Yale University 1939-42; Scientist, Special Studies Group, Division of War Research, Columbia University 1942- 46, Director, Sonar Anlysis Group 1944-46; Associate Professor of Astrophysics, Yale University 1946-47; Chairman, Astrophysical Sciences Department and Director of Observatory, Princeton University 1947-79, Professor of Astronomy 1947-82 (Charles A. Young Professor 1952-82), Director, Project Matterhorn 1953-61, Chairman, Research Board 1967-72; President, American Astronomical Society 1959-61; NASA Medal 1972; Gold Medal, Royal Astronomical Society 1978; Chairman, Space Telescope Institute Council 1981-90; Foreign Member, Royal Society 1990; married 1940 Doreen D. Canaday (one son, three daughters); died Princeton, New Jersey 31 March 1997.