Donat Gotthard Wentzel died of a rapidly developing cancer on 20 February 2013 in Glenwood, Maryland. Although renowned for his work in plasma astrophysics, in particular on cosmic magnetism and electrical currents flowing in interstellar space and in the Sun’s corona, Don considered his educational activities to be among his most important contributions.
Don was born on 25 June 1934 in Zürich, Switzerland, where his father, Gregor Wentzel, was a professor of physics at the University of Zürich. In the late 1940s, the family moved to Chicago. There Don quickly learned English and picked up what was needed to earn his BS, MS, and PhD, all in physics, at the University of Chicago. His thesis, under the guidance of Subrahmanyan Chandrasekhar, was on hydromagnetic equilibria. During his graduate years, he spent a year in Leiden, the Netherlands. After finishing his PhD in 1960, he worked for six years at the University of Michigan; in 1964 he became an associate professor there. He and his family moved to Maryland in 1966, where Don was a professor in the astronomy department at the University of Maryland until his retirement.
The study of acceleration processes of charged particles in the Sun and in supernovae stimulated Don’s interest in kinetic plasma theory in the early 1960s. Later that decade his work on cosmic-ray propagation became his first major mark on the astrophysics community. The effect of resonant proton scattering by Alfvén waves led him to propose, in his seminal 1974 paper, the concept of self-confinement of cosmic rays in the galaxy: Relativistic particles do not spread with the speed of light but are trapped in wavepackets and diffuse through space with the Alfvén velocity. In the 1970s coronal heating in the Sun caught Don’s attention; he soon realized that the corona is so inhomogeneous that Alfvén waves could not explain the heating and that a new approach was necessary.
Don provided significant insights into hydromagnetic surface waves, including their coupling to other waves and their dissipation. He also became interested in kinetic problems of solar-flare radio emissions and developed a theory for noise storms that was translated into Chinese at the time and is still cited today. He liked to play with new ideas; his application of percolation theory to the development of solar active regions is still being discussed.
Typical for his approach was his theoretical derivation of plasma phenomena from first principles. He did not just refer to the highly cryptic theories from laboratory plasma physics at that time but wanted to understand the physics thoroughly. He was always thinking about how he would explain a concept to his students.
Combining his experience in science and teaching, Don wrote The Restless Sun (Smithsonian Institution Press, 1989), which was named Book of the Year by the Astronomical Society of the Pacific.
Countless students remember Don fondly. He patiently supported young people struggling to enter science. In addition to teaching and mentoring Maryland’s undergraduates and graduates in astronomy, he helped to develop an astronomy course for nonscience majors. That course proved extremely popular, at one time attracting more than 3000 students per year. As part of the course, he created activities and labs based on astronomical photographs and other data. He helped set up similar courses nationally and internationally, which often left him with only the summer months for research.
Don was an ambassador of Western astronomy to the rest of the world. Spending a half-year sabbatical in India in 1973 opened his eyes to teaching astronomy in less privileged countries. He became involved with the International Astronomical Union’s (IAU’s) Commission on the Teaching of Astronomy in the 1970s. As commission president starting in 1979, he supported the teaching of astronomy as a medium for science education in scientifically developing countries, and he remained intimately involved in that work through the last years of his professional career.
He organized or taught at eight of the IAU’s International Schools for Young Astronomers. Classes were held in hot and badly equipped lecture rooms during the day, and hands-on experiments were conducted behind simple telescopes during the tropical nights. Don’s rich experience in teaching astrophysics brought to each school clear academic goals and tight fiscal management.
Don supervised visiting-lecturer programs in Peru and Paraguay and helped to develop astronomy curricula in Vietnam, Morocco, the Philippines, and several Central American countries. Tirelessly, he gave a series of lectures during three-week visits to China, Egypt, Iran, Kenya, and other countries. He initiated individual programs with local astronomers, negotiated annual programs and budgets with the IAU, and identified suitable advisers. His goal was a sustainable development in education, and in many countries the legacy of his work is still growing. Many of his students are now teaching classes themselves. In recognition of his extensive efforts in astronomy education, the American Astronomical Society honored Don with its 2003 George Van Biesbroeck Prize for his “long-term extraordinary or unselfish service to astronomy.”
A joyful and peaceful person, Don helped many people whom he met along the way. He was also a connoisseur of good wine. In his honor, his family asks that you buy a good bottle of wine, share it with someone you love, and toast to your memories. Prost, Don!
