Henk van de Hulst

Henk van de Hulst was born on November 19, 1918. As a student, he predicted that interstellar gas clouds could be traced by the 21 cm hyperfine line of atomic hydrogen. This study represented a true breakthrough in astronomy: opening up studies of the Universe to wavelengths other than optical. After the discovery of this line, Henk and others pioneered studies on the distribution of hydrogen in the Milky Way, thereby tracing its spiral structure. During Henk's long career, he was always fascinated by the presence of small particles of interstellar smoke in space and their interaction with electromagnetic radiation. Indeed, he wrote the classic textbook on the interaction of dust grains and light -- Light Scattering by Small Particles -- that, sixty years later, is still widely used. Its elegant and clear presentation of the problem and its solution leaves the reader with a clear appreciation of the topic. Henk van de Hulst has also played a leading role in space research as the first president of COSPAR and through his deep involvement in the Dutch and European Space agencies, SRON, ESRO, and ESA.