I met Hans Bethe 10 years ago, on the morning of his festschrift, a kind of preposthumous memorial that physicists throw for a retiring giant. It was to be an ambitious, two-day event, for Bethe's career spanned almost the entire length and breadth of nuclear physics. In his early years, he worked with Ernest Rutherford, Niels Bohr and Enrico Fermi and then soared to fame with his Nobel Prize–winning discovery in 1938 of how nuclear fires light the stars. He became head theoretician on the Manhattan Project and later helped to explain how aging stars can transform into bombs, exploding as supernovae.

As we talked in his office at Cornell University, Bethe kept steering our conversation toward the ramifications of nuclear science. Like Albert Einstein, Hans Bethe was a citizen-scientist who tried to persuade society to wield the power of atoms wisely. In articles that Bethe published in this magazine, he made the case for nuclear nonproliferation treaties (1950), cautioned against missile defense systems (1968 and 1984), and predicted the necessity of a gradual shift from fossil fuels (1976). As with his scientific discoveries, these insights have withstood the test of time. He died quietly in his Ithaca, N.Y., home on March 6 at the age of 98.