John Bahcall (1934-2005)

John Bahcall's most important and best known achievements were the result of a career-long research into the production of neutrinos by nuclear reactions in the sun. John realized early that measuring the flux of neutrinos emanating from the sun may provide unique information on the goings on in the sun's interior, which can not be probed directly by looking at its surface. The first measurements by Raymond Davis (in the late 1960s) fell short of the results of John's calculations of the time. This discrepancy, which has become known as "the solar neutrino problem" has persisted with improved calculations (mostly by John's group) and new experiments.
While most of the community had tended to impute the discrepancy to poor understanding of the structure of the sun, John had insisted all along that the calculations and the solar models they are based on are not to blame. Instead, he endorsed the minority view that the disagreement is due to some yet unaccounted for new physics, for example some twist in the properties of the neutrinos. John worked on all the theoretical aspects of the problem: Nuclear reaction in the sun, improving the solar models, and propagation of neutrinos in and outside the sun. He dominated the field from his first involvement to his untimely death. It is only recently that new, sophisticated experiments have finally laid the question to rest, dramatically vindicating John's conviction. Fortunately, John was still with us to witness this triumph.
John was a theorist at heart, but during his whole career was closely engaged in experimental and observational endeavors, even as far as making observations himself. His most celebrated effort in this vein was his scientific and science-politic involvement in the approval, building, and operation of the Hubble Space Telescope. John has made an important contribution, that will continue to influence the field of astrophysics in years to come, also by identifying and nurturing promising young scientists, many of whom went on to become scientific leaders.
John has received many international honors recognizing his scientific achievements, among them in 1998 the US Presidential Medal of Science for his theoretical work on solar neutrinos and his role in the development of the Hubble Space Telescope, in 1992 NASA's Distinguished Public Service Medal for his observations and leadership with the Hubble Telescope, and in 2003 the "Dan David" Prize. John was the president elect of the American Physical Society.
But, beyond his crucial contributions to science John deserve special memory in Israel for taking Israeli astrophysics so close to his heart. For over thirty years John actively supported astrophysics in Israel. He was the mentor of many Israeli astrophysicists who were invited to work in his group at the Institute for Advanced study in Princeton. He was of great help in starting and establishing the astrophysics group at the Weizmann Institute and at Tel Aviv University, and was a driving force in the establishment of the Wise Observatory. John visited Israel many times, including once for a sabbatical year. During his visits he not only cooperated with Israeli colleagues and gave professional lectures, but made a point of reaching the younger generations giving popular lectures (in Hebrew) to interested high-school students. John strove constantly to improve his Hebrew and was an avid reader of Israeli literature.
In recognition of his scientific achievements, as well as of his contribution to the science in Israel, John as been awarded honorary doctoral degrees from both the Hebrew University and the Tel-Aviv University. John will be remembered with affection and regard by all his many friends in Israel.

Some biographical information at:
http://www.ias.edu/Newsroom/announcements/Uploads/view.php?cmd=view&id=290