- Professor and Chair, Department of Physics, The College of New Jersey, 2010-Present
- Professor, Department of Physics and Astronomy, Georgia State University, 1993-2010
- Member, School of Natural Sciences, Institute for Advanced Study, Princeton, 2008-2009
- Adjunct Professor, School of Physics, Georgia Institute of Technology, Atlanta, 2008-2010
- Visiting Professor, Department of Astrophysical Sciences, Princeton University, 2000-2001; Affiliated Faculty, 2001-2008
- Astronomy Graduate Director, Georgia State University, 1990-1991; 1994-1999
- Associate Professor, Georgia State University, 1989-1993
- Assistant Professor, Georgia State University, 1986-1989
- Assistant Professor, Dept. of Astronomy and Astrophysics, University of Pennsylvania, 1979-1986
- NSF/NATO Fellow, Institute of Astronomy, University of Cambridge, 1977-1978
- Research Associate, Enrico Fermi Institute, University of Chicago, 1976-1977; 1978-1979