Harold F. "Hal" Levison is a planetary scientist specializing in planetary dynamics. He argued for a distinction between what are now called dwarf planets and the other eight planets based on their inability to "clear the neighborhood around their orbits", although his proposal suggested the terms "unterplanet" and "�berplanet" and used the word "dwarf" to mean something else. Among other distinctions, he is the co-author of SWIFT, a commonly used symplectic integrator that solves planetary equations of motion for periods of billions of years. He currently works at the Southwest Research Institute, Boulder, CO, and studies planetary orbits and their evolution through solar system history. 

March 1st, 1959 in Philadelphia (Age 65)