High Quality Content by WIKIPEDIA articles! Leon Theodore "Lee" Silver (born April 9, 1925), Professor of Geology at California Institute of Technology (Caltech), was an instructor to the Apollo 13, 15, 16, and 17 astronaut crews. Working with the National Aeronautics and Space Administration (NASA), he taught astronauts how to perform field geology, essentially creating lunar geology as a new discipline. His training is credited with a significant improvement in the J-Mission Apollo flights` scientific returns. After the Apollo program, he became a member of the United States National Academy of Sciences in 1974. Currently, he is the W. M. Keck Foundation Professor for Resource Geology, emeritus, at Caltech.