Leon Theodore "Lee" Silver was an American geologist who was professor of geology at the California Institute of Technology (Caltech). He 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 field 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. He retired in 1996 as the W. M. Keck Foundation Professor for Resource Geology, emeritus, at Caltech.

Apollo 13 was the seventh crewed mission in the Apollo space program and the third meant to land on the Moon. The craft was launched from Kennedy Space Center on April 11, 1970, but the lunar landing was aborted after an oxygen tank in the service module (SM) ruptured two days into the mission, disabling its electrical and life-support system. The crew, supported by backup systems on the lunar module (LM), instead looped around the Moon in a circumlunar trajectory and returned safely to Earth on April 17. The mission was commanded by Jim Lovell, with Jack Swigert as command module (CM) pilot and Fred Haise as lunar module (LM) pilot. Swigert was a late replacement for Ken Mattingly, who was grounded after exposure to rubella.