On April 12, 1961, Soviet cosmonaut Yuri Gagarin (1934–1968) lifted off in Vostok 1, becoming the first human in space. His historic flight, in which he made one orbit around Earth, marked the beginning of manned spaceflight. In the more than four decades since then, programs launching humans into space have been carried out by the Soviet Union (later present-day Russia), the United States, and the People's Republic of China. More than 430 humans have flown into space. Most, though, have not flown beyond Earth orbit. Only the United States has carried out human spaceflight missions beyond Earth orbit, sending twenty-four astronauts to orbit and land on the Moon. The Moon revolves around Earth on an elliptical, or oval, orbit. The point in its orbit when it is farthest away from Earth, known as its apogee (pronounced AP-eh-gee), is about 252,780 miles (406,720 kilometers). As of 2004, this is the farthest humans have ventured...