This mysterious event took place in May 1969 while Apollo 10, the fourth crewed mission in the United States Apollo program and a dress rehearsal for the iconic Moon landing two months later, was orbiting the moon. The three-man crew of astronauts John Young, Thomas Stafford and Gene Cernan would hear something so inexplicable that it was quite literally out of this world, something they would later describe as “outer space music.”
The first the general public would hear about this mystifying “music” would be in 2008 when NASA released the previously classified Apollo 10 transcripts, which would of course have people screaming cover-up. However, Apollo 11 astronaut Michael Collins would reveal in his 1974 book Carrying the Fire, that he had heard something similar but just chalked it up to radio interference.
During their orbit, and on the far side of the Moon, Stafford and Cernan were in the lunar lander for a landing rehearsal that took them less than 10 miles above the surface of the moon, while Young remained in the Lunar Command Module. It was during this time that all three men would hear a mysterious hum in the radio instruments and had no idea what to make of it or even if they should say anything to NASA.