Apollo 10 was the 4th manned mission in the United States Apollo space program, and the second (after Apollo 8) to orbit the Moon.
Launched on May 18, 1969, Apollo 10 was a “dress rehearsal” for the first Moon landing, testing all of the components and procedures, just short of actually landing. The Lunar Module came to within 8.4 nautical miles (15.6 km) of the lunar surface, the point where the powered descent to the lunar surface would begin. The success of the Apollo 10 mission enabled the first landing to be attempted by Apollo 11 in July 1969.
At the time, the Apollo 10 crew had the distinction of being the humans who have traveled to the farthest point away from home, some 408,950 km (220,820 nmi) from their homes and families in Houston.
The astronauts of Apollo 10 were Thomas P. Stafford (commander), John W. Young (command module pilot), and Eugene A. Cernan (lunar module pilot).
Did you know that the Moon we see from Earth is always only one side?
It’s called the near side of the Moon — the lunar hemisphere that is permanently turned towards the Earth. Only that side of the Moon is visible from Earth because the Moon rotates about its spin axis at the same rate that the Moon orbits the Earth, a situation known as synchronous rotation or tidal locking.
The opposite side — the hemisphere that always faces away from Earth — is the far side of the Moon, also called the dark side of the Moon. “Dark,” as in unknown, rather than lack of light. The far side’s terrain is rugged, with a multitude of impact craters, including one of the largest craters in the Solar System, the South Pole–Aitken basin.
In 1969, as Apollo 10 orbited the Moon, it entered the dark side of the Moon where, for an hour, the astronauts lost all radio contact with Earth.
The astronauts were completely on their own — no one can hear or see them.
Apollo 10 would emerge from the dark side of the Moon, apparently safe, as if nothing of note had happened.
But there were recorders recording what was going on with Apollo 10 at all times, including during that hour when the spacecraft was on its own. When the spacecraft returned to Earth, those recording tapes were transcribed, without comment, by NASA. The transcripts were classified, and were buried in NASA’s archives.
Later, the transcripts were declassified, but remained in the archives until nearly 40 years later in 2008, when patient researchers combed through the transcripts and discovered what happened during that hour on the dark side of the Moon.
A strange whistling woowoo “music” was heard, coming through the Apollo 10 module’s radio. Below is the recorded conversation between the astronauts, reacting to the “music”:
“The music even sounds outer-spacey, doesn’t it?”
“You hear that? That whistling sound? Whoooooo….”
“Sound like, you know, outer-space type music.”
“Well, that sure is weird music.”
The astronauts mentioned the “music” many times over the course of the hour when the spacecraft was on the dark side of the Moon, completely cut off from all communication.
One explanation offered is that the “music” was “radio interference” between Apollo 10’s radio and NASA.