The Record Cover.
It would have been a gross over-assumption to expect that the lucky finders of The Golden Record would have working knowledge of phonography, so the record’s cover includes the detailed, graphical description of how to extract the information embedded in the platter.
But still, where does one begin? The 1977 NASA geniuses decided it was best to begin with the hydrogen atom, the simplest of the elements with it’s easily recognizable, single electron and proton (pictured lower-left, in its two lowest states). If the aliens can decipher the hydrogen etching, then all else can proceed from there. Hold that thought.
Having already supplied the playback-stylus with the record on-board the spacecraft, the first concern was to communicate how fast to rotate the record; in this case, 3.6 seconds per rotation. Seconds: A man-made unit of time. Enter the hydrogen atom. The Nasa geniuses described the rotational speed as a factor of the hyrdogen atom’s ‘fundamental transition period’ (0.70 x 10-9 seconds). And being scientists, the binary number system was an obvious choice. Then they did the same for the total playing time (1 hour) and the analog waveform length (~8 msec). Throw is a couple more graphics about how to interpret the signal, and the first image appears…. <next>
You can view a more complete description of the cover here.
Clause:
1) There is a prize for less-clever, runners-up aliens who can’t figure out how to use the phonograph: a pictorial representation of our Sun’s location based on 14 pulsars. At least they’ll know where this piece of space trash came from.
2) For super-aliens who easily tackle the phonograph riddle, a piece of ultra-pure Uranium 238 is also embedded in the cover. For extra credit, they can use its 4.51 billion-year half-life to determine the age of the spacecraft.
