A gold-plated copper phonograph disc carried aboard two…

A gold-plated copper phonograph disc carried aboard two NASA probes launched in 1977, now beyond the heliosphere. Intended for any intelligent life that might find it, it contains greetings in fifty-five languages, natural sounds such as thunder and birdsong, music from Bach to Chuck Berry and more than one hundred encoded images. A committee chaired by Carl Sagan chose the contents. Instructions for playing it are engraved on its cover.

The answer in 19 letters