The Arecibo message — humanity’s most famous deliberate radio message to another civilization — was aimed at a star cluster about 25,000 light-years away in 1974, meaning even an immediate reply would not reach Earth until around 52,000 CE - Space Daily

Imagine standing under a tent on a karst hillside in Puerto Rico, on an afternoon in November 1974, watching the dedication of a remodeled radio telescope.For just under three minutes it warbles at the sky. Then it stops. The audience around you has just hear…