Forty years ago, Earth beamed its first postcard to the stars.
The message left our home planet on a warm and sticky mid-November day in Puerto Rico. It has been flying through the galaxy at the speed of light ever since, and in about 25,000 years will arrive at a cluster filled with more than 300,000 stars.
Unlike the radio signals that had been leaking from Earth since the late 1930s, this postcard was the first deliberate transmission to an alien civilization. Written in a way meant to be decipherable by extraterrestrial beings, the message contained some key information about the species that had sent it.
“It was a message that would ...