Welcome back to a Brief-ish History of SETI! In our previous installments, we examined the earliest attempts to find extraterrestrial intelligence (ETI) beyond Earth, as well as one of the most important philosophical underpinnings ( Fermi's Paradox ). We also looked at the first true example of the Search for Extraterrestrial Intelligence (SETI) experiment ( Project Ozma ) and the Drake Equation , followed by the first proposed searches for megastructures ( Dyson Spheres ) and classification schemes for ETIs (the Kardashev Scale ).

Today, we'll examine the first attempt at "active SETI," aka. Messaging Extraterrestrial Intelligence (METI), and what remains the best candidate for a possible message of extraterrestrial origin. These are none other than the Arecibo Message , and the WOW! Signal , two pivotal moments in the history of SETI that remain unrivaled to this day.…