Final answer:
The first successful detection of signals from extraterrestrial civilizations was accomplished in 1952 by Harold Ewen and Edward Purcell using a horn antenna at Harvard University.
Step-by-step explanation:
The first successful detection of signals from extraterrestrial civilizations was accomplished in 1952 by Harold Ewen and Edward Purcell using a horn antenna at Harvard University. They detected interstellar 21-cm radiation, which was an important milestone in radio astronomy and the search for extraterrestrial intelligence.
Since then, astronomers have been continuously searching for signals from extraterrestrial civilizations using different methods and technologies. These searches focus on detecting intentional signals or beacons that civilizations might use to communicate across vast distances in space.
It is important to note that while efforts have been made, there is currently no conclusive evidence of signals from extraterrestrial civilizations. Nevertheless, the search continues, and the discovery of such a signal would have profound implications for humanity.