What type of antenna where Penzias and Wilson testing in 1962 that led to their discovery of one of the biggest piece of evidence supporting the Big Bang Theory

In 1964, Bell Labs scientists Arno Penzias and Robert A. Wilson were conducting experiments with the Holmdel Horn Antenna, an extremely sensitive device originally used to detect radio waves that were bounced off Echo balloon satellites, and later Telstar, the first active communications satellite. These radio waves were so weak, that it became critical to eliminate all possible interference in order to detect them.

Despite taking all conceivable steps to eliminate interference, they continually detected a strange, buzzing noise that was coming from all parts of the sky at all times of day and night. They did a range of additional testing on the equipment, and even removed some pigeons that were nesting in the antenna and their associate detritus. Still, the sound persisted. They ultimately determined that the noise was coming from outside of our galaxy

Almost by chance, they later learned that researchers and astrophysicists Robert H. Dicke, Jim Peebles and David Wilkinson at nearby Princeton University were looking for a way to detect residual radiation that they believed would have resulted from the Big Bang. As it turned out, the radiation detected by Penzias and Wilson was a perfect match for what the Princeton researchers had predicted, and hence made history.

Arno Penzias (left), Robert Wilson (center) and Keith Jefferts (right) look through a model of the universe to the constellation Orion where, for the first time, they discovered carbon monoxide in outer space.

From the archives

An audio recording of the CMBR noise was captured and narrated by Robert A. Wilson. This discovery in 1964 by Penzias and Wilson, announced in a Bell Labs press release, earned the researchers a Nobel Prize in Physics and provided the basis for future astronomical discoveries.    

edit-ion think i read that right so this may be not be right but fun fact sorry

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your answer should be c) enjoy!