Which radio signal was nicknamed the 'Wow!' signal after being observed by Jerry Ehman, later understood to be from hydrogen?

• A. Wow! Signal
• B. Airfares
• C. Cicada 3301
• D. Kryptos

Answer: (A)

The main idea here is recognizing the famous Wow! signal, a standout moment in the search for extraterrestrial intelligence. In 1977, Jerry Ehman detected a strong, narrowband radio burst with an unusual spike in the data using the Big Ear radio telescope. It earned the nickname Wow! because Ehman scribbled “Wow!” next to the printout to mark how striking the signal was.

The reason this signal is tied to hydrogen is that its frequency sits right near the hydrogen line, the natural emission frequency of hydrogen at about 1420 MHz. That proximity made scientists think it could be a deliberate beacon or at least a curious natural-like signal worth investigating, which is why it’s described as later understood to be from hydrogen.

However, the event has never been observed again, so it remains an unexplained candidate rather than conclusive evidence of extraterrestrial life. The other options are unrelated: one is not a radio signal, and the others refer to unrelated puzzles or works, not the 1977 radio burst itself.