May the 4th be with you!

On May 25, 1977, Star Wars: A New Hope hit theaters, forever changing the world of cinema. Months later in that same year, an astronomer named Jerry R. Ehman made a curious observation that’s puzzled the scientific community to this day.

At the time, Ehman volunteered at SETI, the Search for Extraterrestrial Intelligence which was housed at the Ohio State University Radio Observatory. Popularly known as the “Big Ear,” the facility conducted historic surveys seeking extra galactic radio sources from galaxies far, far away… Ehman’s role on the project involved analyzing vast amounts of data recorded on lined paper, all by hand. Then on August 15, 1977, Ehman noticed a rise in signal intensity and frequency, which amazed him so much that he etched in “Wow!” beside the sequence representing the signal. The name caught on and remains widely used ever since.

The sequence lasted 72 seconds and originated from somewhere in the Sagittarius constellation, bearing all the expected characteristics of extraterrestrial origin and remaining the strongest incident of possible alien contact ever captured by mankind. The now infamous sequence, 6EQUJ5, remains renown as the radio signal itself, though without a proper explanation, any person at first glance would assume the letters form some kind of encoded message. In actuality, the six character sequence, as it appears vertically on the Wow! Signal printout, represents the successive values of intensity of radio signals ranging from 0 to 36 received from the Big Ear in each channel at 12 second intervals, with the “U” value at 30.0-30.999, representing the largest value ever observed of its kind. This coding method was devised for the now rather humorous reason of conserving space on the printout, leaving only speculation as to the result if this detection had occurred with modern day technology, where paper space did not take such precedence as it required in the 1970s. Since the Big Ear relied on the rotation of the Earth to perform observations and taking into account the spatial width of the telescope’s observation window, it could only scan a focused area of the sky for 72 seconds. Curiously enough, when the signal appeared, its intensity shifted perfectly, rising for 36 seconds, reaching its peak, then decreasing at the same rate for another 36 seconds until it left the telescope’s line of sight, never to appear again despite tireless search and replication. The signal’s duration and bell shape provided another piece of evidence that this could very well be a signal of extraterrestrial origin, and as predicted by Cornell University Physicists Philip Morrison and Giuseppe Cocconi in 1959, the signal’s frequency landed near the hydrogen value of 1420.41 MHz.

The Big Ear Observatory at Ohio State University. Credit: Bigear.org/NAAPO

Plot of signal strength vs time of the Wow! signal on August 15, 1977. The signal rose and fell during the 72 seconds observation window. Credit: Maksim Rossomakhin

Morrison and Cocconi originally speculated that an advanced civilization might attempt to communicate using radio signals at the same frequency emitted naturally by hydrogen (1420 megahertz), the most common element in the universe. Despite all this, no scientific consensus exists explaining what caused this fascinating event. Scientists pose atmospheric twinkling and space debris as a possible explanation, though these and every other hypotheses remain unresolved. One of the greatest cosmic mysteries of our time, the WoW signal is thought to be the closest we’ve come to interacting with an advanced distant civilization.