In February 2003, astronomers with the search for extraterrestrial intelligence (SETI) project, used a massive telescope in Puerto Rico to re-examine 200 sections of the sky which had all previously yielded unexplained radio signals. These signals had all disappeared, except for one which had become stronger.
The signal – widely thought to be the best candidate yet for an alien contact – comes from a spot between the constellations Pisces and Aries, where there are no obvious stars or planets. Curiously, the signal is at one of the frequencies that hydrogen, the most common element, absorbs and emits energy. Some astronomers believe that this is a very likely frequency at which aliens wishing to be noticed would transmit.
Nevertheless, there is also a good chance the signal is from a never-seen-before natural phenomenon. For example, an unexplained pulsed radio signal, thought to be artificial in 1967, turned out to be the first ever sighting of a pulsar.
1977, The unexplained extraterrestrial “Wow!” signal is detected by an Ohio State University radio telescope
In August 1977 an Ohio State University radio telescope detected an unusual pulse of radiation from somewhere near the constellation Sagittarius. The 37-second-long signal was so startling that an astronomer monitoring the data scrawled “Wow!” on the telescope’s printout.
The signal was within the band of radio frequencies where transmissions are internationally banned on Earth. Furthermore, natural sources of radiation from space usually cover a wider range of frequencies.
As the nearest star in that direction is 220 million light years away, either a massive astronomical event – or intelligent aliens with a very powerful transmitter would have had to have created it. The signal remains unexplained.