# Has Earth ever sent out a repeating signal into space?

My understanding is that for us to confirm that a signal is of artificial origin, we have to get the same signal at least twice. However, as far as I can tell, most of the signals we've sent out to contact extraterrestrials have only been sent once, and thus any extraterrestrial civilizations receiving them would likely dismiss them.

So, have we ever sent a signal at least twice, to make sure that anyone receiving it would realize it is of artificial origin?

• – TildalWave Jan 4 '14 at 20:40
• @TildalWave Thanks, I should have linked that, it was what made me wonder. I knew about the Arecibo Message, but it was only broadcast once, so there was no way to prove it originated from an artificial source. – Canageek Jan 4 '14 at 21:45
• Having a repetitive signal is good (though not perfect-think pulsars) evidence for artificial origin, but there are other ways. If we saw a signal that gave a million digits of $\pi$, we would probably be convinced it was artificial, even if we only saw it once. Similarly, our TV shows are probably repetitive enough to qualify, even if they are not identical. – Ross Millikan Jan 7 '14 at 23:47
• @RossMillikan I set up another question about that: space.stackexchange.com/questions/3276/… – Canageek Jan 8 '14 at 6:46
• Does almost seventy years of "I Love Lucy" count? – Rob Crawford Jan 11 '19 at 22:06