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We transmitted several messages to the space and listening to space for signs of intelligent life for years (SETI).

Assuming they have at least the same technology we have, could they detect these messages we sent out?

If not, how powerful transmitter is needed to make our word heard, let's say, from 1000 light years? Which wavelength we should use to transmit?

ps: Apparently not so many ET related questions on this site, maybe I asked on the wrong site?

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Valid question, but maybe more Skeptics-oriented than practical astronomy. –  Grant Thomas Apr 23 '12 at 14:21
At a distance of many light-years, you're probably down to receiving less than one photon on average from the feeble early years of human radio broadcasting. Plus there's the necessity of waiting thousands of years for the signals to arrive at a location that's 1000 light years away. –  Andrew Apr 23 '12 at 18:30
@Andrew are you talking about just RF leakage from omni broadcasts like FM Radio/TV; or also highly directional signals like some radar beams or the messages SETI deliberately translated. I know the former are a lost cause beyond a few dozen AU for current day tech; but the latter should be detectable at much longer ranges. –  Dan Neely Apr 23 '12 at 21:10
How about a link or citation for "several messages to space" then? I don't know enough about these apparently specific messages to answer without an extended Google romp, which anyone could do. –  Andrew Apr 23 '12 at 22:11
this topic is definitely encompassed as a astronomy topic, which makes it on topic for this site –  lurscher Dec 10 '12 at 1:51

1 Answer 1

Here's a somewhat technical document talking about insterstellar beacons. A beacon would act as a "searchlight", sweeping across the sky, so that the time spent on each target star would be rather short. With a beam aperture able to illuminate 1% of the sky and working at 0.5 Hz they calculate that 6.9 GW power will be "visible" as far as 6000 light years. It would need an antenna array with about 5 km diameter, and the receiver dish would need to be about the same size. Some other systems are also discussed.

The message that was sent from the Arecibo telescope was beamed to a globular cluster (M13) that is 25000 ly away. Not only is the power level probably insufficient to get there, but in 25000 years M13 will no longer be in the beam anyway.

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