If there was a planet orbiting Proxima Centauri (4.3 light years away), and if there were radio dishes, on that planet, the sizes used in the SETI project on Earth, would those dishes be able to detect radio waves coming from the Earth, or would the radio waves be too weak? Tom
I believe the SETI radio dishes on earth are designed to receive radio waves from MUCH larger distances than 4.3 light years. Think of it this way: why would people on earth bother to build those dishes if they can't receive radio waves from the closest star?
Alien Mastermind, That's exactly why I asked my question. If I'm listening to my FM radio, and the signal dies after I move 80 km away from the source, then how would a dish on a planet 9.46 * 10^12 km (4.3 light years) away be able to pick up that signal? Especially since the strength of the signal would decreases by 1/r^2. It seems like an antenna the size of Jupiter wouldn't be able to pick up the FM signal at that distance. Tom
Hi Tom, Your FM signals die after you moved away from the source, as you said 80 km, for the reason : Earth is curved - if you have rely stations / sattelites to strengthen the signal and beam back to cover your current region then you will be able to get the signal fairly well. As for as the radio waves from distant sources concerned the noise signal ratio is more. otherwise you can pick up radio signals from hundreds of light years away too.
Yes Tom you have a point there. Sorry I'm not a specialist there, wish I could know more. I was only thinking lohically; and you must think to yourself that the designers who designed the SETI dishes would never have built it if it's so very weak. There must be other factors involved, such as how radio waves travel in space compared with air (I dont know if there's a difference). Also, the receivers in the SETI dishes are amplified MUCH stronger than your radio, so the signal may be extremely faint yet detectable. Best reguards, Alien Mastermind
If i remember correctly the transmission power of pioneer 10 was about the same as a small light-bulb. And although it was directionality transmitting to us, it was heard clearly from the edge of deep space.... Check this site to work out the collecting area of the detector. http://www.dangermouse.net/gurps/science/radios.html I will also add that the frequency plays an important role in whether it is lost to the background noise.
Hi, it is true that radio telescopes can pick up signals from millions of light years away, but humanity at least is not capable of producing anywhere near the power radiated by these massive sources. But the most powerful (and narrow-band) radio signals produced on Earth would be detectable with current instruments even if they were coming from the other side of the Galaxy. (You can imagine why radio astronomers hate interference then !). Check these out: http://setifaq.org/faq.html#1.2.3
Russell, Welcome to sciforums. This is from the link you provided: "(1) Detection of broadband signals from Earth such as AM radio, FM radio, and television picture and sound would be extremely difficult even at a fraction of a light-year distant from the Sun. For example, a TV picture having 5 MHz of bandwidth and 5 MWatts of power could not be detected beyond the solar system even with a radio telescope with 100 times the sensitivity of the 305 meter diameter Arecibo telescope." This is exactly what I wanted to know. However, the FAQ claims that "narrowband" signals can be detected at a much further distance. What is meant by "narrowband"??? Tom
I'm not a specialist on radio/light propagation but I'll try to explain....basically it has to do with the wave lenght of the signal(cycles per second)....the narrower the wavelength, the more power the signal has. http://csep10.phys.utk.edu/astr162/lect/light/spectrum.html Forget anything I wrote.....I was quite inebriated when I typed it...the Ideas were correct in my head, but obviously came out wrong.
Danforthharris, As far as I know, humans aren't creating X rays or gamma rays that can be detected by alien civilizations living light years away. When we create X rays or gamma rays, either they are very weak, or they are shielded because of their dangerous effects on human tissue. Since humans rarely use X rays or gamma rays due to their dangerous effects, why do we assume that alien civilizations would produce them? It appears to me that X rays and gamma rays would be dangerous for all life forms, including aliens. Tom
