--- On Sat, 7/17/10, mix...@bigpond.com <mix...@bigpond.com> wrote:
> At a distance of 1 light year, a dish with a radius of 100 > m would pick up grand > total of 3E-22 W from a 10 MW transmitter on Earth. I don't > think there are any > 10 MW transmitters, and even if there were, a signal that > small would be > completely and utterly lost in the background noise. >From this page, http://www.faqs.org/faqs/astronomy/faq/part6/section-12.html it is suggested a UHF carrier could be detected at a range of 0.3 ly. If that is true, a passing probe, eavesdropping on nearby solar-type stars could get an idea that there's something near the Sun. I read a paper some time ago, by Jill Tarter I think, that suggested that radar broadcasts (Arecibo transmissions, ICBM early warning radar) could be detected out to a distance of some light-years. The fact that no intelligible broadcast could be detected from a distance of more than ~1/3 light-year is interesting; there could be something as close as Alpha Centauri, and we might never know about it. --Kyle
