Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.3 4.3bsd-beta 6/6/85; site topaz.ARPA Path: utzoo!linus!philabs!cmcl2!seismo!columbia!topaz!milne From: milne@uci-icse Newsgroups: net.sf-lovers Subject: Re: visible civilization Message-ID: <3072@topaz.ARPA> Date: Fri, 2-Aug-85 20:23:43 EDT Article-I.D.: topaz.3072 Posted: Fri Aug 2 20:23:43 1985 Date-Received: Sun, 4-Aug-85 05:52:48 EDT Sender: daemon@topaz.ARPA Organization: Rutgers Univ., New Brunswick, N.J. Lines: 33 From: Alastair Milne >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> The California Aqueduct and Great Wall are visible from the Moon. At night, it is quite easy to see civilization's lights from high orbit. Of course by galactic standards, that's a "relatively low height." <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<< I didn't think the Great Wall was visible from that high, though I could certainly be wrong. I also don't know how much they look like the artifacts of civilisation, rather than spontaneous occurrences. You are quite right about the lights at night, though. I forgot all about that. I understand that flaming oil towers in Libya are easily visible at night, and the Europe and parts of North America are ablaze. Although one would have to investigate the source of the light to see if it were produced by civilisation. I imagine similar patterns of light could be seen on highly volcanic planets. But, as you say, the moon's orbit is at a relatively low height (in fact a fantastically low height) by galactic standards. And that was my main point. In order for extraterrestrials to visit us, they first have to find us, which, because of the unbelievably tiny fraction of the galaxy's -- never mind the universe's -- volume we occupy, will likely be so extremely difficult as to be virtually impossible. Barring, of course, technologies that could give them effective planet-detection capabilities, and swing the odds considerably. But, not having them ourselves, it's hard to say anything about them. Alastair Milne