tag:blogger.com,1999:blog-36234687.post7551587802941572895..comments2023-11-21T05:23:10.921-08:00Comments on Live at the Witch Trials: When could we see ourselves?Iamreddavehttp://www.blogger.com/profile/02768287658329807075noreply@blogger.comBlogger5125tag:blogger.com,1999:blog-36234687.post-16672932918639595492011-11-08T02:23:19.100-08:002011-11-08T02:23:19.100-08:00Thanks Fergal
How does the inverse square law eff...Thanks Fergal<br /><br />How does the inverse square law effect this? If telescopes are getting 2.% better per year. And gdp is growing 2% per year and light is a set % of GDP. And light efficiency is growing x% per year. You cannot just add up the percentages to say how our visible radius is expanding you'd have to take the inverse square law into account?Iamreddavehttps://www.blogger.com/profile/02768287658329807075noreply@blogger.comtag:blogger.com,1999:blog-36234687.post-16431712871631130002011-11-07T09:33:46.009-08:002011-11-07T09:33:46.009-08:00Ed Turner has been working on similar (simplistic)...Ed Turner has been working on similar (simplistic) ideas for a few years now. <br /><br />At the moment, brightness is not the issue so much as contrast. Jupiter has an absolute magnitude of about 19, so I'm guessing the earth is probably about 25 or thereabouts (not -4 as Gonecaving says, that's way too bright). HST has gone as faint as apparent magnitude of 31, so Earth brightness objects are already detectable at reasonable distances.<br /><br />The trouble with finding planets is that they get lost in the glare of their parent star. An alien astronomer, 10 parsecs away would need to be able to cancel out all but one part in 10^10 of the sun's light within a disc only 0.1 arcsec wide to be able to detect Earthshine. Our current technology routines achieves one part in 10^4.<br /><br />I haven't read the paper, so I can't comment on the power law argument, but it would worry me that the lights at night would tend to even out the day-night contrast (which is , making it harder to figure out what was going on down on the planet surface.Fergalhttps://www.blogger.com/profile/02051126328072636787noreply@blogger.comtag:blogger.com,1999:blog-36234687.post-21795338135964483242011-11-07T02:59:27.956-08:002011-11-07T02:59:27.956-08:00Probably not given the distance of those extrasola...Probably not given the distance of those extrasolar planets thus detected: <br />http://en.wikipedia.org/wiki/List_of_extrasolar_planets<br />http://en.wikipedia.org/wiki/Extrasolar_planet#Number_of_stars_with_planetsGonecavinghttps://www.blogger.com/profile/11619805826012140883noreply@blogger.comtag:blogger.com,1999:blog-36234687.post-39005860423120054812011-11-07T02:50:15.975-08:002011-11-07T02:50:15.975-08:00Great comment!
Back of the envelope 1000 parsecs ...Great comment!<br /><br />Back of the envelope 1000 parsecs is more than a billion stars. Which means if life like us was common you would expect to see it?Iamreddavehttps://www.blogger.com/profile/02768287658329807075noreply@blogger.comtag:blogger.com,1999:blog-36234687.post-41409240754476517412011-11-07T01:58:30.328-08:002011-11-07T01:58:30.328-08:00Start here:
http://www.bautforum.com/archive/index...Start here:<br />http://www.bautforum.com/archive/index.php/t-47335.html<br /><br />Absolute magnitude of the earth=-4<br />Now I suspect this is high due to the phase issues mentioned:<br />http://en.wikipedia.org/wiki/Absolute_magnitude<br /><br />Then given the HST observable apparent magnitude:<br />http://en.wikipedia.org/wiki/Apparent_magnitude<br />of -31, and the distance modulus:<br />http://en.wikipedia.org/wiki/Distance_modulus<br />we get ~1000 parsec.<br /><br />Presumable this is anisotropic wrt absorption by interstellar dust. <br /><br />As you say, growth in telescope size and sensitivity of detectors will be a factor as to how this changes.<br /><br />I suppose the real challenge is the differential between the Sun and the earth (~30 degrees of magnitude in brightness) at a separation of 2e-6 degrees at 1k parsec, which may well reduce the distance.Gonecavinghttps://www.blogger.com/profile/11619805826012140883noreply@blogger.com