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From: fritz@utastro.UUCP (Fritz Benedict)
Newsgroups: net.sf-lovers
Subject: Re: visible civilization
Message-ID: <504@utastro.UUCP>
Date: Wed, 7-Aug-85 14:53:08 EDT
Article-I.D.: utastro.504
Posted: Wed Aug  7 14:53:08 1985
Date-Received: Sat, 10-Aug-85 22:47:40 EDT
References: <3076@topaz.ARPA> <1356@uwmacc.UUCP>
Organization: U. Texas, Astronomy, Austin, TX
Lines: 78

> > From: Alastair Milne 
> > 
> > 
> > >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
> > 
> >    I'm told that the Earth is the brightest radio source in this region of the
> >    galaxy, so finding it shouldn't be too hard if you have radio telescopes.
> > 
> > 
> > <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<
> > 
> > 
> >    I'm certainly no expert, but if Earth is brighter than the Sun, in any
> >    band, I'll be very surprised.  You might double check with your source, 
> >    if you can; also about competition with Jupiter, and possibly Saturn.
> > 
> >    There is also the problem of the angular distance of Earth from the Sun,
> >    especially from very distant (ie much more than Alpha Centauri) stars.
> >    I've neither the time nor the inclination to go through the math, but I
> >    suspect it would be difficult, perhaps extremely so, to resolve Earth's
> >    signals from the Sun's.
> > 
> > 
> >    Alastair
> >
> 
> I'm not expert either, but I am a graduate student in Astronomy, and
> Alastair is right, I'm afraid. Jupiter is much brighter in the 
> radio (or anything!) region than the Earth, and Jupiter would be
> quite difficult to resolve from the Sun unless someone out there
> had VERY good resolution on his/her/its radio scope. Also, if Jupiter
> was resolved seperate from the Sun, that would mean someone out there
> wanted to check us out rather than give us a casual once-over...does
> this mean that we're the subject of someone's research project?
> 
> (Incidently, for anyone who cares at all, one of the reasons that
>  Jupiter is brighter than the earth in the radio region is due to
>  the internal heat that it generates. A hot, gassious object like
>  Jupiter would stand out like a sore thumb next to a cold, lump
>  of slag like the Earth...)
> 
>  
> -- 
>                            --- Rob DeMillo 
>                                Madison Academic Computer Center
>                                ...seismo!uwvax!uwmacc!demillo
> 
>  
> 	"...That's enough, that's enough!
> 	    Television's takin' its toll.
> 	    Turn it off, turn it off!
> 	    Give me the remote control!
> 	    I've been nice! I've been good!
> 	    Please don't do this to me!
> 	    I've been nice, turn it off,
> 	    I don't wanna hav'ta see...
> 		...'The Brady Bunch!'"

I think that the concept of BANDWIDTH enters into this discussion. For some very
small fraction of the EM spectrum, the Earth is the brightest object in the 
Solar System. For instance, the 0.1Hz wide video carrier signal broadcast
by TV stations. If you integrate over many frequencies, the Earth is faint.
At some frequencies the Earth (thanks to TV) is very bright compared to the Sun
or Jupiter. The poem is pertinent.


Reference: Life in the Universe, pg 377.
	   ed. by John Billingham
	   MIT Press 1982
	   ISBN 0-262-52062-1

"Little green men are (a very small fraction of) my business"

-- 
Fritz Benedict  (512)471-4461x448
uucp: {...noao,decvax,ut-sally}!utastro!fritz
arpa: fritz@ut-ngp
snail: Astronomy, U of Texas, Austin, TX  78712