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From: demillo@uwmacc.UUCP (Rob DeMillo)
Newsgroups: net.sf-lovers
Subject: Re: visible civilization
Message-ID: <1363@uwmacc.UUCP>
Date: Mon, 5-Aug-85 18:51:56 EDT
Article-I.D.: uwmacc.1363
Posted: Mon Aug  5 18:51:56 1985
Date-Received: Wed, 7-Aug-85 03:26:20 EDT
References: <3076@topaz.ARPA> <1356@uwmacc.UUCP> <1095@umcp-cs.UUCP>
Organization: UWisconsin-Madison Academic Comp Center
Lines: 113

To everyone else out there: I apologize if this should be in net.astro, 
and if it carries on I'll move it there...

For those that are interested,....


> 
> >>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 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. 

To which Charlie Wingate responses:

> 
> As I understand it, the things that make the earth stand out are the 
> following:
> 
>  1) It's very small and obviously associated with a star.  This makes it clear
>     that whatever it is, it's a planet.

There's a couple problems with this argument: first, the earth is
EXTREMELY close to the sun. Even though the sun is a standard so-so
star, it would take extremely fine resolution on a radio scope
to seperate the angular distance. Even if they could do
that, the earth radiates so little heat (virtually its only radio
source, the stuff we generate ourselves doesn't count, I'm afraid...)
that it would be lost in the heat of the sun...again, seperation is
a problem.

OK...giving the aliens the benifit of the doubt: lets say they've taken
the trouble to determine that there is a small, cold body orbiting
the sun...it could be anything. True, it could be a planet...but it also could
be a asteroid, comet, or any other rocky body...and, it doesn't even
have to be a body...it could be an amalogmation of bodies...


> 
>  2) In radio frequencies, it is analomously hot, and NOT on spectral lines.
>

I'm afraid this isn't quite right. The earth, in fact the solar system,
is amazingly boring. It is a rock that generates its own internal heat
(slowly) by nuclear decay of material in the core. The rest of the
heat is reflected. If you are refering to any radio noise that
humans make, we aren't very spectacular either. Our signals, even if
they weren't hampered by the atmosphere, solar winds, noise from
the sun, etc, would attenuate before they got very far away from
us at all.
 
>  3) At certain precisely defined frequencies, it is quite bright-- sometimes.
>     Certain radio telescopes, when operated as radars, are very bright.
>

? I missed your point... ?
 
> If you look at the solar system from the right directions, there are three
> radio sources: two thermal ones, and something substellar which has a really
> wierd radio spectrum: it has lines that are not emission lines, and it is
> really variable.  If your detectors are sufficiently sophisticated, you should
> be able to "see" the earth.  But you have to look at it exactly right.  It
> occults over a very long period, and you have to be looking off of emission 
> lines.  This makes it difficult to find similar sorts of objects, compounded
> by the fact that we have only been doing this for about 20 years, so that only
> our very nearest neighbors could have noticed this.  Someone on Sirius,
> however, wouldn't have too much trouble noticing that our system had something
> really strange in it.

Sorry, Charley, but I really have to "stick by my guns" on this one.
Detecting planets from even NEARBY solar systems is, at best, a painstaking
long complicated process. (You could always argue that advanced civilizations
have really nifty, spifo technology that could pick us out in a sec, but
that is a moot point, since what we are talking about is whether or
not the earth is an OBVIOUS object - at least that's what I'm talking
about...) If it were that easy, we would have done it...the fact is,
after studying a star a mere 6 lys away (Barnard's star), the best anyone
could come up with is a "maybe." There may be 2 large gas bodies in orbit 
nearby, but it may just be an error in the way the plates were taken.
And even these "gas bodies" which should be hot thermal objects, cannot
be resolved from the glare fo a pathetic star like Barnard's. 

The closest we have ever come to finding other planets thermally, was
with the IRAS satellite. It detected "bodies" moving around the
star Vega. (26 lys distance.) However, that is probably a solar system
in FORMATION, since those "bodies" are glowing at amazingly
high temperatures. (Much higher than Jupiter...)

I guess my point is, unless someone out there has some pretty sophisticated
technology...we are quite invisible...at least, ordinary...you couldn't
even get a good Master's Thesis out of us...

> Charley Wingate

-- 
                           --- Rob DeMillo 
                               Madison Academic Computer Center
                               ...seismo!uwvax!uwmacc!demillo

 
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