milne@uci-icse (08/03/85)
From: Alastair Milne <milne@uci-icse>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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 Milnemilne@uci-icse (08/03/85)
From: Alastair Milne <milne@uci-icse>
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
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.
And remember, as I said in my first posting, to pick up any of Earth's
signals at all other than natural ones (and I don't know whether there are
any) you have to be within about 50 or 60 light years. I'm sure no such
signals were generated anywhere on Earth more than 60 years ago, or perhaps
70, when the first crude recordings were done. And at 70 light years'
radius, those signals, weak as they were to start with, must have
attenuated miserably. So I would place 70 light years as the maximum
radius at which Earth could be detected by radio telescopes, if it could
be so detected at all.
Alastair
PS. Thanks for keeping the discussion going. This is rather interesting.demillo@uwmacc.UUCP (Rob DeMillo) (08/03/85)
> From: Alastair Milne <milne@uci-icse> > > > >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> > > 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. > > Alastair Milne I just recently read an article (somewhere) by a shuttle astronaut (someone - boy, this lack of references sure doesn't substantiate my story, does it?) that tried looking for the Great Wall once he was in orbit. He claimed that he could only find it with great difficulty, and while purposely looking for it through the shuttles telescopic cameras. (The first thing he thought was the Great Wall turned out to be a river....) Thought I'd pass that along... -- --- 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!'"
demillo@uwmacc.UUCP (Rob DeMillo) (08/03/85)
> From: Alastair Milne <milne@uci-icse> > > > >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> > > 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!'"
herbie@watdcsu.UUCP (Herb Chong - DCS) (08/05/85)
In article <3076@topaz.ARPA> milne@uci-icse writes: > 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. one of my first year physics project was to calculate how far away the earth could be detected by a radio telescope the size of Aricebo. it turns out that a signal broadcast at the usual operating power of Aricebo can be detected at a distance of some 100,000 light years by a comparable instrument that is pointed toward the transmitter at the right time. the signal is good enough such that two way communications with a 100,000 year delay is possible. this has nothing to do with brightness per se, but correct concentration of the broadcast energy. the cone of transmission would be about 20,000 or so light years across, but undetectable unless you happened to be looking in the right direction at the right time. Some of the project Ceti transmissions using Aricebo were aimed at the Hercules cluster some 13,000 light years away. so, you might say brightness is a relative thing. > 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. you have to remember that the signals from the sun are more or less random (like black body radiation), while the signals from the earth are anything but (contents exempt). that alone would make anybody watching take more interest. something like the Aricebo transmission would be like a supernova in our galaxy in terms of getting someone's attention, but they have to be looking in the right direction. another thing too are the various nuclear tests that have been undertaken in the last forty years. remember that they generate a hefty electromagnetic pulse that propogates in all directions. because they are effectively one time events with no set pattern, they would probably be ignored as glitches in the instrumentation, but they are detectable over very large distances, on the order of a few thousand light years. > And remember, as I said in my first posting, to pick up any of Earth's > signals at all other than natural ones (and I don't know whether there are > any) you have to be within about 50 or 60 light years. I'm sure no such > signals were generated anywhere on Earth more than 60 years ago, or perhaps > 70, when the first crude recordings were done. And at 70 light years' > radius, those signals, weak as they were to start with, must have > attenuated miserably. So I would place 70 light years as the maximum > radius at which Earth could be detected by radio telescopes, if it could > be so detected at all. the key thing is that our regular radio transmissions may be lost in the overall electromagnetic transmissions from other things nearby, but there are a lot of other things besides commercial broadcasts that would be detectable from great distances. the catch is that we've been only noticeable for the last forty years or so, and only in the last twenty or so have we actually tried to make ourselves known. project SETI spent about 6 months transmitting to various nearby stars with such a signal power that even over the distance of thirty or forty light years, a primitive radio would be capable of detecting the signal if someone were listening at the right time in the right place. Herb Chong... I'm user-friendly -- I don't byte, I nybble.... UUCP: {decvax|utzoo|ihnp4|allegra|clyde}!watmath!water!watdcsu!herbie CSNET: herbie%watdcsu@waterloo.csnet ARPA: herbie%watdcsu%waterloo.csnet@csnet-relay.arpa NETNORTH, BITNET, EARN: herbie@watdcs, herbie@watdcsu
mangoe@umcp-cs.UUCP (Charley Wingate) (08/05/85)
In article <1356@uwmacc.UUCP> demillo@uwmacc.UUCP (Rob DeMillo) writes: >>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. >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...) 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. 2) In radio frequencies, it is analomously hot, and NOT on spectral lines. 3) At certain precisely defined frequencies, it is quite bright-- sometimes. Certain radio telescopes, when operated as radars, are very bright. 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. Charley Wingate
demillo@uwmacc.UUCP (Rob DeMillo) (08/06/85)
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 "...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!'"
mangoe@umcp-cs.UUCP (Charley Wingate) (08/06/85)
[Post follow-ups to net.astro, please] In article <1363@uwmacc.UUCP> demillo@uwmacc.UUCP (Rob DeMillo) writes: >> 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. You don't have to resolve it out separately. Assuming for the moment that Earth's radio emissions (human-generated) are at all visible, what will be seen is a star with a wierd secondary which is occulted once a year (in the right direction, of course). This alone, I admit, would not make it evident that the secondary was a planet. But wait.... >> 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. Now wait a minute. This last line is totally off base. We seem to be quite capable of tossing useful radio signals around the solar system, in spite of using inferior equipment and in spite of solar noise. Once you get clear of the atmosphere, the attenuation works against the noise sources too. >> 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... ? The point is that along the line of sight of these beams, the earth appears VERY bright. Bright enough to be used as a radar at interplanetary distances (where the range degradation is FOURTH power). Probability is against detecting such a beam, but, hey, I never said detection was LIKELY. >> 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. At IR wavelengths, yes. But my point is that you have to look at the Sun IN THE RIGHT WAY. It's not technologically very difficult-- it does require a lot of luck. Radio telescopy as we practice it now would never find such an object, because we concentrate on emission lines. Human radio transmissions lie off such lines. >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...) Actually, it was considered to try and look for objects fitting the appropriate description, about ten years ago. (Remember SETI?) As I recall, what killed the thing was the immense improbability of it. Assuming 1 trillion resolvable stars, with one tenth having civilizations generating the right kind of emissions for 1000 years each, you'ld have to examine about 100,000,000 before you found one. >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... All you need is a bigger radio telescope, and luck. This discussion started out from the question of why we haven't been contacted by another civilization. Even granting that the Earth is detectable at interstellar distances, it's clear that probability is heavily against our ever being detected. C Wingate
mangoe@umcp-cs.UUCP (Charley Wingate) (08/07/85)
[followups to net.astro, please] I knew I had sources somewhere.... In the May 1975 _Scientific American_ there is a nice article on searching for extraterrestrial intelligence by Sagan and Drake. A summary of their articles (or parts of it anyway): Arecibo Observatory, when transmitting, is at least a million times brighter than the sun. This signal can be detected by a similar receiver at a distance of about ten thousand light years. A number of other sites have similar capabilities. In the FM and VHF tv bands, the earth is quite bright. A receiver system to detect such signals was conceived of at the time of the article, to be called 'Cyclops'. Employing 1500 antennas of 100 meters each,it would be able to detect such signals out to several hundred lightyears. Such a system would not be beyond our current technology-- but it would be very expensive (~$10G). These observations do not rely on resolving the earth as a separate body. C Wingate
royt@gitpyr.UUCP (Roy M. Turner) (08/07/85)
I believe it was Carl Sagan that wrote once (during the Viking Mars mission)
that from orbit Earth looks uninhabited, too...I suppose he meant to the
naked eye, and on the daylight side...
--
The above opinions aren't necessarily those of etc, etc...but they
should be!!
Roy Turner
(a transplanted Kentucky hillbilly)
School of Information and Computer Science
Georgia Insitute of Technology, Atlanta Georgia, 30332
...!{akgua,allegra,amd,hplabs,ihnp4,seismo,ut-ngp}!gatech!gitpyr!roytmike@bambi.UUCP (Michael Caplinger) (08/07/85)
Actually, the most powerful radio emitters on the planet are early-warning radars, which would look like nearly monochromatic sources along the Earth's limbs. (Since they're pointing roughly horizontally, you couldn't see one near the middle of the disk.) It would be fairly easy to figure out what size antenna would be needed to spatially resolve multiple radars from distance X. I suspect that it would be quite easy to find such objects with planetary- system-baseline VLBI, not to mention the anomolous emission spectrum. - Mike
fritz@utastro.UUCP (Fritz Benedict) (08/07/85)
> > From: Alastair Milne <milne@uci-icse> > > > > > > >>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> > > > > 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
demillo@uwmacc.UUCP (Rob DeMillo) (08/08/85)
> > I believe it was Carl Sagan that wrote once (during the Viking Mars mission) > that from orbit Earth looks uninhabited, too...I suppose he meant to the > naked eye, and on the daylight side... > > -- > The above opinions aren't necessarily those of etc, etc...but they > should be!! > > Roy Turner There seems to be some confusion here as to what we were all originally talking about. Charlie Wingate brought up the point that the earth was quite bright in the radio region. I said "no it ain't" and talked about earth being cold, and a poor radio transmitter compared to the sun, and I threw in a little quip about stuff that we humans generate will be disrupted by the earth's atmosphere, the suns atmosphere, attenuation, etc... Then suddenly people started talking about Carl Sagan...! What I was refering to was radio noise that we humans make with our TV transmissions, shortwave transmissions, etc.... Of course, a radio transmission deliberately beamed into space is going to go somewhere! But that is line of sight transmission, and not what we were originally discussing anyway. (The original discussion was about whether or not the earth is visible in the radio region...we aren't.) ...end of transmission... -- --- 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!'"