radio message to space ...[Fwd: Re: SETI Re: [ASTRO] Encounter 2001 "Cosmic Call"]
LonNic 3.14
-------- Original Message --------
Subject: Re: SETI Re: [ASTRO] Encounter 2001 "Cosmic Call"
Date: Tue, 12 Jan 1999 09:53:43 -0500
From: Yvan Dutil <Yvan....@drev.dnd.ca>
To: se...@sni.net
FOR RELEASE: 9:20 a.m. CST, January 9, 1999
Astronomers Get Ready to Call E.T.
Physicists are announcing today that they have designed a message to
be broadcast in the direction of nearby stars in order to search for
extra-terrestrial intelligence. This project is being presented by Dr.
Yvan Dutil and Stephane Dumas from the Defence Research Establishment
Valcartier, near Quebec City (Canada), to the American Astronomical
Society meeting in Austin, TX. This is the first time in a quarter
of a century that such a cosmic call will be attempted. This experiment is
promoted by the Encounter 2001 project, an international spaceflight
project which is planned for launch into interstellar space in the year 2001.
The complete message is about 400,000 bits long and will be transmitted
three times over a 3-hour period in the direction of the four selected stars.
Then, it will be followed by a series of greetings from people around
the world. The transmission will start on March 15 1999.
This message is much larger in size, duration and scope than
the one sent by Frank Drake on November 16th, 1974 from the Arecibo
observatory which consisted of only 1,679 bits sent over a 3 minute duration.
Finding a transmitter for this task was not easy; the project will use a 70
m (230 ft) Ukrainian antenna equipped with a 150 kW transmitter
broadcasting at 5 GHz (6 cm). Using this antenna, any civilization within
100 light-years
which has access to a radio-telescope with an area of one squared-kilometer
will be able to read the message. The artificial nature of the message
should be able to be detected by similar instruments at distances up to
10,000 light-years. A radio-telescope of this size will be built on Earth
in the near future.
The message itself has been designed using some of the principles of
interstellar communication proposed in the early works of Hans Freudenthal,
Frank Drake and Carl Sagan. Mathematics and physics have been used to
define the message, so that it will be clear and based on universal
concepts. For example, the hydrogen atom can be used to describe
quantities such as mass, electric charge and length. To these basic ideas
were added simple notions of
astronomy, biology, geography and cosmology. Easier concepts and ideas are
at the beginning while the more elaborate ones appear at the end of the
message.
Any true communication is not complete without an answer. Therefore, the
last page of the message invites anyone who reads it to reply, sending
information about themselves.
The message has been built to minimize the loss of information due to noise
introduced into the signal during its interstellar flight. To minimize the
risk of confusion, a set of characters was created which are fairly
different from each other. Redundant information is included to allow
cross-checking of the message. The addition of a frame around each page of
the message, and the inclusion of page and section numbers will also help
the translation process.
For many years, most research projects dedicated to the Search for
Extra-Terrestrial Intelligence (SETI) have scanned the sky trying to
detect any signals sent by extra-terrestrial civilizations willing to
communicate with us. So far, the sky has remained silent. All these
searches have been passive: what is proposed now is to send a
message in order to catch the attention of an extra-terrestrial
civilization.
In order to maximize the probability of detection, the direction of
the transmission has been carefully chosen to include stars similar
to our Sun, and to limit the degradation of the signal
as it travels through the vast reaches of interstellar space. Fortunately,
there is a region between the spiral arms of our galaxy where the signal
can be transmitted over long distances without too much degradation. This
region is situated between 50 and 90 degrees of galactic longitude,
which corresponds roughly to the region of the sky called the "Summer
Triangle". Four stars, clones of our Sun, have been selected from the list
made by the SETI institute. These target stars are located at distances
between 50 and 70 light-years from the Sun.
Target List
Names l |b| a (J2000) d (J2000) Type D(Lyr) V
HD190360 67 1 20h03m37.41s +29d53m48.51s G7V 51.8 5.73
HD190406 57 8 20h04m06.23s +17d04m12.64s G1V 57.6 5.08
HD186408 83 13 19h41m48.95s +50d31m30.21s G3V 70.5 5.99
HD178428 50 4 19h07m57.32s +16d51m12.24s G6V 68.3 6.08
Table headings: l and |b| are the coordinates of the target star in
galactic latitude and (absolute) longitude, while a and d give the Right
Ascension and Declination of the star in the J2000 coordinate system. The
star's spectral type is given next; for comparison, our Sun is a G2V. The
next column gives the distances to each star in light years. The last
column gives the Visual magnitude (brightness) of each star.
For More Information:
Dr. Yvan Dutil (418) 844-4000 ext. 4319 Yvan....@drev.dnd.ca
M. Stephane Dumas (418) 844-4000 ext. 4309
Stephan...@drev.dnd.ca
You can also visit the web site of the Encounter 2001 project:
http://www.encounter2001.com/main.shtml
Lynn Cominsky ly...@charmian.sonoma.edu
Deputy Press Officer, American Astronomical Society and
Professor, Physics and Astronomy Department
Sonoma State University
1801 East Cotati Avenue
Rohnert Park, CA 94928
(707)-782-9380 FAX: (707)-664-3012
http://www.phys-astro.sonoma.edu/people/faculty/cominsky
Anthony Buckland
>
> -------- Original Message --------
> Subject: Re: SETI Re: [ASTRO] Encounter 2001 "Cosmic Call"
> Date: Tue, 12 Jan 1999 09:53:43 -0500
> From: Yvan Dutil <Yvan....@drev.dnd.ca>
> To: se...@sni.net
>
> FOR RELEASE: 9:20 a.m. CST, January 9, 1999
>
> Astronomers Get Ready to Call E.T.
Erik Max Francis
> > FOR RELEASE: 9:20 a.m. CST, January 9, 1999
> >
> > Astronomers Get Ready to Call E.T.
>
> At last! Hooray!
I checked Encounter 2001's website, and didn't find anything about the
contents of the message. The press release suggested that the message
was influenced by Freudenthal in particular (author of _Lincos_) --
anybody have any more details? The press release also says that it's
400 kB long, which certainly could make it a substantial message.
--
Erik Max Francis / email m...@alcyone.com / whois mf303 / icq 16063900
Alcyone Systems / irc maxxon (efnet) / finger m...@finger.alcyone.com
San Jose, CA / languages En, Eo / web http://www.alcyone.com/max/
USA / icbm 37 20 07 N 121 53 38 W / &tSftDotIotE
\
/ Only the winners decide what were war crimes.
/ Gary Wills
Richard A. Schumacher
>> > Astronomers Get Ready to Call E.T.
>>
150 years from now one of Them will come here to eat us.
Of course, they'll find only our intelligent machine
descendants who/which will exterminate Them, so the joke
will be on... Hmm. Them, or us?
Erik Max Francis
> 150 years from now one of Them will come here to eat us.
That occurred to me too (search DejaNews for "Berserker hypothesis").
Though I don't think it's an _obvious_ conclusion, certainly it's
something worth considering before a message is sent.
More importantly, if a message is being sent on behalf of humanity, I'd
like to know what the message says. Four hundred kilobits is not a
small message, if it's in a Lincos-like message. Anyone have any idea?
Sirius B
not familiar with "the principles of interstellar communication" as proposed
by Freudenthal et al.
Peace
LonNic 3.14 wrote in message <369E0D90...@geocities.com>...
Mark Gingrich
> ... Mathematics and physics have been used to define the message,
> so that it will be clear and based on universal concepts. For example,
> the hydrogen atom can be used to describe quantities such as mass,
> electric charge and length. To these basic ideas were added simple
> notions of astronomy, biology, geography and cosmology. Easier
> concepts and ideas are at the beginning while the more elaborate
> ones appear at the end of the message.
Oh, c'mon. The aliens aren't gonna understand all that. I think it
would be a lot more fun to ask them if they've "got Prince Albert in
a can?" ;)
--
~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~
Mark Gingrich gri...@rahul.net San Leandro, California
Erik Max Francis
> Is any of the message in musical form or it all binary? Forgive me
> but I'm
> not familiar with "the principles of interstellar communication" as
> proposed
> by Freudenthal et al.
If by the reference to Freudenthal, they meant his work on Lincos (short
for _Lingua cosmica_, "cosmic language"), then it is binary. Basically
a transmission is sent with the intention of the individual "words" in
the message being decipherable from the context. So you start with
counting (to make it clear what numbers are), then you show equality,
then addition, then multiplication, etc., each time making it clear
(hopefully, anyway) from the context and by repetition what the symbols
mean.
--
Erik Max Francis / email m...@alcyone.com / whois mf303 / icq 16063900
Alcyone Systems / irc maxxon (efnet) / finger m...@finger.alcyone.com
San Jose, CA / languages En, Eo / web http://www.alcyone.com/max/
USA / icbm 37 20 07 N 121 53 38 W / &tSftDotIotE
\
/ Liberty is the right to do whatever the law permits.
/ Charles Louis Montesquieu
Larry Taborek
We have been hitting the transmit button on radio frequencies now for about 50
years (longer for morris code), so the first radio waves to wash over any of
these star systems are going to be 30's and 40's radio broadcasts ("Pearl harbor
was bombed this morning"), followed by 50's television broadcast ("Its howdey
dudie time"), followed by 60's television and radio ("one two three O' clock,
four O' clock rock,", "Beam me up scotty", "thats one small step for man,..." and
then the 70's, 80's and 90's. Each happening real time on dozens, then hundreds
and then thousands of seperate frequencies of growing strength. So these 4 star
systems will get 40 years (or more) of our radio and TV, and then some scientist
is going to send them a 'special' message.
Comon guys.....
What could you possibly tell them that they haven't already figured out? (ho
boy, theres going to be some threads on that question).
Then theirs the questions as to wether anyone is there to listen. Say that
planets are a normal occurance. Give these guys the credit that their targets
are stars like ours. We been around 4 billion years here guys, and only in the
last 40 or 50 could we receive this signal. The odds are like a million to 1.
(or greater by several orders of magnitute, as we have yet to calculate the odds
of life in these solars systems).
Larry Taborek
mike_williams
> What a incredable waste of money and effort.
Do you know how much money and effort is involved? Probably not a lot for
just 3 hours use of a 70 meter radio telescope and a 150kW transmitter.
> We have been hitting the transmit button on radio frequencies now for about 50
> years (longer for morris code), so the first radio waves to wash over any of
> these star systems are going to be 30's and 40's radio broadcasts ("Pearl harbor
> was bombed this morning"), followed by 50's television broadcast ("Its howdey
> dudie time"), followed by 60's television and radio ("one two three O' clock,
> four O' clock rock,", "Beam me up scotty", "thats one small step for man,..." and
> then the 70's, 80's and 90's. Each happening real time on dozens, then hundreds
> and then thousands of seperate frequencies of growing strength. So these 4 star
> systems will get 40 years (or more) of our radio and TV, and then some scientist
> is going to send them a 'special' message.
Within the beam of the SETI broadcast, the signal strength is thousands of
times stronger than that of TV signals. 150kW is a pretty powerfull signal.
For comparison, I believe the more powerful FM stations are about 50kW, but
they radiate their energy through 360 degrees, whereas the SETI signal is to
be beamed directly into the alien's faces.
If the little green men have similar technology to ours, they might be able
to detect the existence of our domestic TV signals at a range of 50 light
years, but the signal would be so faint that they wouldn't be able to decode
them.
>
> Comon guys.....
>
> What could you possibly tell them that they haven't already figured out? (ho
> boy, theres going to be some threads on that question).
>
> Then theirs the questions as to wether anyone is there to listen. Say that
> planets are a normal occurance. Give these guys the credit that their targets
> are stars like ours. We been around 4 billion years here guys, and only in the
> last 40 or 50 could we receive this signal. The odds are like a million to 1.
> (or greater by several orders of magnitute, as we have yet to calculate the odds
> of life in these solars systems).
The hope is that the little green men of HD190360 might have been around
for, say, 1% longer than us - 4.04 billion years - or evolved 1% faster than
us, and thereby might have had technology capable of receiving the signal
for the last 40,000,000 years. It might be a million to one shot, but if the
jackpot does pay off it will have been well worth the gamble.
We could always improve the odds by sending similar signals to a few million
other stars.
--
Mike Williams
M.C.Harrison
>
> years (longer for morris code), so the first radio waves to wash over any of
> these star systems are going to be 30's and 40's radio broadcasts ("Pearl harbor
> was bombed this morning"), followed by 50's television broadcast ("Its howdey
Seems to me that the inverse square law cuts in at some point.
Let us pretend that a good tv receiver can pick up a transmitter that is
a thousand miles away.
What factor of receiver strength will the aliens need?
Going with the figures and gut feeling, I'd go along with fifty light
years as a reasonable site range. Using the inverse square law, I make
that signal around 10^23 times fainter. As such, the aliens will need a
radio receiver that is 10^23 times as sensitive.
Similarily, while a local transmitter is on a specific bandwidth that is
allocated only to it, when exploring a bandwidth given access to all
transmitters in all countries (of a single planet) there are going to be
several transmitters on the same frequency, quite likely using different
protocols, interfering with each other.
Overall, it seems to me that aliens doing a sky survey in fifty years
time will point their receiver towards our planet and see what appears
to be random noise at typical low levels. Not a seti signal at all. If
they could pick up the signals and make something of them, I dunno what,
seems more science fiction than likely.
Even if they could pick up the faint signal against the background
noise, they won't know how to decode it. If they got the signal full
strength, they might work out how to build a television set and view the
images, but with fragments they are on a hiding to nowt.
Jim Batka
Mike, Williams wrote:
The hope is that the little green men of HD190360 might have been around
> for, say, 1% longer than us - 4.04 billion years - or evolved 1% faster than
> us, and thereby might have had technology capable of receiving the signal
> for the last 40,000,000 years. It might be a million to one shot, but if the
> jackpot does pay off it will have been well worth the gamble.
Unless they decide that this signal is sufficient evidence to conclude that we are
a danger to their galactic neighborhood. In which case we have 100-300 years
before they arrive to exterminate the Terrestrial version of life.
At the rate we are going, they'll just need to drop some relativistic bombs or a
few asteroids to ensure our demise.
> We could always improve the odds by sending similar signals to a few million
> other stars.
Great, now we go from a small chance of extermination to a very much larger
one.
You see its not that I'm paranoid. I feel that there will be many civilizations
that want to be our friends. However, it only takes one with a contrary
point of view to ruin our day, err existance.
Before people start sending signals into space on my behalf, I'd like them to ask
for my permission.
Sincerely,
--
Jim Batka
Peterson
dismiss is the simple question regarding the desire of an alien civilization
to talk back. Why would they want to talk back? I doubt that they would. The
odds are great that they would be far beyond our level of technology. If
humans discovered life on mars in the form of an ape type creature what
would we do? Probably go and abduct a few and run a bunch of tests and then
leave them alone and watch. What a great way to look back in time and see
how life develops. Why spoil a perfect history book. Would we try to give
these apes technology about tools, farming, electronics or guns. No its
absurd, they would likely destroy themselves. However if the apes were about
to destroy there own world and render it unsuitable for life we would
probably interviene. So I propose that ET will show up when we put ourselves
on the brink of self destruction.
Chris
Mike Williams wrote in message <19990118....@econym.demon.co.uk>...
>Wasn't it Larry Taborek who once said:
>
>
>just 3 hours use of a 70 meter radio telescope and a 150kW transmitter.
>
about 50
>> years (longer for morris code), so the first radio waves to wash over any
of
>> these star systems are going to be 30's and 40's radio broadcasts ("Pearl
harbor
>> was bombed this morning"), followed by 50's television broadcast ("Its
howdey
>> dudie time"), followed by 60's television and radio ("one two three O'
clock,
>> four O' clock rock,", "Beam me up scotty", "thats one small step for
man,..." and
>> then the 70's, 80's and 90's. Each happening real time on dozens, then
hundreds
>> and then thousands of seperate frequencies of growing strength. So these
4 star
>> systems will get 40 years (or more) of our radio and TV, and then some
scientist
>> is going to send them a 'special' message.
>
>times stronger than that of TV signals. 150kW is a pretty powerfull signal.
>For comparison, I believe the more powerful FM stations are about 50kW, but
>they radiate their energy through 360 degrees, whereas the SETI signal is
to
>be beamed directly into the alien's faces.
>
>If the little green men have similar technology to ours, they might be able
>to detect the existence of our domestic TV signals at a range of 50 light
>years, but the signal would be so faint that they wouldn't be able to
decode
>them.
>
>>
>>
>> What could you possibly tell them that they haven't already figured out?
(ho
>> boy, theres going to be some threads on that question).
>>
>> Then theirs the questions as to wether anyone is there to listen. Say
that
>> planets are a normal occurance. Give these guys the credit that their
targets
>> are stars like ours. We been around 4 billion years here guys, and only
in the
>> last 40 or 50 could we receive this signal. The odds are like a million
to 1.
>> (or greater by several orders of magnitute, as we have yet to calculate
the odds
>> of life in these solars systems).
>
>for, say, 1% longer than us - 4.04 billion years - or evolved 1% faster
than
>us, and thereby might have had technology capable of receiving the signal
>for the last 40,000,000 years. It might be a million to one shot, but if
the
>jackpot does pay off it will have been well worth the gamble.
>
million
>other stars.
>
>Mike Williams
paull
>What a incredable waste of money and effort.
It's probably not that expensive, and someone else "wasting" their effort
shouldn't bother you...
I agree, the chances of anybody (anything?) ever hearing it are infinitely
small.
But if we don't make the call, we'll never know if anybody's home.
JustinM
Jim Batka wrote in message <36A3624D...@sdrc.com>...
>
>
>Mike, Williams wrote:
>
>The hope is that the little green men of HD190360 might have been around
>
>> for, say, 1% longer than us - 4.04 billion years - or evolved 1% faster
than
>> us, and thereby might have had technology capable of receiving the signal
>> for the last 40,000,000 years. It might be a million to one shot, but if
the
>> jackpot does pay off it will have been well worth the gamble.
>
we are
>a danger to their galactic neighborhood. In which case we have 100-300
years
>before they arrive to exterminate the Terrestrial version of life.
>
>At the rate we are going, they'll just need to drop some relativistic bombs
or a
>few asteroids to ensure our demise.
Have you read "The Killing Star" by Charles Pellegrino? SF, of course. It
deals with exactly this scenario....
>You see its not that I'm paranoid. I feel that there will be many
civilizations
>that want to be our friends. However, it only takes one with a contrary
>point of view to ruin our day, err existance.
True.
>
>Before people start sending signals into space on my behalf, I'd like them
to ask
>for my permission.
>
>Sincerely,
>--
>Jim Batka
Regards
JM
Larry Taborek
"M.C.Harrison" wrote:
> Larry Taborek wrote:
> >
> > years (longer for morris code), so the first radio waves to wash over any of
> > these star systems are going to be 30's and 40's radio broadcasts ("Pearl harbor
> > was bombed this morning"), followed by 50's television broadcast ("Its howdey
>
> Seems to me that the inverse square law cuts in at some point.
>
> Let us pretend that a good tv receiver can pick up a transmitter that is
> a thousand miles away.
>
> What factor of receiver strength will the aliens need?
>
> Going with the figures and gut feeling, I'd go along with fifty light
> years as a reasonable site range. Using the inverse square law, I make
> that signal around 10^23 times fainter. As such, the aliens will need a
> radio receiver that is 10^23 times as sensitive.
Well, as radio is about 50 years old and has been propigating since its
inception at the speed of light, your basically saying anyone thats within
the propigation range of the radio broadcasts probably has the technology
to receive it. So thanks for making my point for me.
>
>
> Similarily, while a local transmitter is on a specific bandwidth that is
> allocated only to it, when exploring a bandwidth given access to all
> transmitters in all countries (of a single planet) there are going to be
> several transmitters on the same frequency, quite likely using different
> protocols, interfering with each other.
>
> Overall, it seems to me that aliens doing a sky survey in fifty years
> time will point their receiver towards our planet and see what appears
> to be random noise at typical low levels. Not a seti signal at all. If
> they could pick up the signals and make something of them, I dunno what,
> seems more science fiction than likely.
>
Read on
>
> Even if they could pick up the faint signal against the background
> noise, they won't know how to decode it. If they got the signal full
> strength, they might work out how to build a television set and view the
> images, but with fragments they are on a hiding to nowt.
Well, probably not. Consider this. I got a DSS dish. Its 18 inches in diameter.
Its pointed at a
satellite 26,000 miles away. That satellite (actually 3) has multiple transponders,
each one about
12 watts. And what do I have for a super sophesticated amplifer? A little Sony DSS
receiver.
OK, now consider that some of the radio and TV stations are in the Megawatt range,
and the scale
just went up about a million times. Thats just the transmit side, look what the
aliens would have to
receive it if they just had our current technology. We haven't even figured in the
200 foot wide radio telescope
dish, or the VLA array (synthetic apature of 36 kilometers) and cygenically cooled
amplifers. Oh no
problem. Anyone with this sort of reception technology is probably getting the
initial radio signals
better then Ma and Pa Kettle did with their 1930 Grammaphone radio.
The current sensitivity figures for the VLA are from 1.4 to .06 milliJanskys. 1
Jansky is 10-26 watts
per square meter per hertz. A milliJanskys is 1/1000 of a Jansky.
Frankly, at that level of transmit, and that level of reception, we could probably
pick up radio signals
from several thousand light years away.
Larry Taborek
Larry Taborek
ydu...@my-dejanews.com wrote:
> > JB> Before people start sending signals into space on my behalf, I'd
> > JB> like them to ask for my permission.
> >
> > I suppose I won't be the only person pointing out that you're a bit
> > late demanding permission. We've been announcing our presence for the
> > past 30--50 years and show no signs of stopping any time soon. (Think
> > military, commercial, and scientific radars.)
>
> We have not been that noisy in my own opinion. TV and radio are not very
> powerful transmitter (EIRP=10 MW) and they transmit at fairly low
> frequency therefore the scintillation will kill your signal rapidly.
Oh ok, yah, only 10 megawatts of transmit power. That doesn't sound like
much
does it?
The VLA radio telescope sensitivity is about 1.4 to .06 milliJenskys. 1
Jenskys
is the standard of measurement of radio flux used in radio astronomy, and is
defined
as 10 to the minus 26 power watts per square centimeter per hertz. A
milliJensky is
1/1000 of a Jensky. So were looking at enormous sensitivity here. And this
is per
square centimeter. The VLA, when deployed to its widest extreme, has a
synthetic
aperture of 36 kilometers.
Getting the picture?
>
>
> Military radar have the tendency to change the frequency frequently.
> And do not forget, all those transmitter scan the sky. They do not stay
> on the same spot for long period of time. This will destroy your
> capacity to integrate.
Sure, and their signal carries really no intelligence. But its a nice flag
to wave
around and say "here we are".
>
> Yvan Dutil
>
> -----------== Posted via Deja News, The Discussion Network ==----------
> http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own
Larry Taborek
Hi Jim,
I couldn't agree with you more. I can't think of 1 time in all the history of the
world, where 2 civilizations meet, and the one with the lessor technologied advance
civilization doesn't come out stone cold worse off then before they had met.
Incas and Spanish. Poor Incas. Anyone seen a Inca lately?
How about Native American Indians and the Europeans? Still not some indians around,
but I doubt that many would tell you that their society is better off for the
encounter.
So in short, we got nothing to gain from this experience, and everything to loose.
Larry Taborek
Jim Batka wrote:
> Mike, Williams wrote:
>
> The hope is that the little green men of HD190360 might have been around
>
> > for, say, 1% longer than us - 4.04 billion years - or evolved 1% faster than
> > us, and thereby might have had technology capable of receiving the signal
> > for the last 40,000,000 years. It might be a million to one shot, but if the
> > jackpot does pay off it will have been well worth the gamble.
>
> Unless they decide that this signal is sufficient evidence to conclude that we are
> a danger to their galactic neighborhood. In which case we have 100-300 years
> before they arrive to exterminate the Terrestrial version of life.
>
> At the rate we are going, they'll just need to drop some relativistic bombs or a
> few asteroids to ensure our demise.
>
> > We could always improve the odds by sending similar signals to a few million
> > other stars.
>
> Great, now we go from a small chance of extermination to a very much larger
> one.
>
> You see its not that I'm paranoid. I feel that there will be many civilizations
> that want to be our friends. However, it only takes one with a contrary
> point of view to ruin our day, err existance.
>
> Before people start sending signals into space on my behalf, I'd like them to ask
> for my permission.
>
> Sincerely,
> --
> Jim Batka
Larry Taborek
ydu...@my-dejanews.com wrote:
>
> The purpose a shifting frequency is to elude detection. And even if you
> use a broadband receiver you will loose because the amount of noise you
> will pick get much higher.
>
> Yvan Dutil
>
> -----------== Posted via Deja News, The Discussion Network ==----------
> http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own
Hi Yvan,
I use to be a Gun Fire Control Technican in the Navy. The purpose of
frequency
shifting is twofold. On some phase array radar systems, the radar beam is
aimed by
shifting the frequency slightly, so that the radar beam reflects off the array
at a
different angle. By shifting the frequency back and forth, the beam is made
to sweep
the zone.
The other purpose is to avoid jamming, not detection. All Navy gun fire
control radars
can slew the radar frequency back and forth, so that a jamming signal on the
same
frequency soon becomes a jamming signal on some other frequency that your not
transmitting or receiving on.
But we digress....
Larry
Larry Taborek
Mike, Williams wrote:
>
> I think some sums might be useful here.
>
> Lets take a 10MW omnidirectional radio source and let the waves travel
> outwards for ten years. The wavefront is then sphere, ten light years in
> radius with the 10MW signal evenly distributed across it.
>
> 1 light year = 9.46e12 kilometers. So the surface area of the wavefront is
> 1.12e39 square cenimeters. So the signal strength 10 light years away is
> 8.89e-33 watts/square cm. So at 1.4 milliJenskys you'd need a receiver with
> a surface area of about 804 square centimeters to detect it.
>
> I've recently heard quoted, on another newsgroup, that the SETI guys reckon
> they would be able to detect TV-like signals from about 300 ly away. Since
> the signal intensity drops off with the inverse square of the distance you'd
> need a receiver with a surface area of about 7230 square meters to
> accomplish that.
>
> Each antenna of the VLA is 25m across, so the total surface area is about
> 53000 square meters, so it should comfortably be capable of detecting a 10MW
> omnidirectional signal at 300ly distance.
>
> > The VLA, when deployed to its widest extreme, has a synthetic aperture of
> > 36 kilometers.
>
> When looking for faint signals, *synthetic* aperture doesn't help - actual
> surface area is what counts.
>
> The increased synthetic aperture increases the resolution of the telescope,
> but it doesn't increase the amount of signal that actually falls on the
> receiving surface. Also, the wider the synthetic aperture (and thus the
> higher the resolution) the smaller the field of view becomes, and hence the
> more accurately the scope needs to be pointed. Since we don't know exactly
> where the signal (if there is one) is going to be coming from, it's better
> to use a scope that has lower resolution, a wider field of view and a very
> high gain - i.e. a single large dish.
>
> --
> Mike Williams
Hi Mike,
Thanks for the help here. I love this news group because even when your wrong,
you still get to learn something.
In this case though, your expert math has helped me prove my point. As the sphere
of
our radio signals is only perhaps 50 light years in diameter, it would seem to
both of us to
be very detectable using current technology.
Thanks again Mike,
Sincerely,
Larry Taborek
Larry Taborek
"M.C.Harrison" wrote:
> Larry Taborek wrote:
> >
> > > that signal around 10^23 times fainter. As such, the aliens will need a
> > > radio receiver that is 10^23 times as sensitive.
> >
> > Well, as radio is about 50 years old and has been propigating since its
> > inception at the speed of light, your basically saying anyone thats within
> > the propigation range of the radio broadcasts probably has the technology
> > to receive it. So thanks for making my point for me.
>
> I don't suppose anyone would argue that the signals are arriving at
> planets up to fifty light years away, presuming planets are present.
>
> Note my 10^23 factor, it will become important later on.
>
> > > Even if they could pick up the faint signal against the background
> > > noise, they won't know how to decode it. If they got the signal full
> > > strength, they might work out how to build a television set and view the
> > > images, but with fragments they are on a hiding to nowt.
> > Well, probably not. Consider this. I got a DSS dish. Its 18 inches in diameter.
> > Its pointed at a
> > satellite 26,000 miles away. That satellite (actually 3) has multiple transponders,
> > each one about
> > 12 watts. And what do I have for a super sophesticated amplifer? A little Sony DSS
> > receiver.
>
> Yep, you can have that, fine. your meter dish can pick up 10 watts at
> 30,000,000 meters range in round numbers, approx, for the sake of it,
> that's not unrealistic.
>
> So lets consider something at fifty light years. What changes?
>
> No problem at 30,000,000 meters, but we're talking 50 light years away,
> which is about
> 470,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000 meters
> away, because space really is considerably bigger than might be
> imagined. And, we have to square that ferocious number for the inverse
> square law, so we divide it by 30,000,000 meters and get a signal
> reduction of the order of 2e+20.
>
> Working the discussion in reverse, purely on signal reception, the
> transmitter you are talking about and the receiver you are talking
> about, and not upgrading the alien technology for the time being, the
> signal strength when you increase the distance to the satellite to fifty
> light years drops from the
> 2 milliJansky in your note (0.02 watts on a meter dish) down to the
> rather feeble 2e-22 watts per meter squared, a somewhat more challenging
> proposition.
>
> Now, with our level of technology, to pick up such a signal, if it isn't
> in any case lost due to the presence of random noise levels being higher
> (anyone got figures?) we'd need to use a dish that was 10,000,000
> kilometers in diameter, or increase the transmitter power from 10 watts
> up to the 100,000 megatonne TNT (per second) region. We could combine
> these two so that a one kilotonne TNT per second transmitter was being
> picked up by a dish that was being picked up by a ten kilometer diameter
> dish. I don't think we've been transmitting at that level, though, or
> anything approaching it.
>
> The aliens can have better technology levels, sure, but they still have
> to obey the inverse square law and can't do anything about the low
> transmission power. Also, it is quite likely that they have economics,
> taxes and politics just like us and cannot obtain permission to built
> thousand kilometer wide detector dishes even if their technology was up
> to it.
>
> > OK, now consider that some of the radio and TV stations are in the Megawatt range,
> > and the scale
> > just went up about a million times.
>
> Which knocks a couple of zeros off the bottom of the 470,000... figure,
> or three off the detector sensitivity requirement. I was letting you
> have a transmitter a million times the size with the kilotonne TNT per
> second one. Ok, the aliens have to build a dish that is ten thousand
> meters in diameter instead.
>
> > problem. Anyone with this sort of reception technology is probably getting the
> > initial radio signals
> > better then Ma and Pa Kettle did with their 1930 Grammaphone radio.
>
> Er, no. It is the inverse square law, I'm afraid. Ma and Pa would have
> done better than you trying to get a signal from Pluto, I'd hazard a
> guess, because the distance is squared while the technology roughly
> follows moores law, doubling in annual timeframes. I'll check that.
> Yeah, at the orbit of pluto, you get a signal that is 40,000,000,000
> times fainter than you do at the moment, and would have no chance even
> with a upgraded dish and the best available hardware.
>
> > The current sensitivity figures for the VLA are from 1.4 to .06 milliJanskys. 1
> > Jansky is 10-26 watts
> > per square meter per hertz. A milliJanskys is 1/1000 of a Jansky.
> >
> > Frankly, at that level of transmit, and that level of reception, we could probably
> > pick up radio signals
> > from several thousand light years away.
>
> I dunno if you realise how far that is. Add on another hundred from the
> absurdly large receiver at fifty light years?
Hi MC.
Well its been a education, thats for sure. I did some research on my own and found from
the
SETI main web site a portion of their FAQ http://www.seti-inst.edu/faq.html#anchor322777
which says.....
If the aliens have a SETI setup similar to Project Phoenix, could they
hear
Earth?
In general, no. Most earthly transmitters are too weak to be detectable
by
Phoenix-type equipment at the distance of even the nearest star. The
exceptions are some high-powered radars and the Arecibo broadcast of
1974 (which lasted for only three minutes). To detect "leakage" radiation
similar to our own will require instruments that are many times more
sensitive than what we now have.
So thats a relief.
To all those that have help educate me on the math of distant stars, the propigation of
radio
waves, and the correct spelling of Janskys, my thanks.
I love this group!
Larry Taborek
Larry Taborek
Martin Hardcastle wrote:
>
>
> In the interests of accuracy: it's `Jansky', it's 10^-26 watts per
> _square metre_ per hertz, and the longest baseline of the VLA doesn't
> have much to do with its sensitivity, which is related to the total
> area of the individual 25-metre dishes. The sensitivity in a 12-hour
> observation at GHz frequencies is nominally a few _micro_Janskys,
> according to my copy of the Observational Status Summary.
>
Your quite right about the spelling of Jansky and that its square_meter and not
square centimeter as I had previously posted.
>
> What kills your ability to detect this sort of thing is the
> inverse-square law. A few MW of power is a fairly piddling amount when
> it has to be spread over a sphere light years in extent. The EIRP of
> radars is a lot higher than this, of course. See the sci.astro FAQ,
> question 6, for more on this:
> http://sciastro.astronomy.net/sci.astro.6.FAQ
>
> Martin
> --
> Martin Hardcastle Department of Physics, University of Bristol
> Be not solitary, be not idle
> Please replace the xxx.xxx.xxx in the header with bristol.ac.uk to mail me
Yup, did some research on the web and it seems your quite correct and I was quite
wrong. Oh well, I can't always be right. :-)
Larry
T. Joseph W. Lazio
JB> Mike, Williams wrote:
>> We could always improve the odds by sending similar signals to a
>> few million other stars.
JB> Great, now we go from a small chance of extermination to a very
JB> much larger one. [...] [I]t only takes one with a contrary point
JB> of view to ruin our day, err existance.
JB> Before people start sending signals into space on my behalf, I'd
JB> like them to ask for my permission.
I suppose I won't be the only person pointing out that you're a bit
late demanding permission. We've been announcing our presence for the
past 30--50 years and show no signs of stopping any time soon. (Think
military, commercial, and scientific radars.)
--
Lt. Lazio, HTML police | e-mail: jla...@patriot.net
STOP RAPE | http://patriot.net/%7Ejlazio/
sci.astro FAQ at http://sciastro.astronomy.net/
ydu...@my-dejanews.com
> JB> Before people start sending signals into space on my behalf, I'd
> JB> like them to ask for my permission.
>
> I suppose I won't be the only person pointing out that you're a bit
> late demanding permission. We've been announcing our presence for the
> past 30--50 years and show no signs of stopping any time soon. (Think
> military, commercial, and scientific radars.)
We have not been that noisy in my own opinion. TV and radio are not very
powerful transmitter (EIRP=10 MW) and they transmit at fairly low
frequency therefore the scintillation will kill your signal rapidly.
Military radar have the tendency to change the frequency frequently.
And do not forget, all those transmitter scan the sky. They do not stay
on the same spot for long period of time. This will destroy your
capacity to integrate.
Yvan Dutil
Jim Batka
> Jim Batka wrote in message <36A3624D...@sdrc.com>...
<deletia>
>Unless they decide that this signal is sufficient evidence to conclude that
> we are
> >a danger to their galactic neighborhood. In which case we have 100-300
> years
> >before they arrive to exterminate the Terrestrial version of life.
> >
> >At the rate we are going, they'll just need to drop some relativistic bombs
> or a
> >few asteroids to ensure our demise.
>
> Have you read "The Killing Star" by Charles Pellegrino? SF, of course. It
> deals with exactly this scenario...
Why yes I have (for any that haven't read it, it is a great read with an
interesting lesson).
However, it didn't influence my opinion. I already had formed my opinion
about all of this before reading the book. The book just gave me a very
good reasons for the way I already felt ;).
>
>
> >You see its not that I'm paranoid. I feel that there will be many
> civilizations
> >that want to be our friends. However, it only takes one with a contrary
> >point of view to ruin our day, err existance.
>
> True.
Have a nice day!
--
Jim Batka
JustinM
>
>> Jim Batka wrote in message <36A3624D...@sdrc.com>...
>
><deletia>
>
>>Unless they decide that this signal is sufficient evidence to conclude
that
>
>> we are
>> >a danger to their galactic neighborhood. In which case we have 100-300
>> years
>> >before they arrive to exterminate the Terrestrial version of life.
>> >
>> >At the rate we are going, they'll just need to drop some relativistic
bombs
>> or a
>> >few asteroids to ensure our demise.
I wrote:
>>
>> Have you read "The Killing Star" by Charles Pellegrino? SF, of course. It
>> deals with exactly this scenario...
>
>Why yes I have (for any that haven't read it, it is a great read with an
>interesting lesson).
>
>However, it didn't influence my opinion. I already had formed my opinion
>about all of this before reading the book. The book just gave me a very
>good reasons for the way I already felt ;).
Interesting. I hadn't seriously considered the possibility before reading
the book (For anyone who hasn't, but is interested, the basic premise is
that some, possibly most, civilisations will attempt to wipe out any other
civilisation that they detect, not because they are xenophobic, not even
because they are paranoid, but because any civ that is capable of
relativistic interstellar flight is therefore capable of wiping them out,
either by accident or design (all it takes is one out of control spaceship
hitting your planet). Even if other civs have peaceful intent, the potential
risk is just too great, so wipe them out now!).
The same issues are covered in Greg Bear's Forge of God, but somehow I found
The Killing Star much more persuasive, and I was concerned enough to tell a
couple of (SF-inclined) friends, though they disagreed completely.
I don't know. I think you may have a point.
OTOH, I think a rational course for a civ that didn't want other civs around
would be to send out Von Neumann machines to suppress their initial
development. In which case we wouldn't even be here to argue the case.
Though I do realise that proves nothing. Just because I think it's rational
doesn't mean they will!
Personally, I tend to the POV that we are probably alone in at least the
immediate neighbourhood. On the one hand, life arises fairly easily. On the
other hand, we can think of many mechanism that prevent it getting very far.
My favourite is Gamma Ray Bursters. I skimmed an article today in this
week's New Scientist that suggests that GRBs may have been quite common in
our galaxy until only a few hundred million years ago, thus suppressing the
evolution of advanced life-forms. We might just be the first advanced civ!
>>
>> >You see its not that I'm paranoid. I feel that there will be many
>> civilizations
>> >that want to be our friends. However, it only takes one with a contrary
>> >point of view to ruin our day, err existance.
>>
>> True.
>
>Have a nice day!
You too.
>--
>Jim Batka
>
Cheers,
JM
John Ladasky
>
>> JB> Before people start sending signals into space on my behalf, I'd
>> JB> like them to ask for my permission.
>>
>> I suppose I won't be the only person pointing out that you're a bit
>> late demanding permission. We've been announcing our presence for the
>> past 30--50 years and show no signs of stopping any time soon. (Think
>> military, commercial, and scientific radars.)
>
>We have not been that noisy in my own opinion. TV and radio are not very
>powerful transmitter (EIRP=10 MW) and they transmit at fairly low
>frequency therefore the scintillation will kill your signal rapidly.
>
>Military radar have the tendency to change the frequency frequently.
>And do not forget, all those transmitter scan the sky. They do not stay
>on the same spot for long period of time. This will destroy your
>capacity to integrate.
>
>Yvan Dutil
But the purpose of frequency shifting in radar is to generate
what is known as a "soliton," a pulse of energy that resists dispersion.
A soliton delivers a maximally-focused pulse to a target. This type of
signal might well be detectable on a broad-band receiver from a great
distance. Even with the Earth turning, an observer in space would
probably see several of these in a row emanating from a radar.
--
Rainforest laid low.
"Wake up and smell the ozone,"
Says man with chainsaw. - John Ladasky
Paul V. Piescik
> Incas and Spanish. Poor Incas. Anyone seen a Inca lately?
SNIP
Well, now that you mention it, yeah! 9 days ago. Next meeting on 2 Feb.
mike_williams
> Personally, I tend to the POV that we are probably alone in at least the
> immediate neighbourhood. On the one hand, life arises fairly easily. On the
> other hand, we can think of many mechanism that prevent it getting very far.
> My favourite is Gamma Ray Bursters. I skimmed an article today in this
> week's New Scientist that suggests that GRBs may have been quite common in
> our galaxy until only a few hundred million years ago, thus suppressing the
> evolution of advanced life-forms. We might just be the first advanced civ!
I would have thought that information would have made it seem more likely
that there are lots of other intelligent life forms around.
It's now generally agreed that simple life forms appeared on the Earth
almost instantly (in geological terms) after the Earth became cool enough
for liquid water to accumulate on the surface. This suggests that simple
life forms would probably appear, in the same way, wherever the conditions
are suitable.
If advanced life forms were inhibited on Earth until a few hundred million
years ago, then it looks like advanced life forms appeared on the Earth
almost instantly (in geolocical terms) after the Gamma Ray Busters stopped
suppressing them[1]. This suggests that simple life would probably evolve
into advanced life as soon as the GRBs become uncommon.
If most of the habitable planets in our galaxy started to evolve advanced
life forms at the same time, a few hundred million years ago, then we'd
expect some of them to have evolved a little slower than us and some to have
evolved a little faster. Each life form that evolved a tenth of a percent
faster than us would be tens of thousands of years ahead of us by now.
[1] I assume here that "advanced life forms" includes things like trilobites
which existed 590 million years ago - I don't know by exactly what mechanism
it is suggested thet GRBs suppress advanced life while permitting simple
life[2], so I'm assuming that it affects something that we share with
trilobites but don't share with bacteria.
[2] The few powerful GRBs that still happen occasionally these days don't
seem to affect us very much.
--
Mike Williams
John Ladasky
Larry Taborek <l...@tecnet1.jcte.jcs.mil> wrote:
[snip]
>Consider this. I got a DSS dish. Its 18 inches in
>diameter. Its pointed at a satellite 26,000 miles away.
The satellite is presumably not radiating its signal equally in
all directions... why waste power sending signals away from Earth? So
let's naively assume a factor of ten increase in flux density from this...
>That satellite (actually 3) has multiple transponders, each one about
>12 watts. And what do I have for a super sophesticated amplifer? A lit-
>tle Sony DSS receiver.
O.K, so 36 watts, concentrated onto a tenth of the sky, can be
picked up by an 18-inch (1642 cm^2) dish and apparently cheap equipment.
>OK, now consider that some of the radio and TV stations are in the
>Megawatt range, and the scale just went up about a million times.
But because of the inverse square law, this would only a be a
thousand-fold gain in distance. Actually, the square root of one mil-
lion divided by 36 is only 167.
Still, this is not shabby. With our home satellite equipment
including an 18-inch dish, we could pick up a 1 megawatt signal (again,
concentrated onto a tenth of the sky), which is located 4.3 million
miles away. If we could make the signal even more directional, say,
concentrating it onto 1/100th of the sky, we could pick up a megawatt
from 43 million miles. That's the distance to Mars at closest approach.
(Hmmm. Business idea... :^)
>Thats just the transmit side, look what the aliens would have to
>receive it if they just had our current technology. We haven't even
>figured in the 200 foot wide radio telescope dish,
O.K., let's assume that we're listening with Arecibo, which is
305 meters in diameter. The surface area is 73,062 square meters, or
445,000 times larger than the 18-inch home dish. Ignore gains in amp-
lifier sensitivity for the moment. Let's assume that we're still lis-
tening to that one-megawatt Martian TV station. Assuming that sensi-
tivity scales linearly with the surface area of the dish (it's probably
a bit less than linear) the signal can be 445,000 times farther away.
That's 3.3 light years, less than the distance to the nearest star.
Our transmission needs to be even tighter, perhaps confined to
1/1000th of the sky, in order to be detectable at a significant number
of stars. Or the amplifier technology needs to be *much* more sensi-
tive. You need a 10-dB drop of the noise floor to be heard at 33 light
years, and a 30-dB drop to reach 3,300 light years.
>or the VLA array (synthetic apature of 36 kilometers)
As far as I know, the "synthetic aperture" provides gains in
angular resolution *only*, and not to sensitivity. You can't see dimmer
objects, you can just position them more accurately.
>and cygenically cooled amplifers. Oh no
>problem. Anyone with this sort of reception technology is probably
>getting the initial radio signals
>better then Ma and Pa Kettle did with their 1930 Grammaphone radio.
There are additional problems with frequency drift, as the
source and receiver are located on different bodies that do not move
together. Also, a highly directional signal will probably not be
pointed at the receiver for very long.
I'm not saying that interstellar signal detection is impossi-
ble, but it is still pretty daunting. Once you've found a signal and
you know what you're looking for, you can probably fine-tune things
and pick it up more easily.
ydu...@my-dejanews.com
Larry Taborek <l...@tecnet1.jcte.jcs.mil> wrote:
> > We have not been that noisy in my own opinion. TV and radio are not very
> > powerful transmitter (EIRP=10 MW) and they transmit at fairly low
> > frequency therefore the scintillation will kill your signal rapidly.
>
> Oh ok, yah, only 10 megawatts of transmit power. That doesn't sound like
> much
> does it?
>
> The VLA radio telescope sensitivity is about 1.4 to .06 milliJenskys. 1
> Jenskys
> is the standard of measurement of radio flux used in radio astronomy, and is
> defined
> as 10 to the minus 26 power watts per square centimeter per hertz. A
> milliJensky is
> 1/1000 of a Jensky. So were looking at enormous sensitivity here. And this
> is per
> square centimeter. The VLA, when deployed to its widest extreme, has a
> synthetic
> aperture of 36 kilometers.
>
> Getting the picture?
I get the picture, but if you put the number together, you need a antenna
of at least 1 square km to detect a TV transmitter on the nearest star.
This kind of technology become rapidly expensive as you go farther out.
> > Military radar have the tendency to change the frequency frequently.
> > And do not forget, all those transmitter scan the sky. They do not stay
> > on the same spot for long period of time. This will destroy your
> > capacity to integrate.
>
> Sure, and their signal carries really no intelligence. But its a nice flag
> to wave
> around and say "here we are".
But you have first to detcet them.
ydu...@my-dejanews.com
> >Yvan Dutil
>
> But the purpose of frequency shifting in radar is to generate
> what is known as a "soliton," a pulse of energy that resists dispersion.
> A soliton delivers a maximally-focused pulse to a target. This type of
> signal might well be detectable on a broad-band receiver from a great
> distance. Even with the Earth turning, an observer in space would
> probably see several of these in a row emanating from a radar.
I think you misunderstand the radar technology. Soliton can only be
created in a non-linear medium. To my knowledge, air and vacuum are
nearly a perfectly linear medium. Radar send short pulse to gain
some range resolution (dont forget the speed of light is 300 000 km/s).
The also send very short pulse to avoid detection and defeat jamming.
The effect of short pulse is to broaden the bandwidth of the signal.
The purpose a shifting frequency is to elude detection. And even if you
use a broadband receiver you will loose because the amount of noise you
will pick get much higher.
Yvan Dutil
Martin Hardcastle
Larry Taborek <l...@tecnet1.jcte.jcs.mil> wrote:
>The VLA radio telescope sensitivity is about 1.4 to .06 milliJenskys. 1
>Jenskys
>is the standard of measurement of radio flux used in radio astronomy, and is
>defined
>as 10 to the minus 26 power watts per square centimeter per hertz. A
>milliJensky is
>1/1000 of a Jensky. So were looking at enormous sensitivity here. And this
>is per
>square centimeter. The VLA, when deployed to its widest extreme, has a
>synthetic
>aperture of 36 kilometers.
In the interests of accuracy: it's `Jansky', it's 10^-26 watts per
_square metre_ per hertz, and the longest baseline of the VLA doesn't
have much to do with its sensitivity, which is related to the total
area of the individual 25-metre dishes. The sensitivity in a 12-hour
observation at GHz frequencies is nominally a few _micro_Janskys,
according to my copy of the Observational Status Summary.
What kills your ability to detect this sort of thing is the
M.C.Harrison
>
> > that signal around 10^23 times fainter. As such, the aliens will need a
> > radio receiver that is 10^23 times as sensitive.
>
> Well, as radio is about 50 years old and has been propigating since its
> inception at the speed of light, your basically saying anyone thats within
> the propigation range of the radio broadcasts probably has the technology
> to receive it. So thanks for making my point for me.
I don't suppose anyone would argue that the signals are arriving at
planets up to fifty light years away, presuming planets are present.
Note my 10^23 factor, it will become important later on.
> > Even if they could pick up the faint signal against the background
> > noise, they won't know how to decode it. If they got the signal full
> > strength, they might work out how to build a television set and view the
> > images, but with fragments they are on a hiding to nowt.
> Well, probably not. Consider this. I got a DSS dish. Its 18 inches in diameter.
> Its pointed at a
> satellite 26,000 miles away. That satellite (actually 3) has multiple transponders,
> each one about
> OK, now consider that some of the radio and TV stations are in the Megawatt range,
> and the scale
> just went up about a million times.
Which knocks a couple of zeros off the bottom of the 470,000... figure,
or three off the detector sensitivity requirement. I was letting you
have a transmitter a million times the size with the kilotonne TNT per
second one. Ok, the aliens have to build a dish that is ten thousand
meters in diameter instead.
> problem. Anyone with this sort of reception technology is probably getting the
> initial radio signals
> better then Ma and Pa Kettle did with their 1930 Grammaphone radio.
Er, no. It is the inverse square law, I'm afraid. Ma and Pa would have
mike_williams
> Oh ok, yah, only 10 megawatts of transmit power. That doesn't sound like
> much does it?
>
> The VLA radio telescope sensitivity is about 1.4 to .06 milliJenskys.
> 1 Jenskys is the standard of measurement of radio flux used in radio
> astronomy, and is defined as 10 to the minus 26 power watts per square
> centimeter per hertz. A milliJensky is 1/1000 of a Jensky. So were looking
> at enormous sensitivity here. And this is per square centimeter.
I think some sums might be useful here.
Lets take a 10MW omnidirectional radio source and let the waves travel
outwards for ten years. The wavefront is then sphere, ten light years in
radius with the 10MW signal evenly distributed across it.
1 light year = 9.46e12 kilometers. So the surface area of the wavefront is
1.12e39 square cenimeters. So the signal strength 10 light years away is
8.89e-33 watts/square cm. So at 1.4 milliJenskys you'd need a receiver with
a surface area of about 804 square centimeters to detect it.
I've recently heard quoted, on another newsgroup, that the SETI guys reckon
they would be able to detect TV-like signals from about 300 ly away. Since
the signal intensity drops off with the inverse square of the distance you'd
need a receiver with a surface area of about 7230 square meters to
accomplish that.
Each antenna of the VLA is 25m across, so the total surface area is about
53000 square meters, so it should comfortably be capable of detecting a 10MW
omnidirectional signal at 300ly distance.
> The VLA, when deployed to its widest extreme, has a synthetic aperture of
> 36 kilometers.
When looking for faint signals, *synthetic* aperture doesn't help - actual
g...@tantalus.clark.net
<mi...@econym.demon.co.uk> wrote:
> > The VLA, when deployed to its widest extreme, has a synthetic aperture of
> > 36 kilometers.
>
> When looking for faint signals, *synthetic* aperture doesn't help - actual
> surface area is what counts.
If the source being observed is unresolved (hence has a high surface
brightness) the larger baselines of the VLA does help, since the
signal is then the same on the large and small baselines, but the
noise in the synthesized beam is less in the longer baselines.
JustinM
Mike Williams wrote in message <19990122.061...@demon.net>...
>Wasn't it "JustinM" who once said:
>
>> Personally, I tend to the POV that we are probably alone in at least the
>> immediate neighbourhood. On the one hand, life arises fairly easily. On
the
>> other hand, we can think of many mechanism that prevent it getting very
far.
>> My favourite is Gamma Ray Bursters. I skimmed an article today in this
>> week's New Scientist that suggests that GRBs may have been quite common
in
>> our galaxy until only a few hundred million years ago, thus suppressing
the
>> evolution of advanced life-forms. We might just be the first advanced
civ!
>
>
>I would have thought that information would have made it seem more likely
>that there are lots of other intelligent life forms around.
At first, I thought, huh?
>
>It's now generally agreed that simple life forms appeared on the Earth
>almost instantly (in geological terms) after the Earth became cool enough
>for liquid water to accumulate on the surface. This suggests that simple
>life forms would probably appear, in the same way, wherever the conditions
>are suitable.
>
>If advanced life forms were inhibited on Earth until a few hundred million
>years ago, then it looks like advanced life forms appeared on the Earth
>almost instantly (in geolocical terms) after the Gamma Ray Busters stopped
>suppressing them[1]. This suggests that simple life would probably evolve
>into advanced life as soon as the GRBs become uncommon.
>
>If most of the habitable planets in our galaxy started to evolve advanced
>life forms at the same time, a few hundred million years ago, then we'd
>expect some of them to have evolved a little slower than us and some to
have
>evolved a little faster. Each life form that evolved a tenth of a percent
>faster than us would be tens of thousands of years ahead of us by now.
>
OK, all good and, AFAWK, true points. If the "GRBs (or some other mechanism)
suppressed advanced life until recently" theory is correct, then the Galaxy
should indeed be brimming with life now. However, the link that was being
broken was, I suppose, the development of multi-cellular forms of life, and
perhaps even of single-celled life forms.
What we don't know, of course, is the probability of multi-celled life forms
developing intelligence, followed by technology. My assumption (and I
suppose that of the researchers referred to in the New Scientist article) ,
is that this is fairly low. Obviously, a high probability leads to the
situation you predict.
Without more data, we just don't know. However, I do think it's a possible
explanation for the "Great Silence".
>
>[1] I assume here that "advanced life forms" includes things like
trilobites
>which existed 590 million years ago - I don't know by exactly what
mechanism
>it is suggested thet GRBs suppress advanced life while permitting simple
>life[2], so I'm assuming that it affects something that we share with
>trilobites but don't share with bacteria.
My understanding is that the effects are two-fold. First the initial
wave-front gives you radiation poisoning, to which some simpler life-forms
are more resistant. Subsequently, we get a barrage of charged particles that
generate a set of chemical reactions in the atmosphere that result in
tremendous quantities of nitrous (nitric? - sorry, my chem's not too hot)
oxides.
>
>[2] The few powerful GRBs that still happen occasionally these days don't
>seem to affect us very much.
You have to be within a few thousand light years, and all the GRBs observed
to date have been at cosmological distances.
>
>--
>Mike Williams
Gotta go pub!
Cheers
JM
Sean or Debbie Barr
T. Joseph W. Lazio
yd> [...] you need a antenna of at least 1 square km to detect a TV
yd> transmitter on the nearest star. This kind of technology become
yd> rapidly expensive as you go farther out.
For the record, various radio astronomers around the world are trying
to figure out if a radio telescope with a collecting area of 1 square
km could be built in the first decade of the next century. The
motivations extend well beyond SETI, of course.
>>> Military radar have the tendency to change the frequency
>>> frequently. And do not forget, all those transmitter scan the
>>> sky. They do not stay on the same spot for long period of
>>> time. This will destroy your capacity to integrate.
>>
>> Sure, and their signal carries really no intelligence. But its a
>> nice flag to wave around and say "here we are".
yd> But you have first to detcet them.
Right. That's the point. Radars pump out lots of power in narrow
bandwidths. True, they don't spend very long pointing in any one
direction, but they nonetheless make the Earth detectable over
interstellar distances.
T. Joseph W. Lazio
JB> Before people start sending signals into space on my behalf, I'd
JB> like them to ask for my permission.
>> I suppose I won't be the only person pointing out that you're a
>> bit late demanding permission. We've been announcing our presence
>> for the past 30--50 years and show no signs of stopping any time
>> soon. (Think military, commercial, and scientific radars.)
yd> We have not been that noisy in my own opinion. TV and radio are
yd> not very powerful transmitter (EIRP=10 MW) and they transmit at
yd> fairly low frequency therefore the scintillation will kill your
yd> signal rapidly.
I didn't say anything about TV or commercial radio. I agree, those
are most likely undetectable over interstellar distances.
yd> Military radar have the tendency to change the frequency
yd> frequently. And do not forget, all those transmitter scan the
yd> sky. They do not stay on the same spot for long period of
yd> time. This will destroy your capacity to integrate.
The objective isn't to integrate. The objective is to search for a
signal that is unlikely to have been produced by a natural process.
Radars fit that bill.
The fact that our radars scan the sky simply means that it would be
more difficult for an alien SETI project to confirm a possible
detection.
Erik Max Francis
> No problem at 30,000,000 meters, but we're talking 50 light years
> away,
> which is about
> 470,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000
> meters
> away, because space really is considerably bigger than might be
> imagined.
Something wrong with your counting there. 40 ly = 4.73 x 10^17 m, which
is awfully big, but has nowhere near as many zeroes as you used:
40 ly = 473 000 000 000 000 000 m.
Me thinks you wrote that as 473 x 10^15 m, and then wrote fifteen
triples of zeroes, not 15 zeroes.
--
Erik Max Francis / email m...@alcyone.com / whois mf303 / icq 16063900
Alcyone Systems / irc maxxon (efnet) / finger m...@finger.alcyone.com
San Jose, CA / languages En, Eo / web http://www.alcyone.com/max/
USA / icbm 37 20 07 N 121 53 38 W / &tSftDotIotE
\
/ Love's the only reason why we all keep living
/ Oleta Adams
Erik Max Francis
> 1 light year = 9.46e12 kilometers. So the surface area of the
> wavefront is
> 1.12e39 square cenimeters. So the signal strength 10 light years away
> is
> 8.89e-33 watts/square cm. So at 1.4 milliJenskys you'd need a
> receiver with
> a surface area of about 804 square centimeters to detect it.
How do you figure this? You haven't even talked about the bandwidth, or
sensitivity of the detector.
A 10 MW source with a bandwidth of 1 Hz at a distance of 10 ly = 9.45 x
10^16 m is about 8.9 x 10^-29 W/(m^2 Hz) = 8.9 mJy.
M.C.Harrison
>
> "M.C.Harrison" wrote:
>
> > 470,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000
> > away, because space really is considerably bigger than might be
>
> is awfully big, but has nowhere near as many zeroes as you used:
Er, actually I did the cube part first, hence 1,000 grew to
1,000,000,000. Still all valid aside from than that, so everyone just
ignore that particular bit. Oops :)
M.C.Harrison
>
> "M.C.Harrison" wrote:
>
> > absurdly large receiver at fifty light years?
>
> exceptions are some high-powered radars and the Arecibo broadcast of
Very sensible to check up on what is being said, because that way you
learn stuff. I'd recommend checking the maths on most questions as
people often assume things that cannot be true, they merely look ok.
> So thats a relief.
>
> I love this group!
Which one? <g>
M.C.Harrison
>
> Wasn't it "Larry Taborek" who once said:
>
> > Oh ok, yah, only 10 megawatts of transmit power. That doesn't sound like
> > much does it?
> >
> > The VLA radio telescope sensitivity is about 1.4 to .06 milliJenskys.
> > 1 Jenskys is the standard of measurement of radio flux used in radio
> > astronomy, and is defined as 10 to the minus 26 power watts per square
> > centimeter per hertz. A milliJensky is 1/1000 of a Jensky. So were looking
> > at enormous sensitivity here. And this is per square centimeter.
>
> I think some sums might be useful here.
Never hertz to do sums.
Afore we begin, the Jansky is 10^-26 watts per square meter rather than
centimeter, per hertz, according to Martin Hardcastle who is generally
right.
> Lets take a 10MW omnidirectional radio source and let the waves travel
> outwards for ten years. The wavefront is then sphere, ten light years in
> radius with the 10MW signal evenly distributed across it.
>
> 1 light year = 9.46e12 kilometers. So the surface area of the wavefront is
> 1.12e39 square cenimeters. So the signal strength 10 light years away is
> 8.89e-33 watts/square cm. So at 1.4 milliJenskys you'd need a receiver with
> a surface area of about 804 square centimeters to detect it.
Converting to meters, at 10 ly radius we have 4/3 pi r^2 with radius
9.46e16 meters (as per your figure) and a surface area of 1.12e35 square
meters (also as per your figure) and a signal strength of 8.90e-29 watts
per square meter, again as per your figure.
If detectors are able to work at the milli-Jansky level, then we are
able to receive signals at about ten light years range, and given that
there will be signal degradation, this probably translates into
receiving at the distance of the nearest star system, at 4.3 light years
distance.
> I've recently heard quoted, on another newsgroup, that the SETI guys reckon
> they would be able to detect TV-like signals from about 300 ly away. Since
Not when the signal strength at that range would have dropped to
9.89e-32 as that would require detectors capable of reading a thousandth
of a milli-Jansky, or a micro-Jansky. It is possible that that is the
level at which the signal strength falls below background noise levels
and therefore is no longer theoretically detectable, and that this is
what they meant. Otherwise, they have impressive detection capabilities.
> the signal intensity drops off with the inverse square of the distance you'd
> need a receiver with a surface area of about 7230 square meters to
> accomplish that.
>
> Each antenna of the VLA is 25m across, so the total surface area is about
> 53000 square meters, so it should comfortably be capable of detecting a 10MW
> omnidirectional signal at 300ly distance.
I don't know if you can scale like that. My interpretation of detector
capability is that the detector can identify a signal of that power.
Obviously, the dish has to focus all of a signal to that detector in
order to pick up that signal. With the VLA you would have a number of
dishes with detectors all failing to pick up a signal, not one detector
receiving the signal gathered by all the dishes.
> > The VLA, when deployed to its widest extreme, has a synthetic aperture of
> > 36 kilometers.
> When looking for faint signals, *synthetic* aperture doesn't help - actual
> surface area is what counts.
Signal strength at the receiver, probably.
I'd say SETI were about right with their claim that some signals could
be detected at quite large distances, but that early television is
probably not strong enough to be detected at fifty light year distances.