Re: Total radio noise sent out from Earth

Joseph Lazio <jlazio@adams.patriot.net> wrote in message

Yes, just the natural radio emissions.

So based on these *projections* what are the *actual* measures of flux
for each star within about 5 parsecs distance and is it possible to
list those accurate to +/-0.05 mJy accuracy (may be on the extreme
"edge" of capability)? And if the measurements are made across a range
of frequencies (1 GHz, 3 GHz, 5 GHz,... etc) would the flux peak at
the *same* frequency for each star?

If 0.4 milli-Jansky is projected at the distance of Alpha Centauri
(1.3 parsec) then this implies a flux of 0.1 mJy will be received from
a Sun-like star out to 17 light years (5 parsecs).  Within that
distance range there are at least 5 Sun-like stars (obviously what you
define as 'sun-like' is slightly arbitrary) but I would say: Alpha Cen
A, B, Tau Ceti, Epsilon Indi, <<possibly>> Sigma Draconis - which is
at 18 light years out.

My bottom line question is: If the Earth had been circling around
*one* of these stars and outputting the *same* level of radio noise
that we do... would it *inflate* the natural radio flux coming from
its parent star by a significant amount so as to make *that* star
stick out like a "sore thumb" above all its peers!? And for the
purposes of this question, you can assume that the Earth that we are
listening *from* (here), is deadly "silent" in radio noise so as to
facilitate such detection.

I'd like a straight YES or a NO answer to this last question, please!

Thanks
Abdul Ahad

AI> Joseph Lazio <jlazio@adams.patriot.net> wrote in message
AI> news:<llhdo7w688.fsf@adams.patriot.net>...

AI> After 40+ years of SETI research, has anyone published a summary
AI> of some kind by candidate star [...]

AI> You mean this? [...]

AI> I think that's a *pay* per article service and I'm not even sure
AI> it will give me what I'm looking for. All I'm after is a total
AI> radio flux density number for each Sun-like star within 20 light
AI> years at a given frequency... a quantity referred to as 'S' and
AI> measured in Janskeys.

Oh, you want the *natural* radio emission.  I thought you were trying
to find the best limits from SETI programs.

AI> I want to know, does Tau Ceti have a higher radio output than
AI> Epsilon Indi? Does Delta Pavonis have a higher radio output than
AI> the Sun (Sol)?, etc. so I can compare between them. I would have
AI> thought such elementary data would be available readily, [...].

These are not *elementary* data!

This article summarizes stellar radio emission,
<URL:http://www.ras.ucalgary.ca/SKA/science/node13.html>.  A more
recent version by Steven White is at
<URL:http://www.aoc.nrao.edu/%7Eccarilli/CHAPS/stars.ps>.  He
estimates that a solar-type star at the distance of Alpha Centauri
would have a flux density of no more than 0.4 mJy.  Now a flux density
of 0.4 mJy at frequencies around 1--10 GHz is reasonably easy to
measure.  With the VLA at 1.4 GHz, I've gotten to 0.1 mJy without a
lot of effort in only 1 hr of observing time.  *However*, that
estimate is for a star at only the distance of Alpha Centauri.  At 10
pc, White's estimate would be a flux density of 4 *microJanskeys*.
That's out of reach with current telescopes.  

As White writes, "No main-sequence stars other than the Sun have been
detected so far through their thermal atmospheres ...."  The stars
that have been detected in the radio are unusual ones, having some
kind of enhanced magnetic activity.

You mean this?
http://arjournals.annualreviews.org/doi/abs/10.1146/annurev.astro.39.1.511;jsess
ionid=jNeVYQmKMZMd

I think that's a *pay* per article service and I'm not even sure it
will give me what I'm looking for. All I'm after is a total radio flux
density number for each Sun-like star within 20 light years at a given
frequency... a quantity referred to as 'S' and measured in Janskeys.
Ideally, I'd like this radio flux (S) measured for each star at a
microwave frequency at which the Earth would be expected to outshine
our Sun when surveyed from deep space.

I want to know, does Tau Ceti have a higher radio output than Epsilon
Indi? Does Delta Pavonis have a higher radio output than the Sun
(Sol)?, etc. so I can compare between them. I would have thought such
elementary data would be available readily, but a google search does
not throw up this kind of data.

This is just topline info without even going to the depths of
deciphering ET emissions.

Abdul Ahad

AI> After 40+ years of SETI research, has anyone published a summary
AI> of some kind by candidate star [...]

I think Jill Tarter has published a list of all known SETI programs as
well as the best limits obtained thus far.  However, you'll have to
get ahold of her review article in last year's (?) Annual Review of
Astronomy & Astrophysics.

Off the top of my head, the current best limits on the received fluxes
from ET emissions are around 1E-26 W/m^2.  If you want to convert that
to a *transmitted* power, you have to pick the distance to your
favorite target (keeping in mind that the entire sky has not been
surveyed to this level so that the result might be optimistic).

Converting this to more reasonable units, the limit is 12 GW (D/10 pc)^2.  
That is, a transmitter at a distance of 10 pc would have to be
broadcasting at least 12 GW to be detectable in the best case.

They, who live on the opposite shores of the interstellar ocean on a
planet circling the G2V star Alpha Centauri 'A', could be broadcasting
"Centaurian music" on their FM transmitters in full, digital 3D
surround sound formats 24 hours a day... yet we'd have absolutely no
hint of it! And that star system is virtually on our doorstep compared
to all the other promising 'sun-like' stars tens of light years out...

After 40+ years of SETI research, has anyone published a summary of
some kind by candidate star - something like this, I wonder:-

                      SETI PROGRAM RESEARCH SUMMARY
                               1960 - 2004

================================================================================
Star:       |   Total No of Years  | Peak Frequency:   | Total System
Output:
           |   Active Listening:  |                   |
================================================================================

Alpha Cen A        15.5*               4.2 GHz*               550
GWatt*
Alpha Cen B          ?                  ?                       ?

61 Cygni A           ?                  ?                       ?
61 Cygni B           ?                  ?                       ?

Tau Ceti             ?                  ?                       ?

Epsilon Eridani      ?                  ?                       ?

Epsilon Indi         ?                  ?                       ?

Delta Pavonis        ?                  ?                       ?

Eta Cassiopeiae A    ?                  ?                       ?

================================================================================
* These numbers are made up; not real.

A simplistic summary like this would be really helpful to someone like
me who lacks the technical know-how to interprete the heavy radio
astronomy jargon.

For example, if the total radio noise output (giga-watts) from a
candidate star system is 10% above that expected from a star of that
size and spectral class, may be that might indicate a "hot spot" of
some kind. Also, if the frequency at which the total output from a
star peaks is statistically significantly far removed from the
"average" for a star of its kind, then maybe that would be another
"hot spot", and so on.

I am only interested in a *simplistic* overview summary laid out by
*star*, and particularly keen on SETI results from sun-like stars
within about 50 light years from Earth. I wonder if there's such a
summary available?

Another question I have is what about the radio noise received from a
region *around* the candidate star? If the sky position of the star is
denoted by 'S', is there any measure of radio noise received from say
S + 1 arc-sec, S + 2 arc-sec, S + 3 arc-sec angular separations? This
might flag up if ET has ventured outward from its parent star system,
and is presently en-route on an interstellar voyage to a neighbouring
system...?! Or is that too much in the realm of fantasy???

Abdul Ahad

My guess would be one of the big FM radio stations (except for those
times when a narrow beam of something else happens to be pointing in
just the right direction), so that's somewhere between 88 and 108 MHz.

It's a bit tricky to look for SETI signals in the FM radio band because
the receiver tends to get swamped with local FM radio signals that are
many trillions of times stronger than any signal we might expect from
ET. The same difficulty would arise for any frequency in which the Earth
is bright. The obvious solution would be to build a big receiver on
Pluto or on the far side of the Moon, but that's some way beyond current
SETI budgets.

Great. I find it a struggle to understand precisely how the SETI
'listening' process works as I don't have a background in radio
astronomy, but just picture this hypothetical scenario:-

If you have an Arecibo style dish stationed on Pluto, the outermost
planet in our solar system, and you pointed the antenna toward our
inner solar system at each of three sources in turn: Mars, the Earth
and then the Sun. At a given frequency in the radio waveband, Mars
would be deadly silent. The Earth would give you a signal, due to
intelligence on our planet. The Sun would give you a strong, "natural"
noise signal. Would that sound about right?

Now, if you repeat this listening process over and over with Mars,
then the Earth, then the Sun again, each time tuning your receiver a
different frequency. At a certain frequency of say 'X' GHz, the signal
from Earth would outshine all three bodies in strength - including the
Sun!?  What is that "magic" frequency I wonder?

If we knew what this 'X' GHz was, and we tuned into *that* particular
frequency when listening for inteligent signals from "another Earth",
then the results might *just* show something! Has this sort of thing
already been tried I wonder...after 40 odd years of SETI I'm sure it
has?!

Abdul Ahad

    But if you notice all of our progress in communication has resulted
in reducing the "wasted" energy going into space. If we define
progress as data transfer my local cabel delivers more channels than I
pay for and I get well over two hundred a 5MHz each. And if I added
the 15MHz hidef channels and all the pay channels which are there it
would make the 15 broadcast channels in the area fall even deeper into
the noise. And I get about 350 Mbits of internet on it.

    The higher the frequency the more we depend upon antenna gain rather
than transmitter power. So actually the more advanced the technology
the less wasted energy into space we would expect.

I was hoping to get an idea of the *scale* of total radio noise that
we send out into the cosmos through all our day to day activities like
television and local radio broadcasts, mobile phones, satellite
relays, etc. How much "noise" does the planet's total output amount to
in 'Janskys' (if that is indeed the right measure?!)

This might sound a bit of a dumb Q amongst all you experienced SETI
people... but if an Earth-sized planet in the Alpha Centauri system -
just a stone's throw across the other side of the cosmic "pond" - were
to output the same level of radio noise as ourselves on a planet-wide
scale, how easy would it be to pick up such signals from Earth? Last
question: the radio transmitter onboard the Voyager spacecraft
operates on just 23 watts of power. If (hypothetically speaking)
Voyager was at Alpha Centauri and transmitting in our direction, would
the Arecibo radio telescope have been able to pick up its weak signals
at such a low output?

Thanks
Abdul Ahad