archive: Re: SETI Re: [ASTRO] Encounter 2001 "Cosmic Call"

Re: SETI Re: [ASTRO] Encounter 2001 "Cosmic Call"

Dr. H. Paul Shuch ( (no email) )
Mon, 28 Dec 1998 14:12:48 -0500

>>From: Philip Chien <>
>>Subject: Re: [ASTRO] Encounter 2001 "Cosmic Call"

>> (and if any extra-terrestrial is
>>reading this message and understands it then feel free to drop by for a cup
>>of tea or raktajino.)

According to Douglas Adams, they would more likely prefer a gin and tonic,
or maybe a pangalactic gargle blaster.

>Granted there aren't many
>stars within 50 light years of the Earth which astronomers currently
>believe have terrestrial planets but with every year those signals go
>further out.

In fact, there are likely to be perhaps a thousand terrestrial planets
within 50 LY, although the number which are inhabitable is an open
question. Of the thirteen confirmed extra-solar solar systems, I believe
all are within about 50 LY, and only one detected planet is within its
star's habitable zone. Still, even the SETI professionals are counting on
a fairly high density of habitable worlds. Project Phoenix, the ambitious
targeted search being conducted by the SETI Institute, looks at 1000
sun-like (F, G, and K main-sequence) stars within only 200 LY.

>There are practical limits for the maximum distance a signal can be
>received before its so attenuated it's below the signal-to-noise floor.

Although your equations and calculations are correct, Phil, your conclusion
is suspect. There is NO distance over which a given signal can't be
detected, given the proper combination of capture area and integration
time. And "practical limits" is a rather geocentric concept. Remember
that each time you double distance, free space isotropic path loss
(sometimes mistakenly called "attenuation") increases by 6 dB. But each
time you double antenna diameter, the signal strength improves by 6 dB. So
for any distance, there is some size of antenna which is large enough.

>The odds of somebody in another solar system receiving any signal are _NOT_
>zero. Small yes. Zero no.


>I've heard that Arecibo could "communicate"
>with any similar size radio telescope in the Milky Way, although I don't
>have any reference or evidence to back up that statement.

Frank Drake's "anywhere in the Milky Way" claim was slightly exaggerated.
See "Optical SETI and the Arecibo Myth" at
<> for the exact calculations.

>To me purposely transmitting messages as a commercial endeavor is about on
>the same order of 'pet rocks', sending your DNA in to space, 'imitation
>Titanic necklaces' and other similar frivilous novelties.

That's a little stronger than my statement at
<>, Phil, but I can't disagree.

>Randi commented that God apparently talked to the evangalist on (something)
>Mhz. - within the frequency band used by commercial VHF radios!

Come on now! Everybody knows that God transmits on 1420.40575 MHz.

Nice reading yuor thoughts, Phil. Since I'm not on the ASTRO list, feel
free to forward.

73, Paul N6TX

H. Paul Shuch, Ph.D. Executive Director, The SETI League, Inc.
433 Liberty Street, PO Box 555, Little Ferry NJ 07643 USA
voice (201) 641-1770; fax (201) 641-1771; URL
email work:; home:

"We Know We're Not Alone!"