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From: RonO <rokimoto557@gmail.com>
Newsgroups: talk.origins
Subject: Re: New SETI search
Date: Tue, 27 Aug 2024 09:39:42 -0500
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On 8/27/2024 8:27 AM, El Kabong wrote:
> RonO wrote:
>> On 8/27/2024 2:11 AM, Ernest Major wrote:
>>> On 27/08/2024 06:24, El Kabong wrote:
>>>> Previous searches at Aricebo and other sites looked for
>>>> alien signals at 1420 Mhz.  They picked that frequency
>>>> because it is a hydrogen line.  The thinking is that
>>>> aliens would more likely broadcast there than an
>>>> arbitrary frequency.  It never made sense to me because
>>>> the signal will be attenuated by any hydrogen lying in
>>>> the path, and because if you tune in to the hydrogen
>>>> line, you'll find... hydrogen noise!
>>>
>>> The argument is that the 1420 MHz line is less arbitrary, and is not
>>> absorbed by interstellar dust.
> 
> Any radio signal is less absorbed by dust than optical
> wavelengths.
> 
> 1420 was probably a good pick, but it does have that
> drawback.
> 
>> If the aliens had broadcast at 1420 MHz what would be the frequency that
>> we would detect in an expanding universe?  I realize that some galaxies
>> are moving towards us, but the red shift indicates that most things are
>> getting further away from us in all directions due to the Big Bang.
> 
> Any radio signal we receive will be redshifted.  But we
> are not looking for extragalactic signals, they would be
> way too faint.  We are looking for something here in our
> own neighborhood of the Milky Way, around 10k lightyears
> max.  At that distance the redshift is measurable but
> unimportant, even for a narrow-band receiver.

This example is looking at other galaxies.

Ron Okimoto
>