Basic SETI radio astronomy questions


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Profile Dave
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Message 1406711 - Posted: 23 Aug 2013, 1:26:32 UTC

Hello,

I'm writing a story that involves, in general, the SETI effort. I'm getting quite an education in the subject, at least as far as someone who knew almost nothing about it a month ago. ; )

I want to get the hard science as accurate as I can, and I want to get the speculative science as plausible as I can, so I'm coming up with all sorts of questions. I'm hoping someone here can help.

The questions:

1. I've seen 1660 MHz, 1662 MHz and 1666 MHz mentioned as the Hydroxyl line. According to the IAU list I found online, there are four hydroxyl bands of interest, so how are the three frequencies I mentioned chosen as "the" hydroxyl line, and why isn't there a consensus?

2. If 1420 MHz and hydroxyl (whatever frequency) are at the edges of the water hole, wouldn't those be at risk of potential interference from wide bandwidth signals outside the water hole spectrum?

3. An advanced amateur astronomer mentioned that a likely place for a signal is exactly between 1420 MHz and hydroxyl. Good idea or no? (He used 1662 MHz for hydroxyl, so the frequency he would choose to transmit on if he were ET is 1541 MHz.)

4. Are there any common uses for the frequencies around 2840 MHz or 5680 MHz that would interfere with picking up signals at those frequencies?

I've been an on-again, off-again SETI@Home participant since 2009, but I now have a computer dedicated to the task. I just wish I could get the screensaver to work (it's a Linux computer).

Dave
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Profile tullioProject donor
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Message 1406739 - Posted: 23 Aug 2013, 3:57:39 UTC - in response to Message 1406711.
Last modified: 23 Aug 2013, 3:59:21 UTC

I am a Linux user too and the "show graphics" button is not working on SETI while it works on Einstein@home for binary pulsar search. I posted a query in the Question&Answers section (no graphic window) but nobody replied.
Tullio
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rob smithProject donor
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Message 1406752 - Posted: 23 Aug 2013, 5:11:50 UTC

The answer for the lack of graphics under Linux - nobody has written the code. Mucha the same for the lack of graphics when running on GPUs.
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Bob Smith
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Michael Watson
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Message 1406943 - Posted: 23 Aug 2013, 15:16:00 UTC - in response to Message 1406711.

Hello,

I'm writing a story that involves, in general, the SETI effort. I'm getting quite an education in the subject, at least as far as someone who knew almost nothing about it a month ago. ; )

I want to get the hard science as accurate as I can, and I want to get the speculative science as plausible as I can, so I'm coming up with all sorts of questions. I'm hoping someone here can help.

The questions:

1. I've seen 1660 MHz, 1662 MHz and 1666 MHz mentioned as the Hydroxyl line. According to the IAU list I found online, there are four hydroxyl bands of interest, so how are the three frequencies I mentioned chosen as "the" hydroxyl line, and why isn't there a consensus?

2. If 1420 MHz and hydroxyl (whatever frequency) are at the edges of the water hole, wouldn't those be at risk of potential interference from wide bandwidth signals outside the water hole spectrum?

3. An advanced amateur astronomer mentioned that a likely place for a signal is exactly between 1420 MHz and hydroxyl. Good idea or no? (He used 1662 MHz for hydroxyl, so the frequency he would choose to transmit on if he were ET is 1541 MHz.)

4. Are there any common uses for the frequencies around 2840 MHz or 5680 MHz that would interfere with picking up signals at those frequencies?

I've been an on-again, off-again SETI@Home participant since 2009, but I now have a computer dedicated to the task. I just wish I could get the screensaver to work (it's a Linux computer).

Dave
Dave; The hydroxyl emission lines are: 1612, 1665, 1667, and 1721 MegaHertz, to the nearest MHz. The first three seem to be the most prominent, and are sometimes referred to collectively as the hydroxyl line. Any of these four can also be referred to as the hydroxyl line at one of the given frequencies.
The entire 'waterhole' region of the radio spectrum is not protected from use by others, only 1420 to 1427 MHz. Outside that range, observation are subject to manmade interference. The hydrogen line, at 1420.405 Mhz is about 400 KiloHertz inside this range, which offers modest protection from interference outside that band.
I find no reference to a hydroxyl line at 1662 MHz. If one wanted to take the average of all four hydroxyl lines, which is 1666 MHz, and listen midway between that and 1420 MHz, they'd be using the frequency 1543 MHz.
2840 MHz (twice the hydrogen line frequency) is within a band allocated to aeronautical radio location and meteorological probes (radiosondes, and the like). Quite a bit of interference potential there. 5680 MHz (four times the H. line) is within a band allocated to radio location, and amateur radio. Again, a certain amount of interference potential is apparent.
A good deal of SETI work is, and has been, done on frequencies outside the waterhole. The practice is to make a catalog of frequently interfering signals received at the observatory site, and skip over those frequencies.

Larry Monske
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Message 1411617 - Posted: 5 Sep 2013, 3:07:24 UTC - in response to Message 1406943.

I wonder if SETI has explored the globlar clusters in out galaxy that are much older than the earth. Their life could be much older more chance for delvelopment.These clusters of stars are captured smaller galaxies captured by the milky way.

Profile Bob DeWoody
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Message 1411659 - Posted: 5 Sep 2013, 5:01:13 UTC - in response to Message 1411617.

I think you will find that the dense concentration of stars in globular clusters and the resulting radiation makes those regions not very likely to support life. Just as it is not likely to be found near the center of the galaxy. Plus I have read that life is most likely to be found where third and fourth generation stars abound and the old stars have gone nova or supernova producing the heavier elements that are thought to be needed to support life.
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Profile Dave
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Message 1420686 - Posted: 26 Sep 2013, 20:57:02 UTC - in response to Message 1406943.

Hi Michael,

Thanks for the reply and sorry for the delay in thanking you. I forgot I posted the question, and I guess I figured at that time I'd get a notification email. I guess that means I should visit more often!

Dave

Michael Watson
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Message 1421491 - Posted: 28 Sep 2013, 16:54:16 UTC

Dave; If you go to your account page, you can set your community preferences, so that you'll be notified by email of responses to a post you've made, and of private messages. Michael

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