total stars in "shooting distance range" AP vs MB

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merle van osdol

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Message 1569035 - Posted: 8 Sep 2014, 6:27:56 UTC

Let's see if I can ask this question without making a total ass of myself.

If MB can see out to an effective distance of say,for our discussion, an area including 100,000 stars, how far out can AP see it's chirp-chirp signal?

If I get some answers, I may have to rephrase my question, if I am capable of doing that.
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Message 1569051 - Posted: 8 Sep 2014, 7:51:09 UTC - in response to Message 1569035.  

Some good technical background is in part 1.2.3 of the old Usenet SETI@home FAQ. In essence, the question boils down to how much power the distant civilization beams our way, and that FAQ answer makes it clear that the kind of power we have used for radio transmissions cannot reach very much of our galaxy.

However, the amount of power which could possibly be used by a more advanced civilization doesn't have any absolute bound. The technology to gather and use something like the total output of a star can at least be thought about. Or consider something like finding a way to add artificial modulation to the pulses being generated by a Pulsar, IOW using a radio source which already reaches huge distances and making it carry a message.
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Message 1569056 - Posted: 8 Sep 2014, 8:11:47 UTC - in response to Message 1569051.  
Last modified: 8 Sep 2014, 8:22:44 UTC

Joe,
How much is 'very much'? Just ballpark, guess.
--edit--
By radio transmissions you mean like our radio, tv and radar?
If we spent $50 million a year how strong of a chirp-chirp signal could we
send out. I mean how many light years out would it be good for if they had a simple Ariciebo.

I just looked at your link. Thanks, very good.


Some good technical background is in part 1.2.3 of the old Usenet SETI@home FAQ. In essence, the question boils down to how much power the distant civilization beams our way, and that FAQ answer makes it clear that the kind of power we have used for radio transmissions cannot reach very much of our galaxy.
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Message 1569254 - Posted: 8 Sep 2014, 18:10:49 UTC
Last modified: 8 Sep 2014, 18:32:07 UTC

Technically, a signal goes on infinitely. However, you end up with attenuation and interference from other locations in space and you get to a point where the signal you sent out blends in with the background "hiss."

In open space, like between two galaxies, the attenuation is significantly less than within a galaxy full of dust and gas and stars.

And then you end up with another huge "what if?" problem: was the signal that was sent out omni-directional, or was it focused in one direction? An omni signal takes astronomical (pun sort-of intended) power to travel even halfway across the galaxy, but a focused, directional signal needs much less power to reach the same distance.

[edit: To add more clarification, even with astronomical power (a star) broadcasting light (a radio frequency, technically) in an omni-directional pattern, we have trouble seeing ones on the opposite side of our own galaxy, but we can see individual stars from Andromeda, for example. The space between galaxies is much closer to being an empty vacuum than the space between stars within a galaxy. Sure, we can see the stars on the other side of our galaxy if we change how we look for them (infrared or x-ray), but that's only because most stars broadcast practically the whole electromagnetic spectrum, so there are many ways to "see" them. And also, when a star goes supernova, or turns into a pulsar, there is a focused beam of energy coming from the poles and we can see that practically across the entire universe. Omni vs. directional.

And the reason detecting radio signals becomes so difficult is not just omni vs. directional, but unlike a star, radio signals have a very narrow frequency range, so there's really only one way to look for it, and that is to be listening on the same frequency range.]

Arecibo is a directional antenna (both for transmit and receive). Of course, it all depends on the head that is installed, as well, because if you have a head that is designed in a certain way, you can end up transmitting or receiving on an arc that covers something like 40 degrees.

So it makes more sense to send out directional signals because they need much less power and are more likely to travel longer distances with less attenuation. Like when we send signals up to the satellites in orbit, only something like 5-10% of the broadcast beam actually hits the receiver on the satellite--the rest of it goes on out into space beyond. It would be a 1-in-many trillions shot of being 30,000 light-years away at the exact time and place to be able to even detect that narrow, focused beam that was broadcasted into space.

And even if you DO happen to be in that exact spot at the right time, there will have been so much attenuation that even with very sensitive and advanced detection equipment, you might not even be able to detect it at all. And if you were able to detect it, then you have to figure out what kind of signal it may have been, how to decode it, and then try to make sense of it.

Long story short.. it's finding a needle in a haystack, when the haystack is the size of a planet, and you don't know what a needle is or even looks like. Basically.. you're looking for something that doesn't look like everything else. My understanding of the way we're searching is using the frequency of hydrogen, because it makes the most sense. Kind of like in Contact, a deliberate signal was sent and focused right back at us using the frequency of 'hydrogen * pi' because.. "math and science are the only truly universal language." 1+1=2 in any language, here on Earth or on the other side of the universe.




So that's my take on it. Maybe that answered your question, maybe not. And I realize some of my facts may not be 100% accurate, but they are generally close enough for the context of this discussion.
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Message 1569268 - Posted: 8 Sep 2014, 18:52:58 UTC - in response to Message 1569056.  

Joe,
How much is 'very much'? Just ballpark, guess.
...

Well, assuming e.t. has a more sensitive receiving system than Arecibo (something like the Square Kilometre Array or better), the radio pulses sent by the Arecibo Planetary Radar could be detected out to 1000 light years or so. The Milky Way galaxy has a diameter of about 100000 light years, we're about 27000 light years from the center so star systems are spaced relatively far apart. In short, much much less than 1% of the star systems in our galaxy are near enough for detection of our strongest radio signals.
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Message 1569306 - Posted: 8 Sep 2014, 19:54:16 UTC - in response to Message 1569268.  
Last modified: 8 Sep 2014, 20:02:58 UTC

Joe,
But 1% would still be nearly 3 billion suns. To me that is an awfully large sample of stars. If it's not in there we may be alone.

--edit--
Thanks again for the reference. I gotta hang on 'til 2020! :-)
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Message 1569314 - Posted: 8 Sep 2014, 19:59:01 UTC - in response to Message 1569254.  
Last modified: 8 Sep 2014, 19:59:49 UTC

Cosmic,
That's the water hole of the MB narrowband search or am I still lost?
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Message 1569325 - Posted: 8 Sep 2014, 20:33:07 UTC - in response to Message 1569306.  

Joe,
But 1% would still be nearly 3 billion suns. To me that is an awfully large sample of stars. If it's not in there we may be alone.

--edit--
Thanks again for the reference. I gotta hang on 'til 2020! :-)

There is an theory of a galactic habitable zone. Where stars are less dense in the galaxy and not blurting out radiation that would be harmful to life. Making the number of stars much smaller that may contain planets with life.
With that theory they created a map of the Milky Way galaxy. http://www.hal6000.com/seti/images/yah.png With the red areas denoting potentially to high of levels of radiation for life to be present & our solar system marked in an area between two of these areas.

Another theory is that those stars could have planets with life if the planet were to have a much stronger magnetic field. However that might make it harder to detect intelligent signals from such planets.

If we don't look we won't know.
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Message 1569329 - Posted: 8 Sep 2014, 20:38:12 UTC - in response to Message 1569325.  

Amen Hal.
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Message 1569497 - Posted: 9 Sep 2014, 6:29:03 UTC - in response to Message 1569325.  

Joe,
But 1% would still be nearly 3 billion suns. To me that is an awfully large sample of stars. If it's not in there we may be alone.

--edit--
Thanks again for the reference. I gotta hang on 'til 2020! :-)

There is an theory of a galactic habitable zone. Where stars are less dense in the galaxy and not blurting out radiation that would be harmful to life. Making the number of stars much smaller that may contain planets with life.
With that theory they created a map of the Milky Way galaxy. http://www.hal6000.com/seti/images/yah.png With the red areas denoting potentially to high of levels of radiation for life to be present & our solar system marked in an area between two of these areas.

Another theory is that those stars could have planets with life if the planet were to have a much stronger magnetic field. However that might make it harder to detect intelligent signals from such planets.

If we don't look we won't know.

I watched an episode on How the universe works about that same thing It seems you dont want to live in arm of the galaxy but between tham. Where we are.
Also thats why the lab slpits old tapes to send back to us. As detection im proves letrs have a look at an old tape and see if we get anything. Plus as a bounus it keeps us in work when Aricbo is down.
[/quote]

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Message 1569513 - Posted: 9 Sep 2014, 7:22:23 UTC - in response to Message 1569325.  



our solar system marked in an area between two of these areas.



That does look like we're far out in the uncharted backwaters of the unfashionable end of the western spiral arm of the galaxy.
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Message 1569514 - Posted: 9 Sep 2014, 7:26:52 UTC - in response to Message 1569513.  



our solar system marked in an area between two of these areas.



That does look like we're far out in the uncharted backwaters of the unfashionable end of the western spiral arm of the galaxy.

I think we live in the Persus spur?
[/quote]

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Message 1569518 - Posted: 9 Sep 2014, 7:43:55 UTC

Hal,

One way I can interpret what you said is that it makes more sense to continue on with MB narrowband.
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Message 1569534 - Posted: 9 Sep 2014, 8:59:24 UTC - in response to Message 1569513.  



our solar system marked in an area between two of these areas.



That does look like we're far out in the uncharted backwaters of the unfashionable end of the western spiral arm of the galaxy.

I like to think of it as between Tornado & Hurricane Alley.
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Message 1569718 - Posted: 9 Sep 2014, 21:19:34 UTC - in response to Message 1569518.  

Hal,

One way I can interpret what you said is that it makes more sense to continue on with MB narrowband.

The AP vs MB aspect of your question has been neglected. The advantage of narrow pulses is that each pulse can be very powerful without requiring a continuous supply of high power. A one millisecond pulse sent once a minute would be 60000 times as strong as a continuous transmission for the same average power. That makes the signal reach over 15 times further.
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Message 1569760 - Posted: 9 Sep 2014, 22:26:49 UTC - in response to Message 1569718.  

Joe, what I was responding to was Hal's possible meaning that it was preferable to remain within our sparsely populated part of the galaxy and thereby not needing the long distance power of AP (the short term pulses that you are talking about). I was using MB narrowband meaning narrow in frequency not shorter/narrower in duration. Unless I am getting things all jumbled up which could be the case.
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Message 1569831 - Posted: 10 Sep 2014, 0:43:31 UTC - in response to Message 1569760.  

Joe, what I was responding to was Hal's possible meaning that it was preferable to remain within our sparsely populated part of the galaxy and thereby not needing the long distance power of AP (the short term pulses that you are talking about). I was using MB narrowband meaning narrow in frequency not shorter/narrower in duration. Unless I am getting things all jumbled up which could be the case.

If we take the width of Hal's image as 100000 light years, the outer circle surrounding our position appears to have a diameter just slightly less than 5000 light years by my rough measurements on the displayed image. Expecting our searches to detect anything near that 2500 light year radius requires that the transmitter be more powerful than a civilization at our stage of development could support. Assuming e.t. has the same kind of budgetary constraints we do, but nevertheless has good reason to send out signals with maximum reach, pulses seem more likely to me if they can serve whatever reason the system was built.

The question of motivation of course will remain unanswered until (and probably after) we actually detect some signal which is clearly sent by a technical civilization.
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Message 1569842 - Posted: 10 Sep 2014, 1:35:17 UTC - in response to Message 1569831.  
Last modified: 10 Sep 2014, 1:35:44 UTC

Assuming e.t. has the same kind of budgetary constraints we do, but nevertheless has good reason to send out signals with maximum reach, pulses seem more likely to me if they can serve whatever reason the system was built.

The question of motivation of course will remain unanswered until (and probably after) we actually detect some signal which is clearly sent by a technical civilization.

IMO if we find something it will be a supurious signal which is why I do as many APs as possible
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Message 1569895 - Posted: 10 Sep 2014, 5:44:47 UTC

And Harvard is doing Optical Seti. looking for laser signals. To bad we couldnt crunch them.
[/quote]

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Message 1569927 - Posted: 10 Sep 2014, 8:02:32 UTC - in response to Message 1569831.  

OK, that makes it clearer for me. I didn't realize that that sparsely populated area was itself so huge. In any event I keep coming down on the side of AP. We have been working many years with MB without any success. I don't mean give it up. It could work. Let the people who believe in it crunch themselves to death and I sincerely wish them the best and hope they find it. Me personally I just get off on the idea of AP.


Joe, what I was responding to was Hal's possible meaning that it was preferable to remain within our sparsely populated part of the galaxy and thereby not needing the long distance power of AP (the short term pulses that you are talking about). I was using MB narrowband meaning narrow in frequency not shorter/narrower in duration. Unless I am getting things all jumbled up which could be the case.

If we take the width of Hal's image as 100000 light years, the outer circle surrounding our position appears to have a diameter just slightly less than 5000 light years by my rough measurements on the displayed image. Expecting our searches to detect anything near that 2500 light year radius requires that the transmitter be more powerful than a civilization at our stage of development could support. Assuming e.t. has the same kind of budgetary constraints we do, but nevertheless has good reason to send out signals with maximum reach, pulses seem more likely to me if they can serve whatever reason the system was built.

The question of motivation of course will remain unanswered until (and probably after) we actually detect some signal which is clearly sent by a technical civilization.
                                                                  Joe
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Message boards : Number crunching : total stars in "shooting distance range" AP vs MB


 
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