Eric's weekly post #2


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Eric KorpelaProject donor
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Message 512854 - Posted: 4 Feb 2007, 1:12:05 UTC

Woo hoo! A whole week and I haven't yet broken my promise to post once a week. (It's not Sunday here yet, so it still counts.)

I've been on pseudo-vacation since I submitted the NASA proposal on tuesday. My parents are in town, and Angela is doing her best to make sure I don't work on my "vacation." She's taking a nap right now, so as long as she doesn't wake up, I'm in the clear.

I don't have anything earth shattering to discuss today. I should mention that some Astropulse (a search for radio pulses that could come from ET or from evaprating black holes or pulsars) work units went out in beta last week, for the first time in a long time. You can get some description of Astropulse here. Yes. You read the date on that right. Astropulse has been stalled due to lack of forced labor... um... I mean a graduate student. Josh von Korff has been on the case for a little while and is making some progress.

Since I don't have that much new to discuss, I'll answer a question that appear in response to last week's post. The question was "Will the Allen telescope array render SETI@home obsolete?" As with most things in science, the answer is yes and no.

Any telescope will have its advantages and disadvantages. Those advantages and disadvantages affect how science is done with that telescope. There are really two characteristic to a telescope that affect how capable it is at doing SETI. Those are the collecting area, and the size of the field of view of the telescope (also called its beam size). For a single dish, those two parameters are inversly proportional to one another. A small dish has a large field of view. A small dish has a large field of view. That explains why you don't need a telescope in order to align a 14-inch (35 cm) digital satelite TV dish.

Arecibo's advantage is obvious. It's big. Really big. That means it has a large area for collecting radio signals. It also has the smallest beam of any single radio dish the new multibeam receiver has 7 beams, each of which is 3 arcminutes in diameter. (The size of a baseball seen from 100 meters away.)

The ATA is an array of radio telescopes. Arrays allow you to break the proportionality between area of the dish and the beam size. In an array, the size of the beam is inversely proportional to the largest spacing between the telescopes of the array, and the collecting area is proportional to the number of telescopes.

If the ATA gets fully assembled, its collecting area will still be less that that of the Arecibo telescope, but its beam size will be much smaller.

With Arecibo, we tend to do surveys. We look at the whole sky for potential signals. ATA, because it has a smaller beam is more suitable for point searches. If you want to look for signals from the 500 nearest stars, you want ATA. If you want to look for signals coming from anywhere in the sky, you want Arecibo or another large single dish (Parkes, GBT). To do both, you want both.

Of course, right now we have funding problems, which you have no doubt heard about. And Arecibo has funding problems, and will be shut down in five years if alternative funding isn't found. You may not have heard that ATA also has some funding issues. Right now I am not certain what fraction of the telescopes in the planned array will be built. The electronics that are required to generate the beam from the telescope data (the beam former) is also expensive, so funding determines how many simultaneous beams can be used. I think the current plan is for at least three beams, but if the beam former is behind schedule funding constraints may reduce that to two.

For what it's worth, my opinion is: "When you are looking for a needle in a haystack more eyes are better than fewer."

--
Eric
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Message 512891 - Posted: 4 Feb 2007, 2:14:46 UTC - in response to Message 512854.

For what it's worth, my opinion is: "When you are looking for a needle in a haystack more eyes are better than fewer."

And a misfit or two for comic relief when you stick yourself with that needle. ;)
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Message 512903 - Posted: 4 Feb 2007, 2:52:41 UTC - in response to Message 512854.

Of course, right now we have funding problems, which you have no doubt heard about. And Arecibo has funding problems, and will be shut down in five years if alternative funding isn't found. You may not have heard that ATA also has some funding issues.


Wow. Things sound really grim. What's the source of the funding cuts? Is it our government and it's "war on terror", or was there a pre-determined amount of time they were willing to fund it before they felt it was time to cut it off? Or what?

What does that mean personally and professionally for you? Worse case scenario, if things were shut down sooner rather than later, what would you do next? How would you feel about it?
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Message 513265 - Posted: 4 Feb 2007, 20:24:42 UTC

I know that, per David Woolley's messages of several years back, the stick Seti receiver hadn't been using the entire Arecibo dish at one time, ever. It had been using perhaps only a tenth of the dish at one time. I don't know whether the Alfa receiver uses all the Arecibo dish at one time or not. That has never been made clear to me. If so it would have to be handling off-axis signals coming in from an angle to the dish. Otherwise it could only be looking at the zenith. The stick used portions of the big dish; those portions were always normal to the stick and thus on-axis. The stick could catch any part of the sky up to 19 degrees away from the zenith. Signals off-axis by 19 degrees to the big dish as a whole would be affected by all kinds of gross aberrations but, maybe it's possible that the secondary and tertiary antennas could rectify them. Or, maybe a larger part of the dish is used with Alfa. It is not clear how much of the big dish is used at any one time by Alfa.
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Message 513304 - Posted: 4 Feb 2007, 22:10:38 UTC - in response to Message 512903.


Wow. Things sound really grim. What's the source of the funding cuts? Is it our government and it's "war on terror", or was there a pre-determined amount of time they were willing to fund it before they felt it was time to cut it off? Or what?


I'm not sure I could point fingers at any one factor. Funding for astronomy is a tiny fraction of overall NSF funding. Funding for the entire NSF is a tiny fraction of federal funding. Increased funding for other things during times of decreasing revenue doesn't help, and makes it impossible for the NSF budget to grow. Even if the NSF budget grows, astronomy isn't considered a national priority. Congress and the president set the priorities for the federal budget, so overall the responsibility lies there.

Arecibo's funding cut has short term and long term costs. Short term, another organization that does radio astronomy and has facilities in West Virginia and New Mexico asked the powerful senators from those two states to earmark money in the NSF budget for them. The obliging senators earmarked several milion dollars more than the facility requested. The earmarks don't change the total NSF astronomy budget, it just diverts money from where the NSF wanted it to go into projects in New Mexico and West Virginia. Puerto Rico doesn't have voting representation in the senate.

Long term, there are a lot of new facilities coming on line, and if there was no chance of budgets increases for Astronomy, older facilities need to be shut down.

I can speak to the cause of ATA's troubles. I'm not involved directly. I think that the original agreement was that Paul Allen would provide seed funding, and that the SETI Institute would need to find other funds for completion. I know NSF has given them some, but the required amounts might be too much for NSF to handle.


What does that mean personally and professionally for you? Worse case scenario, if things were shut down sooner rather than later, what would you do next? How would you feel about it?


It means that a lot of planned projects might not happen. The ALFA sky surveys might not be finished. And if there are, there will be a period of time when there are no instruments capable of making followup observations. I guess our next option would be to take our equipment elsewhere, Parkes, or an array that supports multiple beam formers. Regardless, it would most likely be outside of the U.S. SETI@home will still have a large amount of data from ALFA left to sift through (unless the amount of volunteers we have increases by a large amount).

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Message 513313 - Posted: 4 Feb 2007, 22:20:26 UTC

(cross-posted in Technical News section)


@Eric,

Any chance of finding out what discussions you all had about the BOINC User Survey Results.

Any surprises crop up?

Are you going to be, or have you started to, implement anything as a result of the survey?

Have the results confirmed anything in particular that you may have suspected?

How useful did you find the survey?

Will the survey be published in a paper, explaining the results and providing some conclusions/comments?

And many more questions on a similar vein.....

-kinhull


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Message 513358 - Posted: 5 Feb 2007, 0:40:15 UTC


SETI@home will still have a large amount of data from ALFA left to sift

through (unless the amount of volunteers we have increases by a large amount).


What if the Number of Volunteers *Suddenly* Does Jump - say Double - will this create a Problem? What would You Suggest in this Event?

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Message 513368 - Posted: 5 Feb 2007, 0:54:48 UTC - in response to Message 513313.

BOINC User Survey Results.

Will the survey be published in a paper, explaining the results and providing some conclusions/comments?


I notice that Section 64. Recruiting and retaining volunteers of the BOINC.pdf as is listed in the News section of the BOINC website, mentions a few things.

Were these a result of the survey?



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Message 513456 - Posted: 5 Feb 2007, 4:55:36 UTC - in response to Message 513265.

I know that, per David Woolley's messages of several years back, the stick Seti receiver hadn't been using the entire Arecibo dish at one time, ever. . . . It is not clear how much of the big dish is used at any one time by Alfa.


Unless I'm doing my math wrong, using the flat feed, we were typically getting an effective diameter of 145 meters or 16500 m^2 of collecting area at 85% efficiency (for point sources), not counting digitization losses. That's about 25% of the dish.

In the gregorian dome, depending upon exact azimuth and zenith angle, we typically get an effective diameter of 240 meters or 45000 m^2 of collecting area at 85% efficiency (also for point sources), again, not counting digitization losses. That's about 62% of the full area of the dish, and 4.5 times the collecting area of the full ATA (if the full ATA gets enough funding to be built).

As I said, I'm not saying one is better than the other or that it should be an either or proposition. I'm saying ATA is better for some things, AO is better for others.
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Message 513688 - Posted: 5 Feb 2007, 19:21:13 UTC

Thanks, Eric. Interesting.
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Message 513777 - Posted: 5 Feb 2007, 22:46:13 UTC

Eric, I heard some years ago about plans to make a super-telescope using three telescopes placed different places on the Earth, so the whole planet will function as a telescope. Has this been developed further? Or was it only discussions?


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Message 513796 - Posted: 5 Feb 2007, 23:25:13 UTC - in response to Message 513777.

Eric, I heard some years ago about plans to make a super-telescope using three telescopes placed different places on the Earth, so the whole planet will function as a telescope. Has this been developed further? Or was it only discussions?

See the VLBA site for the U.S. version, and Jodrell Bank's VLBI site for European efforts.
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Message 513853 - Posted: 6 Feb 2007, 1:51:42 UTC - in response to Message 513777.
Last modified: 6 Feb 2007, 1:53:12 UTC


Eric, I heard some years ago about plans to make a super-telescope using three telescopes placed different places on the Earth, so the whole planet will function as a telescope. Has this been developed further? Or was it only discussions?


If you aren't talking about VLBI, maybe you are thinking of the Square Kilometer Array (SKA) which would have a total collecting area of 1 million square meters. It is still in the development stages. The rumours are that site selection has been narrowed down to two sites. One is Australia, the other is scattered through several countries in south africa. I believe that the design is leaning towards medium size (20-40m) dishes, rather than a few Arecibo style dishes, or a bazillion small dishes. Reducing the number of dishes descreases the complexity of the electronics at the cost of reducing the angular range for a single dish position.

I'd be surprised to see first light before 2020.


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