Earth's Radio Telescopes Combining Forces 119
Slatterz writes "I own a basic 70mm telescope, which I'm sure Galileo would have given his right arm for in 1609. In fact, this year marks exactly 400 years since Galileo first pointed a telescope at the skies — discovering the moons of Jupiter and helping to prove that the universe doesn't revolve around us. As a mark of respect, the United Nations has declared 2009 the International Year of Astronomy. Official festivities kick off this week in Paris and, to help start the celebrations, 17 radio telescopes in Australia, Asia, Europe and the Americas will track three quasars using something called "real-time Very Long Baseline Interferometry" — basically creating hi-res images by combining their data to simulate a telescope as large as the Earth. Sounds cool."
And to kickstart the celebrations (Score:5, Funny)
the United Nations has declared 2009 the International Year of Astronomy. Official festivities kick off this week in Paris and, to help start the celebrations ... a giant light display and a firework!
Re: (Score:2)
a firework!
"Oh my God, in my telescope, a fast moving bright object! What can it be, is it a meteor, is it a plane?"
*PAAAH*
"Aaah my eye! It's blind!! It's blind!!!"
Re: (Score:2, Funny)
2009: The year of the Astronomy Desktop...
Ups, sorry! ;)
Comment removed (Score:5, Interesting)
Re:And to kickstart the celebrations (Score:4, Informative)
It's a pity few even realize what a problem light pollution is.
Indeed. Galileo made many of his observations from the city of Venice. Back then, you could still see the stars from a city center. Now, even the outer suburbs are pretty degraded.
If you care about changing this (and a lot can be done), join the International Dark-Sky Association [darksky.org].
Re: (Score:2)
In October of 2008, I on a motorcycle trip in southeastern Tennessee. That night at the campground was the first I ever saw the Milky Way band in the sky.
I think that is sad that I was 37 years old the first time to see it with my own eyes.
Re: (Score:2)
Well, that's something to blame your parents for, but if they were similarly deprived, there's no benefit to recriminations. Just show them the sight yourself, and make sure to educate any other kids in the family.
A few years ago I was visiting a friend in his late 40s ... actually I was there because I wanted to show him Comet Hyakutake [wikipedia.org], so that dates it to 1996-03-24 or -25. Which was stunning enough, given that he has
Re: (Score:2)
must be some version of southeastern tennessee that I'm not familiar with! I've lived here all of my life. I'm guessing you're talking about somewhere in Polk County, though?
Tellico Plains. Near Deal's Gap.
Re: (Score:2)
It took you this long to foe me? LOL, after our exchange when you called Obama a nigger [slashdot.org] I can't believe it took you this long. All the racists hate me.
Re: (Score:2)
No, sad is being an open racist and not realizing that someone might keep track of you. Thank goodness for that good old net anonymity, right? Lets you have balls of steel.
(for instance, I never called anyone in particular a nigger)
Ahh, my bad... you said that you'd never vote for a nigger in a discussion about Obama. Truly I am indeed stupid for thinking that you were referring to Obama himself as the nigger in question.
I "foe"d you because you're stupid,
So... one could say you are intolerant of stupidity? That's sounds about right. By the way, stupidity is hating someone because they have more or l
Re: (Score:2)
I've been a blackhat "hacker" in the past.
though I don't want to toot my own horn so much (as you).
Yes, you come across as both eloquent AND modest. The true mark of a learned man is in how he uses the word nigger.
Tell me, what is harder:
1. Bookmarking a post from an exchange you've had with a racist.
2. Marking someone as "foe".
About the same effort, no? And while it may be silly for me to care what people post on Slashdot, you fall into the same category. For you, the hot button is when someone makes a "stupid" post... for me, it's when someone makes it harder for my children to live where they want. No
Re: (Score:2)
it's about you actively remembering me and what I've done and seeking me out.
You are quite memorable. Open racists are extremely rare these days. Most of your ilk are 15-year-olds posting as anonymous coward. I probably wouldn't have remembered you if you hadn't foed me and triggered my memory.
reading posts and replying to them as necessary doesn't entail caring about anything particularly.
Unless you are a bot, that statement is pretty absurd. Why would you take the effort to reply to something unless you cared about it?
I also don't make it harder for your stupid children to live anywhere.
Yes, you do. And on several levels. First, there is the discomfort factor. Have you ever been verbally assaulted just because your skin is the wrong color? It su
Re: (Score:2)
I can't imagine how glorious things must have been a century ago.
Well if you have money take your telescope and get out to sea somewhere. There isn't a whole lot of light pollution in the middle of the Pacific or Atlantic.
Re: (Score:1)
Well if you have money take your telescope and get out to sea somewhere. There isn't a whole lot of light pollution in the middle of the Pacific or Atlantic.
It's quite hard to hold a telescope steady while on a boat.
Re: (Score:2)
Eh, depends on the boat or ship that you are on but that's a pretty valid point that I hadn't thought of. Still, you'll see more stars with the naked eye or a good set of binoculars than you will with most telescopes on land in light polluted regions.
At sea? (Score:5, Funny)
Well if you have money take your telescope and get out to sea somewhere.
Yeah, and you can bring a grandfather clock to keep time. And if you're bored, you can bring along a Jenga set. Everyone loves boat Jenga.
Re: (Score:2)
You're halfway there. Bring up Google Maps, satellite view, and just scan across the ocean. You'd be surprised how many tiny little uninhabited islands there are out in the ocean. Too small and remote to build a permanent settlement on, they are perfect platforms for temporary telescope sites. If you're really interested in a truly dark sky and maybe a little party time, get a large group together, charter a boat from the nearest mainland, setup your telescopes on one side of the island and your BBQ pit
Re: (Score:2)
Re: (Score:1, Informative)
Re: (Score:2)
IIRC it potentially messes with animals that use the moon to navigate.
Re: (Score:2, Interesting)
Depending on where the light pollution is, the effects vary.
2. Some research suggests it messes with people's circadian rhythms (which can lead to insomnia and possible long-term health effects)
3. It can prevent numerous plants from flowering (they think it is always summer)
4. Sea turtles may migrate in the wrong direction when they hatch
5. Predator-prey relations may be skewed
6. Giant mutant spiders that eat all the insects attracted to the lights
Re: (Score:3, Funny)
So what other downsides are there?
I can't cause mischief as easily.
Re: (Score:2, Funny)
...which, of course, would not affect my radio telescope at all. But could you please turn off your phone!
Wiki help (Score:5, Informative)
Since the 1970s telescopes from all over the world (and even in Earth orbit) have been combined to perform Very Long Baseline Interferometry. Data received at each antenna is paired with timing information, usually from a local atomic clock, and then stored for later analysis on magnetic tape or hard disk. At that later time, the data is correlated with data from other antennas similarly recorded, to produce the resulting image. Using this method it is possible to synthesise an antenna that is effectively the size of the Earth. The large distances between the telescopes enable very high angular resolutions to be achieved, much greater in fact than in any other field of astronomy. At the highest frequencies, synthesised beams less than 1 milliarcsecond are possible.
Re: (Score:2)
The summary made this sound like something that should be already happening. Thanks.
Re: (Score:2)
VLBI is 51 years old (it actually started in the late 1960's [nrcan.gc.ca]) but it is high quality eVLBI that is basically a product of our century (made possible by all of that nice optical fiber criss-crossing our planet).
Re: (Score:2)
VLBI is 51 years old (it actually started in the late 1960's [nrcan.gc.ca]) but it is high quality eVLBI that is basically a product of our century (made possible by all of that nice optical fiber criss-crossing our planet).
Think about what you typed. VLBI is 51 years old... started in late 1960's. You're sort of right, but it reads wrong.
Let us assume January 1, 1965 is the start of the "late" 1960's (being the latter half). That would give us 2009-1965 = 44. I'm not sure if I suck at math, but from what I can tell 44 != 51.
Did a little reading, the first use of VLBI started in '67, so it's only 42 years old, the technique that led to VLBI, using "closure phase" during interferometric observations, was first demons
Re: (Score:2)
Good catch.
VLBI is 41 years old.
(Sorry, too little coffee early in the AM.)
This is called eVLBI (Score:4, Interesting)
This is called eVLBI [evlbi.org], and it is now done routinely to, e.g., determine the Earth's rotation (UT1).
From a networking standpoint, one interesting thing is that eVLBI requires high bandwidth (1 Gbps is typical), but can tolerate fairly high loss rates (because the actual cross correlation coefficients are rarely as high as 10^-3). This makes it an excellent candidate for an Internet scavenger service [internet2.edu], where packets are sent at "less than best effort," i.e., with the understanding that they can be dropped if there is any congestion at all, so that eVLBI can use all available bandwidth without choking out other uses. The same technology may prove to be very useful for P2P services [ietf.org].
Re: (Score:2, Insightful)
The same technology may prove to be very useful for P2P services [ietf.org].
Indeed. One of the biggest problems with P2P in general is all the congestion it creates by opening so many simultaneous connections. P2P could be much more useful for these kinds of background transfers that are obviously best for scenarios like eLVBI.
With a 'less than best effort' strategy, you'll end up only using the 'extra' or 'leftover' bandwidth and not your whole pipe.
The story the other day about a P2P firewall (which has other more glaringly obvious problems than just being P2P) could make use o
Re: (Score:2)
Note that that is "1 Gbps per telescope." It does add up.
Re: (Score:1)
If you look at VLBI [wikipedia.org] it says that it's been used to make "infrared and optical images...". If this technology has applications in the visible light wavelengths is it not possible to array together a large number of optical telescopes similarly?
I understand that timing is the big problem (the light has to assemble in perfect sequence to make it work). Could this be overcome with higher interconnect speeds (eg internet2)?
How long until we have another Seti@Home with amateur optical telescopes?
Re: (Score:2)
Not quite. It says "similar techniques have also been used to make infrared and optical images of stellar surfaces"
In the optical, interferometry is done by actually combining light from two or more telescopes [navy.mil]. So, first, the telescopes have to be close enough to do that. Second, the atmosphere limits your coherence between remote sites to 10's or 100's of meters at most (longer separation are possible in the IR than in the optical). Third, the wavelength is much smaller (a factor of ~ 10,000, typically), s
A telescope as large as the Earth (Score:2, Funny)
Re: (Score:2)
Why? Incase he rises from the grave in zombie rage?
Even so i doubt hed goto all the effort of defying nature and causing zombie havoc for some unit conversion errors. Id of thought the whole light pollution issue would have ticked him off more.
Re: (Score:2)
If you were sent to Hell for more almost 350 years just for telling the truth you'd be a little pissed off, too!
Re:A telescope as large as the Earth (Score:4, Interesting)
What strikes me as funny as if there was/is a God he must have a fantastically disgusting mean streak. Technically it was the Church under the Pope that like burned Gallelio right? The same Church who God supposedly told he would honor the decisions they make down here. So if the Pope condemned Gallelio to hell for telling the truth then he would be there being flayed constantly.
Of course there are other ways you can take that, but since we're talking 100% hypothetical BS I figured I'd be lazy and take the wordings at face value. Alternate beliefs and theories include bits like that "promise" being bullshit by the Church so they can keep power, or God telling lies to people down here and doing whatever He wants up there, etc etc.
Slightly less off topic though I've always wondered what past great scientists would do with modern technology. I blame Star Trek for putting the idea in my head, what with Data and his holodeck friends of Einstein, Freud, Edison and so forth. I wonder if in some cases if these "greats" are only great because they had primitive tools and were more adept at using those and would be considered mediocre if they had modern gear and knew how to use it.
After all, using an IR or Radio telescope is different than using an optical one.
Re: (Score:2)
I wonder if in some cases if these "greats" are only great because they had primitive tools and were more adept at using those and would be considered mediocre if they had modern gear and knew how to use it.
After all, using an IR or Radio telescope is different than using an optical one.
I don't know. A lot of people had some of these tools available to them or the means to make them. I think if we took someone really exceptional from the past and put them in the modern settings, they'd still provide amazing insights.
You said it yourself - they were more adept at using the tools of the time. Who's to say that they wouldn't be more adept at using the tools of *our* time as well after learning how to use them?
Re: (Score:3, Funny)
After all, using an IR or Radio telescope is different than using an optical one.
Most of the differences are in how they're built though, and using them is pretty much the same, right?
I mean once they're built, you just point the big end around the sky. With the optical ones you look through the little end, with the radio ones, you put your ear on the little end, and with the IR ones, you put..I dunno, something you want to warm up.... a TV dinner or something on the little end. Astrology isn't so hard.
Re: (Score:2)
Uhh, no.
Head you consulted Wikipedia [wikipedia.org] before posting, you would have seen that Galileo died of natural causes. You're probably thinking of Giordano Bruno [wikipedia.org], but he was killed because of his theological views, not his scientific views.
What did happen is that Galileo was convected by the Inquisition on a suspicion of heresy (namely, holding heliocentric views even after they were declared contrary to Scripture). He was ordered t
Re: (Score:2)
If you were sent to Hell for more almost 350 years just for telling the truth you'd be a little pissed off, too!
I'd think Hell would have the better libraries.
Re: (Score:3, Interesting)
You wouldn't want to upset Galileo on this date...
When I was in Florence I actually got to go see his grave. It's located in the Basilica of Santa Croce. Michelangelo's grave is also located there. They are on opposite ends of the church within sight of each other.
Rumor has it that during one of the many floods that hit Florence the remains of each came up to the surface and they had to guess at who was who when they reburied them. I don't know if this actually true or just something they tell the tourists but I paid my respects to both graves.
If you want ot get in the hobby. (Score:4, Informative)
Dont get a crappy scope. it will simply discourage you.
go to orion at http://www.telescope.com/control/main/ [telescope.com] and buy a 8" dobsonian.
you will see things that the guys that have the cheap crap cant.
you will also have a crapload more light gathering than any small lens telescope can hope to have, giving you better star views and even seeing color very well.
http://www.telescope.com/control/product/~category_id=dobsonians/~pcategory=telescopes/~product_id=08943 [telescope.com] is a PERECT beginners telescope. it works fantastic and does not have the crapload of problems and poor viewing that anythign smaller would have.
Also if it can be bought from walmart or radio shack or even elder beerman, it's crap. do not buy it.
I have one of those and the 12" big brother to it. the 8" I loan out all the time to people interested in astronomy and they freak out when they look at saturn and see the rings seperated from the planet unlike a lesser scope can do.
the only drawback is a 8" scope can BLIND YOU if you observe the moon without filters.
Re: (Score:2, Funny)
Dont get a crappy scope.
you will see things that the guys that have the cheap crap cant.
you will also have a crapload more light gathering
it works fantastic and does not have the crapload of problems and poor viewing that anythign smaller would have.
Also if it can be bought from walmart or radio shack or even elder beerman, it's crap.
You seem to have a "crap" fetish. 2 girls 1 reflector?
Re: (Score:2)
Re: (Score:2)
And also join your local astronomy club. Very important. You'll learn more that way and have. And if you can't afford the scope, buy some decent 10x50 binoculars. (Garrett Optical makes decent ones and yes, just use the ones you have if you have some. And yes, we could argue the numbers all day, feel free to use any binoculars you want. Google "binocular astronomy" for tips.) Download Stellarium and/or Cartes du Ciel to see what is in the sky.
Aside from light pollution, this is clearly the second golden
Re: (Score:2)
And he was kidding about the moon blinding you w/o filters. ITs brightness is a surprise, but you'll be able to see afterwards.
He may have been kidding, but I thought I had done just that [slashdot.org].
Re:If you want ot get in the hobby. (Score:4, Informative)
the only drawback is a 8" scope can BLIND YOU if you observe the moon without filters.
It didn't blind me when I looked at the moon through the Amherst College 18" refractor [wikipedia.org] but it sure didn't feel good. I had a flashing disk of light in my field of view for about 5 minutes after. I wish the instructor had been a little more aware of the danger.
Re: (Score:2)
He looked at the Sun through his telescope without any filter. It put permanent spots in his vision.
Do not try this at home. In fact, only try this after sunset but before sunrise no matter where you are.
Re: (Score:2, Interesting)
The price of these telescopes is simply amazing. For a little less than $400 (I assume you have to add shipping and other stuff) you can get http://www.telescope.com/control/product/~category_id=classicdobs/~pcategory=classicdobs/~product_id=08943 [telescope.com] that 8" dobsonian you mentioned. I only went there because of your link and the NOVA/PBS show I watched on home-built astronomy. Basically you can buy a really decent telescope for about the same price as you can build your own, so if just getting started (like I
Re: (Score:3, Informative)
Buy some decent binoculars or just use the ones you have around the house. You'll start enjoying them now as opposed to waiting until save up the $400. I started with a telescope even though many people recommend binoculars for beginners. I think I use my binoculars now just because it is so easy. Shoot, I've even gone outside between innings of watching the Red Sox on TV! (And yes, I'm aware of dark adap
Re: (Score:2)
But be sure to have a tripod for them, or at least something firm to use as a stand. You'll be able to see the four Galilean moons of Jupiter quite easily with a tripod, but you'll struggle to hold the binoculars steadily enough just by hand.
Re: (Score:2)
Yes! What he said! I agree! Almost...
A reclining beach chair with arms goes a long way and costs less than binoculars. A long stick can also be used along with the chair to add stability.
I personally use image stabilized binoculars, but these can be expensive.
Re: (Score:2)
You'll be able to see the four Galilean moons of Jupiter quite easily with a tripod, but you'll struggle to hold the binoculars steadily enough just by hand.
Eh, I have no problem seeing the moons just holding the binoculars by hand unless Jupiter is very high in the sky.
A tripod certainly doesn't hurt though.
Re: (Score:2)
My goal is to see all of the Messier objects with them.
That's a cool goal. I've always thought it was really funny how what started as a "List of stuff I don't give a damn about (because they're not comets)" has essentially become "List of cool stuff for an amateur to look at."
Re: (Score:2)
Even a good pair of binoculars will show a significant chromatic abberation with the point (or near point) sources of stars and planets. You are still better off investing in a reasonably priced reflector.
Re: (Score:2)
Chromatic aberration is highly over rated in my book. Yes, a reflector will have none, that's why I own two. Aside from just looking at the moons of Jupiter, binoculars really aren't made for planets. Nor do I think they are made for individual stars, or even doubles.
When I use mine I'm hunting clusters, open clusters in particular. Or nebula, or galaxies.
I've seen the Helix, the Veil, the North America and the nearby dark nebula Le Gentil 3, I've seen countless galaxies. I've never once cared about chr
Re: (Score:3, Interesting)
I have to tell a story on myself. I borrowed a 4" telescope from my college, and set out to look at various celestial wonders. Everything was fine until after looking at the moon (and having tried both eyes), I was blind! (Or so I thought). I stumbled into the house, but strangely, I could see. I went back outside, and I couldn't see anything. I finally figured out that the moon's image was bright enough to stimulate my cones and at th
Re: (Score:3, Interesting)
I get a very good view of Saturn with my old 5" Newtonian. Can't make out the Cassini division, but the rings as separate from the planet are perfectly clear.
Re: (Score:2)
the only drawback is a 8" scope can BLIND YOU if you observe the moon without filters.
Do you mean permanent blindness or just an after-image?
if permanent, do you have any kind of citation for that? I'm an astronomer, and I've only ever heard of neutral density filters being needed for comfort, not safety. For the moon - the Sun does of course need suitable filters even with the naked eye.
Observing the moon without filters can be slightly eye-straining through larger scopes, true, and it does cause an after-image which fades in a couple of minutes.
Hmm, google has nothing about viewing t
Re: (Score:2)
As an astronomer, perhaps you could do me a favor. Do you know of a site that predicts conjunctions of Jupiter's Galilean satellites from Earth's perspective? I'd like to know when those four moons are _very_ close together, and preferably not in front of or behind Jupiter as seen from Earth. I know that the inner three are in a binary 1:2:4 rumba, but the fourth one (Callisto) doesn't like to dance.
If nothing else, are the Jupiter-centric Keplerian elements published anywhere? Thank you in advance.
Re: (Score:2)
That would certainly make for a nice photo.
I'll do a little digging to see if I can find a better solution and will post it if I find one.
Re: (Score:2)
Do you know of a site that predicts conjunctions of Jupiter's Galilean satellites from Earth's perspective?
Sky and Telescope has a Javascript utility [skyandtelescope.com].
JPL's Horizons [nasa.gov] on line system includes major satellites and will also provide orbital elements.
The USNO Nautical almanac also has this information if you want it in print.
Re: (Score:2)
Oh, yes, and Starry Night [starrynightstore.com] will also do this. That might be best if you just want to do amateur astronomy.
I am sure that there are lots of other choices out there, but these are what come to mind right now.
Re: (Score:2)
I'd like to know when those four moons are _very_ close together, and preferably not in front of or behind Jupiter as seen from Earth.
Never. The inner 3 are a Laplace relationship [arxiv.org], and are never close together. So, among other implications, the arrangement shown at the end of 2001 A Space Odyssey cannot happen.
I highly recommend Murrary and Dermott [amazon.com] if you are interested in the physics of this.
Re: (Score:2)
Re: (Score:3, Informative)
Dont get a crappy scope. it will simply discourage you.
Yes, it is hard to do VLBI with a telescope that is less than 5 meters in diameter. Also, you will need a good clock. VLBI has been done with Cesium or Rubidium standards, but I would strongly recommend that you pick up one of the excellent Russian masers [qtmrussia.com]. They will easily fit in your garage.
More info for IYA2009 (Score:3, Informative)
For more information, the website for all of the events in the International Year of Astronomy is here. [astronomy2009.org] It really is amazing what you can see when you get away from light pollution.
Re:More info for IYA2009 (Score:5, Informative)
Here are some events to look at this year:
http://www.seasky.org/astronomy/astronomy_calendar_2009.html [seasky.org]
Most can be seen with a simple pair of binoculars. Probably better off with those than with the $100 wal-mart telescope.
And back in the day, there used to be a daily email service with things to look at every night. Unfortunately, I can't find it now...
Re: (Score:2, Informative)
Stop calling the man by his first name (Score:3, Funny)
Have some respect and call him Galilei. Do people say "Albert's theory of relativity"?
Why? (Score:2)
Why would anyone find a family name more respectful than a personal name? If your name is Joe Brown, and people start referring to your work as done by "one of the browns", it's hardly a personal boost.
Anyway, when people mispronounce your surname, it's definitely going to be unflattering. I can see that happening a lot, with Galilei.
Re:Stop calling the man by his first name (Score:5, Interesting)
Interesting.
They [google.com] say:
Re: (Score:1)
Interesting. They [google.com] say:
Who says Leonardo unless they are talking about a ninja turtle? Isn't it DaVinci in common usage?
Re: (Score:1)
My contribution to the (Score:4, Informative)
My contribution to the IYA2009 is two fold.
First, I'll be speaking at least twice this year on astronomy to the public. Once at my local library, next week actually on the Winter Constellation, and then again this summer at the local Audubon Society on Binocular Astronomy. Places like these are hungry for smart people like us to talk to the public about our passion.
The second is that I've vowed to get out and do more public observing. This is where you setup your telescope in a busy place, like in a square downtown, and exhort the public to "Come see the Moon!" You can read about one of my adventures last year at http://notthepainter.com/2008/07/come-see-the-moon/ [notthepainter.com] . You can even do outreach to your friends, I've auctioned off star parties at a charity auction, and I brought my telescope to Thanksgiving dinner!
The point is, this is the year that you, the astronomer, should try and make a difference. (Oh, and for those who think you need to be super experienced to do it, you don't, I've been doing this almost 2 years now, hmm, maybe 3, I've been having so much fun I forget.)
If nothing else... (Score:3, Insightful)
Re: (Score:2)
Exercising such coordination is hardly needed, as this has been done pretty routinely for nearly forty years.
Galileo Thinks Your Gear Sucks (Score:2, Funny)
Considering he gave up his sight to use the dinky little thing he owned, the fact that he'd only give up his right arm doesn't say much about your telescope.
Revolving around us? (Score:1)
Right Arm or Left Nut? (Score:1)
I RTFA and the summary states he would give his right arm. The article seems to say he would have given his left nut. I'm confused here.
I thought there's not supposed to be conflicting information on the internet.
The real reason for combining telescopes (Score:1)
Terrible Idea (Score:1)
Earth's Radio Telescopes Combining Forces (Score:1)
Not exactly a planet-sized radio telescope (Score:5, Interesting)
While the resolution of a large array can be similar to one gigantic dish, this does not mean it is as sensitive. No matter how spread the array, it is (at best) only as sensitive as the sum of its individual elements. What is nice though is that as some sites rotate out of the array, others can be brought online, which allows for continuous monitoring of a single patch of space. Even a giant array in the desert like the VLA [nrao.edu] is not capable of performing this feat since it is still just one point as far as the planet is concerned.
Mal-2
Re: (Score:2)
I beg to differ - it is the size of the planet, it just has some holes in it !
Backyard VLA (Score:2)
Some years ago I ran into a site to combine a large # of backyard radio telescopes into the largest VLA on the planet. I can't find it on the web any more which leads me to believe it didn't work out.
However, it is an interesting idea.
Does any one have a current link or know what happened?
Re: (Score:2)
Do you mean the GMRT [tifr.res.in] in India ?
It's operational [tifr.res.in].
Sure, Galileo gets all the attention and credit! (Score:4, Interesting)
The Center of the Universe (Score:2)
... helping to prove that the universe doesn't revolve around us.
Ah, but it does - it is just a matter of choosing your coordinate system.
Re: (Score:2)
principles of syntheic aperture (Score:3, Informative)
Re: (Score:2)
While you're absolutely correct, I would point out that you can get some useful data from intensity interferometry in the optical wavelengths. The mechanics of the process means that you get the square magnitude of the mutual coherence, which means a direct reconstruction of an image is impossible. But, this is a problem faced in other areas, particularly x-ray crystallography, so there are ways to reconstruct the image based on some known information about the scene. In imaging a star or planet, you kno
Re: (Score:2)
The real trouble with intensity interferometry is that you have only the square root of the sensitivity of phase interferometry, so typically you can only detect the very brightest sources.
The Narrabi [wikipedia.org] intensity interferometer, for example, used 10 meter optical dishes [nasa.gov] IIRC and could only detect the brightest 32 stars, so it was substantially less sensitive to light than the human eye. (Great angular resolution, but very insensitive.)
Re: (Score:2)
Absolutely right, although we have some advantages now that we didn't when the Narrabi experiments were run. First, detectors have improved: higher response speed and higher quantum efficiency do make things easier. This might be able to double the sensitivity at most though (I'd have to find hard data and run numbers, and I need to do other things today).
However, there are some other ways to improve the SNR. By using a splitting up the incoming light into multiple spectral bands and correlating the sign
Re: (Score:2)
Good post - you raise some points that I have wondered about.
Back when the Narrabi interferometer was in use, even a cooled photomultiplier might have a quantum efficiency of 10 or maybe 20%. Now, with CCDs, 80 % is possible, so that is a factor of 4 or so right there.
BUT, now there are all of these big light buckets looking for Cherenkov radiation from cosmic rays [nasa.gov], and (as you point out) computer resources are dirt cheap, so the question I would have is, could you do useful "parasitic" observations using,
Re: (Score:2)
Interesting, thanks for pointing out that article. Bandwidth synthesis actually looks like something I was about to start looking for, although I was hoping to use the varying frequency to induce phase diversity to help with phase-reconstruction methods.
Also, I know there have been a few papers written on using Cherenkov arrays (sorry, don't have my resources with me), although I'm not sure if any have actually been implemented. In the same vein, I've idly wondered if the big mirror-farm style solar plant
Re: (Score:2)
The optical SETI people are interested in using solar arrays at night [cwru.edu] (as light buckets), and at least some of them can be pointed accurately enough to point at a given star, so I think that the answer to your question is yes. This is discussed further in SETI 2010.
Re:not higher magnification ? (Score:4, Informative)
Really, it all comes down to what's known as Fourier optics. In the far field from a distant source, the mutual coherence (cross-correlation) of the light is the 2-D Fourier transform of the original image, through the van Cittert-Zernike theorem. If you're at all familiar with FTs, the components further from the origin correspond to the highest frequencies. So a larger telescope (essentially an analog IFT in this way of thinking, simulating propogating the wave pattern back to the source) is able to cross-correlate the light between the two furthest points on the aperture, allowing you to take into account higher frequency ranges, and get higher resolution.(1)
Therefore, there are two reasons for increasing a telescopes size:
1. You collect more photons, improving signal quality
2. You increase the resolution as you're able to gather more components of the Fourier band. This is limited on Earth due to the seeing effects of the atmosphere, unless you start dealing with adaptive optics.
This kind of work, using multiple apertures to synthesize a much larger one, gets you the second result without much help on the first, but at a much cheaper price. By manually taking the cross-correlations(2), you can get a map of the Fourier field of the image and computationally compute the original image from it.
(1) This is also why blockages over parts of the aperture don't have an obvious effect.
(2) which is why this only works with radio, optical frequencies are much too high to record the actual waveform, so physical beam transmission is necessary over carefully controlled (to 10 nanometers) path lengths.
Re:not higher magnification ? (Score:5, Informative)
Yes, this aperture synthesis is done to increase resolution, not sensitivity. In fact, all known radio sources have a finite size for VLBI (because of the inverse compton effect), and so source brightness starts to decline as baselines go towards two Earth radii. While VLBI has been done from space, if we placed a VLBI antenna on (say) Mars, there would almost certainly be no source visible on Earth-Mars baselines for any obtainable antenna size.