Worlds Largest Telescope?

AndersBrownworth writes "With a unique take on "Distributed Computing", the PhotonStar Project aims to search for laser transmissions from extra terrestrial life by harnessing amateur astronomers who have an optical telescope with a laser detector, a GPS and a computer with a net connection. I think it would be interesting to get a large number of computer controlled optical telescopes together that have GPS and CCD capabilities and build the world's largest optical telescope. The concept wouldn't be much different from New Mexico's VLA Radio Telescope. Given the falling prices of computer controlled optical telescopes, a project like this might not be far off."

WARNING!

[docbrown42]

DO NOT LOOK INTO LASER BEAM (from an alien race) WITH REMAINING EYE!

Yes, it WOULD be different

[wowbagger]

quoth the submitter:

The concept wouldn't be much different from New Mexico's VLA Radio Telescope.

Actually, it would be. The VLA works because all the signals are brought together and correlated - they are carefully time synced (to the nanosecond) and then combined.

The same trick in the optical domain is called interferometry, and requires that the actual LIGHT from each 'scope be brought together - you need not only the brightness (which a CCD would record), but the phase and polarization of the signal (which a CCD won't record).

So you cannot use an array of 'scopes world-wide to create a virtual array.

What you can do, and what optical SETI is all about, is to have each scope looking at a different star (or star field) at each time.

In a way, comparing the two is like comparing a 64-way NUMA cluster to a Beowulf cluster - one will work well with one big program of many threads sharing data (NUMA/interferometry), and one will work well with many small independent programs (Beowulf/optical SETI).

Re:virtual array for pulse detection does make sen

[wowbagger]

And had you READ my POST, you would have seen that I was not addressing the article, but rather the poster's wild-assed and incorrect statement about making a VLA from all those amateur scopes.

Re:Yes, it WOULD be different

[lirkbald]

Right. I would have made this comment if it hadn't already been here. I'd also like to mention the CHARA project [gsu.edu], located at Mount Wilson Observatory. This *is* the equivalent of the VLA, but in the optical domain.

I'm no astronomer, but I saw it when I went up there for a tour, and it looks very cool. Really fascinating that, in spite of it's close proximity to the 'light pollution' of Los Angeles, Mount Wilson is still doing Real Astronomy.

Re:Yes, it WOULD be different

[Ole Marggraf]

You should also mention ESO's [eso.org] VLTI [eso.org] here, the Very Large Telescope [eso.org] Interferometer at Mt. Paranal, which is just taking its first shots...

Don't forget about the Square Kilometer Array

[nomel]

in Australia.

Site are here [skatelescope.org], here [man.ac.uk], and here [csiro.au].

Some technical details are here [csiro.au].

From the later,
The antenna has "...a proposed collecting area at low frequencies (150 MHz to 1.5 GHz) of roughly 1 km2 (or 106 m2) - the equivalent of more than one hundred dishes of 100 m diameter. In contrast, the largest and most sensitive existing array has a physical area approximately one hundred times smaller than this."

That's pretty big. :)

Re:Don't forget about the Square Kilometer Array

[astroboscope]

in Australia.

Just to clarify, the SKA isn't built yet, and AFAIK a site has not yet been chosen. I know that at least the U.S/Mexico, Australia, and China would each like to have it in their backyard.

For comparison, 1 sq. km = apx. 100 million amateur telescopes. Doable? In a properly enthusiastic world, yes, but not (yet) with CCDs, because they're just too darn expensive. So how about 2.5 billion digital cameras/webcams pointing up? ;-)

For a fairer comparison, the next rilly big optical telesco

This is a very cool idea

[MousePotato]

I know that the idea of trying to use this as a vlt type thing is kind of moot(not an astronomer just a hobbyist mind you) but it does provide some interesting possibilities.

Huge catalogs could be created and used for comparisons that could lead to additional comet discoveries for example. If the system is using gps it is possible to have some time sync though not to the hyper accurate clocks that vlts use. I think it would still be useful information, especially to the amateur astronomy crowd.

I wonder wh

1 foot accuracy of lat-long+altitude required.

[Vellmont]

The project requires you know the position of your telescope to within 1 foot in all lattitude, longitude, and altitude. (Timing is critical and you need to know if a pulse arrived within a nanosecond of each other. 1 nanosecond is about 1 foot.) Standard GPS gives you somewhere around 15-30 foot accuracy at best. How are they planning on getting the needed positional accuracy if GPS doesn't provide it?

I do remember quite a while ago NASA developing some statistical method of getting extremely accurate GPS positional data from taking masses of GPS data over many weeks (IIRC it was accurate to something like centimeters). Unfortunately it was just a newspaper article, so the details were lacking. Could this be how they plan on getting the accurate positional data? Anyone know more about this?

Re:1 foot accuracy of lat-long+altitude required.

[sploxx]

Yes and enough statistics could indeed lead to a big interferometry telescope, other than the post above suggests?
I mean, if some photons with a slight time difference (1nns) get onto two CCDs in two different parts of the world and they are only read at a rate of 10Hz, there should be information in the jitter of signal that could be used to reconstruct timing by collecting enough data. Or is that impossible?
I'm not making a statement here, rather asking people in this business these questions.

Re:1 foot accuracy of lat-long+altitude required.

[spuke4000]

I'm really not an expert on this, but as I understand it getting *very* accurate lat/long/alt measurements with a GPS is just a matter of waiting. Each measurement is out +/- 10 meters (approx.), but if you average a large number of these measurements you can get a very precise position. This takes several weeks, but it shouldn't be a problem in this case.

Again, I could just be talking out of my ass here, so if anyone has more experience feel free to correct me.

Re:1 foot accuracy of lat-long+altitude required.

[jstott]

I do remember quite a while ago NASA developing some statistical method of getting extremely accurate GPS positional data from taking masses of GPS data over many weeks (IIRC it was accurate to something like centimeters). Unfortunately it was just a newspaper article, so the details were lacking. Could this be how they plan on getting the accurate positional data? Anyone know more about this?

This goes back to the days when the military was still limiting the accuracy of civilian GPS units. They did th

A good way of ruling out false positives

[Doctor Fishboy]

This is an interesting method, because it really irons out systematic effects due to the local patch of atmosphere above any one telescope.

The atmospheric turbulence causes 'scintillation' of starlight (a rapid, small variation in stellar brightness), and for the very short exposures they're proposing, it'd be difficult with just one telescope to pull out an ET laser modulated signal from the atmospheric generated scintillation.

Distributed telescopes with accurate positions would pull out a laser signal very easily.

Cute trick.

Dr Fish

Re:A good way of ruling out false positives

[MousePotato]

Here is the thing that this leaves me wondering about optical seti and ET lasers; wouldn't lasers be red shifted so far over by the time the light would actually arrive here that they would appear as microwaves instead of lasers thus negating the optical requirement? You should be able to pick that up with radio telescopes instead of optical one no?

Just curious. I don't know and I am not a physicist or astronomer. If someone could explain this to me I sure would appreciate it.

Re:A good way of ruling out false positives

[Doctor Fishboy]

For stars within our galaxy, the largest difference in line of sight velocity between a star with an ET laser system and our Solar system is about 400km/s, not enough to cause a red/blue shift from the visible to the infra-red or radio.

Red-shifts *could* be important for looking at more distant galaxies, but looking for ET signals from other galaxies is ruled out, partially because the inverse-square law makes the laser beem too dilute over those distances, and the intergalactic medium would cause very sli

Re:Great asset to the perv market...

[astroboscope]

focus all the telescopes on your neighbors window and watch her get undressed from every angle!

One telescope looking thru the window and 9999 looking at the walls of the house?! Your request for telescope time is denied!

A couple of unmentioned problems

[astroboscope]

The proposed system relies on the simultaneity of pulse arrival times to distinguish real pulses from noise photons. The poorer the synchronization, the poorer the signal to noise ratio.

Unfortunately the refractive index of the atmosphere is not uniform, and turbulence makes it vary fairly quickly and unpredictably. In other words, the same effect that makes stars twinkle should scatter the arrival times by an amount that I'm guessing is much more than a nanosecond. So distributed small telescopes are

Um. How about this probability equation

[A55M0NKEY]

P( Amateur Astronomer ) * P( Has Optical Telescope ) * P( Has Lazer Detector ) * P( Has GPS ) * P( Has Computer With Net Connection ) * P( Has Heard of this Project ) * 6 billion people on planet earth = 4