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."

Comments

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: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, 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 VLTI here, the Very Large Telescope 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, here, and here.

Some technical details are here.

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. :)

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.

[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.

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

[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 slight smearing of the beam signal, and you'd have to use a much lower transmission rate to make a digital signal keep intact over the distance.

In addition, even though a laser beam is 'beamed', optical diffraction causes a fundamental expansion of the beam that, over long enough distances, dilute the light down to noise levels - we couldn't see a laser signal for the light of other stars in the galaxy.

ET laser searches are restricted to stars in our galaxy.

Dr Fish

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