A friend has been thinking that if we could bounce a laser off the reflectometers left behind during the Apollo missions, it would go a long way toward proving the landings.

The question is, would it be feasible to get thousands of people during next month's eclipse to try to bounce small lasers simultaneously and would the effects of thousands of small devices be additive and perhaps visible?

Thanks.

Would the dust in the lower atmosphere scatter the light from those small lasers? You'd also have to have pretty high levels of precision to hit those reflectors.

Here is a link that explains how the lunar distance is measured with lasers. Very interesting.

http://sunearth.gsfc.nasa.gov/eclips...olloLaser.html

Thinking that atmospheric diffraction and beam width at this distance would make precision less important and with thousands of participants odds of enough photons hitting would improve dramatically.

You're right about the width. The link I found above says the beam is 4 miles wide at the distance of the moon!!

Maybe if some of these people actually observed the measurements being made?

This is all about participation. Pointing errors and power problems are eliminated with sheer numbers. Envision 1 million people doing this across North America at the same time. The totallity of the eclipse lasts less than 30 minutes. This is all about perfect geometry (full moon at nearly mid-night), perfect lighting conditions (it's a total eclipse...so we are talking dark), and lots and lots of lasers hitting the four targets from thousands (millions) of different angles at the same time.

Here is what is said about it in the link I cited above:

"The reflectors are too small to be seen from the Earth, so even when the beam is precisely aligned in the telescope, actually hitting a lunar retroreflector array is technically challenging."

An then

"Once the laser beam hits a reflector, scientists at the ranging observatories use extremely sensitive filtering and amplification equipment to detect the returning signal, which is far too weak to be seen with the human eye. Even under good atmospheric conditions, only one photon is received every few seconds."

I would be concerned that - given these difficulties - attempting this experiment with millions of contributors across the United States would only produce a result that would appear to support the contentions of the Lunar Conspiracy Theorists.

By the way - welcome to the board getsoutalive and francis7.

The goal here is to get a reflection...we do not want to visualize the actual reflectors. Keep in mind...the result may not be readily apparent with the naked eye, but using a moderately sized telescope with a CCD camera doing a long exposure, you will (in my opinion) get a reflection from all four stations.

Welcome to the board getsoutalive and francis7, always good discussion here.

I don't think numbers alone will get very far in producing anything visible. As dgruss23 pointed out, hitting the reflectors themselves will be pretty challenging. Beyond that, you have to consider where the reflection will actually end up. A beam pointed at the moon on the horizon hitting a flat surface won't ever return to earth so most of the light would seem to be non-additive. The alternate case of light being reflected directly back to where it came, which I seem to recall is an interesting property of the moon's surface, produces the same results. All of the beams would return to their origin, but much to faint to notice. Laser light is also coherent which means it won't spread out much as it travels further from its source. That would require pretty accurate pointing by all 1 million people whether they hit the reflectors or not.

Rich

Here is another link. They use a 30" telescope and the observations take several hours so the total phase of the eclipse may be too short for what you're advocating.

http://www.lpi.usra.edu/expmoon/Apol...ents_LRRR.html

Don't you all remember? Massive numbers of people aiming lasers at the moon has already been attempted, with no detectable effect. :-)

http://www.usatoday.com/tech/2002/01...t-interest.htm

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Rich,
Thanks for the welcome. The interesting quality of these relectors (LRRR's) is that they are made with cube-edge prisms, which reflect light back at exactly the same angle it comes in on. After that, it becomes a problem in quantuum probability...get enough photons on target, and they all come back (the ones that hit). There are four LRRR's on the moon (3 American left by Apollo and one Russian/French) that are VERY widely spaced. This is not a question of "will it work" but more of a question of "is it worth trying". I have already consulted an optical engineer who is a GIANT in the world of American Amatuer Astronomy, and his answer to the second question is a huge "YES". The only problem is one of participation....you in?

I guess it depends upon your goal. If you're goal is to see if you can get a measurable result then I think it is a neat idea. It would be interesting to see how many photons could be detected if thousands or millions simulaneously pointed their lasers at the moon . What about the green lasers.

But if your goal is to convince lunar conspiracy theorists of anything - which is what I took the original post to be about, then I don't think it would generate anything more compelling than what the ongoing lunar ranging experiments have already accomplished.

dgruss23,
You got it...we are looking for results...if it shuts up the lunar conspiracy loonies...so much the better. From a physics perspective...with the right receiver and enough participants, this should work. To address the last experiment that failed...I propose this to be done during a lunar eclipse, which presents some very interesting opportunities regarding the relevant geometry (full moon at zenith) which is completely dark except for light refracted through our atmosphere. Yes, green lasers would work at least a thousand times better because our atmosphere refracts blue and green and absorbs red, but the availability of red lasers FAR exceeds green. Also, I propose to measure results using telescopes and CCD cameras. The QE (quantum efficiency) of some consumer camera's approach the ability to detect individual photons. If you end up seeing it with the naked eye, I would not complain.

Welcome, Newbies!

Interesting idea, but doomed to failure, I'm afraid.

Even if all the technical problems could be overcome, and millions of folks aimed their laser pointers at just the right spot at just the right time, any reflection we see would be quickly ridiculed by the HBs as "bouncing off a shiny rock or something else natural" rather than a reflector.

Prove it's a reflector and they'll say it was landed there last month by a robotic probe.

Prove it's an old reflector and they'll say it was landed there in 1969 by a robotic probe.

HBs are classic examples of, "My mind's made up. Don't confuse me with the facts."

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Jim,
Could care less about the HB's (whatever those are, but I think I can come to an accurate assumption). The LRRR's are mapped with an extreme amount of accuracy as well as having been there for a historical amount of time. The point here is to do something that is extremely unusual, using the reach of the Internet to do it, and having (hopefully) some very cool results afterwards.

I've been looking through some research sites of the locations actually doing these lunar ranging studies and another question comes to mind. How many of the typical red lasers would be needed to equal the output of one of the lasers utilized by the research groups? When you look at the technical aspects of accurately pointing the laser, I think you'd be hard pressed to get enough people to produce as many measurable photons as the single lasers utilized at the research sites. Heres another link:

http://almagest.as.utexas.edu/~rlr/dda.html

Note that they have to do some filtering to even locate these laser photons.

Just using intuition on this, but...

Assuming that the laser light spreads out a few km heading to the moon as well as on the return...

Since the spread out returned light only reflects back to within a few km of originator, then only light from the lasers within a few km of you will actually bounce back to you. You are completely blind to reflections of all other of Earth's lasers by the reflector. So who cares if there are a billion laser pointed at the reflector. It only sends you light from those near your vicinity.

However, a iny fraction of light from each of the other billions of pointers will come back at you via diffuse reflection on lunar soil.

So... I'm willing to predict that:
1) The diffuse lunar soil reflection is not enough to be seen by you
and
2) The mirrored reflection that bounced to you is even dimmer.

What eclipse?

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This one. Coming next month.

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I think this suggestion takes the definition of light pollution to a whole new level. :wink:

Oh, right. Will I be able to see it in the UK?

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Yes (scroll down). Though it looks as if you won't be able to see it for long.

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Okay, so suppose you gather 1000 friends in one spot and each has half a dozen laser pointers, so the 2 km diameter return is in the same area. (Assuming the beam spreads to 2 km diam over the distance to the moon, then the return beam starts with the reflector diameter and spreads from there. Thus ~2 km diameter on return.)

You still have the problem of aiming the 6000 lasers precisely enough to hit one of the 4 reflectors. Any not hitting the reflectors will hit the lunar soil, which is much less reflective.

If you could get all 6000 laser pointers to hit a reflector, could you get enough light back to detect it (either visually, or more likely with a telescope and CCD device)?

Alternately, how much reflectivity can you get from the lunar soil? I imagine 6000 2km circles non-overlapping across the whole of the visible face. Even in full lunar eclipse, I'm thinking the return on this won't be worth diddly.

So if you could get a detectable level of return from the 6000 lasers, then you have the challenge of (a) getting 6000 lasers in one area, and (b) getting them all accurately pointed at the laser reflectors, as opposed to generically at the moon, or even at "the big crater on the left".

Obviously, this was the wrong forum to post this idea...you guys are as bad as the Lunar Conspiracy nuts. The only guaranteed way this will not work is if nobody tried it. What do you have better to do the night of the eclipse? Worst case scenario: you get to watch an eclipse as opposed to trying to prove something people have been (foolishly) arguing about for over 30 years using only words. In my opinion, you are doing nothing at all to help your own cause. You are merely arguing with a bunch of idiots who believe that everything is fake and probably wear foil on their heads to block the "mind control rays". Don't fight a battle of wits against un-armed people.
You are all losing site of some very important points as well as adding a lot of garbage assumptions:
1. We are NOT interested in Laser RANGING. This is a very complicated process that involves accurately TIMING reflected PULSES over enormous distances. The folks at the McDonald Observatory don't have a problem with signal acquisition...this happens quite easily.
2. As such, we would not be sending TIMED PULSES, but rather would be using continuous wave devices.
3. Pointing is easier than you think...a laser beam with an initial width of less than 7mm would be over 7 kilometers wide when it reached the lunar surface. The return would NOT be a beam, but rather a diffraction ring over 20 kilometers wide. Now I am not going to get into a complicated explanation of quantum physics here, but the more beams you put on the reflector would not create more diffraction rings, but would reinforce the initial ring if the beams are within proximity of the returned ring. This means the diffraction ring would get bigger and brighter with every laser you add. The pointing is accomplished by aligning a laser (preferably green 532 nm), with your telescope using the finder scope holder. As it is an eclipse, you would have ample opportunity to locate, identify and align to the target area BEFORE the moon goes dark.
4. The return (if there is one) would PROBABLY (maybe not) only be visible to a CCD camera assuming a moderate (several thousand) participants.

Ultimately, you cannot say it will not work just as I cannot say it will work. All we can do is try. There are four possible outcomes:
a. No one sees anything
b. It will only be visible on long exposure CCD images taken through a telescope
c. It will be visually visible through a telescope
d. It will be naked eye visible

These are in descending order of probability. If you have nothing better to do the night of May 15 (which I suspect of most of you) unless there is a Star Trek or Battlestar Galactica marathon on the Sci Fi channel...go out at 11:30 pm EDT and check out the eclipse. If you can, shine a laser at it. Who knows what will happen? No one does.

I've pointed to 3 links that indicate a host of reasons as to why it won’t work. Assuming a single person lucks out enough to hit a reflector the beam will be 20 km in diameter upon return to earth (following quote taken from one of the links):


“Laser beams are used because they remain tightly focused for large distances. Nevertheless, there is enough dispersion of the beam that it is about 7 kilometers in diameter when it reaches the Moon and 20 kilometers in diameter when it returns to Earth. Because of this very weak signal, observations are made for several hours at a time.”
Then this is what they go through to detect the photons:

“The MLRS laser pulse contains 3 x 1017 photons. In lunar mode only a few return to pass through the receive system. A typical lunar return rate is a few signal photons per minute. We use single photo-electron detection devices and as large an optical throughput in the green as possible. With the large number of noise sources, it is impossible to identify a returning photon from the moon without filtering, both physical and mathematical. Range gating provides a temporal filter. A pin-hole aperture provides a spatial filter. A spectral filter allows only the proper color photons to pass through to the receive system. The spectral filter must be as narrow as possible in wavelength to eliminate as many noise photons as possible, transmitting as many proper photons as possible. These requirements change with lunar phase and sky conditions.”


If you have the equipment at your disposal to do all this then great. Go for it. I’ll borrow a laser from someone and shine it through a telescope. Then you can do all the stuff listed in the above paragraph and come back and tell us what you found. But the people on this board look hard at the evidence – and based upon the equipment and methods used to measure a scant several photons per minute and other points politely made by other people on this thread, you’re looking at option “a” from your list.

As I said before, when you get option "a" for a result you'll have only added support to the conspiracy theorists position. Can you picture it. Thousands of people shooting lasers at the Moon simultaneously. Media coverage and lots of conspiracy theorists watching. Since there will be nothing to see the conspiracy theorists will start doing cartwheels (or whatever they do for fun) over your telescope.

As opposed to it working and you not having anything to argue about anymore.....but there be no fun in that....right? Not one of the links you posted can rule this out AT ALL. It has never been tried:
1. during a lunar eclipse
2. using the correct wavelenght laser (green)
3. been aimed at a single LRRR
4. had broad participation
5. done with telescopes and CCD cameras looking for results

But god forbid anyone should attempt anything that could possibly fail and give a bunch of morons (they have already proven themselves that) more ammo to continue to believe no one landed on the moon even though the McDonald Observatory performs laser rangefinding off the moon every day. Like I said...this was definately the wrong forum for this. Arguements are won with proof, not further arguements. This is apparently someplace to merely argue. Proving anything is obviously irrelevant here.

Lunar eclipse: doesn’t last long enough.

Using the correct wavelength laser (green): They’re more expensive and thus hard to come by - as you noted earlier in the thread.

Been aimed at a single LRRR: Do you have a way to do that? A 7 km diameter laser beam (at the moon’s distance) doesn’t guarantee high precision when you’re talking about an object the size of the Moon.

Had broad participation: If you had broad participation with the equipment needed to accurately target a reflector this would mean something. A million people with inadequate equipment for the task and no clue what they are doing will not be any help.

Done with telescopes and CCD cameras looking for the results: Have you looked at the list of filter/analysis steps required to locate these few photons per minute?

Personally, I could care less about the lunar conspiracy theorists myself. They’re irrelevant, but the ORIGINAL POST said this:

In terms of proving the landings it is safe to say that you will accomplish absolutely nothing with this idea. A few photons gathered in a CCD isn't going to convince those people. Instead you’ll create a nice show which will not deliver anything promised or even hoped for.

However, you seem to want to do this for scientific reasons. I say that is great, but you haven’t yet indicated how you plan to pull it off. As you say the McDonald Observatory does it all the time … so why aren’t you interested in the lessons learned from their efforts?

~ You haven’t explained how you will deal with the noise sources.
~ Do you have the Range gating, pin hole aperature, and spectral filter.
~ Are you prepared to deal with the sky conditions because they say the requirements change with sky conditions.

I’m sure that if you explained how you’re going to handle all of that you would get a bunch of people from this board interested in what you want to do. I think it would be really neat if amateur astronomers could perform lunar ranging measurements.

Here’s an idea, If you have the equipment, take a trip to within 20 km of the McDonald Observatory and see if you can confirm detection of the photons.

You need to read a few more threads in the different forums before you decide if that is true. I thought we were DISCUSSING reasons why it will or will not work. I haven’t seen this as combative arguing. Actually, I think people have been trying to give you advice on how to turn the idea into something feasible. I posted those links so you would be aware of how the professionals do it. I would think that would be helpful information in figuring out how you’re going to do this.

Francis7,

Are you going to give this a try? Just curious.

Yes...we are going to give it a go weather permitting. If you are interested in the telescope proceedure we have put together, shoot an e-mail to my yahoo account.