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Interestingly, one thing we DID do that's observable from earth is to put an array of retroreflectors onto the moon, so that we can bounce a laser off of it. h

Interestingly, one thing we DID do that's observable from earth is to put an array of retroreflectors onto the moon, so that we can bounce a laser off of it. https://secure.wikimedia.org/wikipedia/en/wiki/Lunar_Laser_Ranging_experiment https://secure.wikimedia.org/wikipedia/en/wiki/Lunar_Laser_R... My sample size of moon landing skeptics (1) didn't dispute that we've been to the moon, he just didn't believe that we did it in 1969, but if you do run into a skeptic this is pretty good evidence that we made it there eventually, or at least requires the conspiracy to be much more involved =).

ck2 16y ago
But so few photons come back, sometimes I wonder if the measurements are within a margin of error or reflection off atmosphere. Mythbusters did a good episode on the moon skeptics though.
- gchpaco 16y ago
  You can measure the distance by modulating the laser and checking how time shifted the reflection is. The moon is pretty close for light but it's measurable.
- gus_massa 16y ago
  If someone say honestly that they receive the photons coming from the moon, then they must get a number of photons that is bigger than the error margin, preferably a few times bigger than the error margin. If it is smaller they can't be sure that it is not some noise. The data about these measures is hard to find. But after some googling the best data I could find are in http://physics.ucsd.edu/~tmurphy/apollo/highlights.html http://physics.ucsd.edu/~tmurphy/apollo/highlights.html . It it possible to make some estimations from the graphs. There are three sets of three graphs. They are very similar, so let's see only the first one. In the first graph there is a dark line in the center that shows that there are more photons coming at the expected time, than before or after that time. The signal is easy to see, but it is difficult to get any numerical values from this graph. From the second graph it is possible to read some numerical values. Each bar shows the number of photons that arrive in a 100 ps interval. They have probably a Poisson distribution, but for simplicity let's approximate that by a Normal distribution. Before the peak, there are approximately 10 +/- 10 photons coming every 100 ps. (These values are estimated from the graph with a lot of zoom, I can't be very sure about them. The values seem to be scattered between 0 an 20, so I assume that the average is ~10 and the standard deviation is ~10.) These are the photons that come from others sources. So if no mirror is present in the moon, or the laser dos not have enough power, then this is the expected value during all the experiment. At the peak, there are approximately 400 photons in the same time interval. The difference between this value and the average of the first values is like 40 times the standard deviation. So it is almost impossible that they get these peaks by a random chance. For example, the probability to get a value that is bigger than 5 standard deviation is less than 1E-6, for 10 standard deviation it is less than 1E-23, and for 40 standard deviation it is almost almost 0. And they get not only one, but 8 intervals with more than 100 photons. After the peak, they get more photons than before the peak for technical problems. I see something like 20 +/- 20. Whit these numbers, the chance of a 400 photons peak is bigger, but still almost 0, but I think that the correct way to do the estimations is using the first values. The third graph is an auxiliary measure with an earth based mirror to get the dispersion caused by the system. The analysis in the web page is more elaborated. They estimate the shape of the mirror and use the data from the third graph to explain the shape of the peak.
- harshpotatoes 16y ago
  This is relevant. http://arxiv.org/pdf/0710.0890v2 http://arxiv.org/pdf/0710.0890v2 The gist of the story is: Use a large telescope to not only increase your collecting area, but focus your beam onto that surface: turn that measly 1 milliradian divergence laser into a 1 microradian divergence laser.
si2 16y ago
As a 'skeptic' I don't doubt that objects have been to the moon, but not humans. Its not possible.
bootload 16y ago
".... but if you do run into a skeptic this is pretty good evidence that we made it there eventually, or at least requires the conspiracy to be much more involved =) ..." There is another conspiracy buster. Get the skeptic to explain why the CDSCC [0] - the prime receiving station for the moon landing dish in Parkes, NSW, AUS, received the signal directly from the moon via the 3m S-band antenna during the Apollo 11 EVA? [1] [0] http://en.wikipedia.org/wiki/Canberra_Deep_Space_Communication_Complex http://en.wikipedia.org/wiki/Canberra_Deep_Space_Communicati... [1] http://www.parkes.atnf.csiro.au/news_events/apollo11/the_plan.html http://www.parkes.atnf.csiro.au/news_events/apollo11/the_pla...
- commandar 16y ago
  The kind of loon that's going to insist the entire thing was an elaborate soundstage production isn't exactly going to be swayed by claims that the signal, which they think was fake anyway, was received at a given location. The laser retroreflectors are at least observable now, which is a pretty big distinction.
- gaelian 16y ago
  Minor correction: Canberra and the CDSCC are in the ACT (Australian Capital Territory), not New South Wales. It's OK though, everyone forgets about the ACT.
  - bootload 16y ago
    "... New South Wales ..." I sourced that from wikipedia, didn't x-check that. Canberra, yeah I know that place ~ http://www.flickr.com/photos/bootload/sets/72157623926679594/ http://www.flickr.com/photos/bootload/sets/72157623926679594...
    - gaelian 16y ago
      You got it. Canberra[1], the bush capital. Come for the CDSCC, stay for the relaxed prostitution and pornography laws. 1. Despite what Wikipedia says, it's actually more commonly pronounced "Can-bra" because Australians are lazy.
quellhorst 16y ago
Image of a laser hitting a reflector on the moon: http://upload.wikimedia.org/wikipedia/commons/e/e1/Goddard_Spaceflight_Center_Laser_Ranging_Facility.jpg http://upload.wikimedia.org/wikipedia/commons/e/e1/Goddard_S...
- drusenko 16y ago
  Ah, that image is a bit deceptive. It looks like the laser is bouncing off the reflector on the moon, when in fact they are two separate lasers aiming at a spacecraft: http://www.nasa.gov/multimedia/imagegallery/image_feature_1768.html http://www.nasa.gov/multimedia/imagegallery/image_feature_17...

ck2 16y ago

But so few photons come back, sometimes I wonder if the measurements are within a margin of error or reflection off atmosphere. Mythbusters did a good episode on the moon skeptics though.

gchpaco 16y ago
You can measure the distance by modulating the laser and checking how time shifted the reflection is. The moon is pretty close for light but it's measurable.
gus_massa 16y ago
If someone say honestly that they receive the photons coming from the moon, then they must get a number of photons that is bigger than the error margin, preferably a few times bigger than the error margin. If it is smaller they can't be sure that it is not some noise. The data about these measures is hard to find. But after some googling the best data I could find are in http://physics.ucsd.edu/~tmurphy/apollo/highlights.html http://physics.ucsd.edu/~tmurphy/apollo/highlights.html . It it possible to make some estimations from the graphs. There are three sets of three graphs. They are very similar, so let's see only the first one. In the first graph there is a dark line in the center that shows that there are more photons coming at the expected time, than before or after that time. The signal is easy to see, but it is difficult to get any numerical values from this graph. From the second graph it is possible to read some numerical values. Each bar shows the number of photons that arrive in a 100 ps interval. They have probably a Poisson distribution, but for simplicity let's approximate that by a Normal distribution. Before the peak, there are approximately 10 +/- 10 photons coming every 100 ps. (These values are estimated from the graph with a lot of zoom, I can't be very sure about them. The values seem to be scattered between 0 an 20, so I assume that the average is ~10 and the standard deviation is ~10.) These are the photons that come from others sources. So if no mirror is present in the moon, or the laser dos not have enough power, then this is the expected value during all the experiment. At the peak, there are approximately 400 photons in the same time interval. The difference between this value and the average of the first values is like 40 times the standard deviation. So it is almost impossible that they get these peaks by a random chance. For example, the probability to get a value that is bigger than 5 standard deviation is less than 1E-6, for 10 standard deviation it is less than 1E-23, and for 40 standard deviation it is almost almost 0. And they get not only one, but 8 intervals with more than 100 photons. After the peak, they get more photons than before the peak for technical problems. I see something like 20 +/- 20. Whit these numbers, the chance of a 400 photons peak is bigger, but still almost 0, but I think that the correct way to do the estimations is using the first values. The third graph is an auxiliary measure with an earth based mirror to get the dispersion caused by the system. The analysis in the web page is more elaborated. They estimate the shape of the mirror and use the data from the third graph to explain the shape of the peak.
harshpotatoes 16y ago
This is relevant. http://arxiv.org/pdf/0710.0890v2 http://arxiv.org/pdf/0710.0890v2 The gist of the story is: Use a large telescope to not only increase your collecting area, but focus your beam onto that surface: turn that measly 1 milliradian divergence laser into a 1 microradian divergence laser.

si2 16y ago

As a 'skeptic' I don't doubt that objects have been to the moon, but not humans. Its not possible.

bootload 16y ago

".... but if you do run into a skeptic this is pretty good evidence that we made it there eventually, or at least requires the conspiracy to be much more involved =) ..." There is another conspiracy buster. Get the skeptic to explain why the CDSCC [0] - the prime receiving station for the moon landing dish in Parkes, NSW, AUS, received the signal directly from the moon via the 3m S-band antenna during the Apollo 11 EVA? [1] [0] http://en.wikipedia.org/wiki/Canberra_Deep_Space_Communication_Complex http://en.wikipedia.org/wiki/Canberra_Deep_Space_Communicati... [1] http://www.parkes.atnf.csiro.au/news_events/apollo11/the_plan.html http://www.parkes.atnf.csiro.au/news_events/apollo11/the_pla...

commandar 16y ago
The kind of loon that's going to insist the entire thing was an elaborate soundstage production isn't exactly going to be swayed by claims that the signal, which they think was fake anyway, was received at a given location. The laser retroreflectors are at least observable now, which is a pretty big distinction.
gaelian 16y ago
Minor correction: Canberra and the CDSCC are in the ACT (Australian Capital Territory), not New South Wales. It's OK though, everyone forgets about the ACT.
- bootload 16y ago
  "... New South Wales ..." I sourced that from wikipedia, didn't x-check that. Canberra, yeah I know that place ~ http://www.flickr.com/photos/bootload/sets/72157623926679594/ http://www.flickr.com/photos/bootload/sets/72157623926679594...
  - gaelian 16y ago
    You got it. Canberra[1], the bush capital. Come for the CDSCC, stay for the relaxed prostitution and pornography laws. 1. Despite what Wikipedia says, it's actually more commonly pronounced "Can-bra" because Australians are lazy.

quellhorst 16y ago

Image of a laser hitting a reflector on the moon: http://upload.wikimedia.org/wikipedia/commons/e/e1/Goddard_Spaceflight_Center_Laser_Ranging_Facility.jpg http://upload.wikimedia.org/wikipedia/commons/e/e1/Goddard_S...

drusenko 16y ago
Ah, that image is a bit deceptive. It looks like the laser is bouncing off the reflector on the moon, when in fact they are two separate lasers aiming at a spacecraft: http://www.nasa.gov/multimedia/imagegallery/image_feature_1768.html http://www.nasa.gov/multimedia/imagegallery/image_feature_17...