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Until today, I had never once heard anyone ever mention these "reflectors" which apparently were placed on the Moon at the landing site in order to verify from Earth that humans were there.

On https://en.wikipedia.org/wiki/Moon_landing#Historical_empirical_evidence , it says:

Many conspiracists hold that the Apollo Moon landings were a hoax;[76] however, empirical evidence is readily available to show that human Moon landings did occur. Anyone on Earth with an appropriate laser and telescope system can bounce laser beams off three retroreflector arrays left on the Moon by Apollo 11,[77] 14 and 15, verifying deployment of the Lunar Laser Ranging Experiment at historically documented Apollo Moon landing sites and so proving equipment constructed on Earth was successfully transported to the surface of the Moon.

It further links to: https://en.wikipedia.org/wiki/Lunar_Laser_Ranging_experiment

However, the second link doesn't mention anything about the purpose of this being to verify that humans landed on the Moon. It goes on to mention the year "1962", which is before any humans had allegedly set foot on the Moon, and apparently they could still do the "experiment" without any reflectors in place, so what does this really prove?

This could become a conspiracy theory in itself; that they added this story about the reflectors long after the fact. However, I'm not saying anything -- I'm just wondering what the point of them was and why this has never been brought up as a way to verify the moon landings, if almost anyone can do it with some equipment.

Russell Borogove
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Kenichiro
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  • Only using a lunar retrorflector it is possible to measure the distance with a resolution of centimeters, not possible when using the Moon itself as reflector. – Uwe Apr 25 '20 at 17:47
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    There is no way anyone can know why you haven't heard of this, and it is 100% incorrect that "it has never been brought up". For example, they are mentioned in our canonical "How do we know the Moon landings are real" answer: https://space.stackexchange.com/q/28172/6944 – Organic Marble Apr 25 '20 at 17:51
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    "Why haven't I heard of this before" is an unanswerable question, since it has to do with your specific education. The information about the LLRE experiments is extensively available, has been talked about extensively in communications and media at the time. There are transcripts discussing their placement on the moon in the Apollo record. Many papers have been written about the results from using them to measure distance to the moon. Also, this sounds like part of a moon-landing conspiracy theory. Thus the downvote. I suggest removing the conspiracy stuff and asking a specific question – Dan Hanson Apr 25 '20 at 17:51
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    I’m voting to close this question because no one can know why you haven't heard of this. – Organic Marble Apr 25 '20 at 17:58
  • If you search here for posts containing "lunar retrorflector", you get 10 hits, the oldest from 2013. – Uwe Apr 25 '20 at 18:10
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    I've known about the retro reflectors since I was a kid, from some kid's educational book about the solar system. I'm willing to bet there are plenty other things neither of us have ever heard of that are just as interesting as the reflectors. – BMF Apr 25 '20 at 18:42
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    This admittedly long Astronautics and Aeronautics, 1970 pdf from a 1972 publication mentions the retroreflectors on pages 26 and 210. – notovny Apr 25 '20 at 19:06
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    relevant XKCD -- from October 31st 2014. They weren't "placed on the Moon at the landing site in order to verify from Earth that humans were there" They were to improve the accuracy of the experiment. The equipment needed to perform the experiment is still pretty sophisticated. –  Apr 25 '20 at 19:17
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    The Wikipedia page you reference was added in 2002 –  Apr 25 '20 at 19:22
  • The question is salvageable by edit if the title is ignored; in my opinion it was not necessary to close. – Russell Borogove Apr 25 '20 at 20:53
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    @RussellBorogove I agree that it could have been and can still be salvaged, and a few times I've seen a heavily down-voted question rise back to positive score after that. Since you have a good feel for what adjustments would help why not go ahead and make an edit, if that doesn't automatically put it back into the review queue then just vote to re-open manually, then I will too and possibly others will as well. I think there is a good question in here to go along with its very instructive answer! – uhoh Apr 26 '20 at 00:17
  • These reflectors were even a plot part of a Big Bang Theory episode (S03E23, 2010)… – DarkDust Apr 26 '20 at 06:31

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However, the second link doesn't mention anything about the purpose of this being to verify that humans landed on the Moon. It goes on to mention the year "1962", which is before any humans had allegedly set foot on the Moon, and apparently they could still do the "experiment" without any reflectors in place, so what does this really prove?

As JCRM notes, the purpose of the retroreflectors was not to verify that humans have landed on the moon. At the time, almost no one doubted that humans had landed on the moon; moon landing denial is a relatively recent trend promoted by grifters and attention-seekers with no respect for truth. The purpose of the reflectors was to accurately measure the distance to the moon.

Re-read the paragraph mentioning a 1962 experiment more carefully:

The first successful tests were carried out in 1962 when a team from the Massachusetts Institute of Technology succeeded in observing laser pulses reflected from the Moon's surface using a laser with a millisecond pulse length. Similar measurements were obtained later the same year by a Soviet team at the Crimean Astrophysical Observatory using a Q-switched ruby laser. Greater accuracy was achieved following the installation of a retroreflector array on July 21, 1969, by the crew of Apollo 11, and two more retroreflector arrays left by the Apollo 14 and Apollo 15 missions have also contributed to the experiment.

In other words, a ranging laser was bounced off the bare surface of the moon in 1962, and the arrays placed by the Apollo missions allowed similar experiments to be conducted more accurately.

It's not remarkable that you, or anyone else, hadn't heard of the laser retroreflectors; they were one of many independent scientific experiments placed during the Apollo missions. They certainly weren't a story added after the fact; they were called out in the press kit publicly released a couple of weeks before the Apollo 11 launch:

During their two hours and 40 minutes on the surface, Armstrong and Aldrin will gather geologic samples for return to Earth in sealed sample return containers and set up two scientific experiments for returning Moon data to Earth long after the mission is complete. One experiment measures moonquakes and meteoroid impacts on the lunar surface, while the other experiment is a sophisticated reflector that will mirror laser beams back to points on Earth to aid in expanding scientific knowledge both of this planet and of the Moon.

And also in the the Apollo 11 Mission Report delivered in November of 1969:

Both crewmen evalu­ated their mobility on the lunar surface, deployed the passive seismic and laser retro-reflector experiments, collected about 47 pounds of lunar material, and obtained photographic documentation of their activities and the conditions around them.

These are just two of many Apollo-era documents that mention the retroreflector experiments.

Russell Borogove
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