Bouncing a laser off the moon

[Khadaji]

In an episode of The Big Bang Theory the geeks bounce a laser off an object left by us on the moon and record the time it takes to get it back - thus proving that we had been there.

I had seen the episode, but it never occurred to me that the writers hadn’t done their homework - I assumed it could be done.

Yesterday some people at work were discussing it and then asked if the experiment could really be done at home by your average-every-day man. (What does it say about me that everyone turned to look at me, to see if I had done it?)

I did a quick internet search and could not find directions - so I turn to the dope to see if anyone can point me to a DIY instruction kit to bounce a laser off the moon, like the experiment on The Big Bang Theory.

[naita]

Not a conclusive cite, but seems to be a competent analysis:

http://scienceblogs.com/builtonfacts/2010/12/all_right_im_gonna_delay.php

Thus I regret to say that lunar ranging is probably not in our club’s future. It’s also probably not something the intrepid cast of the Big Bang Theory could have done on their roof with a few shots from a small laser, given that it wasn’t passing through collimating optics (ie, a large telescope). Still, it’s not impossible and I think a dedicated and well-equipped amateur group could probably do it. If you succeed, let me know!

[running_coach]

Mythbusters did that one on the NASA Moon Myths episode.

From here.

The Apollo astronauts left behind special equipment on the Moon like reflectors that scientists can bounce lasers off of.

confirmed

The Mythbusters went to an observatory equipped with a high powered laser. They first fired at the bare lunar surface but did not detect the laser bouncing back. Then they pointed the laser at a reflector left behind by NASA and received a confirmed bounce.

As I remember the episode, by the time the reflected light came back, it was only a few photons and required special equipment to even detect the return.
Video.

[Bosda_Di_Chi_of_Tricor]

Bouncing a laser off the moon

…from your skull-shaped Global Conquest Secret Headquarters, atop a mountain?

[Morgenstern]

They showed a rerun of that Mythbuster’s episode a few days ago. It was the the episode debunking the conspiracy theorist and their claim of a fake moon landing. In the the final test, they bounced the laser beam off some equipment abandoned on the moon by the Apollo mission.

[Khadaji]

Thanks for the great answers! So it seems that:

1. Yes, it can be done
2. No, probably not as a DIY experiment…

Great info, I’ll give it a few more days to see if anyone can point me to DIY instructions, then report back to the crew.

[njtt]

The guys on BBT are hardly amateurs. Leonard is an experimental research physicist specializing in lasers, Raj is an astronomer, and Howard is a NASA engineer, all at a top flight institution (Sheldon’s abilities are less relevant). If anybody could do this, it would be these guys.

[Pork_Rind]

There was a fun thread on Reddit commenting on a Mythbusters episode where they attempted the same thing. The general consensus, especially after a guy chimed in who has actually worked on a lunar ranging project, was that no way could you do it without enormously expensive equipment, the right location, and some other things I can’t remember…

http://www.reddit.com/r/askscience/comments/qw30x/can_an_amateur_astronomer_test_the_lunar_laser/c40xg1r

@acornboy

I was a grad student on the APOLLO (Apache Point Observatory Lunar Laser Ranging Operation) project that was shown on Mythbusters. The short answer is no way. You need laser that can shoot enough photons in a short pulse that you’ll get some back in the return pulse (shoot 1017 green 532 nm photons per pulse). You need sensitive detectors because, even if you shoot 1017 photons up, you’re only going to get about 1 photon back (we used avalanche photodiodes). You need fancy filters and timing electronics, because, when you are only getting 1 photon back, you need to turn the detectors on in as little a time as possible to minimize false detections from background light. You need a big telescope to maximize the number of photons you get (we used the 3.5 meter telescope at Apache Point). And you need to set this all up in a place with minimal background light and minimal atmospheric distortion (seeing). http://physics.ucsd.edu/~tmurphy/apollo/apparatus.html I guess you could do all these things on your own, but you would need about $1 million and a couple years of time to set it up.

Edit to add: that 10 to the 17th photons, not 1017.

[Chronos]

In the the final test, they bounced the laser beam off some equipment abandoned on the moon by the Apollo mission.

It wasn’t abandoned equipment, it was a device that was deliberately left on the surface for precisely this purpose. It’s pretty simple-- All you need is three mirrors attached at right angles at their corner.

And the BBT characters doing this on the roof of their apartment is a clear case of exaggeration for the sake of the story, like almost everything else on a sitcom.