What Neil and Buzz Left on the Moon

If we had detected some non-zero change in G, that would be big news.

In general, because G' is a signed quantity, I would expect any experiment to be quoting double-sided errorbars. If G increases, one thing happens, if G decreases, the opposite happens, so the difference is discernable.

I'd take 0.0 to be their reported central value.

Short version is you're talking about a value, they're talking about a first derivative of that value.

I can take two COTS cheap canned 64 MHz oscillator modules like the ones on your computer motherboard, and the mfgr claims they'll output something within 100 ppm of 64 MHz. Once the temp stabilizes they'll individually be WAY more stable than 100 ppm comparing right now to an hour ago, but whatever it is they oscillate at, it'll be within 100 ppm of each other.

If you graph the output of NTP, perhaps via Munin or any number of other sysadmin tools, you'll see most of those devices are very stable from hour to hour, at a basically fixed offset from the correct frequency.

A couple years ago there was a ham radio construction project in QEX etc along the lines of using a crude computer grade COTS osc, feeding it thru the equiv of a hundred-something times multiplier, and using it as a local oscillator. I built a couple and they're ridiculously stable, although all over the map. I don't have an 1152.000000 MHz oscillator although from memory they were all within 10 or so ppm of each other (better than the rated 100ppm)

Edited to add, if you're running Debian Linux and NTP, take a look at /var/lib/ntp/ntp.drift. The generic COTS dell 6-U server one of my images runs on, ticks very stable and precisely -40.069 ppm low compared to reality and it never varies. On the other hand, my "desktop" running basically the same software but on generic dell desktop hardware is at present running +9.615 ppm fast at this instant although it varies a bit more (probably due to temp swings).

G is notoriously hard to measure accurately.

Wikipedia's entry on the topic suggests that you read a 1997 review paper at http://iopscience.iop.org/0034-4885/60/2/001 . That abstract starts:

> Improvements in our knowledge of the absolute value of the Newtonian gravitational constant, G, have come very slowly over the years. Most other constants of nature are known (and some even predictable) to parts per billion, or parts per million at worst. However, G stands mysteriously alone, its history being that of a quantity which is extremely difficult to measure and which remains virtually isolated from the theoretical structure of the rest of physics. Several attempts aimed at changing this situation are now underway, but the most recent experimental results have once again produced conflicting values of G and, in spite of some progress and much interest, there remains to date no universally accepted way of predicting its absolute value.

The Wired article confirms that it's hard to measure, with some examples of the difficulties.

However, G* M is not hard to measure accurately. We believe the Earth gains about 100,000 kg per year from meteors, and in any case, the Moon and the Earth have changed by much less than one part in a million over the last few decades. So any change in G* M should be due to a change in G, even if we can't measure G directly.

This is of course also why we don't know the mass of the Earth better than a few hundred parts per million.

Yes but last I checked when the tide went out it doesn't go out to the moon and push it a little bit, so blaming the tide is nonsensical at best. If you want to make a one line quip about it. It would be more accurate to say it is because the Earth spins faster than the moon revolves around the Earth. After all once the Earth stops spinning faster than the moon revolves there will still be a tide but the moon will stop moving away from the Earth.

say no more... wait. say more.

Thanks for the link, I appreciated the short but informative explanation.

Today I learned the moon is spinning away from the Earth while the Earth's rotation is slowing down, and by the time this dance movement ends, a day on the Earth will last a month!

... I've known about the widening orbit of the moon, but I only just realized that if the moon was rotating in a different direction, it would eventually spiral down to the earth.

Imagine living on such a planet, with a large gravity capture moon, that provides a definite sell by date to living on the surface.

And of course for the curious, no the moon was not 'skimming the surface of the earth' a million years ago as would be implied by a 'continual' increase of 3.8 cm/yr in the orbit.

The earth is not homogenous, and so the gravitational force experienced by the moon is not constant. This results in a transfer of angular momentum between the two, speeding up the moon slightly (and slowing the earth even more slightly as the transfer is proportional to mass)

> TL; DR - The earth's rotation drags the tidal bulge faster than the moon's orbit slowing the earth and giving more energy to the moon which moves it into a higher orbit.

Is there no way that this is a misinterpretation of the facts? Couldn't the answer be that the Earth is losing mass through its atmosphere (into space), and due to having less mass, the moon has less gravitational pull with the Earth, and the orbit becomes larger?

best issue a 'notice to airmen' if you go this route, pointing multiple-tens-of-watt lasers skyward is going to get you into a lot of trouble if you're not careful about it.

> just a handful of photons make it

I was looking at the moon the other night and though, "Holy fuck the sun is powerful." The light is reflected off not that reflective grey dust/rock and is fairly freaking bright.

For that matter, from Earth examples, its not terribly hard to find places with volcanic obsidian laying around vs nearly pitch black non-reflective areas.

Doesn't help that people were not randomly bouncing laser beams off the moon before the landings.

"so there exists a peculiar shiny field of obsidian rocks on the surface in that particular area, so what?"

If it were a religious claim that (fill in the blank) put a gold tablet up there, skepticism would be seen as healthy.

Personally I think the ham radio AMSAT guys should drop an active transponder on the moon, so EME antennas don't have to be so elaborate. Of course it would only work half the time and temperature cycles would be brutal on the poor thing, but still...

The problem with moon hoax theories is that, in the modern day, we're accustomed to extremely realistic CGI. What we don't realize is that in 1969, it would have been harder to FAKE the moon landings than to actually land on the moon.

This video explains why: http://www.youtube.com/watch?v=sGXTF6bs1IU

> But for a few years starting in 1969 we routinely soft landed a rocket on an unmapped alien surface

Er, no, we didn't. Before we started landing people on the moon, we sent a series of unmanned mapping missions to the moon so that we wouldn't be trying to land on an unmapped alien surface. [1]

[1] http://en.wikipedia.org/wiki/Lunar_Orbiter_program

The landing was shown live in the USSR. On USSR TV owned by the USSR government.

In the middle of the cold war.

There is a question I've always wanted to ask someone who's convinced that the moon landings were faked.

Where the line is between fake and real? Was it the entire Apollo program or just the six landings? Obviously there has been some space travel by humans at the time. In your view how far did we get before faking the rest? Did we just stop with Gemini and say 'screw it the rest is too hard'?

I can acknowledge that it seems superficially anomalous to have people flying to the moon using slide rules, but it's not like NASA just pointed a finger and decided to go. There were a number of steps along the way where each step makes sense compared to the next one. If Apollo 8-10 were real, then 11 seems entirely plausible.

Well, that would mean that NASA also faked the Apollo 13 incident, in order to regain public interest in their fake landings.

Well, technically, you could argue that the Apollo astronauts WERE aliens while they were on the moon.

I've not had the pleasure of meeting any tin-foilers that were that far gone.

"I do wonder, though, why the Sea of Serenity doesn't get a mission name tied to it."

1) Too depressing that 17 was probably the last time a human being will ever visit the moon, so lets not talk about it.

2) General lack of selenological (is that even a word?) knowledge. Its like saying I've never visited Ireland, although I have been to Dublin and Galway and a couple places in between, or some similar static type language failure like that. The armchair lawyers like to point out that the mission planners didn't use that name on the map for the landing, but the scientists in charge of the reflector did, or something along those lines.