
What Neil and Buzz Left on the Moon - jacquesm
http://science.nasa.gov/science-news/science-at-nasa/2004/21jul_llr/
======
brey
probably a minor and tedious point, but it bugs me when journalists do this:

> (3) The universal force of gravity is very stable. Newton's gravitational
> constant G has changed less than 1 part in 100-billion since the laser
> experiments began.

technically worded correctly, but this language implies that we know it IS
changing, by some small but non-zero amount.

actually, we haven't detected any change at all - so there's every chance it's
NOT changing - but if it is, it's changed less than this small amount which
our instruments won't measure more accurately than.

> No variation of the gravitational constant is discernible, (dG/dt) / G =
> (0.0±1.1)x10–12 /yr

[http://ilrs.gsfc.nasa.gov/docs/williams_lw13.pdf](http://ilrs.gsfc.nasa.gov/docs/williams_lw13.pdf)

~~~
joshuahedlund
Can you explain how that reconcile with this recent news?[0] "Their tests
yielded a new G value of 6.67545 × 10−11 m3⁄kg s2, which is higher than the
current accepted value by about 240 parts per million"

Of course, that particular experiment could just have had some corrupting
factors, but how do you know what experiments support a constant value and
which ones don't without approaching tautology?

[0] [http://www.wired.com/wiredscience/2013/09/high-
gravitational...](http://www.wired.com/wiredscience/2013/09/high-
gravitational-constant/)

~~~
dalke
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](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.

~~~
ISL
It's precisely because almost all gravitational dynamics are controlled by G*M
(for some M) that G is so poorly-known. We're forced to do terrestrial
experiments, and they're extremely difficult.

G is very seductive. It seems obvious that we should be able to measure a
fundamental constant of nature to better than 14 ppm (or, if you take the
scatter of current measurements, 100s of ppm), but it's really really hard.

------
adaml_623
> (1) The moon is spiraling away from Earth at a rate of 3.8 cm per year. Why?
> Earth's ocean tides are responsible.

What a terrible explanation. I've done a physics course or two so I understand
the physical process of how ocean tides are responsible (I think). But for
your average person that's just silly.

Q. How do trees grow? A. Nuclear Fusion

~~~
adaml_623
exo762's reply is making my head hurt so here's a link in case you're curious
as to how the tides are making the moon spiral outwards.

[http://www.windows2universe.org/kids_space/moon_orbit.html](http://www.windows2universe.org/kids_space/moon_orbit.html)

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.

~~~
Tuna-Fish
... 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.

~~~
mixmastamyk
Was thinking about that too. It is sad that the moon is leaving us, but the
opposite would be a lot worse. Could we survive such an event? Perhaps by
chilling on Mars for a few thousand? years.

~~~
Tuna-Fish
Few thousand would be lowballing it rather lot. An impact of that magnitude
would melt the entire surface, boil the oceans, and strip off the atmosphere.
It would take hundreds of millions of years for earth to recover, if it ever
would.

Also, Mars is not that hospitable to life. The best option I see would be
putting as much people and industry in orbit as possible, and try to live from
asteroids.

~~~
ars
> An impact of that magnitude

It wouldn't be an impact. For the moon to reduce its orbit to the point that
it impacted the earth it would be moving rather slow as orbital objects go.

It would be more of a gradual merging as chunks of rock and ocean moved
between the two bodies.

~~~
rohansingh
Exactly. See:
[http://en.wikipedia.org/wiki/Roche_limit](http://en.wikipedia.org/wiki/Roche_limit)

Basically, in this scenario the moon would either come down in chunks or would
form a set of rings.

~~~
mixmastamyk
Yes, I was thinking a -3.8cm per year rate, and did contemplate the
"squishing" that the moon Io has to deal with. Just pulled the timeframe from
my rear end, probably would take that long just to get the process started. :/

------
acoyfellow
Isn't this what they did on the Big Bang Theory? I remember an episode when
they shot a laser at the moon to ping it.

------
nileshtrivedi
Is it possible for anyone to use that reflector to calculate the earth-moon
distance? What kind of laser is used for this? Do we know the precise location
of the reflector?

~~~
exDM69
There is a Mythbusters episode about moon landing hoax conspiracy theories
where the hosts visited an observatory to test the lunar retro reflectors.

The laser they used was pretty big (don't know/remember the numbers) but the
more impressive part was the detector. Despite the huge laser, just a handful
of photons make it there and back and twice through the atmosphere.

Overall it didn't look like something you do on your back yard with off the
shelf equipment, but it might be doable by a motivated hackerspace crew with a
lot of time and some money on their hands.

~~~
jacquesm
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.

~~~
exDM69
Yes, better report to the authorities _before_ you go waving a huge laser at
the moon. In my home country, owning a laser this big requires a permit in the
first place. You would definitely need to report it to the local aviation
authority, who would re-route flights and notify aviators.

A few weeks ago there was a music festival with some big laser decorations and
they actually changed the approach path to the largest airport in the country
for the weekend.

------
mkoryak
how can people still deny that we went to the moon when that thing has been
sitting there since? Id think that those people who think that there was no
moon landing would have done a fair amount of research about it, and would
have learned of the existence of this man made thing there.

~~~
smky80
I don't think humans have walked on the moon. I wouldn't bet my life on it,
and I don't have a complete narrative as to the why/how of it, but I'd put the
odds at over 50%.

It's something of a technological anomaly. A few years back the Apollo program
had been in complete shambles, burning the Apollo 1 astronauts to death. 30-40
years later, we are still crash landing probes into the surface of planets and
blowing up space shuttles. But for a few years starting in 1969 we routinely
soft landed a rocket on an unmapped alien surface, and then launched it again
and docked with the command module orbiting at 3000 mph? It just doesn't seem
to "fit".

I've seen enough historical examples to know that you CAN dupe most people
most of the time.

Most people seem to be convinced by the "social proof". I really believe if it
were the other way around, no one had heard of the moon landings, and you were
going around telling people "no really, we landed on the moon, drove a car
around on it and played golf!" ... that you would be completely ridiculed.

Anyway, not here to start a huge debate, just providing an answer to a
question.

~~~
blackhole
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](http://www.youtube.com/watch?v=sGXTF6bs1IU)

~~~
lutusp
> in 1969, it would have been harder to FAKE the moon landings than to
> actually land on the moon.

All true, and it would have been much, much harder to keep it all completely
secret for decades. Virtually no secrets survive that long.

~~~
cantrevealname
> _completely secret for decades. Virtually no secrets survive that long._

How do you know that? If a secret _did_ last for decades, you wouldn't know
about it.

I can actually give a couple counterexamples: two _big_ government secrets
that lasted 3 decades:

(1) A US bomber accidentally dropped a hydrogen bomb out of an airplane into
the dessert near Albuquerque, New Mexico, triggering a conventional but non-
nuclear detonation. This happened in 1957 but was kept secret until 1986 -- a
span of 29 years. "It was only in 1986 when an Albuquerque newspaper published
an account based on military documents recovered through the Freedom of
Information Act." (ref:
[http://www.hkhinc.com/newmexico/albuquerque/doomsday/](http://www.hkhinc.com/newmexico/albuquerque/doomsday/)
)

(2) The British were regularly reading encrypted German messages by around
1940. The codebreaking of the German Enigma machine was one of the greatest
secrets of World War 2, and the British shared the knowledge with the
Americans. This secret was revealed in 1974--after 34 years--because of two
books by key intelligence figures. (ref:
[http://en.wikipedia.org/wiki/Ultra#Post-
war_disclosures](http://en.wikipedia.org/wiki/Ultra#Post-war_disclosures) )

In both cases, at least dozens of people--but more likely hundreds of people--
would have been privy to the secrets.

I'm certainly not endorsing conspiracy theories about fake moon landings. I'm
commenting only about the persistent meme that big secrets are quickly
exposed: it's not necessarily true.

~~~
lutusp
>> completely secret for decades. Virtually no secrets survive that long.

> How do you know that? If a secret did last for decades, you wouldn't know
> about it.

No, I meant secrets that quickly came out (that weren't secret for long),
versus things that were only revealed after a long time. It's a reasonable
yardstick for the degree that things can be kept secret "for decades", my
claim.

Things that really have remained secret:

* Where Jimmy Hoffa's body is buried.

* What happened to Judge Crater ([http://en.wikipedia.org/wiki/Joseph_Force_Crater](http://en.wikipedia.org/wiki/Joseph_Force_Crater))

* What women want. Freud famously asked. but no one knows, certainly not women. This may belong in a different category, since it's not clear that anyone knows the secret.

> A US bomber accidentally dropped a hydrogen bomb out of an airplane into the
> dessert near Albuquerque, New Mexico, triggering a conventional but non-
> nuclear detonation. This happened in 1957 but was kept secret until 1986

So that's in the never-revealed secrets column? Just checking.

> This secret [Enigma] was revealed in 1974--after 34 years--because of two
> books by key intelligence figures.

Actually, it was because of the British Official Secrets Act, that required
silence on sensitive matters until the government granted permission, and that
was obeyed by all concerned. The books were't simply published, after due
consideration they were vetted by the authorities in advance of publication.
That example belongs in the well-kept secrets act, because everyone involved
obeyed the rules until given permission to do otherwise. If it had been a 50
year silence requirement, I suspect that it would still have been obeyed.

But I think you'll agree that rare exceptions don't disprove rules.

> I'm commenting only about the persistent meme that big secrets are quickly
> exposed: it's not necessarily true.

Not "quickly exposed", that's not a position I took. Thirty or forty years is
sufficient validation for my original claim.

------
BigTuna
LRRR/CTD: Lunar Ranging Retro Reflector/Conspiracy Theory Demolisher

~~~
ColinWright
In what way does this demolish the various conspiracy theories? When
confronted with evidence of man-made items on the Moon, the tin-foilers just
say they were put there by robots.

Or aliens.

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

~~~
mixmastamyk
Yea we're aliens!

------
sgloutnikov
[http://www.startalkradio.net](http://www.startalkradio.net) \-- Latest
episode (Part 1) with Buzz Aldrin was very good. Next week for Part 2.

------
reidrac
It always puzzles me that most people think that only Armstrong and Aldrin
went to the Moon, although 12 men have walked on its surface.

May be it's me but I couldn't help thinking that the title of this article
seems to help spread that idea: only Neil & Buzz went to the Moon, and it
happened only once.

~~~
R_Edward
TFA does go on to reference "reflectors in the Sea of Tranquility (Apollo 11),
at Fra Mauro (Apollo 14) and Hadley Rille (Apollo 15), and, sometimes, in the
Sea of Serenity. There's a set of mirrors there onboard the parked Soviet
Lunokhud 2 moon rover..."

That would sort of imply that it happened more than once. I do wonder, though,
why the Sea of Serenity doesn't get a mission name tied to it.

~~~
VLM
"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.

------
Jdfmiller
Wasn't this covered in an episode of Big Bang Theory? AKA the fount of
relevant scientific knowledge..

~~~
unwind
Yes, in the episode called "The Lunar Excitaion"
([http://bigbangtheory.wikia.com/wiki/The_Lunar_Excitation](http://bigbangtheory.wikia.com/wiki/The_Lunar_Excitation)),
it's Season 3, Episode 23, aired first on May 24 2010.

