Measuring The Distance From Earth To Moon

lewiz writes: "Tom Murphy at UW is attempting to measure the distance between the Earth and The Moon to the nearest millimetre according to this BBC News article. 'His tape measure will be a giant telescope at Apache Point in New Mexico. Retroreflectors left on the surface of the Moon by various space missions, including the Apollo 11 lunar landing, will also come in handy.'"

Comments

That is...

[I.T.R.A.R.K.]

...if the moon landing *actually* happened.

Re:That is...

[redcliffe]

Aren't some people dumb? It would require the knowledge of 15 million people to hoax the moon landing, as well as being harder than it would be to really land there.

Re:That is...

[Anonymous Coward]

Not so.
Not so at all.
I mean were you there?

heh

[Anonymous Coward]

for a hoot, search for "lakjsdf;laksdjf" on Google. You never know.

Re:heh

[Anonymous Coward]

Searched English pages for asldfk. Results 1 - 9 of about 13. Search took 0.18 seconds.

Did you mean: asldkf

"The moon is moving away from Earth."

[scott1853]

Isn't this better than moving closer to Earth?

Re:"The moon is moving away from Earth."

[Peyna]

Depends, the moon moving away from the Earth could seriously affect tides. Of course, it's not going to happen any time soon, even by geological standards, but it is still significant.

Re:"The moon is moving away from Earth."

[Nightpaw]

Yes, but the moon moving closer to the Earth could seriously affect how squished I get when it lands on me.

Re:"The moon is moving away from Earth."

[Anonymous Coward]

When discussing the possible disastrous effects on the environment, remember that earth not always has been like this and will not remain like this forever.
The environment, and especially the climate, is changing all the time. Right now it is favourable to us, but it will not remain like this.

Oddly Enough...

[CheshireCatCO]

... according to my Solar Systems Dynamics textbook, we already know the rate at which the Moon is receding from the Earth: 1 nanometer/second. Which is, of course, a better precision than this group seeks to take on. But that measurement probably used the Doppler shift. It just goes to show that it's much easier to measure radial velocities than distances!

Re:Oddly Enough...

[iamdrscience]

shhh!!!! don't tell the organization that's funding their research that!!!!

Re:Oddly Enough...

[p3d0]

Bzzztt. The speed that the moon receeds wasn't measured directly, especially by doppler shift of all things. It was calculated from the kinetic energy gained by the moon from the Earth from tidal forces.

Re:Oddly Enough...

[Anonymous Coward]

1 nanometer/second. Which is, of course, a better precision than this group seeks to take on.

Hmm, one significant digit isn't very precise. And significant digits are all that matters: any measurement in centimeter/year can be converted to nanometer/second (or to attometer/nanosecond, or to meter/century...) it's just a speed that is measured.

Re:Oddly Enough...

[RedWizzard]

according to my Solar Systems Dynamics textbook, we already know the rate at which the Moon is receding from the Earth: 1 nanometer/second. Which is, of course, a better precision than this group seeks to take on.

At the bottom of the BBC article is a link to a previous BBC article from 1999 that says that the "McDonald Observatory Laser Ranging Station near Fort Davis in Texas, US, regularly sends a laser beam through an optical telescope to try to hit one of the reflectors". So I'm not sure what's special about the new article. Anyway the McDonald Observatory people have measured the velocity of the moon's recession at about 3.8 centimetres per year. That's where the 1 nanometer per second figure comes from. So it's not better precision at all, they've just used very small units.

Re:Oddly Enough...

[doooras]

ok, so McDonald's has an Observatory Laser Ranging Station, but they still can't manage to give me fries that aren't cold.


(humor, folks... or at least a poor attempt at it, i'm not really THAT dumb)

Re:Oddly Enough...

[Anonymous Coward]

We could not measure Doppler shift due to motion of 1 nm/s. That is far too small. Even with the Moessbauer effect we can only measure Doppler shifts due to motion of a few mm/s.

The way they measure recession rate of the Moon is to measure distance directly via bounce time from the corner reflectors left by US and USSR (+ France?). Because of systematic error in a direct distance measurement it is not unusual to have a situation where you know the speed of something better much than you know its distance.

If you can set up a standing wave to a corner reflector it is conceivable that you could use interferometry to measure speed very precisely. But the standing wave must last longer than

a) the bounce time and

b) wavelength used (optical ~ few um) divided by speed

So one would have to track the thing for on the order of an hour. From what I've heard these things are pretty much hit or miss, so unless and until we put a live marker in place that is likely impractical.

Re:Oddly Enough...

[Anonymous Coward]

That is a velocity measurement, this is a distance measurement. (Sorry to be pedantic, but that's what physics is all about.)

Re:Oddly Enough...

[LadyLucky]

Oh my...

It's also one picometer/millisecond! that's even more precise. I wonder what kind of instrumentation they use to measure such small distances....

:-)

Re:Oddly Enough...

[RedWizzard]

If they are planning on taking five years to measure the distance once I'll be very suprised. They will be measuring the change in distance over time, i.e. the velocity of the moon's recession.

Re:Oddly Enough...

[Anonymous Coward]

The resolution of the new group is a spatial resolution, not the same as the velocity resolution.

You're comparing apples and oranges.

I could measure the rate of the receding moon
With 1 mile resolution, but if I measured it long enough I could calculate a rate of 1nm/s.

Re:Oddly Enough...

[Anonymous Coward]

The BBC article says again and again that they will measure the distance. That is the important quantity so far as gravity etc are concerned. Measuring the gravitational constant better helps you make more precise predictions about a very wide variety of things.

That said, they might as well measure the rate of change of the lunar orbital parameters whiel they are at it. But they basically get this for free from the distance measurements, which are the real goal.

Re:Oddly Enough...

[RedWizzard]

Well the major goal of the research does appear to be into gravitation, but quoting the article:

Dr Robert Massey, an astronomer at the Royal Observatory, Greenwich, UK, said the Moon was moving away from the Earth by a few centimetres each year. He told BBC News Online: "The experiment will give much more accurate measurements of this changing distance."

Given the moon is receeding at about 2.8cm/year a measurement of the distance to the moon precise to the nearest mm will be obsolete in about a week so they'll certainly be interested in the velocity of the movement.

Re:Oddly Enough...

[-brazil-]

Significant digits are not all that matters when you're operating in a real-world scenario where you have many factors that act as a constant noise.

Re:Oddly Enough...

[a random streaker]

I recall them doing a laser measurement just this way on a PBS show 10 years ago, maybe an Alan Alda-hosted thing, can't remember.

At the time, they said the accuracy of the measurement was +/-5 inches. How did they improve this? Of course, if it's truly randomly +/55 inches, many measurements averaged would give you the right answer, but still...

Re:Oddly Enough...

[gorilla]

Even if it wasn't receeding, it would still change. The orbit isn't the theoretical perfect elipse, which could only happen in a universe with only two objects. In ours, the Sun pulls the Moon towards it more when they're closer than when they're futher apart, so the orbit is biased towards the sun. This also happens to a smaller extent with all the other planets, though you can almost ignore it.

Re:Oddly Enough...

[RedWizzard]

At the time, they said the accuracy of the measurement was +/-5 inches. How did they improve this?

With laser ranging it is the accuracy of your timing device that determines the accuracy of the measurement (since you're measuring the round trip time of the laser pulse). For the new project (which is called APOLLO btw and has a web page here) they can measure to a precision of a few picoseconds which is well beyond what would have been possible 10 years ago I expect.

Am I reading this right?

[Captain_Jackass]

"This is essentially measuring the weight of gravity, and this is the only type of project that can currently do that[...]"

Huh? since when did forces have weight

Re:Am I reading this right?

[Gaccm]

Force = Weight.

the formula for Force is: F=ma, replace a with the acceleration caused by gravity and you got weight.

Re:Am I reading this right?

[Peyna]

F != W.

Weight is the measure of attraction between two masses, such as the gravitational force between the Earth and you. But force certainly does not equal weight.

Force is also a vector, which weight is not.

Re:Am I reading this right?

[Anonymous Coward]

How bout "Weight = a Force", and that's all that really matters in this case.

Re:Am I reading this right?

[dangermouse]

Weight is too a vector. You weight X lbs, straight down. :)

Re:Am I reading this right?

[Compuser]

Weight _is_ a vector. Weight _is_ a type of
force. Remember, mass is a number, weight is
a vector.
I think when they say weight of gravity they
mean that gravitons or grabity waves have
non-linear dynamics, i.e. they interact with
themselves and Einstein equations are needed to
deal with this self-consistently. But the simplest
way to correct Newtonian gravity is to analyze
corrections from gravity interacting with itself,
which could be worded as measuring weight of
gravity.

Re:Am I reading this right?

[Kwikymart]

"Huh? since when did forces have weight> "

Mass does not equal weight. Weight is measured in Newtons (usually), which happends to be what force is measured in. Mass is measured in kilograms. If you go to the moon, your mass will be exactly the same when compared to here because it is only a measurement of the quantity of matter.

On the moon a body will fall at around 1/6 of the rate of velocity that it does here on earth (about 9.8 m/s^2 here, 1.62 m/s^s there). On the surface of the earth, your weight in newtons is equal to 9.8m/s^2 times your mass (f=ma). Using that same equation, your weight on the moon would be 1.62 m/s^2 times your mass.

Re:Am I reading this right?

[Peyna]

Weight is a gravitational force, thus acting on 2 objects, and pulling them either towards or away from each other. I don't know of any bi-directional vectors.

Re:Am I reading this right?

[qedigital]

Gravitational force (classically speaking) follows, of all things, Newton's Law of Gravitation:

F= -(G*M1*M2)/r^2

which states that force between masses M1 and M2 is proportional to the masses and inversely proportional to the square of the distance between them. The constant G ('Big G') is currently the subject of debate but lies somewhere around 6.672E-11 m^3/(kg*s^2).

The negative sign indicates an attractive force between the masses. In short, the gravitational force is attractive, not "bi-directional".

Finally to clarify, the weight of a body is equal to the magnitude of the gravitational force on the body.

ie. W = m*g (scalar)

Re:Am I reading this right?

[denzo]

The weight in "W = m*g" in your case is a scalar because you chose to make the acceleration due to gravity, g, a scalar. If g were treated as a vector (g), W would also be a vector. Thus, W = m*g

The gravitation force isn't a bi-directional force per se, but it can still be broken down into x, y, and z components (and thus a vector) in order to simulate gravitational forces between multiple particles. All you have to do to find Fx, Fy, Fz (and make a new vector F to be = {Fx, Fy, Fz}) is to multiply your scalar F by a trigometric function, and now you can treat gravitational forces between particles as vectors, and can do stuff like summation of forces of multiple particles on a specific particle to find out where it'll be pulled.

You are in effect saying that gravitational forces are not vectors only because the equations you presented only yield scalar answers. You neglected to consider that these forces in fact behave as vectors when you have the interaction of multiple particles, or when one particle is moving with respect to the other. Your equation is a scalar only because the two particles are on the same axis, thus requiring no axis component breakdown into a vector (if that makes any sense).

Re:Am I reading this right?

[dangermouse]

The thing you're ignoring is that 'weight' is a measure of gravitational force between two objects relative to one of the objects.

That's what makes it useful. The earth does not weight 150 lbs. on me, nor do the earth and I weigh 150 lbs. toward each other. I weigh 150 lbs. on earth.

Weight is by its nature unidirectional, and since the relative direction doesn't ever change, it can safely be treated as scalar. And is.

Re:Am I reading this right?

[big_hairy_mama]

The earth does not weight 150 lbs. on me, nor do the earth and I weigh 150 lbs. toward each other. I weigh 150 lbs. on earth.

I think you're debating English, not the nature of gravity. Who says that the Earth doesn't weight 150 lbs on you? I think the only reason why you weigh 150 lbs on Earth is because you are smaller than the Earth, and therefore it's easier for the human mind to imagine that image.

If you have a really big rock, it still weighs something "on" the Earth. OK, what if you have an even bigger rock, say the size (and mass) of the moon. Now who weighs what on what? It's totally arbitrary, and stems only from a human's view of the universe from our extremely low-altitude vantage point.

Weight is most certainly a measure of the attraction between two objects, relative to *each other*. Which one of the objects we pick to be the "base" for that comparison is determined entirely arbitrarily.

Re:Am I reading this right?

[pmc]

Weight _is_ a vector

Well, yes and no. I know the equation suggests it is (W = m.g, where bold represents vectors. But weight is not used as a vector, and it leads to silly conclusions if it is.

For example, I weigh myself here to be 100kg (or 980N) - what is the direction of this weight vector: towards the centre of the earth. Thought experiment time. Two 100kg men weight themselves, on at the north pole, one at the south pole. What is the sum of their weights?

Well, if weight is a vector then the sum is zero. If, however, you take weight as a scalar then it is 200kg. What people mean when adding weights only works if weight is a scalar. Basically, defining weight as a vector fails the common sense, similar to defining glass as a liquid as opposed to a solid.

All that is happening is that specialists are taking a word that is in common usage (weight in this case) and defining a new (and different) techincal meaning for the word, which is similar to but distinct from the everyday meaning. Then they complain when people use it in the everyday sense.

Re:Am I reading this right?

[Fleming's Left Hand]

Why do I have to be surrounded by fricking idiots? Force = Weight The easiest way to demonstrate this is using Newton's Second Law: F=ma The weight of an object is equal to the product of the object's mass and the acceleration of free fall (due to gravity). Therefore weight IS a force and also a vector.

Re:Am I reading this right?

[a random streaker]

Your little body certainly does pull the entire mass of earth down onto it, just a little bit.

What % of your weight is the earth attracting you and what % is you attracting the earth?

Re:Am I reading this right?

[dangermouse]

No, in a two-body system each body would have a weight relative to the other. There's no "shared weight". There just isn't, by definition of "weight" as a physical term. So yes, weight is a vector, but you always use it to describe the force acting upon one body due to another body, and the direction is always toward the other body. It's unidirectional, and the direction (within the system) is always the same. If you're measuring the weight of A on B, the direction is toward B. If you're measuring the weight of B on A, the direction is toward A. Only in a larger system do you care about the actual positions of A and B, and at that point you tend to stop talking about weight and start talking about attractions in mutual terms.

This is why, in terms of English, weight is treated as a scalar... because we always know which two bodies we're talking about, and which one's weight we're measuring relative to the other. In other words, if we're talking about the weight of some body on earth (and we usually are), we know that the weight is toward the earth so we can just leave that part out. Incidentally, we also know, roughly, the gravitational acceleration between the two bodies, so we tend to ignore that, too, and just treat weight as a measurement of mass... which it is, if you just go to the trouble of doing the simple math to throw away a constant and ignore an obvious direction.

You're right, the Earth does weigh 150lbs. on me, in physical terms. In English terms, that's an absurd image, as "weight" is generally assumed to be the property of a smaller object with reference to, say, a planet. So there I was debating English. But I still debate your contention that physical "weight" is bidirectional. It's just a measurement that can be taken from either side with the same result. :)

Re:Am I reading this right?

[Peyna]

F = ma = The force of an object is equal to the product of it's mass and acceleration. No mention of weight...

Here is a more formal statement of Newton's Second Law for you:

The acceleration of an object as produced by a net force is directly proportional to the magnitude of the net force, in the same direction as the net force, and inversely proportional to the mass of the object.

Force != Weight. As far as everyday life is concerned they might be pretty similar, but they are not one in the same thing. Acceleration does not have to have anything to do with gravity either. In many cases it does, but not always.

Weight IS a particular force in certain instances. When you're sitting here on earth, the force of gravity on you is equal to the product of your mass and ~~ 9.8 m/s^2.

Just don't go throwing around statements like "Force = Weight" when you mean that weight is a particular force in certain instances. You are going to mislead high school physics students reading /. and then we'll all be in for it.

Re:Am I reading this right?

[denzo]

Your little body certainly does pull the entire mass of earth down onto it, just a little bit.

Right. Here's an example: Pluto's moon, Charon, is only slightly smaller than Pluto itself. Since Pluto's moon is quite big relative to Pluto, both objects "wobble" as they orbit the sun. Even Earth wobbles a little bit because of our moon, but not as much since our moon is significantly smaller than the earth. The Space Shuttle causes a microscopic wobble in the Earth that we can't measure.

The only thing keeping our moon from crashing into us, or Pluto and Charon from crashing into each other, is the orbital velocities. If you held Pluto and Charon at a standstill away from each other, they would both move towards each other and collide (with Charon accelerating towards Pluto slightly faster).

Every single particle in our universe has a gravitational force with respect to every other object in the universe... but small masses or great distances make them irrelevant.

A human standing on Earth will exert their weight on the Earth, and also feel the reaction of that weight on their feet. Therefore, the weight acts in both directions (remember Newton's equal and opposite reaction). A human in mid air will accelerate towards the Earth pretty fast, and the Earth's acceleration to the human is so minute (on the order of 10^(-22) m/s^2) that it can be ignored.

Re:Am I reading this right?

[Anonymous Coward]

Kilograms are not weight, they are mass. In common speech it may be called weight, primarily, I would suggest, because people were so used to using pounds, which are weight.

Honestly, what good does this metric system of yours do if you can't keep straight what is what?

Of course you are right, weight is commonly used to specify the magnitude of its vector, much like velocity, in everyday usage.

Re:Am I reading this right?

[Gambit253]

The highest physics I ever took was in HS and I know that weight is always a force. It's just normally counteracted by something called a normal force of opposite direction but same magnitude. In the end you end up with a net force of 0. The best argument is not "Force = Weight" but "Weight is a Force"

Re:Am I reading this right?

[Anonymous Coward]

All that is happening is that specialists are taking a word that is in common usage (weight in this case) and defining a new (and different) techincal meaning for the word, which is similar to but distinct from the everyday meaning. Then they complain when people use it in the everyday sense

hacker... cracker ... cheeze!

Re:Am I reading this right?

[lemley]

And I quote from my University Physics text:

The weight of a body is a force, a vector quantity, and we can write as a vector equation:

weight(vector)= mass x gravtity (vector)

Note that gravity is your local value of acceleration due to gravity (which for most of us does not vary too much from 9.81 m/s^2).

Re:Am I reading this right?

[(void*)]

You are right, but you forget one thing. The specialists are the one using the word consistently, if differently from everyone else. It is the nonspecialists who sometimes use it to mean mass, and sometimes use it to mean the vector. It's pretty obvious which party is confused, and which party isn't.

Re:Am I reading this right?

[Jonavin]

Interesting points, but...

with Charon accelerating towards Pluto slightly faster

Relative to what? When 2 objects are accelerating towards each other, how can you tell one is faster than the other?

Re:Am I reading this right?

[big_hairy_mama]

You're right, the Earth does weigh 150lbs. on me, in physical terms. In English terms, that's an absurd image, as "weight" is generally assumed to be the property of a smaller object with reference to, say, a planet. So there I was debating English. But I still debate your contention that physical "weight" is bidirectional. It's just a measurement that can be taken from either side with the same result. :)

That really was my only point -- I guess I got a little bit carried away :)

Re:Am I reading this right?

[Fleming's Left Hand]

I'm not making any attempt to confuse high-school physics students. The truth of the matter is that weight is a force. This cannot be denied.

Weight is the force exerted upon an object by another object. It is measured in Newtons and is a force. Weight is a force. Saying they are similar is like saying mozzarella is similar to a cheese. It IS a cheese and therefore the same. All cheeses may not be mozzarella, similarly all forces are not weights. But weight is a force.

If you're standing on the moon then your weight will depend on the acceleration of free fall on the moon and of course your mass again (N2L: F=ma). Yes there will be other forces acting upon you (such as the gravitational pull for other bodies such as the Earth and the Sun) but your since your weight depends on the acceleration of free fall, these forces are taken into account, despite the fact they are extremely minute.

Your statement of Newton's Second Law is exactly the same as the one I quoted, except for the fact you have rearranged the equation for some unknown purpose.

Anyone heard about the new anti-gravity apparatus they've come up with? Sounds pretty interesting but like it will be utterly useless for at least ten years, by which point they will hopefully have been able to reduce the force of gravity to a useful amount.

How do you check the accuracy?

[nurightshu]

I mean, it's all well and good to say you're going to measure this sort of thing, but how can we be sure he's correct? I could just as easily say that the exact distance from the center of the earth to the center of the moon is 385,137.473 KM.

In fact, what if these scientists are just using this as a cover to get a lot of funding money. Look for the research team to be on vacation in the Bahamas next month. When they come back, they've got a request for funding on a project about angels and pinheads...

Re:How do you check the accuracy?

[CheshireCatCO]

Same way we ever check, have another group do an indepenent measurment or make them show their data and analysis?

Re:How do you check the accuracy?

[Anonymous Coward]

Umm, did you miss the point? first off, how do we know the second team didn't just take the money, guesstimate and take a trip to the islands? Second off, if the second team is wrong, who's right? You want to bring on a third team? Point is, in Science you never know if you're right until your observations match up to a well formed theory, within a margin of error. There is no theory which dictates the distance from earth to moon on the millimeter scale, therefore there is no check on our observations. There is no way to tell that some whacked out relativistic effect is affecting our measurement, or that the methodology is just plain wrong and nobody has noticed yet. Look into Thomson's original measure of the charge of a single electron. His experiment was extremely clever, but in the calculations he forgot to take into account the viscosity of air. As time went on, various experimenters reproduced the experiment, but somehow their data was just a little higher than Thomson's, so they chalked it up to bad data, phase of the moon, god playing dice, etc. Nobody dared doubt that the great Thomson's clever experiment could be wrong.

Re:How do you check the accuracy?

[oo7tushar]

Thing is that they're probably not looking for the center of the Earth. The Earth, moon or any object upon which there is a changing gravitational field is not static.
In other words, the center of the Earth is constantly shifting from one point to another. All non-gaseous planets are continously evolving (like Io, you know, one of Jupiters moons). Thus getting an exact measurement from the centers is wrong the millisecond that you get it.

What this study is more useful for is doing these measurements over time and finding out some sort of gravitational pattern.

It's like an MRI scan for the Earth but we've got a very large scanner and we've moved the emitters to the Earth and are using the Moon to bounce. Potentially we could determine how the shape of the earth changes by measuring the distance to the moon (since we know how fast it recedes).

So the data obtained from this experiment has many many uses (not just those that are listed here).

Re:How do you check the accuracy?

[Anonymous Coward]

You just set up an inspection team at the bahamas. Now that i have patented this idea i am quite willing to participate ;)

Re:How do you check the accuracy?

[gorilla]

There is no theory which dictates the distance from earth to moon on the millimeter scale, therefore there is no check on our observations.

Yes there is. Newton's laws, modified by relativity, and a big of geometry allow you to calculate the distance using only the mass of the earth and the orbital period. In theory, if you had the mass & the orbital period known to enough accuracy, then you could calculate the distance.

The newtonian formulas are:
a=v^2/r, a=acceleration, v=orbital velocity, r=radius.
a = G m / r^2, G=Newton's constant, m = mass
v=circumfrence / orbital period

With known m & orbital period then you can solve for r.

Of course, in real life, it's going to be much easier to measure the distance to the moon than the mass of the Earth, and the theory ignores the influence of the rest of the universe, so it's not going to be 100% accurate, so even in Newton's time they measured it, except they used parallax methods.

Research?

[Anonymous Coward]

This is exactly the sort of uninteresting waste of money we don't need at this point in time. If we've got talented people and the expensive equipment, why waste their time on a trivial academic exercise like this? NASA doesn't even have enough money to get a little robot to the moon correctly, people are starving to death in this very country every day, and yet someone is dedicating their time and money to this?

Hate to be all bitter here, but come on lets reevaluate our priorities!

Re:Research?

[taylor]

Two things:

(1) Before we can even discuss basic science research, we need to agree that such fundamentals are important and thus deserve tax dollars. I find it irrelevant that the money comes from NASA for this discussion.

(2) As mentioned in the article, this experiment hopes to measure to unprecedented accuracy the rate of change of the distance between the Earth and the moon. Why is this useful? If it can be done accurately (the conditions of which I will discuss in a moment) it would allow a determination of the self-interaction of gravity, e.g. graviton-graviton interaction. This is fundamentally different than Newtonian gravity, and, as mentioned elsewhere, the simplest way to explain in our nascent theory of quantum gravity the Einstein field equations without solving the actual math. On a much larger scale, the determination of the Hubble constant and how it changes with time also measures this. Finding the argument that it is preferable to do such measurements in one's backyard when possible I leave as an exercise to the reader.

With respect to the potential accuracy (vs. precision) of such measurements I will note the following. First, current gravity meters based upon atomic fountains are accurate enough to find Cave complexes in Afghanistan and see people moving around in them. (c.f. Steve Chu's recent work at Stanford with atom interferometers); we have a very detailed picture of our local gravitational field available to us. Second, considerations such as chaos theory and effects of the other planets are relatively straightforward to deal with. Back at the beginning of the 20th century they had already done it for Mercury and still had a discrepancy, at 43 arcseconds per century in its orbit(c.f. this explanation). That's over 10 times smaller all the other planets' influence, and that was calculated before computers. It seems to me the greatest unknown is the tectonic structure of the moon and the associated vibrations in the mirror. I suppose that radar rangefinding, given the scale of these variations, would be sufficient for most purposes.

Finally, some of the past results of this experiment, from the Nasa site

From the ranging experiments, scientists know that the average distance between the centers of the Earth and the Moon is 385,000 kilometers with an accuracy of better than one part in 10 billion. Laser ranging has also made possible a wealth of new information about the dynamics and structure of the Moon. Among many new observations, scientists now believe that the Moon may harbor a liquid core. The theory has been proposed from data on the Moon's rate of rotation and very slight bobbing motions caused by gravitational forces from the Sun and Earth.

Ranging has also determined that the length of an Earth day has distinct small-scale variations of about one thousandth of a second over the course of a year, caused by the atmosphere, tides, and Earth's core. In addition, precise positions of the laser ranging observatories on Earth are slowly drifting as the crustal plates on Earth drift. The observatory on Maui is seen to be drifting away from the observatory in Texas.

Umm, the distance isn't constant

[DeafDumbBlind]

The moon revolves around the earth in an eliptical orbit, not a circular one. Unless he's talking about getting the average distance.

Re:Umm, the distance isn't constant

[AllTheGoodNamesAreTa]

My thoughts exactly!

So is he trying to get a precise estimate?

Re:Umm, the distance isn't constant

[Russ Steffen]

I'm guessing a critical detail got lost in the translation to journalist-english. That is, that they are not looking for a simple distance estimate, but a refined estimate of the moon's orbital parameters (or Keplerian elements or ephemeris datum, whatever term you prefer). From that, given a time you can solve for the distance.

Re:Umm, the distance isn't constant

[Anonymous Coward]

I like your sig, it is mad funny. Eating Jesus is what them christians do. HAHAHAHAHAHA

Re:Umm, the distance isn't constant

[Anonymous Coward]

Also the surface features on the Earth and Moon are much larger than 1 mm.

But the scientists have already thought about all these things, and taken them into account. That's why they're the scientists and we are the people who sit around all day posting to slashdot.

Re:Umm, the distance isn't constant

[Rothfuss]

Yeah. Good point.

There is no way he could actually want to track the distance between the earth and moon over the course of the entire eliptical orbit and then compare the data from one year to the next. That would be silly. Maybe you should send him an email and point out his mistake. Scientists like that.

Nice work.

-Rothfuss

Re:Umm, the distance isn't constant

[rarose]

Uh... simply: No. The moon doesn't revolve around the earth. Both the moon and the earth revolve around the center of mass of the earth-moon system. This center of mass is thousands of kilometers away from the center of the earth.

Re:Umm, the distance isn't constant

[Bradee-oh!]

And not only that, but the ellipse isn't even constant. At the same point in any given Earth year, the moon is in a different part of it's orbit and due to the varying relative position of the sun and the other planets, the moon is never really at the same position and the same orbital trajectory twice. (At least twice in a reasonable amount of cosmic time)

3.8 cm

[niola]

Well, if the moon is moving 3.8 cm away from the Earth every year, that does not bode well for life on this planet next millennium. Since gravity is so important to our climate I would imagine that this could have bad long term effects.

I remember reading something a while back about ancient Egyptians believeing there were two suns int he sky. I wonder if what they saw was a much closer moon back then?

All throughout the Earth there is evidence of dramatic gravitational changes int he past. For example, below all the ice in the northern reaches of Canada there are vast reserves of coal. Since coal is made through the decay of organic matter, it means there had to be a massive forest up there at some time. Then in the deserts of Africa there are mountains where they find seashells like 1000 feet above sea level.

Perhaps the moon pulling away from the Earth has caused many of the major changes on the Earth...

--Jon

Re:3.8 cm

[Hitokage_Nishino]

Think about what you are saying.

The moon is currently around 260,000 km at its nearest point in orbit. 3.8cm per year is not a significant distance over a couple years, or even 10,000 years(by which the moon has drifted 380m).

Re:3.8 cm

[Peyna]

Not sure why the parent was marked as a troll, but given the age of the Earth, and a movement of 380 m in 10,000 years, I would assume it could have had a significant effect on the Earth millions of years ago.

Re:3.8 cm

[qurob]

3.8cm/year * 4000 years = ~ 150m

Not far enough to differe

Re:3.8 cm

[dvdeug]

At the rate of .0038 m/yr, a billion years ago it was only 3800 km closer. Out of roughly 300,000 km between us and the moon, it still doesn't make much difference.

Re:3.8 cm

[Anonymous Coward]

According to stellar evolution models, the sun is about 10% brighter than it was 100 million years ago. I would think this to have a much stronger effect than a 0.5% stronger lunar tide.

Re:3.8 cm

[dvdeug]

As others have pointed out, 10,000 years at 3.8 cm per year is only 380 meters. Out of over 250 thousand kilometers, that's not much change.

The gravitational effects of the moon on the Earth are fairly minor. Losing the moon would kill the tides, and creatures that depend on them, but that's about it.

The standard explanation for coal in cold areas and seashells way above sea level is continental drift and tectonic action. No moon gravity explanation necessary.

Re:3.8 cm

[ColaMan]

All throughout the Earth there is evidence of dramatic gravitational changes int he past. For example, below all the ice in the northern reaches of Canada there are vast reserves of coal. Since coal is made through the decay of organic matter, it means there had to be a massive forest up there at some time. Then in the deserts of Africa there are mountains where they find seashells like 1000 feet above sea level.

Perhaps the moon pulling away from the Earth has caused many of the major changes on the Earth..

*cough*Plate Tectonics!*cough*

Coal was generally formed from about 300 to 65 million years ago. That's a lot of time for them continents to wander. That 'massive forest up there' was probably some massive forest down here 300 million years ago.

Re:3.8 cm

[dragons_flight]

Once upon a time, the moon was part of the Earth. Billions of year ago, well before any known evidence of life on Earth, the partially formed Earth was hit by a planetesimal in the primordial solar system. The impact caused a large glob of primarily molten material to spew off the surface of the Earth and coalesce into what is now the moon.

Ever since then the moon has been slowly drifting away from the Earth. It doesn't drift away because of the original impact, that energy long since dissipated; the moon is sliding back as tidal forces between the Earth and the moon dissipate small amounts of angular momentum. Eventually the Earth and the moon will become face locked, so that not only do we see the same side of the moon all the time, but the Earth will have slowed so that the same side is always facing the moon. This is a long time away since the earth day will have to slow till it's as long as the moon's period or about 30 times longer than today's day. The moon will not escape however.

To answer your question though the moon has moved less than 1/10000 of a percent since the Egyptians, so no it wouldn't seem that much bigger. In the last 50 million years the moon would have moved around 1%. Because the lunar interactions slow the Earth's spin we know that the Earth probably once spun around twice as fast as it does now (12 hour days). Yes the changes would have had an impact on the Earth and on life, but the change is very very gradual. If you want to look for big effects on the Earth you probably ought to consider more drastic influences like volcanism, earthquakes and large meteors. And just to confuse it all, plate tectonics has no end of fun moving stuff around on the surface of the Earth.

Re:3.8 cm

[niola]

a billion years ago it was only 3800 km closer

May not seem like a lot, but that is like a 1% difference which is actually quite a bit :)

Well, on the bright side we are more likely to get hit by a meteor before the moon moves another km :)

--Jon

Re:3.8 cm

[lewellyn]

For a much more rational and thought out theory on the origin of "fossil" fuels and other hydrocarbons see Thomas Gold's website.

His book, The Deep Hot Biosphere is very insightful and most of the information and theories in it are also covered in depth on his website.

Re:3.8 cm

[Anonymous Coward]

Actually, that would be .038 m/year. There is only 100 cm in 1 m, not 1000.
So it would have moved 38000 km.

Re:3.8 cm

[Anonymous Coward]

260.000 MILES, not km.
This is getting to be a classical mistake in space exploration...

Re:3.8 cm

[VikingBerserker]

Ah, but has the rate of lunar recession been constant for that billion years? Admittedly, my knowledge of Newtonian physics is rusty at best. Constant orbits are easy to calculate, but spiral paths and the factors involved would just make me dizzy.

Re:3.8 cm

[gorilla]

And that's assuming that the rate is constant. In actual fact it's not, it's increased over time.

Re:3.8 cm

[Anonymous Coward]

You are making an assumption that is incorrect. The universe did not exist a billion years ago. Even 10,000 years is a little too far back. Please refrain from spewing junk science and RELIGIOUS FAITH.

Re:3.8 cm

[gorilla]

We don't have to calculate it, we can measure it. From this page:

This paleontological evidence comes in the form of tidal rhythmites, also known as tidally laminated sediments. Rhythmites have been subjected to intense scrutiny over the last decade or so, and have returned strong results. Williams (1990) reports that 650 million years ago, the lunar rate of retreat was 1.95±0.29 cm/year, and that over the period from 2.5 billion to 650 million years ago, the mean recession rate was 1.27 cm/year. Williams reanalyzed the same data set later (Williams, 1997), showing a mean recession rate of 2.16 cm/year in the period between now and 650 million years ago. That these kinds of data are reliable is demonstrated by Archer (1996). There is also a very good review of the earlier paleontological evidence by Lambeck (1980, chapter 11, paleorotation)

Re:3.8 cm

[AndrewRUK]

3.8cm/yr is 0.038m/yr, which, over a billion (1,000,000,000) years gives 380km, which is even less of a difference :-)

Re:3.8 cm

[Peyna]

I can't believe I'm replying to this, but your statement makes no sense at all.

Unless maybe you're a solipsist or something.

Re:3.8 cm

[AndrewRUK]

Err... Please feel free to ignore that, I was wrong. It is 3800km. Opsies :-)

Proof of Moon mission?

[Anonymous Coward]

So if they are using stuff that the Apollo missions supposedly left up there, will that prove once and for all to the conspiracy theorists that we actually did go to the moon?

Re:Proof of Moon mission?

[Wheaty18]

I'm sure the conspiracy theorists will come up with something... they always do, regardless of how ridiculous their theories are. See: FOX.

Re:Proof of Moon mission?

[I.T.R.A.R.K.]

"will that prove once and for all to the conspiracy theorists that we actually did go to the moon?"

No. Because you know they will just find something else to bitch about.

Re:Proof of Moon mission?

[glwtta]

I have a theory that FOX doesn't really exist and it's only a conpiracy to make us think we are dumber than we really are.

Re:Proof of Moon mission?

[Dahan]

The conspiracy theorists say that there hasn't been a manned mission to the moon, not that nothing's ever been put on the moon via an unmanned craft.

Re:Proof of Moon mission?

[redcliffe]

Except for the Flat Headed Flat Earth Society who seem to think that none of it is real.

Re:Proof of Moon mission?

[Markus Landgren]

The reflector left on the surface by Apollo 11 has already been used for various experiments. If those experiments did not convince you, neither will this one.

Re:Proof of Moon mission?

[Anonymous Coward]

Does anyone have a url that shows photos of the landing sites from earth? I don't think I've ever seen any taken by a large observatory...

BTW has Hubble taken any pics of the moon?

Alternative Solution

[nurightshu]

...Check the Odometer on the Apollo 11 capsule.

Re:Alternative Solution

[nurightshu]

:s/Odometer/odometer.

I hate it when I do that.

Re:Alternative Solution

[Peyna]

In response to your sig:

If he stopped the puck, why on earth would he pass it to someone on the opposing team?

Re:Alternative Solution

[Nightpaw]

:s/Odometer/odometer.
I hate it when I do that.


You must be German.

Re:Alternative Solution

[KILNA]

I thought you just had a measuring device for Odo.

Re:Alternative Solution

[Anonymous Coward]

I thought you just had a measuring device for Odo

You should see the meter I have to watch the taco consumption.

Re:Alternative Solution

[CokeBear]

The way I read this sig, Jesus and Gretzky are on the same team... Jesus (the goalie) makes the save, then passes the puck up to Gretzky, who is on his team. Gretzky then takes the puck and scores on the net at the other end of the ice. (But its not my sig, so I might be wrong)

Re:Alternative Solution

[Anonymous Coward]

well, normally when you see that phrase, it's more like "Jesus saves, but Gretzky scores on the rebound!"... oh well

Re:Alternative Solution

[Steve B]

Check the Odometer on the Apollo 11 capsule

Too late -- Drudge just reported that Clinton rolled back the odometer when he tried to sell the capsule to the ChiComs.

Re:Alternative Solution

[isaac_akira]

Is that the unit of measure that is constantly morphing into other units of measure?

Re:Alternative Solution

[Hektor_Troy]

Such as millimiles?

Yes - it's a pun(k).

Wouldn't it change?

[b0r0din]

I don't think the earth has a perfect orbit with the moon, so I would assume that the distance is not entirely constant. Am I wrong? Can anyone shed some "light" on the subject?

But my old encylopedia...

[heliocentric]

My old encylopedia says it's precisely 300,000 km and it also says that "someday we hope to go there."

All that and the Kaiser Wilhelm still doesn't know what to do with his country.

Re:But my old encylopedia...

[Nightpaw]

Hmmm, mine says it's 80,000 leagues to the moon and that it causes insanity.

Oh, and asbestos is a miracle mineral that will render the House Of The Future completely fireproof.

Re:But my old encylopedia...

[Anonymous Coward]

Hmmm, mine says it's 80,000 leagues to the moon and that it causes insanity.

Isn't it 80,000 leagues under the secant?

Re:But my old encylopedia...

[rat7307]

Mine says something similar, but apparently there are currently tensions in Vietnam.... I think I'll stay away this holidays!

Re:But my old encylopedia...

[Yorrike]

You guys have some pretty out-of-date information right there.

Checking my up to date encylopedia, I am informed that the Moon is, in fact, at a distance of 28 billion feet, 12 horse's heads and 3 grandmas from the Earth. while the Sun's orbit around the Earth is at the slightly greater distance of 54 billion feet, 6 Grandmas and a duck.

Re:But my old encylopedia...

[heliocentric]

While on tour of the Strasburg Railroad's locomotive repair area the tour guide mentioned how they work hard for great accuracy. On cue, the one machinist yelled to the other "How big do you want that rod?" to which the other replied "Two hammer handles and a fist."

Re:But my old encylopedia...

[Rand Race]

It couldn't be more wrong... it's 79,670 leagues. ;-)

1,912,000 Furlongs

76,480,000 Rods

1,912,000,000 Links

3,846,000,000,000,000,000 Angstroms

1,753,000 Cable's Lengths

210,300,000 Fathoms

3,786,000,000 Hands

181,700,000,000 Lines

1,090,000,000,000 Point

90,860,000,000 Picas

0.002571 Astronomical Units

1.283 Light Seconds

841,300,000 Cubits

180,300 Mezhevaya Verst

97,950 Ri

240,800 Millarium

Old news

[Anonymous Coward]

This has already been done, years ago. I can't recall the exact reference, but it was one of the examples used in calc class. Interesting stuff, but how about some modern news?

Re:Old news

[Anonymous Coward]

The University of Hawaii Lure Observatory
on Maui, was built in 1974 for this exact
purpose. see

http://koa.ifa.hawaii.edu/Lure/

think they do laser ranging on satellites now,
to measure Earth plate tektonics?

So?

[Carlos Laviola]

Sorry, but so fucking what, dude? Go do something actually important like trying to find a cure for cancer or AIDS.

Re:So?

[Anonymous Coward]

And what have you done to solve the worlds problems?

Re:So?

[belg4mit]

Very few world-altering innovations result
from somebody who set about to actually make
those changes occur. Innovation and
discovery result from generally fucking around with stuff.

Re:So?

[SpacePunk]

I'm sure that knowing the distance from the Earth to the moon down to the millimeter will go far to solving the Earths problems.

Perhaps some scientist somewhere will do important research like where all the damn socks go that dissapear in clothes dryers.

In either case it's money well spent, it is.

-

Re:So?

[Anonymous Coward]

> find a cure for ... AIDS.

I guess someone bummed about not being able to have wild, unprotected, promiscuous, homosexual anal sex with strangers anymore.

Re:So?

[andymoe]

no no this is good, there are too many people anyway

FRONTPAGE ROCKS :-P

Re:So?

[Anonymous Coward]

The GOD of Lauderattes!

Eddie Izzard, knows all!

+1 (Has a link)

Factor that in

[FredBaxter]

I hate to second guess people (OK, makbe I don't, so sue me), but I just hope they do take this movement into account when they do their measurements, since it will take time to bounce signals back and forth, and more importantly nanometers will add up over several years until they are just a little bit significant. (60 sec x 60 min x 24 hrs x 365 days x 5 yrs x 1 nanometer = 157,680,000 nanometers, or .15768 meters) Feel free to check my math, it's late...

Re:Factor that in

[oo7tushar]

Not exactly sure what you mean by "since it will take time to bounce signals back and forth".

We know that the moon recedes at 1 nanometer per second. Since they're trying to determine nearest millimeter they don't care about how much it's receding or even if it is. As far as they're concerned, it doesn't move farther away in a day or even a few months.

Also, it takes just over 2 seconds for light to get there and back so we're looking at a 2 nanometer change in the whole time. Also, this nanometer movement will change as the moon gets farther away.

Thus they don't have to worry about movement (tis less than the 5% error range they're "allowed")

hope that's kinda helpful

Confirming the moon landing?

[Cryptnotic]

Gee, if they have a telescope that can see stuff on the moon in that kind of detail, does that mean that they can now confirm that the moon landing wasn't faked?

Cryptnotic

Re:Confirming the moon landing?

[Anonymous Coward]

If someone doesn't believe the moon landings were real, why would they believe someone was able to see what the astronauts left?

Re:Confirming the moon landing?

[Fenris2001]

Gee, if they have a telescope that can see stuff on the moon in that kind of detail, does that mean that they can now confirm that the moon landing wasn't faked?

Uh... what? Nobody's talking about about looking at the Moon at a high resolution - merely measuring the distance from the Earth to the Moon with high precision. You don't need to see the mirrors the Apollo landers left to use them. The beam spot size of a laser projected from Earth is a few kilometers wide when it gets to the Moon.

Re:Confirming the moon landing?

[Anonymous Coward]

does that mean that they can now confirm that the moon landing wasn't faked?

They can, but how do you know the moon landing confirmation wasn't faked?

Re:Confirming the moon landing?

[doooras]

it was not faked. i know that for a fact. hell, you can see a man there every full moon.

Re:Confirming the moon landing?

[Arlet]

Ha, you're going to 'confirm' this supposed moon landing by showing doctored photographs ? Try again.

Re:Confirming the moon landing?

[redcliffe]

No. We're just going to confirm that you are a certifable idiot.

Old news

[El Cabri]

It's been a long time there are permanent earth stations around the globe doing that. Maybe bigger telescope is more precision (I've heard of centimeter-precision so far).

It was the theme of a science exam I took in 1994 to enter a college. Every aspect of it, including the ways the moon mirrors are designed so that they always send the light back to its source (vaguely mentionned in the article)

Wipe-cut to the next scene...

[Tony Shepps]

...his wife [sobbing]: "Dammit Tom! You could measure how far it was to the moon! But you couldn't see the distance between... between US!

Re:Wipe-cut to the next scene...

[Anonymous Coward]

I'd guess the distance between the US and the moon is about the same as the distance between the earth and the moon.
Unless you by by B.A., then it'll be much longer, cost you more, and your'll have to go via London.

Re:Wipe-cut to the next scene...

[Anonymous Coward]

Don't worry, I bet that the wife of a guy like this has the distance between her nipples measured to sub-millimeter accuracy, and the distance change over time graphed.

You mean we actually landed on the moon???

[Anonymous Coward]

How is light going to reflect from space junk left on the surface, if we have never been there!!!! All the conspiracy theorists know that fact. The next point... all the conspiracy stuff started because we couldn't see the space junk left on the moon to prove we were there!!!! OK, let me ask you this, way haven't they pointed Hubble at the moon to take a closer look!!!!! Is the government worried that its secret will get out!!!!!

Re:You mean we actually landed on the moon???

[Anonymous Coward]

while the US have not yet been, the Russians have sent bits of metal up. To scan it... They all reported back
"Yeap It's the moon" (but in Russian o/c: "Bodka Bodka moon Bodka!")

Re:You mean we actually landed on the moon???

[Anonymous Coward]

Well, if you really want to know it's because even the seemingly dim sunlight reflected off the moon would burn the Hubble's optics to a crisp. Then again, why would someone who doubts the moon landing believe that the Hubble really is in orbit, seeing as those shuttle astronauts had to go up there to fix it a while back?

The moon is a rediculus liberal myth.

Re:You mean we actually landed on the moon???

[BTWR]

If you would like to know... Hubble cannot look at the moon because they way it's optics work (designed to look into deep space), the moon travels too darn fast for it relative to earth that viewing it is unfeasable. However, back in 2000, a group of astronomers from Hawaii managed to actually manipulate Hubble into viewing it. See summer 2000 of Sky & Telescope or Astronomy, I forget which one. It was very interesting (although it had to be at lowest power, so this was not to see details of the moon, but rather to demonstate the feasability of this act.) BTW, I'll most definately get a "0" for this, even though it is informative, since I always get a zero, but anyway... :-)

Re:You mean we actually landed on the moon???

[Anonymous Coward]

Yes, you are absolutely right! Americans have never been to the moon, and the Soviet Union still exists and is wanting a world-wide communist revolution.

Re:You mean we actually landed on the moon???

[haedesch]

There has been a world wide communist revolution!!This commie - free world has just been pulled over your eyes to blind you from the truth!

Re:You mean we actually landed on the moon???

[Oggust]

So is "bodka" russian for the well-known swedish "bork" then?

/August.

Re:You mean we actually landed on the moon???

[Markus Landgren]

About Hubble, let's do the math:

The distance from the Earth's centre to the centre of the Moon is about 384400 km. Subtract one Moon radius (1737 km) and one Earth radius (6378 km) and Hubble's orbital altitude (very rougly 500 km), and we get a minimum distance between Hubble and the lunar surface of 375800 km.

The planetary camera has a pixel width of 0.046 arcseconds. Let d be the width of one pixel on the lunar surface.

Then d = 375800*tan(0.046")km = 0.084km = 84m, and that is why nobody has tried to use Hubble to photograph the descent stage of the lunar lander.

The importance

[SpacePunk]

This kind of research is as usefull as a lip reading class for the blind.

-

Useful?

[Nick Smith]

Why can't he do something more useful? Like measure the cheese composition of the moon...?

Current estimates predict that all known gorgonzola deposits on Earth will be depleted by 2016. We need to think about cheese-mines on the moon now, before it's too late...

Re:Useful?

[krogoth]

He should be contributing to the Linux kernel! Who needs another measure of the distance to the moon?

Re:Useful?

[Lectrik]

Why can't he do something more useful? Like measure the cheese composition of the moon...?

Current estimates predict that all known gorgonzola deposits on Earth will be depleted by 2016. We need to think about cheese-mines on the moon now, before it's too late...

and don't forget we can also use the laser to shine in the eyes of the moon-men to annoy and distract them while we are stealing the cheese from their mines

Mooting points.

[blair1q]

- The moon's orbit about the Earth is a 100-page equation, not a constant.

- The Earth's rotation is not circular (it "sloshes").

- The Earth's shape is not constant.

- The Earth's mass is not constant, so the general relativistic field in which the moon orbits is not constant.

- Okay, so we know where that telescope is relative to the moon. Now where is it relative to my house? To Washington? To Wendy's?

- Isn't this just an attempt by the Bush White House to wag the dog to distract attention from the fistfight the President and Vice President had during the game Sunday?

--Blair

Re:Mooting points.

[Anonymous Coward]

Ohhh by the [g|G]od[dess], I want a wendys (burger). They have all closed in England, but I realy liked 'em!

'retroreflectors'?

[dangermouse]

Are those anything like, um, reflectors? Or mirrors, even?

Re:'retroreflectors'?

[zudark]

Like them, yeah... :) But not just mirrors. Retroreflectors reflect light back on a course essentially parallel to the incoming rays. This makes them kind of creepy to look into, since no matter how you rotate them, there's an eye staring DIRECTLY back at you :)

To see this in person, walk up to a surveyor at a construction site sometime... if you're lucky and they're using an optical total station, there'll be someone walking round with a pole w/ a corner cube reflector (a type of retroreflector) on top. This is used so that the pulses of light coming out of the total station get reflected back to the station no matter how the pole guy has the pole oriented.

Another good example is the material highway signs and license plates are coated with -- they show up in your headlight beams so well because much more of the light reflecting from their surface heads back toward the light source (the headlights, very close to being in line with your eyes) rather than being scattered or reflected off into a less useful direction.

Check out http://www.leica-geosystems.com/ims/product/tps500 0_reflectors.htm for some pics...

Re:'retroreflectors'?

[Anonymous Coward]

well, yes and no.

the lunar retroreflectors are designed such that light hitting them will be reflected back to its source no matter what its angle of incidence.

a normal mirror (or reflector, if you will) does not have this property; without it, the laser you shine at the moon will most likely reflect uselessly off into space.

Re:'retroreflectors'?

[dangermouse]

Ah, right on. Thanks... I'd never heard the term.

Re:'retroreflectors'?

[gorilla]

Another common use is the material that they put on kids & workout clothing so that they show up well at night. The light from the car headlamps hits the material, is reflected back parallel to the original beam, and thus the driver can see the kiddies before he hits them.

Re:'retroreflectors'?

[Anonymous Coward]

Hey they are just a perfect corner cubes man. If you got 3 plains at perfectly 90 deg calculate the angles of incidence and refraction for a ray incident on one of the planes. Now don't muddy the water by actually using values use variables like A and 90-A etc. Anyhow if the corner is perfect of close then a laser incident on one of the faces of the corner will bounce out paralel to the incident beam. Let us asume the corner is represented by the axis x,y,z. asume leaser with vector (a,b,c) incident on a plane. By symetry it doesnt matter. Next calculate the angles of incidence to the plane it hits and the angles of refraction. Procede 2 do so for the next 0,1,or 2 bounces. Anyhow its trivial and I'm bored so someone else can finish the math ...

Reflectors on the moon? It's a lie !!!

[bani]

... according to Bart Sibrel :D

To sum up: "we never went to the moon, hence there are no reflectors on the moon."

Moderators: Put down the crack pipe and the mouse. Step away from the keyboard. Take a DEEP BREATH and READ. This is not a troll. I repeat. This is not a troll.

No, I don't believe the "moon hoax" loonies. Anyone with an above-kindergarten education can easily refute the "moon hoax" loonies claims.

For your amusement, this is the gallery of the 'barking mad'...

Some anonymous kook
Bill Kaysing
Ken Overstreet
"mpeeters"

Re:Reflectors on the moon? It's a lie !!!

[dunkelfalke]

reflections from the russian lunokhod which landed to moon softly (first soft landing on the moon)

:-)

Re:Reflectors on the moon? It's a lie !!!

[Anonymous Coward]

We live in sad times, when the 'touched' people you link to are using technology that came about largely due to the space race to spew forth their personal venom.
Wanna bet these guys are all baby boomers that somehow got turned down by NASA? And they couldn't let go?
If I had the money, I'd strap these poor fellows onto a Saturn V and send them to the Moon.
Wanna bet they'd start asking for astronaut training?
I'd ask them what for? You're not going anywhere!

Re:Reflectors on the moon? It's a lie !!!

[laserjet]

I hate to ask... but, has anyone actually seen the video on moonmovie.com? I am wondering if it is any good or not.

another question: don't we have telescopes good enough that we could see things that were "left" on the moon, like the lunar rovers, their boots and gloves, etc.? It would seem that would put the "did we really land on the moon?" controversey to rest....

Re:Reflectors on the moon? It's a lie !!!

[andycal]

I don't have a link, but I recall reading ( I think it was a FAQ from HBO's Earth to moon series) that the atmosphere limits image resolution to a point that it isn't possible to get an image from a land based telescope that will show the decent modules and lunar rovers left on the moon.

I also suspect that orbiting telescopes can't be configured to focus so close. ( like trying to use binoculars to look at your hand)

It does leave me wounding just how powerful the laser must be to be scattered by the atmosphere on the way up and the way back and still be visible.

Re:Reflectors on the moon? It's a lie !!!

[rootmonkey]

From kaysing's site:

NTHS: How much space stuff since 1959 has been real? What space stuffis real today? Did the challenger blow up? Did NASA know it would blow up?
BK: Yeah, and you know why it blew up? Because Christa McAuliffe, the only civilian and only woman aboard, refused to go along with the lie that you couldn't see stars in space. So they blew her up, along with six other people, to keep that lie under wraps. I claim that Christa McAuliffe was murdered.

These people are f*cked up.

Re:Reflectors on the moon? It's a lie !!!

[mdwebster]

The moon isn't all that close. Even Hubble can only get a resolution on the order of 100-meters or so. Pretty impressive, but far too large to discern a lander.

Re:Reflectors on the moon? It's a lie !!!

[TMB]

For your amusement, this is the gallery of the 'barking mad'...

The definitive list can be found on crank.net. If you ever want a good laugh, try reading through the sites listed as "illucid". ;-)

Why do cranks always pick on either cosmology or the moon? I want to see a crank theory of horizontal branch morphology or AGB stars! :-)=

[TMB]

Re:Not even eliptical.

[Anonymous Coward]

Because of the combined gravitational effect of the Earth and the Sun, added with the tidal effect of Earth, the orbit of moon is far from from being an eclipse too!

Therefore the question is What is this guy up to?

Ex-squeeze me?

[phliar]

From the article:

But the task is not as simple as it sounds. The beam of light must hit the retroreflectors, each about the size of a suitcase, on the lunar surface.

This is made even trickier by the fact that the beam will be about 2 kilometres (1.2 miles) wide by the time it reaches the Moon.

Stupid gits!

Much easier to hit that suitcase-size reflector with a beam that's more than a mile wide than with one that's pencil thin!

My tax dollars at work...

[ChaoticPup]

How refreshing to know our tax dollars are going to be spent to fund this project for five years.

This is like trying to measure Bill Gates' wealth to the penny.

The moon's orbit varies by far more than 1 millimeter all the time. There are all sorts of influences, including the earth's gravity, the sun's gravity, Jupiter's gravity -- as well as factors that will introduce error into the measurements, such as refraction of the laser in the earth's atmosphere.

Besides, I've already measured the distance with my trusty golf rangefinder. :o)

-- CP

Re:My tax dollars at work...

[pclminion]

The moon's orbit varies by far more than 1 millimeter all the time. There are all sorts of influences, including the earth's gravity, the sun's gravity, Jupiter's gravity -- as well as factors that will introduce error into the measurements, such as refraction of the laser in the earth's atmosphere.

Therefore, by measuring the distance to an accuracy of a millemeter, we might be able to gain some insight about: earth's gravity, the sun's gravity, and Jupiter's gravity. The point of this experiment is not to know how far it is to the moon. The point is to better understand the moon's orbit, and the various influences which affect it.

Re:My tax dollars at work...

[Anonymous Coward]

Actually, according to his webpage, the purpose is to perform a precision test of general relativity.

The project is called APOLLO.

Re:My tax dollars at work...

[ChaoticPup]

Therefore, by measuring the distance to an accuracy of a millemeter, we might be able to gain some insight about: earth's gravity, the sun's gravity, and Jupiter's gravity. The point of this experiment is not to know how far it is to the moon. The point is to better understand the moon's orbit, and the various influences which affect it.

That's a good first volley, and it's obviously easy for someone to agree with your point. I had already considered your position and dismissed it prior to my original post, though. I'm afraid I oversimplified my point in a "too short" message. I apologize.

We may indeed gain more information about the moon's orbit -- but there are too many variables to go much beyond that unless we can get an equally accurate measurement of everything else in the picture.

When this guy gets to the point that he can record instantaneous snapshots of the precise position (to the mm) of every influencing body in the solar system, along with the strength and direction of the solar winds (as measured at the moon) and everything else that may enter the picture (including atmospheric and gravitational effects on the laser beam itself), he'll be able to approach a reasonable look at the true influence of gravity. Until then, improving his accuracy on one variable isn't going to improve the precision of the overall picture very much.

As "cool" as it may be, a high school discussion on experimental precision shows it to be an exercise in burning cash, IMHO.

--CP

Re:My tax dollars at work...

[Jebuslovesyou]

better than those dumb christmas cards that the send you...

Parallel space.com article

[Anonymous Coward]

The parallel article contains this ghastly analogy:

Murphy's real motivation is to test Einstein's General Theory of Relativity, which is
based on an assumption that gravity affects a feather and a bowling ball in the same
manner. You cannot test this in your home, because air keeps the feather aloft.

I forget -- was Einstein the guy who dropped the balls off the tower or the one who was hit in the head with an apple?

Re:Parallel space.com article

[rarose]

No no no... Wasn't Einstein the guy that shot the apple off his kid's head?

In any case, it was nice to learn why birds can fly... where's my damn feather suit?

Re:Parallel space.com article

[geekoid]

nonono Einstein was that guy who went around and planted apple seeds, thus giving us gravity.

Re:Parallel space.com article

[Derek Pomery]

In all fairness, General Relativity is a refinement of Newtonian gravity.

So, since it is based on the same underlying theory, I don't see why the article isn't technically correct, if a little vague.

Oh, the *OTHER* UW

[Boone^]

Here I was expecting to see some research from the Badger state, but once I read the article I was kinda relieved. :)

I mean, we've all taken our laser pointers and attempted to reach the moon, but this guy gets paid to do it. Kudos, I guess.

Re:Oh, the *OTHER* UW

[Anonymous Coward]

M-I-N-N-E-S-O-T-A

Minnesota!

Minnesota!

Yayyyyyyyyyyyyyyyyyy Gophers!

ReMooting points.

[Anonymous Coward]

Alright BLAIR (if that's really your name), I'll unmoot some of your points.

• the equation size depends on what font you use. I've seen it fit on the head of a pin.
  
• The earth's rotation has nothing to do with it, because the moon's revolution around the earth is in complete lockstep with the Earth's rotation. This is why there is a dark side of the moon that light never gets to.
  
• Yes it is. Until you can PROVE the crazy ideas like "the earth's shape changes", Ockham's Razor says that I'M RIGHT.
  
• Let me teach you a little equation about relativity. It's called e=mc^2. It means that even though the mass of the earth isn't constant, neither is the mass of the moon. Consequently, everything washes out--everything's relative.
  
• Tell me how to get to your house from the
  telescope and I'll tell you how to get to the moon.
  
• The Cheney rumor is just a cover-up. George is stuck in an abusive relationship that he is scared to leave. Everybody knows that Laura beats him whenever he doesn't have dinner ready on time.
  

Re:ReMooting points.

[Anonymous Coward]

Prove that the Earth hasn't changed shape in billions of years.

Re:ReMooting points.

[doooras]

we all know the earth is banana shaped.

Re:ReMooting points.

[BlueUnderwear]

Actually the earth's shape changes daily, due to tidal forces. Indeed, the moon's attraction does not only influence the water but also the rocks. Granted, due to their rigidity, the rocks move less than the water, but it's still two feet.

Re:ReMooting points.

[alfredw]

Ok, ok, I'll take the flamebait... Hopefully this'll be educational or something...

the equation size depends on what font you use. I've seen it fit on the head of a pin.

Granted. Your point, however, is completely irrelevant. I've seen the entire Encyclopaedia Britannica crammed onto one CD-ROM. That doesn't make it any less complex. This is the point made by blair1q. The equation is difficult to solve, and probably do-able only by using numerical methods. This gives you an approximation to arbitrary accuracy, depending on how much time you have to waste calculating.

The earth's rotation has nothing to do with it, because the moon's revolution around the earth is in complete lockstep with the Earth's rotation. This is why there is a dark side of the moon that light never gets to.

You're right about the lockstep part. The Earth's rotation, however, is being constantly slowed down by - everyone's favorite - friction! The tides created by the moon in Earth's oceans cause friction when the water runs over the ocean floor. This force, albeit small, is always in a direction opposite to the Earth's rotation. Hence, the Earth is slowed and will eventually become tidally locked with the moon, just like the moon is locked with us.

Yes it is. Until you can PROVE the crazy ideas like "the earth's shape changes", Ockham's Razor says that I'M RIGHT.

Every seen a mountain range? Compare the Rockies to the Appalaichans. The Rockies are jagged, newly formed. The Appalaichans have eroded significantly. Hence, their SHAPE HAS CHANGED. As mountains are a part of the Earth, ...

Let me teach you a little equation about relativity. It's called e=mc^2. It means that even though the mass of the earth isn't constant, neither is the mass of the moon. Consequently, everything washes out--everything's relative.

Furthermore, Earth's shape and mass change everytime we're nailed by a meteoroid. Whether it burns up in the atmosphere (and contributes gaseous mass) or hits the ground (and adds extra pebbles), Earth masses rises by this process.

Of course, we can lose mass to the atmosphere escaping too. Hell, I suppose everytime a nuclear fission reaction happens in a power plant, we lose a little mass.

Your point that this will all balance out in the end is ill-founded. Why would you expect mass-loss to be equal to mass-gain? The processes by which it happens seem unrelated to me. Neglecting the effects of atmospheric leakage and fission (and everything else I forgot to think of - like space launches), you could argue that all mass from meteors and dust comes from the moon originally, thus conserving the Earth-Moon system's mass. Unfortunately, we keep finding rocks from Mars, the Belt, or elsewhere. So no dice there. The system is not closed.

Tell me how to get to your house from the
telescope and I'll tell you how to get to the moon.

I find this unlikely unless you're the designer of powerful rocket motors, such as the F-1 or the SSME.

Anyway, I think that's enough ranting for one day :)

Re:ReMooting points.

[Anonymous Coward]

The earth's rotation has nothing to do with it, because the moon's revolution around the earth is in complete lockstep with the Earth's rotation. This is why there is a dark side of the moon that light never gets to.

You're right about the lockstep part.

No, he is not ! The moon's revolution around the earth is in complete lockstep with the MOON's rotation. And of course, he/she is completely off on the dark side stuff.

Re:ReMooting points.

[Laser_47]

There is no dark side of the moon. Matter of fact it's all dark! (thump-thump, thump-thump, thump...)

Actually light does hit the far side of the moon, but we can't see it from the earth. The lockstep of the moon's rotation and it's orbit around earth means that one side always faces us, but when the moon is new (dark) the far side is lit up, we just can't see it from our vantage point.

To less than an inch? Why more?

[fractaltiger]

Please don't mod this down: finding the precise value of PI has also been very controversial.

The issue is that the value of PI has been calculated to various millions of digits, while the distance to the moon is not even constant. The current data wouldn't differ much with this newly added research.

Re:To less than an inch? Why more?

[Anonymous Coward]

precise value of PI has also been very controversial.

Not since antiquity when pi was proved irrational.

those short distances are EASY...

[nomadic]

If anyone's interested, I've correctly measured the distance between the Earth and the Sun.

It's 1 AU.

The Real Tom Murphy

[Tom7]

Fuck that! I'm the real Tom Murphy!

Re:The Real Tom Murphy

[XBL]

No-no, my uncle is the real Tom Murphy.

Re:The Real Tom Murphy

[ImaLamer]

So, 'Tom', why the fuck are you wasting our money on this?

Re:The Real Tom Murphy

[doooras]

won't the real tom murphy please stand up?

When those extra 29 mm are just too much.

[corporate zombie]

http://sunearth.gsfc.nasa.gov/eclipse/SEhelp/Apoll oLaser.html

If my tax dollars are going into this I'm ready to call the first time it was done "good enough for government work".

-CZ

PS - Preview shows the URL with a space between "Apoll" and "oLaser". If that's there on the final submission then take it out.

Re:When those extra 29 mm are just too much.

[4181]

From the referenced Apollo Laser Ranging article:

From the ranging experiments, scientists know that the average distance between the centers of the Earth and the Moon is 385,000 kilometers with an accuracy of better than one part in 10 billion.

Quite a coincidence!

Re:When those extra 29 mm are just too much.

[Anonymous Coward]

385,000.000000 +/- 0.000029 km. Ha!

Which part of the Earth?

[guttentag]

The article says we already know the distance between the center of the Earth and the Moon, but Murphy wants to get as accurate a measurement as possible, and suggests that it will be accurate to the nearest millimeter.

Unfortunately, he's not really measuring the distance between the centers of the two planetoids... he's measuring the distance between the top of some piece of equipment on the Moon and the lens of his telescope.

This reminds me of the human genome project. At some point, the scientists announced, "we've finished mapping the human genome! It's finished!" And as it turned out, it wasn't anywhere near completion. I believe it's still unfinished.

Scientist: "We're going to measure the exact distance between the center of the earth and the center of the moon."
Janitor: "So, why is it off by billions of millimeters?"
Scientist: "Picky, aren't we? It's close enough!"

Is modern science really so desperate to inspire interest in people? Lies are not impressive.

Re:Which part of the Earth?

[recursiv]

Right. I'm sure they won't take into account the fact that the telescope isn't at the center of the earth.

I believe these people know more about what they are doing than you do. At least give them the benefit of the doubt. But wait... you don't even have a reason to doubt.

Well, failing that, don't talk unless you know what the hell you're talking about.

moon cheese

[rehannan]

For years man thought the moon was composed entirely of cheese. In 1969, we finally made the journay to discover the truth. After three years of manned exploration, we found no cheese. Thirty years later, we've yet to return.

Re:moon cheese

[Yorrike]

It brings to mind quotes from the Simpson's:

The Moon. For several years she has fascinated Mankind

And the Monty Burns classic:

For centuries, man has wanted to destroy the Sun

Millikan?

[phliar]

Look into Thomson's original measure of the charge of a single electron. His experiment was extremely clever, but in the calculations he forgot to take into account the viscosity of air.

Which original measure? He knows about viscosity of air in his study of falling water droplets formed in a Wilson cloud chamber by ionisation caused by radium, since he uses Stokes' law for viscous drag of a spherical object. (Millikan later did the oil-drop experiment, where he had to account for the fact that at the scale of the oil drops, air's viscosity needs to be corrected.)

Or did you mean some other experiment?

Oh no!

[ImaLamer]

Tom: Umm... the text book has 385,137.473 KM

Fellow worker: So?

Tom: I've got 385,137.471, should warn someone?.... ah, um... what are you doing?

Fellow worker: CALLING THE WHITE HOUSE!

What should we expect from this 'experiment'? A warning that the moon is going to crash into the Earth in 2003? Come on! Put the money towards something useful, like... figuring out why we aren't on Mars when NASA admits we could have been there in '85 if we kept on schedule.

UW one of top drinking schools

[mrmaster]

If he is from university of Wisconsin are we sure he isn't doing this research at a bar?

Re:UW one of top drinking schools

[Anonymous Coward]

thats washington numbnuts.

washington
westvirgina
wisconsin
wyoming

In other news...

[Anonymous Coward]

In other news...

The struggling software company, "VA Software," announced major work-force restructuring. Innovative cutbacks include outsourcing the piss-poor copy editing at the popular side, "Slashdot."

As of January 16, 2002, the second-rate news site, "BBC News Online," will take over the difficult job of embarassing the literate community.

When reached for comments, the BBC News Online writers commented, "Coding webages in Notepad rawks!!!!!!"

Re:In other news...

[Anonymous Coward]

The link is to the low graphics version, you can get the bandwidth eater here.

Re:Hey..

[Maude Frickert]

Just checking in ...

Please read this correction

[Anonymous Coward]

According to this article from the BBC, you are mistaken. The distance was measured directly over a period of decades.

Parallel space.com article

[4181]

The parallel article contains this ghastly analogy:

Murphy's real motivation is to test Einstein's General Theory of Relativity, which is based on an assumption that gravity affects a feather and a bowling ball in the same manner. You cannot test this in your home, because air keeps the feather aloft.

I forget -- was Einstein the guy who dropped the balls off the tower or the one who was hit in the head with an apple?

Improved correction

[Anonymous Coward]

One measurement as of 1994 was: 3.82±0.07 cm/year

The reference is: Dickey, J.O. et al.,
"Lunar laser Ranging: A Continuing Legacy of the Apollo Program"
Science 265: 482-490. (July 22, 1994)

(And just to be absolutely clear, I am not suggesting that they used the Doppler effect! They used the same direct measurement technique described in the BBC article referenced by slashdot.)

Re:Improved correction

[p3d0]

Thanks for the info. You are right of course. My comment about kinetic energy was wrong.

However, what I meant by not measuring the recession speed "directly" was that the yearly recession of the moon is swamped by other factors like the eccentricity of the moon's orbit, rotation of the Earth, etc. Whatever velocity you measure will have no relation whatsoever to the moon's rate of recession.

Nearest Millimeter???

[Anonymous Coward]

This might make sense if the moon were a perfectly smooth sphere, but it's not. Then there is the earth orbit and rotation to consider. Using RADAR? All things considered, give me a break! Assuming a measurement is obtained it won't have the accuracy of a broken watch which is right twice a day. This measurement will only be correct once a month!

Why not...

[spooky ghost]

$ ping moon
PING moon (212.58.226.40): 56 octets data
64 octets from 212.58.226.40: icmp_seq=0 ttl=2000 time=1.283 s

1.283 x 300000000 = 385000000

So the moon is 385000 km from earth. Easy!

Re:Why not...

[srw]

> 64 octets from 212.58.226.40: icmp_seq=0 ttl=2000 time=1.283 s

This should really be a tad over 2.566s. Remember, a ping time is round-trip. Also, there's some processing time on the other end before it responds.

Still, cute, anyways. :-)

Find The Distance With Hot Grits & CowboyNeal

[Lethyos]

The solution is simple. Pour hot grits down CowboyNeal's pants and record how long it took for him to hit the moon. After that, create a /. poll asking which is the best way to calculate the distance between the earth and the moon with CowoscopeNeal as one of the options. Multiply the time by the number of votes CowoscopeNeal gets, divided by the error margin and you should have your distance.

Disprove this picture

[Anonymous Coward]

if you still think Nasa sent men to the moon, disprove the evidence in this picture.

This Picture

Re:Disprove this picture

[Anonymous Coward]

I do not see anything in the photograph that would change my mind about the Apollo missions. You either have a bad prescription or no education. either way, leave science to scientists, not religionists.

Re:Disprove this picture

[fscking_coward_2001]

Just for argument's sake, what *evidence* is in the photograph?

Re:Disprove this picture

[geekoid]

Oh Jeez, not this picture, again.
"Oh look no stars..aaaaaaiiiyyyyy"
dude, there is too much light on the moon to see stars. when your on the side that happens to be where the sun light, or earthlight happens to be shining. I've been through all the "evidence" hat gets presentsed as "proof" the moon landing was faked, and its all explainable in clear easy consice maner, using small words.

Re:Disprove this picture

[Anonymous Coward]

I think I see what he/she is talking about. I'll have to look at more pictures to confirm.

Interesting, thanks.

Hrmmm.....

[Jeff_Hagen]

Your tax dollars at work.....

You wonder why the taxes in the US are so high

Re:Hrmmm.....

[foolish youngster]

Jesus H Christ, the USA has the LOWEST rate of taxation in the industrialized world. Its complete morons like you who whine and complain about taxes when our schools are so horribly underfunded, most kids never see an up to date science book, where kids see scientists as something evil or suspicious and music programs, among other critical aspects of public education are being shut down due to the lack of available tax dollars. The Federal Government has been totally taken over by corporations that hate being regulated, and oppose taxation for this very reason. You are obviously one of those super greedy capitalist fanatics that refuse to take even basic responsibility for living within a society. Quit your whining and move to some fascist south american country where your blather is tolerated.

Re:Hrmmm.....

[geekoid]

Man I'd love to see your post published in major newspares, maybe people will buy a clue.
Cut taxes, Gimme stuff!
Persoanlly I think all school should get a perfered tax treatment status, and everytime there is a budget hit, take it out of road maintenance first. Then will see how long people want to lower taxes.

Another totally worthless experiments

[trenton]

How about this one: build a clock that can be taken to sea. What good is that? We already have accurate clock on the shore. Oh, right, you can figure out your latitude. And, in the process, invent roller bearings and bimetallic strips, two extremely useful technologies, ones we weren't even trying to create. That turned out well for us, huh?

The moon distance measurement is obviously good. It seeks to do something no one else has ever achived. Even if the results aren't interesting, the new techniques used are. Anyone that doesn't see its intrinsic value is shortsighted.

Re:Another totally worthless experiments

[raytracer]

Oh, right, you can figure out your latitude.

Longitude, not latitude.

I can see it now...

[anonymous loser]

"Ok, I'll hold THIS end..."

careful, in another 100 million years...

[supernova87a]

Lots of people seem to know that the moon is moving farther away from the earth, but did you know that the earth's rotation is slowing down?

These two phenomena are actually related -- the orbital angular momentum that the moon is gaining (moving farther away) is taken from the earth's rotational angular momentum. Gradually, but measurably, the earth *is* slowing down. You might have heard of leap seconds? These are to compensate (partially) for the slowing in fact!

Eventually (ok, in maybe 100 million - 1 billion years) the earth and moon will orbit/rotate at the same angular velocity, so that at that time, we will always see the same face of the moon, and the moon will always see the same face of the earth!

Better pick which side of the earth you'll want to live on, otherwise if you pick wrong, you'll *never* be able to see the moon... :)

Retroreflectors are handy for motion capture

[Anonymous Coward]

but that's mostly useful for games, and this is a linux site... not much call for motion capture with "hunt the wumpus"... :-)

how about...

[Anonymous Coward]

measuring the distance between the Earth and the SUn precisely? My guess is just under 1.01 AU's.

Am I missing something here?

[Anonymous Coward]

Where exactly did they (if) land to place these mirrors? Surely it was WAY to hot on the face we always see to place them there? Must have placed them bloody accurately to be of any use to us...especially since that flag was blowing quite violently in the wind :-)

troll, troll, troll

[warez_d00d]

Boring, dude.

20 second rule sucks. Some people can type faster than than, you know Taco?

Re:troll, troll, troll

[Anonymous Coward]

what the hell are you talking about?

maybe Tom should focus on

[Anonymous Coward]

Maybe Tom should stop wasting his time with nearest mm measurements and instead provide conclusive proof that man landed on the Moon.

With all the talk of sending a manned mission to Mars, I have to wonder how that rickety peice of crap lunar module ever made it to the Moon and back with three living passnegers; and why we havent taken the trouble and time to build a small base on the moon for scientific research like Oh I dunno, simulating a manned mission to the Red Planet?

Cant even put an damn manned station in orbit without it falling apart, how you gonna get to Mars....

Interesting fact...

[Ryano]

If all of the articles published on this topic were stacked one on top of the other, they would reach the moon and back 3.42 times.

Or should that be 3.46?

I found an easier way...

[Anonymous Coward]

www.mapquest.com

Measure this...

[PegQuin]

Are they measuring to the biggest, nearest rock or the smallest most further rock? Modern man can't even accurately measure his penis--so what's the point? Is there good money in this?

significant digits / error / order of magnitude

[SCHecklerX]

"Tom Murphy at UW is attempting to measure the distance between the Earth and The Moon to the nearest millimetre

That's pretty stupid, considering the distance will obviously change more than a millimeter all the time. Hell even the astronaut's footprints will be several millimeters thick, assuming they are undisturbed still. So...within a millimeter of *what*, exactly?

Already done with accuracy of 3mm

[jdfekete]

If you look at the french project "Station de Télémétrie Laser-Lune" at http://wwwrc.obs-azur.fr/cerga/laser/laslune/llr.h tm, you will see it has already been done with good precision (3mm).
You can download all the results already, day by day, from 1996.
Since it's not in english, it can't be real!

Re:Already done with accuracy of 3mm

[4181]

Here is the article in a more (or less) barbaric language.

Re:Already done with accuracy of 3mm

[Anonymous Coward]

Just a comment that research groups from the
U. MD. College Park and U. Texas have been measuring the earth-moon distance using pulse
lasers and telescopes since the mid 1970's. The
primary challenges are generating a short (~ 0.05 nanosecond) laser pulse, and detecting the few photons that actually make the round trip.

Re:Already done with accuracy of 3mm

[Publicus]

Yeah right. They have not.

Clever

[gaudior]

/usr/lib/units

Too many sig figs?

[Dop]

Isn't measuring this distance to the nearest millimeter a little bit pointless? I'd imagine variations in surface elevation and orbital distance would throw it off.

Accountants

[Anonymous Coward]

So long as Anderson isn't counting up anything.

Murphy's New Law

[vortexSurpher]

The purpose of this experiment is explained much better in this Space.com article

"The distance by itself isn't very interesting," Murphy said in a telephone interview.

Murphy's real motivation is to test Einstein's General Theory of Relativity, which is based on an assumption that gravity affects a feather and a bowling ball in the same manner.

"This probes at the fundamental characteristics of gravity, which is the most important force in our daily lives," Murphy said.

Murphy's Special Law of Relativistic Gravity: Anything that can go wrong with gravity, will go wrong with gravity, and it will happen relative to me.

I guess Murphy's first Law wasn't enough. Now they need a special case for if the moon falls on you.

*sigh*

[Anonymous Coward]

It's a sad day in Moderationland when a comment like this doesn't get modded up.

Problems seeing the reflectors

[Motheius]

Won't he have some problems seeing the reflectors on the lunar sound stage in the California movie lot? I am pretty sure the mountains between New Mexico and California will get in the way.

Which part of the moon?

[markmoss]

How do you get an "accurate to one millimeter" measurement to an object covered with dust grains, plus pebbles, rocks, boulders, mountains and craters? Doesn't your value change depending on whether you measure to the top of that 1 mm sand particle. or to the rock it's on?

OK, they say they are trying to measure the center to center distance, but they don't get that directly. The real measurement is from a telescope mount on top of a mountain on Earth, to a retro-reflector on the Moon. Do you actually know the height of that mountain at the observatory to 1 mm? And can you correct that height to the day the measurement was taken? (Some sorts of subsoil will shrink and swell depending on water contact, sometimes resulting in the ground rising and falling a few feet annually. I'd think that deep down in a mountain would be rock so it wouldn't do that, but in most cases the whole mountain is either rising or falling by at least millimeters a year, and if there is any soil cover weather changes might change the height by a few millimeters.)

And on the moon, you are measuring to a reflector which is basically laying where the astronauts dropped it 30 years ago. How would the distance from the reflector to the center of the moon be measured? Laser beams & navigational gear in satellites orbiting the moon? What satellites?

remember high school science

[Graymalkn]

Although I applaud the attempt at such fanatical precision as something that is A.) challenging B.) informative and C.) possibly producing unexpected technological advances, the actual goal of measuring the distance to the nearest milimeter is a bit silly.

Why? Because the surafce of the moon is not perfectly flat. There are hills and valleys, meaning that level of precision is going to far exceed the level of inherant uncertainty.

But still, a worthy task.

Wider beam makes hitting target harder???

[Asikaa]

"But the task is not as simple as it sounds. The beam of light must hit the retroreflectors, each about the size of a suitcase, on the lunar surface.

This is made even trickier by the fact that the beam will be about 2 kilometres (1.2 miles) wide by the time it reaches the Moon."/I>

Oh-kay.... so it would be less tricky if your laser beam was, say, 2 millimeters wide by the time it reaches the moon?

This is quite vague.

[Anonymous Coward]

What "distance" are they talking about? They are trying to "exactly measure" the distance between two spheres. Is this a measurement between the centers of each sphere, or the shortest distance between the surfaces? Also, if they are measuring the distance between the surface of Earth and the Moon's surface, wouldn't that be difficult from Earth's little tendency to turn?

precession of Mercury

[Anonymous Coward]

The precession of the orbit of Mercury was known in the late 1700's, at least as far back as Leverrier.

Hmmm

[Anonymous Coward]

I just wonder if theyre going to take in account that the speed of light is not a constant in their measuring.... I mean if they want an exact measurement

Check the odometer

[bluetoad]

The Americans reckon they've been to the moon. Why don't they just check the odometer on one of their spacecraft.

Who cares

[Municipa]

Do we really need to know how far the Moon is from the Earth? What good can come from it?