Wikipedia:Reference desk/Archives/Science/2014 February 25

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February 25

Is any moon phase more fuel efficient for rocket approaches than all others?

I was thinking it seems more efficient fuel-wise to shoot a rocket for the moon on the day that the moon is at first quarter and aiming your rocket to meet it in its path because this way the moon is behind the earth in the earth's orbit around the sun running "forward" to meet the rocket while the rocket is going "back" to meet it. Is there truth in this? Were the moon missions made while the moon was at roughly the same phase, or at different phases and phase doesn't affect fuel efficiency? 75.75.42.89 (talk) 04:08, 25 February 2014 (UTC)

I'm not sure if phase of the moon mattered but its orbital velocity is used. See Circumlunar trajectory and its references. Similar types of trajectories are were used by other spacecraft with Jupiter and Saturn to accelerate them to the outer reaches of the galaxy at speeds that would require tremendous amounts of fuel. I believe all the conic slices are available and the orbital velocity of the object adds to the spacecraft velocity in mathemagical ways. This reference has more details. As the earth rotates at rate relative to the moon, launch windows were specified at certain hours of the day. To launch in daylight is related to the phase of the moon so it appears the desire for a daylight launch specified phase and time of day as well as unfavorable days. The Sun (other than being the source of daylight) didn't seem to be a large determiner of launch windows. --DHeyward (talk) 05:25, 25 February 2014 (UTC)

No. The Moon's phase tells you about the position of the Sun, but the position of the Sun is irrelevant to fuel efficiency. Think about an astronaut moving from one side of a space station to the other. Is it easier for him to move when he's on one side of Earth's orbit as opposed to the other? The answer is no, because the space station is extremely small compared to its distance from the Earth, so all of the space station experiences the same acceleration due to Earth's gravity. Similarly, the Earth-Moon distance is very small compared to their distance to the Sun, so the angle of the Sun is irrelevant to fuel efficiency.

However, the moon phase does matter for landing. Astronauts presumably don't want to land during new moon, because they either have to land in the lunar night, or they have to land on the far side of the Moon (which is out of radio contact with Earth). Both options are highly dangerous. --Bowlhover (talk) 05:35, 25 February 2014 (UTC)

Sorry to overuse the word "phase." I know the happenstance amount of light on the moon has nothing to do with it. The important part in my thinking was the moon moving forward in the direction that the earth is going around the sun while the rocket goes back, so they are coming toward each other, which happens to be the situation at first quarter. 75.75.42.89 (talk) 12:40, 25 February 2014 (UTC)

Remember that the earth-moon system is in 'free fall' around the sun. Just like the astronauts in the ISS are floating around in a zero-g environment. The only time you feel the sun's gravity is when you're rigidly attached to one of those bodies somewhere other than at its center of gravity and tidal forces come into play...but that force is gone once you leave the earth's surface and doesn't reappear until you land on the moon. The distances travelled in going from Earth to Moon are negligable compared to the distance to the sun, so the sun exerts almost exactly the same force on the Earth, Moon and Rocketship - so they all fall freely together. As others have pointed out, by far the most important factor in choosing a launch date is whether there will be sunlight on the landing site during the mission - and that's strongly determined by the choice of landing site and the phases of the moon throughout the time on the surface. SteveBaker (talk) 13:55, 25 February 2014 (UTC)

Has the elliptic orbit of the Moon been a factor in choosing launch dates? The distance to Earth varies from around 363000 to 405000 km, but I don't know the effect of the Moon moving faster when it's closer. Earths rotation around its own axis gives you some free speed when you launch towards East from near the Equator. The Moon doesn't orbit in the equatorial plane so is it a factor whether the Moon is in a good direction? PrimeHunter (talk) 22:13, 25 February 2014 (UTC)

Side topic: The "outer reaches of the galaxy" are currently not within reach, by any stretch of imagination. There have only been very few spacecraft which left the solar system at all, most notably the Voyager and Pioneer spacecraft, and it doesn't really matter if they go to the outer or inner reaches of our galaxy, or advance spinward, or whatever; it will be thousands of years before they get to other stars, and these stars are like next door neighbors in a large city.

Keep in mind that if "the moon [is] moving forward in the direction that the earth is going around the sun while the rocket goes back, so they are coming toward each other", you don't gain anything, because you have to burn more fuel to slow down WRT the moon to enter its orbit, and for a return mission, you have to burn more fuel on the way back to Earth to build that relative velocity back up. - ¡Ouch! (^{hurt me} / _{more pain}) 06:48, 28 February 2014 (UTC)

Scientists and theorists who lived to see their theories be replaced/debunked

What are examples of scientists and theorists who came up with theories and hypotheses which at first become widely accepted, but lived to see their theories or hypotheses eventually be replaced, "improved", or debunked due to advances in scientific knowledge and that their theories no longer held up with newly-discovered information? Narutolovehinata5 ^tccsdnew 04:21, 25 February 2014 (UTC)

Neils Bohr and the Bohr atom is an obvious example of a theory that was very influential (Nobel Prize) and then replaced by a more complete theory during the creator's lifetime. Dragons flight (talk) 05:11, 25 February 2014 (UTC)

Actually, Niels Bohr. --Stephan Schulz (talk) 07:21, 25 February 2014 (UTC)

Albert Einstein, who called his introduction of the cosmological constant the greatest blunder of his life. It later transpired that the cosmological constant actually exists, but is of the opposite sign than what Einstein proposed. So Einstein blundered twice: the first time by introducing the constant, the second time by retracting it. --Bowlhover (talk) 05:24, 25 February 2014 (UTC)

We don't know if Dark Energy is adequately described by a cosmological constant yet. If it is, it has the same sign Einstein proposed. Einstein originally included it to balance gravity and hence provide a steady-state solution - thus it had a positive value. Now we think it may be even larger (if it is constant at all), hence driving the acceleration of the expansion of the universe. --Stephan Schulz (talk) 07:21, 25 February 2014 (UTC)

At a pinch, one might mention J. J. Thomson here - his discovery that cathode rays consisted of subatomic particles, specifically electrons, won him a Nobel prize. He lived long enough to see his son George Paget Thomson win a Nobel prize for demonstrating that electrons were subject to diffraction - as waves. Of course, Thompson senior wasn't exactly 'debunked' by Thomson junior, in that wave-particle duality implies that they are both right, depending on what it is you are trying to measure. AndyTheGrump (talk)

The world owes quite a bit to Isaac Newton's dalliance in alchemy. Also, physics was in great decline at the end of the 19th century and the industrial. There were only a few esoteric "loose ends" to wrap up but planetary motion, electromagnetics and mechanics were well understood in a practical sense. Then quantum mechanics and relativity monkey-wrenched everything. --DHeyward (talk) 05:45, 25 February 2014 (UTC)

Does "theorists" include economists? They are proved wrong all the time. HiLo48 (talk) 07:27, 25 February 2014 (UTC)

Only theories whose field of work is in the sciences or mathematics. Which is why this question is in the Science Reference desk in the first place. Narutolovehinata5 ^tccsdnew 07:30, 25 February 2014 (UTC)

Using the strict language of science, hypotheses are intended to be either debunked or not upon further investigation, or in light of experimental evidence. A scientist will often say "I hypothesize that X is true, and here is an experiment I can do to see if that's correct"...time passes and we find that..."The experiment was successful in showing that X is in fact false - which is a useful result." It is often the case that one devises experiments specifically to test ones own hypotheses. That's just how the scientific method works. I'd imagine that just about every scientist would come out with hypotheses that they themselves debunk. In many cases, it really doesn't matter whether the hypothesis is "X is true" or "X is false" - and the scientist is not supposed to care which hypothesis is made prior to the experiment that proves or disproves it.

Theories, on the other hand, are an entirely different matter. A scientific theory is supposed to be a proven fact - and when one of those is disproved, it can be a huge deal...and if it's disproved during the lifetime of it's discoverer, then that's an even bigger deal.

So this question should really be about theories and not hypotheses. SteveBaker (talk) 13:42, 25 February 2014 (UTC)

Here's what I teach my students: A theory is an explanation, a hypothesis is a guess. When you say "I have a theory about X" you don't mean "I have a guess about X" you mean "Here's how I can explain X..." Your theory may be also a hypothesis (that is, an explanation which doesn't have evidence to support it yet) or it may be a well established theory (with lots of evidence). But the word "explanation" is the best near synonym for what a "theory" is. Theoreticians are scientists who are primarily concerned with explaining why things happen. Einstein was a theoretician because his primary concern was coming up with explanations for why the world works the way it does. --Jayron32 15:12, 25 February 2014 (UTC)

(Off-topic, but that word is terribly overloaded. In addition to the hypothesis/explanation/body-of-knowledge confusion, some theories are just not much like the others!) SemanticMantis (talk) 15:31, 25 February 2014 (UTC)

N rays were popular for a year or so, our article implies, before they were considered imaginary—well before their discoverer's death. הסרפד (call me Hasirpad) 19:25, 25 February 2014 (UTC)

Lamarkian evolution, which held that animals evolved new traits in their own lifetime, and passed those down to their offspring, was replaced by Darwinian evolution. However, more recent discovers suggest that Lamark wasn't entirely wrong, and some adaptations acquired during an individual's life may actually be passed down (see epigenetics). StuRat (talk) 20:02, 25 February 2014 (UTC)

Lamark was dead before the Darwinian revolution, so he didn't get to see his theories displaced, which is what the original question asked about. Dragons flight (talk) 20:10, 25 February 2014 (UTC)

Many early Soviet theorists considered their principles "scientific", which, according to an article linked from the Main Page today, caused some of their followers to have heart attacks or commit suicide or engage in rioting when, on 25 February 1956, their leader delivered the speech On the Cult of Personality and Its Consequences, overturning some of the rather non-scientific things they had been encouraged to believe in over the preceding 25 years or so. Not quite what you were after, but interesting. --Demiurge1000 (talk) 20:33, 25 February 2014 (UTC)

One might mention Fred Hoyle, who was instrumental in the development of the Steady State theory, which was plausible in its day but which came to be rejected during his lifetime by almost all cosmologists, particularly after the discovery of the cosmic microwave background. He went to his grave continuing to reject the idea of a Big Bang (a name which he had coined in derision). Deor (talk) 20:52, 25 February 2014 (UTC)

Examples from philosophy are, almost by definition, very rare. There is, however logical positivism, which has been pretty soundly refuted. One of its chief proponents, A.J. Ayer, even said years later something like "the problem with logical positivism was that nearly all of it was false." --— Rhododendrites ^talk |  19:36, 26 February 2014 (UTC)

Albert Einstein

Albert Einstein we all are amazed beacause of his knowledge which may be in terms of theory of relativity,Energy relation,or any other theory! I heard that pieces of his brain are still studied ,aren't they? if Yes,then which information is achieved? — Preceding unsigned comment added by Sadhana savkare (talk • contribs) 13:13, 25 February 2014 (UTC)

We have an article, Albert Einstein's brain. -- Finlay McWalterჷTalk 13:16, 25 February 2014 (UTC)

FINDING smart dust

What's most depressing about the Snowden disclosures is that, though providing a good excuse to change the law to start using archived "private" communications against people, they provide such a tiny sliver of the total surveillance going on. Not a word about antivirus software or drone surveillance, for example. But I think the cardinal omission is that of smart dust, which was developed 20 years ago and was publicly "smaller than a grain of rice" 15 years ago. With the use of a "dead drop" site by Robert Hanssen prior to 2001, it should be apparent that surveillance of parks, especially in the U.S. capital zone of northeastern Virginia, would be a top priority. Clearly, a person visiting that area should be able to gain extensive access to any park plausibly usable for such a purpose, nor can "smart dust" readily be removed. Therefore, blowing the lid off the NSA monologue and exposing direct surveillance of conversations on U.S. soil in classic totalitarian fashion should primarily require some effective means of finding the "dust".

Now obviously the dust will be designed to be hard to find. I assume it knows better than to transmit when someone is standing next to it (and it knows...) Presumably it also is designed to stick to other objects so it doesn't wash away in the rain (at least, unless it is truly no better than the crude prototype and simply settles as gravel, in which some sort of density sorting might work). Likely it would be necessary to locate the dust in situ. The usual vulnerability mentioned is the antenna -- is that necessarily unavoidable? I keep reading about devices that supposedly can be woven into fabrics, etc. - do these have an exemption from the need for a conductor? What kind of equipment do you need to visualize small conductors on a field, so they can be plucked up for further analysis?

Another option is terahertz. Two years ago there was discussion of using cell phones as terahertz scanners.^[1] Can you program something small and cheap to spot traces of nearly pure silicon as would be found in most semiconductor chips, and thereby spot the dust with it? What are the odds it doesn't have that?

Any further ideas? Wnt (talk) 14:27, 25 February 2014 (UTC)

[2]. AndyTheGrump (talk) 14:31, 25 February 2014 (UTC)

@AndyTheGrump: that doesn't deserve a response, but I'm going to give one anyway. I'm not basing my suspicions on some twelfth-hand story I heard on the Internet. My initial comment was based on a) that Barrett Brown, who investigated NSA contractors, including Booz Allen Hamilton before the Snowden disclosures, named HBGary as his nemesis, which is a company with extensive anti-virus business associations^[3]; b) the fact that I personally saw a very small white aircraft flying rapidly and noiselessly over a site where Bush was going to speak in 2005; and c) that Snowden hasn't mentioned either of these things. They say he has the "keys to the kingdom" but I think he has more like the key to the maid closet off the front parlor.

As for the smart dust itself, I should emphasize that the article is about something that was actually made in the late 1990s. Therefore, it is possible for people to answer this question even if they assume that one would have to be a raving lunatic to suppose that the NSA would do anything with a spy invention in their hands other than file it away in a warehouse.

Last but not least, tinfoil hats get a bad rap insomuch as they are an experimental method. Maybe if this guy had tried using one, he would have realized he was not under microwave attack and refocused his attention on some more likely cause, such as the all too common noise pollution in supposedly (but not) "subsonic" frequencies. At worst, at least anti-noise advocates would have had the benefit of the credibility and political pull that an act of terror generates; at best, he might have become an effective advocate for real environmental improvement. Wnt (talk) 15:27, 25 February 2014 (UTC)

I won't comment on the scope of your suspicions, but I share your curiosity of what has become of this smartdust DARPA/ RAND project led by the Berkeley team. Here's a link to a relevant search, from which you can download several pdfs describing more recent progress from that lab [4]. As for antennae, I'm pretty sure there's no way to transmit EM radiation without a conductor. There are some clever ways to get more mileage out of smaller antennae, e.g. Phased array (as a hilarious side note, Neal Stephenson is mentioned as some sort of inspiration for smartdust, and he also relies heavily on phased array magic in some of his fiction). Final nitpick: tinfoil hats are just devices. Perhaps one can perform experiments with them, but that's not the use and rhetoric that the advocates of such headgear usually promote! SemanticMantis (talk) 15:34, 25 February 2014 (UTC)

The link you provide appears quite useful. Already [5] from 2001 points out that, even then, they were more seriously considering optical transmissions by reflecting light or from a laser diode rather than centimeter-long antennae. Back then, the power limitations would have held the transmission down to a million bits per day, which would be somewhat unsatisfactory for audio surveillance, but I suppose they have 'improved'. Wnt (talk) 15:43, 25 February 2014 (UTC)

Ha, looks like they thought The Diamond Age was an instruction manual! Glad the link helped that search tool reveals all kinds of crazy stuff :) SemanticMantis (talk) 15:59, 25 February 2014 (UTC)

Putting a sail on an airship

If you put sail on an airship, could you just use the wind to travel? The airship would need to be in the middle of the sail (imagine a mast with an airship in the middle), or have a sail on each side for balance. Ĩnstead of using the sail (wings) for lift, it would use them for being dragged by the wind. Flying (sailing) against the wind would be impossible, but you still get predictable winds in some parts of the world. Could that work? OsmanRF34 (talk)

You don't need a sail - the wind will take the airship with it anyways (and the same is true for aircraft, which is why you have a difference between air speed and ground speed). A sail on a ship make sense because the wind moves the ship against the resistance of the water. Without that resistance, the airship moves with the wind, anyways. A sail might accelerate it marginally faster, but wont affect the final speed. Of course, such airships are generally know as balloons. There are different success and failure stories about making them go where you want - see e.g. (fictional) Five Weeks in a Balloon and (real) S. A. Andrée's Arctic Balloon Expedition of 1897. --Stephan Schulz (talk) 16:29, 25 February 2014 (UTC)

So, it doesn't matter what proportions you get between mass and surface? And also the shape or orientation are indifferent? At the end everything will be flying with the same speed as the wind? OsmanRF34 (talk) 16:34, 25 February 2014 (UTC)

Exactly, yes. --Stephan Schulz (talk) 16:38, 25 February 2014 (UTC)

Well, the strict answer is: "Eventually, yes". At the moment that the airship lifts off, it is stationary with respect to the ground. The pressure of the airflow on the windward surface will gradually accelerate it until it's stationary with respect to the airflow...but yes, it doesn't matter what size or shape the craft is, without some kind of thrust, it'll eventually be travelling at the same speed and direction as the airflow. The shape and size will alter the time it takes to attain that final speed - but not what the final speed actually is. SteveBaker (talk) 19:34, 25 February 2014 (UTC)

• Planes have lift because they go faster than the air through which they are flying and the wings convert part of the forward thrust into lift. A plane going at the same speed as the air will stall and crash--unless there's an updraft like birds of prey spiral in, in which case what you have is a glider. μηδείς (talk) 17:14, 25 February 2014 (UTC)

An interesting example of that is a kite. It looks like the kite string is holding it to the ground - but when you cut the string, it doesn't sail up into the air - but instead falls to the ground. That's a little counter-intuitive - but it happens because the force on the string is holding the kite stationary as the air moves past it. From the point of view of the airflow, the kite string is pulling the kite through the air - so it can gain lift just like an airplane. When you cut the string, that force disappears, the kite rapidly speeds up until it matches the speed of the air - then (since it's heavier than air), it simply falls to the ground. SteveBaker (talk) 19:34, 25 February 2014 (UTC)

Yes, Steve, the dynamics of kites is a particulary interesting and usefull observation. μηδείς (talk) 22:19, 25 February 2014 (UTC)

The reason that airships have a streamlined shape and has engines, is so that they are able to go in a different direction to the wind. If you only want to go in the same direction, you only need a balloon which is much cheaper. Getting back to where you started is usually an issue though. Alansplodge (talk) 18:13, 27 February 2014 (UTC)

Could humanity get rid of the moon?

Could humanity get rid of the moon and how much would it cost? 212.96.61.236 (talk) 03:32, 25 February 2014 (UTC)

No. And too much.

And why are you asking this question here? This is the computer reference desk. AndyTheGrump (talk) 03:43, 25 February 2014 (UTC)

All you have to do is build a death star. The death star was able to destroy Alderaan in a matter of seconds. Why do you want to destroy the moon, though? :-/ —Best Dog Ever (talk) 03:55, 25 February 2014 (UTC)

So, in short, the US government won't get rid of the moon (wanted to link to the White House's petition response but couldn't), even if, as a group of humans, they could? (Couldn't resist, sorry.) - Purplewowies (talk) 04:29, 25 February 2014 (UTC)

Check out this video, about what it takes to deorbit a moon in Kerbal Space Program. He does calculations for the smallest moon in the game, Gilly. It should be noted that Gilly is only 26 km across, orbiting a planet 10 times smaller than Earth. --Bowlhover (talk) 05:42, 25 February 2014 (UTC)

The consequences of a disappearing moon are explained in a book I have called What would happen if aliens stole the moon and 100 other questions or similar; a collection of silly questions with scientific answers written by readers of New Scientist magazine. After the tides stop, all life on Earth would eventually stop. 81.145.165.2 (talk) 13:10, 25 February 2014 (UTC)

Further I had a physics teacher who explored this question when asked by a student. Unsurprisingly the time taken for one man on a hang glider to tow the Earth a few feet was... I do not recall how many million years.81.145.165.2 (talk) 13:12, 25 February 2014 (UTC)

Why would all life on Earth disappear if the tides top? Beings living in coastal tidal waters would be affected, in the same way as lots of human activities and migrating fish like salmon. But all life? All bacteria, cockroaches and the like? OsmanRF34 (talk) 17:54, 25 February 2014 (UTC)

I'm strongly skeptical of that claim. I think there is good evidence that life on earth wouldn't have started without tides - but now that life is well-established, I doubt that it's so important. There are arguments that the tides drive some ocean currents and that without these, the climate would be dramatically altered - but the claims for this are a bit tenuous. Also, it's not true that there would be no tides on Earth without the Moon - there are tides produced by the Sun too...they are rather weak (1/180th of those produced by the moon) - but they are very regular and without the disturbing influence of the moon might produce a resonance effect in some parts of the ocean that would result in much higher tides...but again, it's unclear. SteveBaker (talk) 19:19, 25 February 2014 (UTC)

Winds/storm surge also vary the sea level. And, even if the sea level was constant, I'd think that would have some benefits for people, too. It would certainly make designing docks and locks a lot easier. StuRat (talk) 19:29, 25 February 2014 (UTC)

(ec) All life wouldn't disappear, that's just crazy talk. But tidal wetlands are the most productive environments on earth by a huge factor. There'd be a mass extinction comparable to the K/T and Permian extinctions, and probably a severe effect on atmospheric oxygen levels. μηδείς (talk) 19:26, 25 February 2014 (UTC)

Wetlands have many cool animals and plants not found elsewhere, and are important for many endangered species. However, they cover only a small portion of the Earth (about 2%) and most of those are either freshwater or sub-tidal marine (i.e. saltwater deeper than low tide). The portion of wetlands that are strongly tidal are only a small fraction of all wetlands. Getting rid of all tidal wetlands would have only a small effect on biodiversity (no where near the 30% of genera seen at the KT), and almost no impact on things like oxygen. More expansive ecosystems, including open ocean, tropical rainforest, and subtropical forest each produce much more oxygen than wetlands do. Dragons flight (talk) 21:27, 25 February 2014 (UTC)

This post is addressed to the original poster. Jehovah's Witnesses have published information at http://wol.jw.org/en/wol/d/r1/lp-e/1102010231#h=11:0-12:382, describing the moon as the perfect "neighbor".

—Wavelength (talk) 19:36, 25 February 2014 (UTC)

What has that got to do with anything? I'm sure the Whirling Dervishes have a view on whether the moon is nice or not, but I fail to see the relevance when the OP is asking whether it is possible to get rid of the Moon, on the Science desk. 86.157.25.240 (talk) 20:38, 25 February 2014 (UTC)

The details mentioned there seem to me as relevant as previous comments about tides.

—Wavelength (talk) 20:53, 25 February 2014 (UTC)

Is it IP 86's contention that Wavelength misrepresented the nature of the reference he gave, or that IP 212 is incompetent to judge such a reference, and that we therefore need to hide this from the eyes of the children? μηδείς (talk) 21:21, 25 February 2014 (UTC)

The IP's contention is that replying to the question "could we get rid of the moon?" on the science desk, with a link to a long religious article about how the Strong anthropic principle means that Jesus is the Archangel Michael, on the justification that it contains a single paragraph which vaguely refers to ideas which have already been brought up with links to relevant Wikipedia articles earlier in the conversation while using these as a jumping off point that "this is not a coincidence" and therefore the Watchtower Bible and Tract Society is God's representative on Earth, is in fact the sort of thing that spoils a reference desk's reputation and looks like simple spammy proselytising. It is not a suitable reference. Or shall we start linking to the Bhagavad Gita on questions about elementary particles? This is not Yahoo Answers. We don't just chuck out random opinions and hope the OP sorts it out. 86.157.25.240 (talk) 21:41, 25 February 2014 (UTC)

Who are "'we", IP 86? You seem to be engaged in debate. Wavelength isn't. Neither am I with you on this after this remark. μηδείς (talk) 21:46, 25 February 2014 (UTC)

You know what? I said I wouldn't pursue this, and I won't. You asked a question, and I answered it. If you do not want replies, perhaps you should not ask questions. I agree that if "we" includes you, then my statement would probably not be correct. I'm not replying further, so say whatever you like. 86.157.25.240 (talk) 22:04, 25 February 2014 (UTC)

• Primary production (amount of Carbon fixed by photosynthesis) on average world-wide (excluding permanently ice-covered areas) is about 426gC/m^2/y while the production of saltwater tidal marshes averages about 8,000g for the southern US.[6] Bogs average about 250g. The conversion of well-oxygenated productive tidal marshes to bogs would mean the end of near-shore fishing, the death of the current ecosystems, a mass extinction of fish, shellfish, migratory birds, and shorelife. The end of tides would doom sea turtles, horseshoe crabs, innumerable numbers of beach and freshwater breeding ocean fish to go extinct, as well as reef life which is largely dependent on tides for both oxygenation and reproduction. There's be a significant long-term and permanent drop in atmospheric O2 production. But yes, it would be easier to build docks in now stagnant, lifeless water becoming ever more shallow from land-runoff and useless for any purpose by people dying off from oxygen deprivation and starvation. μηδείς (talk) 21:46, 25 February 2014 (UTC)

If we could remove the moon from orbit, it would be also be possible to move another moon into it's orbit, for the sake of novelty. Or we could just put an artificial gravity generator in it's place. If we could do one, we could do the other. If. I'm also assuming the OP meant move and not destroy.--Auric talk 22:05, 25 February 2014 (UTC)

Perhaps the replacement moon could be made made of green cheese, and enlarged a bit to provide the same mass as the old moon. It would have interesting oceans like Europa and an atmosphere, once the components of the fresh cheese had sorted themselves out under the pressure of gravity, per http://www.stwing.upenn.edu/~fitz/humor/moon_cheese.html. Edison (talk) 22:28, 25 February 2014 (UTC)

Actually, we could move the moon by sending well-aimed asteroids past it to deflect its orbit. But there's no indication that there will ever be any such thing as an artificial gravity generator. μηδείς (talk) 22:32, 25 February 2014 (UTC)

• Yes! Just close your eyes: "Albert Einstein is reported to have asked his fellow physicist and friend Niels Bohr, one of the founding fathers of quantum mechanics, whether he realistically believed that 'the moon does not exist if nobody is looking at it.' To this Bohr replied that however hard he (Einstein) may try, he would not be able to prove that it does, thus giving the entire riddle the status of a kind of an infallible conjecture—one that cannot be either proved or disproved." See: If_a_tree_falls_in_a_forest. You can prove this for yourself: just close your eyes and see (or not see) --- and the moon has gone.--Aspro (talk) 22:53, 25 February 2014 (UTC)

People who raise this canard should be shot. They can simply close their eyes and they won't be. μηδείς (talk) 23:00, 25 February 2014 (UTC)

If you archive this discussion will it go away? (please)  ;)  71.20.250.51 (talk) 00:12, 26 February 2014 (UTC)

They could if they built Gort. He was capable of destroying the earth if necessary, so he could certainly destroy the moon. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:28, 26 February 2014 (UTC)

• Actually, the numbers are quite interesting. If we assume 75% ocean, 25% land, 2% of which is tidal marsh with the same productivity on average as the US south, we get:

Ocean: 75% surface X 140 g/M^2/y = 105

Tidal: 02% surface x 8,000 g/M^2/y = 160

Earth: 23% surface x 426 g/M^2/y = 98 (overestimate, since average does not include icecap in area)

Total = 363

Tidal % = 160/363 = 44%

Meaning tidal marshes produce 44% of our oxygen. Even a 4% drop in global oxygen would be catastrophic, and a 10% drop would be widely fatal. Most warm-blooded life would perish within a geologic eyeblink. μηδείς (talk) 00:52, 26 February 2014 (UTC)

• I just want to point out that this estimate is not very close to the truth at all. Medeis is right that tidal wetlands are highly productive on a per-meter-per-year basis, but most of global C fixation comes from photosythesis in tropical forests, savannahs, and grasslands (which is associated with O2 production, etc.). Here's a good reference that explains our best recent estimates of how much different biomes contribute to the global C cycle [7]. All wetlands combined contribute only ~7% of global net primary production, as summarized by this 2009, highly cited, peer-reviewed article. So I'm confident that tidal wetlands cannot produce 44% of Eearth's yearly O2. But I won't be back to discuss, this whole thread is a mess, I'm surprised nobody has closed it under WP:CRYSTAL, or "we do not speculate on the ref desks." If anyone wants to ask a serious question about productivity of terrestrial biomes, the global carbon cycle, or oxygen production, I'll be happy to supply more refs at that point. SemanticMantis (talk) 16:54, 26 February 2014 (UTC)

So you haven't paid any attention at all, then? I said that if the estimate, based on the claim above mine (not my claim) that tidal marshes amount to 2% of the Earth's surface, was off by a factor of 10, their destruction would still amount to a minimal decrease of 4% of the planet's oxygen production. You yourself say seven percent, and this doesn't count the amount that would be lost due to decay. A permanent ten percent drop in oxygen, with loss of most fisheries and coastal livelihood would be catastrophic. Your source is not accessible with a sign in. I confirmed my estimate with a wetlands restoration expert, who said at best I was off by a factor of two in my per/meter estimate of 8,000gC/m^2/year. μηδείς (talk) 01:22, 27 February 2014 (UTC)

If you reread my comment above, the 2% was for all "wetlands", and I explicitly noted that tidal marshes are only a small portion of total wetlands. Also, your 8000 gC/m^2/yr is from particular marshes noted for having unusually high productivity. An average marsh might only be 2000-3000 gC/m^2/yr. According to Mantis' citation, the average for all wetlands is only 1200 gC/m^2/yr. I agree with Mantis that 44% is just comically high. Dragons flight (talk) 02:00, 27 February 2014 (UTC)

You're still getting a huge productivity given your figure. the 160 relative figure goes down to 24 all wetland, 105 all ocean, and 98 for the land surface, of which 24/(24+105+98)= 10.66% of the earths primary production coming from wetlands. By far the greater amount of that production will be from tidal wetlands, again, since bogs have only a fifth the productivity of the 1,200g you quote. The point stands, a 5-10% drop in oxygen production combined with rotting organic matter would cause a huge extinction event. But I can understand your wanting to attack the 44% figure and ignored that I suggested it might be of by a factor of ten if your goal is merely rhetorical victory. μηδείς (talk) 15:50, 27 February 2014 (UTC)

"Could humanity get rid of the moon and how much would it cost?" - The OP doesn't ask if humanity would survive. They only ask if it is possible, and how much it would cost. --Onorem (talk) 01:14, 26 February 2014 (UTC)

Your skill at criticizing others seems to outpace your ability at answering the question you criticize others for not addressing, Onorem. And you have already been told, yes, we can get rid of the moon rather easily with well placed asteroid flybys that would slowly tug it out of orbit. How much it would cost? We don't do predictions. I suspect you already knew that as well. μηδείς (talk) 01:34, 26 February 2014 (UTC)

When responders give irrelevant responses instead of answering the question, Onorem has every right to criticize said responders. You are the only person who claimed that asteroid flybys could be used to get rid of the Moon--except you gave no reference for that claim, no scientific justification, and no other reasoning to back up that assertion. In fact I'm rather skeptical of the claim, because I'm not sure spending energy to bring asteroids near the Moon is better than strapping rockets to the lunar surface and moving the Moon that way. Finally, a cost estimate for a hypothetical scenario is not a prediction. --Bowlhover (talk) 02:31, 26 February 2014 (UTC)

The IP 81 is the one who brought up the extinction of life. So why is Onorem criticizing responders to 81 instead of criticizing 81 directly? That doesn't make sense... unless... it's the old double-standard again. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:16, 26 February 2014 (UTC)

And by the way, I'm not criticizing 81 - he raises a perfectly valid question: What would be the consequences of destroying the moon? ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:18, 26 February 2014 (UTC)

You are right. Asking whether we can destroy the moon, then not mentioning it would kill us, is like asking whether we can slit our throats, but ignoring the sequelae. Yes, you can both do it and (briefly) survive the act. μηδείς (talk) 04:35, 26 February 2014 (UTC)

Asteroids outside the orbit of the moon are the same as boulders above a wall on a mountain. Crashing them into the wail requires aiming them, not towing them uphill first. We have the theoretical knowhow, and have had it since Newton. But your ignorant, lawyerlike defense of Onorem is sweet. μηδείς (talk) 02:36, 26 February 2014 (UTC)

Surely you know it's not that easy - otherwise we'd have much more extensive studies of Venus and Mercury. I don't doubt there are clever ways to sling asteroids around, but it's not quite that easy. (True, I think if we ever get rid of the moon it will be like the Pyramid of Djedefre, borrowing a little at a time until eventually there's nothing much left...) Wnt (talk) 03:50, 26 February 2014 (UTC)

Well, yes, you need rockets, not wishes. That's physics 101, for non-science majors. (I am fairly sure Bowlhover's major was τρογλοδυτιζειν, however, given his edit summary.) If you want the exact orbits, all I can say is that they would be orbits more distant from the sun than the moon at lunar aphelion. If you want an exact orbit, post the question at the math desk. μηδείς (talk) 04:31, 26 February 2014 (UTC)

You don't seem to know much about orbital mechanics. Asteroids in the asteroid belt don't magically fall down to Earth's orbit because they are themselves in orbit around the Sun. To make them intersect Earth's orbit, you need to slow the asteroid down by several kilometers per second, thus reducing its perihelion to 1 AU. For this type of orbital change, a Hohmann transfer is usually one of the most efficient methods--and the required delta-V is given by the equations in that article. It turns out that getting from Earth to the asteroid belt takes approximately 9.5 km/s, which is nearly negligible compared to the additional 4.7 km/s that the asteroid needs to be slowed by to encounter Earth. This is without counting the 11 km/s needed to get into a heliocentric orbit in the first place.

Of course, not all asteroids are in the asteroid belt--some near-Earth objects pass closer to Earth than even the Moon, and take very little delta-V to move around. Unfortunately they are almost all tiny compared to the Moon.

I am still not convinced that using asteroids is more fuel-efficient than strapping rockets to the Moon directly. Even if it is, I'm definitely not convinced that the plan is feasible. If your point is that humanity can get rid of the Moon eventually, in the far future, possibly near the heat death of the universe, I can't disagree. After all, Apollo has already returned Moon rocks to Earth--just keep on returning rocks and eventually the Moon will be gone! For any sane interpretation of the OP's question, however, the answer is an unequivocal NO --Bowlhover (talk) 06:56, 26 February 2014 (UTC)

Actually trying to answer the question. The easiest way might be to try and change the orbit so it has a Parabolic trajectory. We can calculate the Escape velocity of the moon using

$v_{e}={\sqrt {\frac {2GM}{r}}},$

where G = 6.67×10⁻¹¹ m³ kg⁻¹ s⁻², M is the mass of the Earth 5.97219×10²⁴ kg, and r is the radius of the moons orbit, 3.844×10⁵ km. This is approximately 1.4km s^-1. The current speed of the moon is 1.022km s^-1 and it mass is 7.3477×10²² kg so it current kinetic energy is 3.82×10²⁸ J and the needed energy for escape is 7.203×10²⁸ J. Roughly double. Looking at Orders of magnitude (energy), 10²³J is the total we could get from using all the uranium on earth, so nuclear power could not do it. Thats also the energy of the biggest asteroid to ever hit the earth, so galactic billiards does not seem likely. 10²⁴ J is the total energy from the Sun that strikes the face of the Earth each year. We could potentially divert all that energy to our moon moving task and it would only take 10 thousand years. --Salix alba (talk): 09:09, 26 February 2014 (UTC)

Does that mean we could get rid of that pesky moon by just covering one side with mirrors so it gets sped up in its orbit every time it is at right angles to us and the sun and going away from the sun? Could we do the reverse as well and get a large amount of extra valuable minerals added to the earth by slowing it down? Dmcq (talk) 17:48, 26 February 2014 (UTC)

Treating the mirror-coated Moon as an ideal solar sail and assuming we can accelerate it over the course of half of each orbit, I get an acceleration of 1.17*10^-15 m/s/s, or 0.018 meters per second per million years. That gives a total delta-V of 92 m/s by the time the Sun enters its red giant phase. --Carnildo (talk) 02:48, 27 February 2014 (UTC)

It wouldn't be a good idea in any case, as it could possibly mess up Mars' orbit, and many years later, after life has re-evolved on Earth, future scientists will say that Earth's moon was created by a collision with a 'body many times bigger than Mars - the Grey Planet' (which would be our old Moon). KägeTorä - (影虎) (TALK) 22:49, 26 February 2014 (UTC)

I actually started working that out, came up with something like 10^5 kg of light being reflected off the Moon each year... bogged down on the thrust calculation. But thinking about it, it can't work out well. When you absorb the light and use it to make, say, rocket propellant, you can use the energy with somewhat passable efficiency to raise the Moon higher. But if you reflect the light, most of that energy keeps going; you can't be extracting any more than the teeny bit of energy lost to the redshift, I think (hmmm, in what frame, the Earth, Moon, center of gravity...?) Wnt (talk) 22:47, 26 February 2014 (UTC)

Not sure of my calculations either but I get about a kilometer and hour extra speed every 20000 years, which is much faster than I expected really. So it wouldn't take all that long to get rid of it. Dmcq (talk) 00:27, 27 February 2014 (UTC)

Sorry looked at my calculations again and I missed a factor of a thousand so Dragon's flight's figure below is probably more like it. Easily done with metric ;-) My figure then would be less than theirs probably because they've considered having a push all the time whereas I was only doing it for part of each orbit of the earth. Dmcq (talk) 09:27, 27 February 2014 (UTC)

If you are just reflecting light (and not absorbing the energy and using it for other useful work), I get an impulse of about 30 m/s per billion years. Dragons flight (talk) 02:21, 27 February 2014 (UTC)

I suppose technically you could make two absolutely perfect mirrors, one on the lunar surface and one sitting stationary above it, funneling sunlight into them perhaps from other orbiting mirrors (with various processing) and reflecting the light between the two "billions and billions" of times until it dribbles out the edges so redshifted its energy is spent. But I'm not so clear on whether there is any known optical technology that can align the light from a wide region of space (the sun) into a beam so tight that it can bounce back and forth reliably in the cavity until its energy is mostly used up. And it lacks the .. simplicity .. of masquerading Luna as Iapetus. -- erm, on second thought, the mirror can't merely be stationary in Lunar orbit, but must actually be so far away that Earth or something else is holding it back, or else its gravity is pulling the Moon back as much as the light pressure is moving it forward. Which makes this much more demanding still. Wnt (talk) 08:44, 27 February 2014 (UTC)

If one captured the energy of the photons one would have to use part of the moons mass as rocket fuel to get thrust rather than using the photons themselves like a mirror does. So basically one would have to cover the place with solar cells and ion motors neither of which are terribly efficient currently. With a bit of improvement and using robots to do the work we could I'd guess get rid of it within a couple of hundred thousand years but that really is finger in the air. Dmcq (talk) 09:40, 27 February 2014 (UTC)

It can be done within a few years time frame as follows. You would need machines that can copy themselves. You then put a self sustaining set of machines that can copy themselves on the Moon. These machines will build solar panels and other devices needed to power themselves and they will do whatever needs to be done on a large scale on the Moon (see the responses by others above). But all this can be done in a time frame of a few years, not hundreds of thousands of years, because of the exponential growth of self-replicating systems. Suppose e.g. that you start with a small solar panel factory that is just 1 square millimeter in area and which copies itself every week. The area of the Moon is about 3.79*10^13 m^2 so by the time you have 3.79*10^19 of these machines you'll have covered the entire lunar surface, but that only takes about 65 weeks. Covering the entire lunar surface by solar panels thus takes a little over a year and will provide for 1.3*10^15 Watt of electricity if they have an efficiency of 10%. Count Iblis (talk) 13:51, 27 February 2014 (UTC)

So you want to deconstruct the Moon?

Remember that the exponential growth is eventually bounded by the energy input – I assume you'd suggest solar power. After the machines assemble enough "grey mass" to tackle larger projects, they could finish coating the Moon with solar arrays and build a mass driver to launch pieces of the Moon into space. That wouldn't be horribly inefficient; they have to collect several times the Moon's gravitational binding energy, though. The main causes of overhead would come in

• the inefficiency of solar power generation, an overhead of about 8 times the energy that's converted to power
• the cost of cutting the Moon into mass driver slugs – I think that one can be readily estimated, in that it's not entirely unlike some mining and processing operations on Earth
• the cost to make the Neumann probes replicate themselves, which could be negligible since you only need enough probes to erect the solar arrays and the mass drivers, and mining. Most energy would be taken by the actual mass driving
• the inefficiency of mass drivers, which shouldn't be too high, either
• the fact you have to eject the mass even faster, or else you get a dust cloud where the moon used to be, which could even recollapse. We should throw all those slugs way out of the Earth's gravity well to be on the safe side – nuking it from orbit will not be an option.
• any kind of maintenance, including waste heat management.

In any case, I don't think that waste heat would introduce a whole new kind of upper limit, because the Moon is quite dark already, which means that most radiation hitting it is converted into heat right now.

I think we need around 50 times the gravitational binding energy as radiation input to get rid of the Moon. That's 50 times above mentioned 4e28J over 1.3e15W, which is 1.5e15 seconds or roughly 0.5e8 years - 50 million years. The lower bound would omit the factor 50 and we get... wait for it... 1 million.

p.s. I hope I got the math right. - ¡Ouch! (^{hurt me} / _{more pain}) 07:31, 28 February 2014 (UTC)

I was thinking of ion thrusters where the atoms would be sent away at a good fraction of the speed of light. Dmcq (talk) 13:54, 28 February 2014 (UTC)

(Late reply) Ion thrusters are good if you have to conserve fuel. If you have half a moon to throw around, energy is the primary concern. (As a rule of thumb – no rocket science involved here – you go with 50% reaction mass if you don't know how much reaction mass you should use. The main issue with the mass driver idea is that you have to throw the reaction mass out through a retrograde escape path, and it must be "faster" (relative velocity to today's Moon) to escape Earth, not to propel the Moon itself... so you would have a quite low reaction mass percentage (about 20%?) but still not as low as a typical ion thruster. - ¡Ouch! (^{hurt me} / _{more pain}) 07:01, 5 March 2014 (UTC)

Orange (and vitamin content)

I heard the vitamins you gain from eating one orange fruit is the same as u eat 6 or more than 6 oranges. Is it true? If it is true how? — Preceding unsigned comment added by 196.0.4.86 (talk) 18:42, 25 February 2014 (UTC)

No, of course that's not true - if you eat six, you get six times the amount of whatever is in it.

HOWEVER: The amount of vitamin C in a single orange is between 70 and 100 milligrams. The recommended Daily Amount (RDA) for Vitamin C is 90 mg for adult men and 75 mg for adult women. So you one orange provides enough vitamin C for most people - and eating six of them won't help you any because you simply don't need that much. Of course there are many other ingredients in an orange - and I'm not going to bother to track down all of them. SteveBaker (talk) 18:56, 25 February 2014 (UTC)

• I am not absolutely sure I understand IP 96's question. But Vitamin C is a highly water-soluble molecule, and quickly excreted in the urine. It can also cause diarrhea in excess. So, if one orange carries a good amount of Vitamin C, you will not necessarily get any extra benefit by eating even more oranges, just to have it quickly excreted. Of course there is medical controversy over the benefits of high doses of Vitamin C, perhaps others will comment, but that strikes me largely as fringe science. μηδείς (talk) 19:00, 25 February 2014 (UTC)

Indeed, there is some controversy...but I feel that the RDA numbers are the most widely accepted - and therefore what we should suggest here. OTOH, our local pharmacy sells 1000mg vitamin C pills, and people are evidently buying them. Some people do recommend crazy-high doses like this (especially to fight of the common cold...despite all evidence that it has no effect whatever on the duration or symptoms - unless you are engaged in routine vigorous exercise in an extremely cold climate). However this article says that excessive amounts of Vitamin C (beyond that which you'd normally get in a healthy diet) "may cause abdominal cramps or pain, chest pain, dental erosion, dizziness, diarrhea, faintness, fatigue, flushing, gut blockage, headache, heartburn, increased risk of lung cancer, increased risk of Parkinson's disease, inflamed esophagus, injection site discomfort, nausea, red blood cell complications, skin tingling or irritation, slowing of endurance training, thickening of blood vessels close to the heart, urinary complications, and vomiting."...so beware! SteveBaker (talk) 19:06, 25 February 2014 (UTC)

What, no warning that if you stop breathing, you should stop taking Vitamin C and call your doctor immediately? μηδείς (talk) 19:16, 25 February 2014 (UTC)

Yesterday I had 800 grams of potatoes and 400 grams of Brussels sprouts for dinner (these are typical quantities of potatoes and vegetables that I normally eat every day). The amount of vitamin C I got from this dinner alone is about 500 mg. The other meals I eat also contain vitamin C, I think I get to about 700 mg on most days. So, I don't think 1 gram/day is all that crazy. Perhaps the RDA is too low by a factor of 10 because most people don't have a healthy lifestyle. If you don't get enough exercise then you have to stick to a diet to make sure you don't get obese. If you then also eat unhealty foods that contain little amounts of vitamins (Big Macs), there isn't much room left to get your vitamins. But if this lifestyle is the norm, then that will cause the RDA to become skewed to reflect this situation. Count Iblis (talk) 18:25, 27 February 2014 (UTC)

The RDA was originally assessed as the minimum necessary to prevent symptoms of deficiency. As one person puts it, following RDA vitamin C means you probably won't get scurvy [8] -- but it doesn't necessarily mean that's a good way to live, if (like you), you can get a much higher supply of C from natural (e.g. not processed for concentration) sources like fresh veggies. In my opinion, they should be called "minimums to prevent disease", not "Recommended" amounts. Here is more academic discussion of the topic [9]. SemanticMantis (talk) 19:03, 27 February 2014 (UTC)