Wikipedia:Reference desk/Archives/Science/2008 May 4

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May 4

Blue and green eye color in Africans

Does anyone have information on a Klein Wollendorf Syndrome" When I attended the Univ. of Pittsburgh back in the 70's I was doing some research in color preference and I happened on this book Titled the Klein Wollendorf Syndrome which documented the occurences if bright blue eye color in sub saharan Africans. They also documented the occurences of people who were born with emerald green eye color and the white of the eye was yellow instead of white. The book included many pictures of the people with the eye colors. The authors said widespread documentation was difficult because in previous generations many of the children born with the eye colors were killed at birth because they were considered cursed. I have lost my bibliography so I don't have a publisher or dates. If any one has any information, please respond. —Preceding unsigned comment added by Chaniatreides (talk • contribs) 06:06, 4 May 2008 (UTC)

I expect you are referring to Klein-Waardenburg syndrome (OMIM: 148820), also known as Type III Waardenburg syndrome. It results from a mutation in PAX3 and, among other things, manifests with melanocyte deficiencies (hence the eye colours). A PubMed search with the term should provide all the info you need. By the way, the book you refer to is probably: Jenni Soussi Tsafrir, Light-eyed Negroes and the Klein-Waardenburg Syndrome, London, Macmillan, 1974, ISBN 0333140729. Rockpocket 06:49, 4 May 2008 (UTC)

We really do have a page on everything! ;-) Waardenburg syndrome--Lisa4edit (talk) 09:46, 4 May 2008 (UTC)

A four-hour day

I'm wondering just how life might be different if the days were 4 hours long (defined as 3600 seconds, where a second is defined in relation to the speed of light as is current). Would we still have the same sort of circadian rhythms? -mattbuck (Talk) 06:41, 4 May 2008 (UTC)

Hold on, are you talking about an actual day (i.e. the earth's rotation around the sun) being 4 hours or some random definition of a day as being 4 hours?. If it's the former then our circadian rhythms would presuambly have evolved in such an environment and would therefore be best adapted to a 4 hour day. If the later, well it would be irrelevant out circadian rhythm would still be best adapted to a 24 hour day Nil Einne (talk) 07:44, 4 May 2008 (UTC)

There was a study a few decades ago (before the Internet). They put some subjects in a bunker, cut off from any outside light source. They were not allowed any clocks and could choose when to switch on their electric lights and declare it "daytime" and when to sleep equating "nighttime". Most of the subjects adjusted to a "day" longer than 24 hrs. (I'll see if I can find that mentioned somewhere.)--Lisa4edit (talk) 09:36, 4 May 2008 (UTC)

Seems to be mentioned on Circadian rhythm Nil Einne (talk) 12:43, 4 May 2008 (UTC)

That was it, the results were refuted I see. Thanks for pointing that out. I had apparently never read that article far enough. --Lisa4edit (talk) 16:11, 4 May 2008 (UTC)

An experiment with an 8-hour "day" has been ongoing for several hundred years. Large numbers of humans have been placed in artificial environments and required to be active for four hours and then be (more or less) at leisure or sleeping or four hours, sometimes for years at a time. Some humans adhered to this schedule from childhood until (relatively) old age. I refer of course to the watch system of the (british) navy and other navies. -Arch dude (talk) 23:33, 4 May 2008 (UTC)

What would a YY chromosome person look like?

Is it possible that a person has YY chromosomes? Is it possible to create a person from two Y chromosomes from a male? If not, just for fun what do you think a person with such chromosomes would act like or look like? —Preceding unsigned comment added by 70.219.182.238 (talk) 07:46, 4 May 2008 (UTC)

It is possible for humans to have YY, but only in combination with a X, giving them XYY syndrome. XYY people tend to have slightly lower IQs an increased risk of learning difficulties. You can even get people with XYYY and XXYY syndrome, though they tend to have more severe difficulties.

The human Y chromosome is tiny and contains very few genes. It largely contains those genes necessary for becoming male, SRY for example. In humans the X contains lots of genes many of which have nothing to do with sex determination and are essential for life. Examples include a gene to make blood clotting proteins. So, at least in humans, everyone needs at least one X or else they do not develop. Therefore a person with YY sex chromosomes would probably look like a jelly bean, before aborting in utero. Rockpocket 08:26, 4 May 2008 (UTC)

Is it possible for the Y chromosome to be genetically engineered to be able to hold the necessary genes, making it possible for just YY human beings? —Preceding unsigned comment added by Jue2 (talk • contribs) 08:34, 4 May 2008 (UTC)

Well, currently the technology is not available for humans, but it would probably be feasible to do that in experimental animals. That would be the functional equivalent of putting the SRY region (the gene that makes you a "male") into an X chromosome. This occasionally happens in humans due to chromosomal translocation. The result is individuals that have female haplotypes but male phenotypes. The only major problem is that those males are infertile. Speculating now: If you could pick all the essential genes on X on put them on a Y (lets call that Y*) you would have all the genes required for life. But YY* people would still have problems, because they would have two doses of the genes on the Y chromosome, including SRY. That would result in the same difficulties seen in XYY males. Females get around the dosage problem by lyonisation, but males could not do that. They way around this would be to engineer a Y*O male (with just one modified Y chromosome). Would that male survive and be healthy. Who knows?

By the way, it turns out that YY embryos abort before implantation, thus in humans a YY would only last a week or two so after conception before aborting. Rockpocket 09:03, 4 May 2008 (UTC)

So it would be easier for women to exist without men, than men to exist without women. That is a very scary thought. What gene in the Y chromosome decides gender? The Y chromosome has few few genes compared to the X so, why couldn't engineers move that gene in the Y to the X chromosome? Jue2 (talk) 09:22, 4 May 2008 (UTC)Jue

Yes. Womankind could theoretically exist without men when human cloning becomes a reality (because all you need then is a womb in which to carry the XX clone). Why else do you think all those male dominated societies have outlawed human cloning ;)? As I said above, the principle male sex determining gene in humans is SRY and nature occasionally moves SRY into the X chromosome by unequal chromosomal crossover, resulting in XX male syndrome. Rockpocket 10:01, 4 May 2008 (UTC)

I find the thought amusing. A species without females--now that would be scary. Imagine Reason (talk) 02:44, 5 May 2008 (UTC)

So check out New Mexico whiptail and be afraid, be very afraid :-). 87.81.230.195 (talk) 08:08, 30 March 2009 (UTC)

Time Travel is Impossible

Time travel just can't happen, otherwise we already would know about it. Not to mention the paradoxes it would cause. Travel back in time and kill my mother before I was born. I guess my question is, "does anyone believe time travel is possible? If so please explain it to me." —Preceding unsigned comment added by Jue2 (talk • contribs) 09:30, 4 May 2008 (UTC)

Our Time travel article may be of interest to you. I suppose that there is at least someone who believes that it's possible. --hydnjo talk 10:47, 4 May 2008 (UTC)

There are consistent theories that allow for time travel, but they're quiet restrictive. For example, you can't generally travel back to before the time machine was created. Exactly how it would work with paradoxes, I don't know - I expect you would simply find that you can't change anything because you were there doing exactly the same thing "the first time round", and just didn't see yourself. (The main alternative theory is that you would travel back to an alternate reality and change that one, rather than your own.) --Tango (talk) 13:09, 4 May 2008 (UTC)

The expression Time travel usually is understood to only move the traveler in time. If you'd allow travel to another destination (or another universe) you remove quite a few roadblocks. Moving a person also makes things a whole lot less likely. If you could figure out how to send the information to assemble a person (as proposed for SciFi "transporters") things would also become easier. Traveling to the past I'd still think highly unlikely. But I keep encountering things that everyone used to think were impossible. ( see "Humpty Dumpty" for a recent event.) Lisa4edit (talk) 15:13, 4 May 2008 (UTC)

Time travel is not imposssible, I have already told you that tomorrow - don't you remember? SpinningSpark 15:40, 4 May 2008 (UTC)

The real question is, "Can an all-powerful god alter the past?" Imagine Reason (talk) 22:37, 4 May 2008 (UTC)

Why would an all-powerful god need to alter the past if he was all powerful and all knowing? I've managed to go back in time before. It was easy, but really noisy as well. bibliomaniac15 Do I have your trust? 03:58, 5 May 2008 (UTC)

I was only concerned with the ability to change the past. An all-powerful god may not be all-benevolent. He may well decide to play dice with our lives and change our past on a whim. Imagine Reason (talk) 15:56, 5 May 2008 (UTC)

Time travel paradoxes vanish when parallel universes are considered. Amelia Earhardt had no role as an aviatrix in World War 2 in the parallel universe where she vanished in the 1930's. Judge Crater never got appointed to the U,.S. Supreme Court in the parallel universe where he vanished mysteriously. Charles Lindbergh Jr. never became President of the United States in the parallel universe where he was kidnapped and killed as a toddler. In the parallel universe where a time traveller altered history the alteration would be accepted as part of that time stream's history. Edison (talk) 03:44, 5 May 2008 (UTC)

Another argument for the impossibility of time travel is that if there were ever in the future a year when time travel became possible, then a traveller would have announced his presence in our time or in our past, and we would all know that time travel was possible. In the parallel universe model of reality, there could be many time streams where time travel has been shown to be possible, just not in this one (yet). Consider then whether it is ever the case than some supposedly deranged individual is picked up and tells the police/psychiatric personnel that he is from the future. Would we even hear about it? If the time traveller were not incautious enough to announce his presence that way, but were only allowed to arrive with no equipment, clothing, or other physical evidence inconsistent with this time, and screened to act as a scientific observer, he might pass unnoticed (but certainly not without having caused this time stream to be altered in some way). Even such a prudent observer would inevitable get the last place on the elevator, causing someone to miss his medical appointment, causing their cancer not to be detected in time. Or he might take a seat in a restaurant which otherwise would have been occupied by one half of a couple who therefore did not meet, marry, and give birth to a world leader, as in the Butterfly effect. Edison (talk) 12:40, 5 May 2008 (UTC)

That whole issue with nobody coming back and telling us they're from the future disappears if you impose the "you can't travel back to before the time machine was created" restriction, which I believe is imposed by most (if not all) ideas for time machines based on General Relativity. --Tango (talk) 12:59, 5 May 2008 (UTC)

It is easire to envision time travel where the "booth" is the arrival point, because the traveller thereby does not arrive inside another person or a tree, but there are probably ways around the claimed general relativity prohibition. Edison (talk) 18:54, 5 May 2008 (UTC)

the question of time paradox is largely contingent on your theory of what time is to begin with. The logical answer to the most basic time paradoxes is "you couldn't because you didn't" or "it's possible because you did." Basically, the argument is that "changing the past" is a meaningless phrase; because the past already occured, it can't be changed. Think Twelve Monkeys or the first Terminator movie. --Shaggorama (talk) 09:24, 8 May 2008 (UTC)

Does any one know what this is

Hi I would like to know what article this could go in. I found this in the Blue Mountains New South Wales. I may even have better images of this

. --User:Adam.J.W.C. (talk) (talk) 10:38, 4 May 2008 (UTC)

I guess you can't wait till it's matured into a moth. :-) [1] narrows it down to LYMANTRIIDAE or "Tussock Moth" "are so-named because the Caterpillars of many members have four long dense dorsal tufts of hair. Many also have other hair pencils, and also two coloured dorsal glands on abdominal segments six and seven." --Lisa4edit (talk) 12:03, 4 May 2008 (UTC)

If you have lots of time you might find it here [2]Lisa4edit (talk) 12:41, 4 May 2008 (UTC)

I forwarded your identification request to Wikipedia:Wikiproject Lepidoptera. If they don't contact you soon, try going over to the project page and picking out a few contributors to contact directly in case the project page doesn't get regular visitors. --Shaggorama (talk) 09:38, 8 May 2008 (UTC)

Constructing a lunar orbital station by firing materials from the moon

My dad is writing a science fiction novel and has a Clarkesque desire for realism. He's described a situation to me but the maths is pretty complicated and well beyond my knowledge. The figures used below are our guesses at plausible numbers, if these guesses are unreasonably high or low for the practicalities of the situation, please say so and we can revise. The situation is as follows:

Suppose we are constructing a space station in an equatorial orbit around the moon at a height around the order of 300km. It is being constructed from materials mined on the moon, and they are being launched up to meet the station by a linear accelerator on the moon's surface. The materials are launched in ~200 tonne payloads and the accelerator can impart acceleration no greater than, say, 4 G. The accelerator can be built on an incline but if it can be laying flat to the ground this would be preferable. Suppose the construction platform begins with a mass of 1000 tonne, this will of course increase with each payload and the added mass and momentum will obviously alter the orbit of the platform itself. The payloads are capable of minor course alterations but aren't equipped with large rockets or anything. The payload "catching" mechanism on the construction platform requires payloads travelling no faster than 0.1 m/s (or something else plausible). Is this situation workable, and what kind of length / launch speed / angle / timing are required for the launcher?

It seems to me like we'd need the payload to reach the platform at the payload's apoapsis (highest point) and the platform's periapsis (lowest point). However, the fact that the platform will be changing orbit with each payload makes the whole thing too difficult for me to see how to approach since I don't know enough about orbital mechanics to know how the orbit will be changing. Any ideas? Thanks, Maelin (Talk | Contribs) 10:43, 4 May 2008 (UTC)

The orbit of the platform won't change - the mass of a satellite doesn't feature in the equations for it's motion (it cancels out). As long as it stays significantly less than the mass of the moon, you don't have to worry. There will be a transfer of momentum when you catch each payload, but for the catching to work you'll need them going quite slowly relative to each other anyway, so I think you can ignore that. Have you read out article on mass drivers? I think that's what you're describing. It doesn't have many technical details, but it might help a little. What you probably want is the platform to be in a circular orbit, and then the payloads launched at a pretty shallow angle (horizontal would be fine). I think you would then need the payloads to fire small rockets at the appropriate point to circularise their orbit slightly lower than the platform, then when they catch the platform up they fire again to lift them up to it and reduce their relative velocity so the catching can work. I'm not entirely sure about how launching things into orbit with mass drivers works - most applications I've seen seem to involve giving them escape velocity, but putting things into orbit should be possible, I'm just not sure how big a rocket you would need for the circularisation (certainly smaller than you would need for an actual launch). --Tango (talk) 13:21, 4 May 2008 (UTC)

If the space station is in any particular orbit, and the momentum of a 200 tonne addition is added to it, without firing a rocket to match orbits, the orbit of the combination will inevitably be different from that of the space station initially. I see two non-rocket solutions. The ugly one is that the space station starts in its desired orbit. Each time a payload docks with it, the orbit would change somewhat. To avoid this, the payload could fire off a small part of its mass at a high velocity (spring? cannon? electromagnetic thruster? compressed gas?) This could have the same effect as firing a thruster. The downside would be that these correction ejections would then be flying around the moon in orbit, unless they were fired off with escape velocity, ideally to ultimately impact the Sun or perhaps some planet the Moon dwellers didn't like (Heinlein had a story of throwing rocks at the Earth from the Moon, as I recall). The elegant solution is to have the initial part of the space station in an orbit which differs from the final desired orbit in a carefully calculated way. Then each time it catches a payload, the orbit of the combination moves toward the desired orbit. When all the payloads have been caught, the orbit has shifted exactly to the desired orbit. (Difficult to calculate? Aw gee, orbital mechanics is HARD!) Edison (talk) 13:45, 4 May 2008 (UTC)

Requiring a relative velocity of less than 0.1 m/s sounds like matching orbits to me. I expect small station keeping thrusters on the platform would be enough to correct for any relative momentum not shed before catching. --Tango (talk) 13:55, 4 May 2008 (UTC)

There is a cumulative effect here. One payload you might get away with if it is small and slow, but if you are trying to significantly increase the size of the station, eventually you are going to have to correct the orbit in some way. Fuel for thrusters can only arrive through the payload which I think is what the original concept is trying to avoid. Don't forget that any payload launched ballistically from the surface is going to end up in an orbit which will intersect its starting point (ie it is going to try and fly through the mass of the moon). Therefore there MUST be a correction to the payload by some means to insert it into a working orbit. If this is done by the station catching it, it will inevitably impart a momentum to the station in an undesirable direction. You might be able to do something clever with tethers though. SpinningSpark 14:17, 4 May 2008 (UTC)

As long as the exhaust velocity is greater than the relative velocities of the payloads when caught, bringing fuel up shouldn't be a problem. The OP said the catching mechanism required the relative velocity to be less than 0.1m/s, so station keeping should be easy. It's slowing the payloads down (or speeding them up, depending on perspective) that's hard - tethers could work, and are certainly more interesting to read about than rockets. --Tango (talk) 14:27, 4 May 2008 (UTC)

You could employ a tether or [3] might work. You could at least use it to get rid of some need for corrections as far as I understand it. This is way out of my league but maybe s.o. else can develop the idea, or say why it won't fly. Lisa4edit (talk) 15:57, 4 May 2008 (UTC)

It might be possible with 2 accelerators 90 degrees apart. They would cancel each other out. Catching the payloads wouldn't be a problem either. Each accelerator sends one payload into orbit. the 2 payloads collide and the resulting single payload would have a very low velocity relative to the station. I doubt that its really feasible but it should good enough for a science fiction story.Em3ryguy (talk) 19:13, 4 May 2008 (UTC)

Why would they collide? I can't see a way to get them to be in the same place at the same time. --Tango (talk) 19:41, 4 May 2008 (UTC)

"The payloads are capable of minor course alterations". If their orbits are in the same plane then they must cross someplace. Also the collision doest have to be anywhere near the station. After the collision the resulting single payload can then drift slowly to the orbiting station on the other side of the moon. Half of the payloads will do so in a slightly lower orbit and half in a slightly higher orbit. As a result, the orbiting stations orbit would not be changed.Em3ryguy (talk) 20:38, 4 May 2008 (UTC)

Their orbits will cross, sure, but they won't both reach the crossing point at the same time. Also, the term "orbit" is a little misleading - the payloads will crash back to Earth before completing one complete orbit if they don't do something to circularise it. --Tango (talk) 20:42, 4 May 2008 (UTC)

They dont have to actually collide. They can use many mile long tethers to simply orbit one another. We are talking about fiction here, yes?Em3ryguy (talk) 21:42, 4 May 2008 (UTC)

We're talking about hard science fiction - the idea is that it is actually physically plausible (given sufficiently advanced engineering). There are all kinds of things you can do with tethers, but I'm not sure what you're suggesting... --Tango (talk) 22:19, 4 May 2008 (UTC)

The collision of the 2 payloads circularizes the orbit. Thats the whole point.Em3ryguy (talk) 02:33, 5 May 2008 (UTC)

The idea is ridiculous, even if the launch was synchronised perfectly so that the two payloads did meet at aposelene the collision would not do anything to help match orbits with the station. It will just result in crushed payload canisters. A collision does not add energy to the system so it cannot possible achieve the orbit desired. As for the tether, if you launch at 90 degrees, the two payloads are going to end up tens of thousands of miles apart before they meet again - that's a lot of string to reel back in!SpinningSpark 02:44, 5 May 2008 (UTC)

90 degrees apart in longitude. they are 1000km apart. After the collision the orbit of the combined object should be circular.Em3ryguy (talk) 05:50, 5 May 2008 (UTC)

I may possibly owe you an apology for an AGF failure, that actually works, at least with one sample orbit calculation I did in an attempt to prove you were talking nonsense. However, the idea is still ridiculous. The orbital radius required is 3x10⁵. The mass of the moon is 7.35x10²² times G=6.67x10^-11 gives μ=49x10¹¹. Plugging all that in to the vis-viva equation gives an orbital velocity of 4000 m/s. Assuming the original launch is in a highly elliptical orbit so that 1/a > 0, then the velocity of the payload prior to impact is ${\sqrt {2}}$ of that, ie 5700 m/s. So, you have two objects travelling at 5700 m/s, one in a rising orbit, one in a falling orbit, meeting at approximately right angles (closing velocity is 8000 m/s). The collision is required to be elastic, a) because loss of energy will lose orbital speed and fall back to the moon and b) an inelastic collision will destroy the payloads. You therefore need some kind of catcher mechanism on the payloads. I cannot even begin to imagine a mechanism that would work at those speeds without, as I said before, resulting in crushed, not to say vaporised, payloads. SpinningSpark 09:27, 5 May 2008 (UTC)

I've made a silly mistake in the calculation above. The orbital radius is not 3x10⁵, it is 3x10⁵ plus the radius of the moon which comes out to 2x10⁶. Luckily for the world and the environment, I do not launch rockets professionaly. All the velocities are around 40% of that stated. The closing velocity is 2400 m/s (4800mph). Still a lot more than can be handled by a catcher but launching in a less elliptical orbit would considerably reduce the closing velocity. The limiting circular orbital case has zero closing velocity. I am beginning to change my mind, there may be some mileage in this idea after all. SpinningSpark 11:04, 5 May 2008 (UTC)

You are using absolute velocities. You have to use relative velocity. they are both in nearly circular orbits so their relative velocity should be small. The simplest way to estimate the relative velocity would be to determine their average absolute orbital velocity then calculate the angle at which their orbits cross.Em3ryguy (talk) 11:27, 5 May 2008 (UTC)

Is my statement that the limiting case of circular orbits has zero closing velocity not the same thing? For the calculation above of highly elliptical orbits the closing velocity is correct and they will meet at right angles ie at ${\sqrt {2}}$ the individual absolute velocities. SpinningSpark 12:15, 5 May 2008 (UTC)

Ignore the station for a moment and concentrate on each payload. A payload is ~200 tonne. If yo uuse a mass driver on the moon's surface and have only small thrusters to use later, the mass driver cannot place the payload onot a circular orbit. The payload goes ballistic as it leaved the mass driver, which means that it is in a lunar orbit that will come back to the same point (i.e., the mouth of the mass driver) unless quite a bit of additional energy is applied somewhere, and the thrusters you describe cannot do this. So you need to find a way to impart a supstantial amount of energy to your payload after it leaves the mouth of the mass driver, If your mass driver is aimed horizontally from the top of a very high peak, You will have an entire lunar orbit in which to add energy before the payload hits the mass driver, and you will not need to add very much energy. to get into a non-intersecting orbit (an extremely low lunar orbit.) From there, you can continue to add energy at a slow rate until you reach the 300Km orbit. The most cost-effective way to add energy will depend on your scenario. One possibility is to place a small mass driver on the payload and shoot a few rocks backwards to get into extremely low lunar orbit, and then use an ion drive for the rest of the (slow) trip to 300Km. You would have a many payloads in transit. Salvage the mass driver and ion drive when the payload reaches teh station and return them to the surface to use on the next payload. -Arch dude (talk) 23:16, 4 May 2008 (UTC)

It is possible to do it without circularising the orbit, you just have to fire the payload at sufficient speed that it's apoapsis meets the platform. You then need some way to catch the payload, and it will be travelling at a relative velocity significantly greater than the 0.1 m/s the OP was after. You would then need quite significant station keeping efforts to stop the the platform moving. I think the end result is that you either need to relax the requirement on the catching velocity, or relax the requirement on how much thrust the payloads can generate (using rockets, ion drive, tethers, whatever). Either would work. --Tango (talk) 23:46, 4 May 2008 (UTC)

For the station to "catch" the payload, it must deliver enough energy to the payload to move the payload from a lunar-intersecting orbit to a 300Km circular orbit. A passive "catch" will merely average the momentum of the station with the momentum of the payload. After many "catches" the station will intersect the moon if the payloads have the same momentum vector. Aha! is there a set of mass driver positions on the moon's surface that can impart a zero average momentum on the station? Each payload will need to contribute enough total energy to circularize its own orbit, and the station will need to store the extra energy, so we do not have a zero-velocity intercept and we need an energy-transfer mechanism at the station such as another mass driver acting as a catcher. -Arch dude (talk) 00:45, 5 May 2008 (UTC)

A rotovator can solve the <0.1m/s problem. Here's a NASA study into how it might be done from Earth [4]. In the case of the moon you might not need to launch at all, just pick it up off the surface!SpinningSpark 03:10, 5 May 2008 (UTC)

I don't understand... if each payload can circularise its own orbit, we don't have a problem... --Tango (talk) 12:56, 5 May 2008 (UTC)

The constraints of the original question imply a ballistic launch with just the capability for "minor corrections". Circularising the orbit in nearly all launch scenarios is a major delta-v event and has gone outside the scope of the question as stated IF achieved from the payloads own on-board resources. Anyway, I was only trying to think outside the box and give an answer more interesting than rockets. Picking up the payload directly from the surface with a rotating tether certainly fits that bill imho. SpinningSpark 18:08, 5 May 2008 (UTC)

I was replying to Arch dude, not you. --Tango (talk) 21:53, 5 May 2008 (UTC)

No one has looked at the viability of the proposed launch system yet. Allow me to have a go. From my previous calculation above (both the flawed and the unflawed versions) we have,

$\mu =49\times 10^{11}$

and it is going to be convenient to use;

${\frac {\mu }{10^{6}}}=49\times 10^{5}$

The radius of the moon is 1.7 x 10⁶ For an orbit as near circular as possible to give good match with the station a near horizontal launch is needed that just makes it to the 0.3 x 10⁶ height required. The semi-major axis of this orbit is;

$a={\frac {2\times 1.7+0.3}{2}}\times 10^{6}=1.85\times 10^{6}$

and the launch velocity required is given by;

$v^{2}=49\times 10^{5}\left({\frac {2}{1.7}}-{\frac {1}{1.85}}\right)$

$v=1765\,\!$

The length of the linear accelerator required can be determined from;

$v^{2}=2ax\,\!$

since the accelerator is specified to be 4G acceleration

$2a\approx 80$

and,

$x=38940\,\!$

You need to build an accelerator around 40km long to make this work. SpinningSpark 12:07, 5 May 2008 (UTC)

So get those solar powered bulldozers to work piling up lunar soil to make the launch platform. Edison (talk) 12:44, 5 May 2008 (UTC)

40km sounds doable to me, given the kind of future engineering we're talking about. I think the accelerator is possible. --Tango (talk) 12:53, 5 May 2008 (UTC)

If it left the lunar surface tangentially at a point and continued in a straight line 40 km. how high would the terminus have to be? This would determine, along with the angle of repose of lunar soil, the mass which would be needed to construct it, unless it was built like a roller coaster out of a trellis structure or a series of towers. Edison (talk) 18:52, 5 May 2008 (UTC)

According to the back of my envelope, the end would be 460m high. In lunar gravity, that shouldn't be too hard to achieve. I'm not sure the track needs to be level, though, it may be able to follow the surface without too much difficulty. Or, you could just find somewhere with an appropriately angled hill (or close enough, and make just small adjustments). --Tango (talk) 19:27, 5 May 2008 (UTC)

40km is no big deal -- we build structures on that scale all the time. Based on similarly large structures (roads, railroads, etc.), assuming you had enough manpower, it would take about a year to build. --Carnildo (talk) 21:39, 5 May 2008 (UTC)

Building it straight-line (ie tangential to the curved surface of the moon) is uneccessary. It is only the angle at the point it leaves the accelerator that counts. It could be built on a geodesic (lunadesic?) with just the final section angled to the desired trajectory - like an aircraft carrier deck. However, you may not even want to do this depending on the orbit you are trying to achieve and the payload recovery scheme adopted. A flatter track gets a less elliptical (more circular) orbit and it may only be necessary to angle it up sufficiently to clear obstacles like moon mountains. SpinningSpark 06:23, 6 May 2008 (UTC)

This is the dad who asked the question - it's over thirty years since I did physics. Lunar orbit velocity is about 1820m/s, so I see the problem as horizontal and vertical components. Horizontal component to achieve is 1820m/s, and vertical component needs to be such that lunar gravity of 1.622m/s/s will decrease it to zero at 300KM height. Thus, a small amount of force should then be able to circularise the orbit as the payload is already at orbital velocity. But I am not sure if my logic is correct. I also can't recall how to calculate the vertical component, and thus the angle of launch and the launch velocity and the length of the launcher. The 4G (i.e. 40m/s/s) is a nominal figure. Thanks for the comments guys. —Preceding unsigned comment added by 192.158.61.140 (talk) 06:28, 7 May 2008 (UTC)

I'm not sure you can just resolve it into components like that, since which direction is "horizontal" will change with time (due to the curvature of the Moon's surface). I think the conventional way to put something in orbit using a mass driver would be to launch (almost) completely horizontally and then, at apoapsis (greatest distance), fire rocket motors (or use any other form of propulsion) to circularise the orbit. My back of the envelope calculations show that the required delta-V for the launch would be around 1.8km/s and the required delta-V for the circulisation would be around just 0.1km/s. I expect you can afford to just slap a rocket motor to the payloads and get your 0.1km/s, it seems pretty small in comparison to the energy you're using in the initial launch (although that energy doesn't need to be lifted, which obviously helps quite a lot). --Tango (talk) 01:57, 8 May 2008 (UTC)

The Solid

Hello. I dissolved a solid into water. I added silver nitrate and the solution turned milky white. I added barium nitrate and the solution did not change. I added potassium thiocyanate and the solution turned reddish brown. I know that I am not allowed to post homework questions but I guess that the solid is a salt like sodium chloride. What is the solid? Thanks in advance. --Mayfare (talk) 17:15, 4 May 2008 (UTC)

"I know that I am not allowed to post homework questions[...]What is the solid?". Oh come on now...at least try posting your reasoning in detail and asking someone to see if you are doing it correctly and getting the right answer. DMacks (talk) 19:36, 4 May 2008 (UTC)

You will probably want a table of solubilities. Your textbook may provide a simple one; we have Solubility table which may be a bit overwhelming. Check whether each combination of the ions present in solution will precipitate. Nimur (talk) 16:31, 5 May 2008 (UTC)

gf has atopy

Hey. I like my girl, and I'm attracted to her, but she has pretty bad atopy all over her body and it's a real turn-off. It's hard because I can't be honest about it, and here (Japan) there are a lot of people with atopy but I'm not sure if they give them proper treatment because they have a tendancy (the country and the people do) to be scared away from stronger drugs. That means that she might be stuck with it for life. I don't know what to do because it's really hard for me when we get intimite and stuff, but I don't want to be a heartless asshole to her. Any advice? Heh. 218.229.72.166 (talk) 20:28, 4 May 2008 (UTC)

I assume you're referring to eczema, in which case I don't think we can help you. I don't think there is anything non-medical you can do about it, and we can't give medical advice. I suggest you talk to her about it and suggest she get treatment, if she isn't already. As for what treatment to get, I'll leave that to the doctors. --Tango (talk) 20:45, 4 May 2008 (UTC)

Yeah eczema. The problem is she is getting treatment, or at least I'm pretty sure she is. It's a very common to see people with eczema around Tokyo (from what I can tell); I think it has to do with genes and the environment that they are forced to live in. I think it also has a lot to do with the treatment they receive here. There are loads of medicines that you can get in the west (let's say the US) that you can't get here; most people won't touch birth control pills, Tylenol is very hard to come by (and the most of the alternatives suck), and even stuff like protein supplements are incredibly weak here. Original research of course. Hmmm... 218.229.72.166 (talk) 21:09, 4 May 2008 (UTC)

It can sometimes help to specifically ask the doctor for something stronger. They may be reluctant to suggest it, but might still prescribe it if asked. --Tango (talk) 22:16, 4 May 2008 (UTC)

I guess you've already read Atopy, Eczema and Atopic dermatitis. Our Allergy article may also hold some clues. Treatment varies by country and individual physician, but no one has come up with a "cure all" or "magic bullet" yet. This is not a case of one place having a cure and patients in the other not having access to it. Individual causes and results vary and some treatments like Corticosteroid can turn out to be worse than the original condition. Avoidance of the allergic trigger is your best bet. That may be easy, like a change in diet, switching detergents, avoiding certain materials in clothing and bedding, or it may be impossible if the trigger is ubiquitous. What is beneficial to some (e.g Omega-3 oils, oatmeal cream) can be a trigger to others (sea-food allergy, grass allergy). Finding a trigger can be a lengthy process. Rotation diets that avoid related food families for 2 weeks in succession could help narrow down food triggers. (OR: that worked for my cousin who had tried everything including cortisone and psychotherapy). Long holidays in as different an environment as you can find can also aid in narrowing things down. Good luck. --71.236.23.111 (talk) 23:06, 4 May 2008 (UTC)

Careful - you're bordering on giving medical advice there. We can't do that. If the OP wants medical advice, he needs to go to a doctor. --Tango (talk) 23:33, 4 May 2008 (UTC)

Sorry, my bad. I had not intended to. Despite the fact that it very rarely happens we didn't have any page on rotation diet or the like (maybe I just haven't found it yet under a different heading?). What it so puzzling to some people who are new to allergies is that there are no clear answers. It's not like some other conditions where "If A, apply B" gets comparatively consistent results. That's why you're way ahead in the game once you've identified the triggers. I certainly did not want to give any medical advice. I was merely trying to caution against second guessing the lady's physician too hastily, just because there are no immediate results. Sorry for not phrasing it less ambiguously. 71.236.23.111 (talk) 04:39, 5 May 2008 (UTC)

I can't give any medical advice (not just because it's not allowed, but because I don't have any to give). However, I can give relationship advice, and however you choose to deal with it, I would suggest you don't just try to ignore it. If it really bugs you now, it's not likely to bug you any less over time. You don't have to be a heartless asshole to say -- nicely and without sounding like you're pressuring her into anything, and certainly not when you're about to be intimate -- that hey, honey, I think they might be able to do something about the eczema. If the condition is treatable, then you're both suffering from it for no good reason; I doubt she's enjoying it either. And when I say nicely? I do mean nicely. "You should get that looked at," for example, doesn't qualify. "I hate to say this, but that really turns me off," doesn't, either. "You know, I just read somewhere that the new drugs for treating that type of skin are really efficient, have you thought about trying them out?" would probably work better. I mean, if she's the type that is going to absolutely take offense no matter what, then it'll happen, but at least you can minimize the damage. I mean, this is the type of stuff people have to learn to talk about in relationships anyway, so you're going to have to bite the bullet sooner or later -- if not on this, then on something else of a comparable nature... -- Captain Disdain (talk) 01:43, 5 May 2008 (UTC)

your relationship probably won't last very long if you are "turned-off" by your partners body. If she's receiving treatment, then the problem is really yours, not hers. If you can't learn to adjust, or at least be honest with her about how you feel (despite potentially activating her insecurities about her disorder) then you are probably never going to be that happy with the realtionship. Consider at least confiding in a friend about this or if you have one, talking to a therapist. --Shaggorama (talk) 09:44, 8 May 2008 (UTC)

The science of baseball

Please inform the intellectual side of my brain about the science of baseball. The physics of throwing fastballs, the advantage of a pitchers mound, how atoms play a part. Etc. I hope it isnt too far out to suggest quantam mechanics, and/or 'the butterfly effect" will affect the outcome of the game. If it weren't for page space, bandwidth, etc I would only halfway jokingly ask you to break down a typical game atom by atom :)--Baseball and and and Popcorn Fanatic (talk) 21:44, 4 May 2008 (UTC)

Quantum mechanics will have no noticeable effect on baseball - it only has a affect on very small scales, eg. individual atoms and smaller, a baseball is much larger than that. Chaos theory (the butterfly effect) may have a small impact, but I doubt anything particularly significant. Newtonian mechanics should be all you need. You might find our Trajectory article interesting. Aerodynamics also plays a role - particular if you put spin on the ball, as I understand it. If you want to get down to the atomic level, the reason the ball bounces back when it hits the bat (rather than going straight through - matter is mostly empty space with just a few tiny particles every now and then, so there would be plenty of room for the ball to go through the bat) is due to the electrons repelling each other due to electrostatics (it's probably much more complicated than that - it's not my field, but I think that's the basic idea). If you have any specific questions about a particular part of the physics of baseball, feel free to ask, otherwise I'm not sure what else to say. --Tango (talk) 22:13, 4 May 2008 (UTC)

Some people ("grr...mother!") think I read too much into this game. When I say I want to know everything, I mean EVERYTHING! Every player's RBI & slugging percentage. Every players on base history all the way back to college. Even the molecular structure of the beer consumed by the drunk standing next to me (soon to be vomited on my shoe). Whats the psychology behind him? I'll bet he treats his kids bad.

I also want to know where I can get information on how all MLB teams chose thier uniforms.We all like vacuum cleaner physics and other trivial science stuff. That's my argument here.--Baseball and and and Popcorn Fanatic (talk) 22:35, 4 May 2008 (UTC)

Googling for "The science of" baseball gets you several thousand places to look. Please feel free to ask for specific information or explanation. Otherwise it might be easier to define which wikipedia pages are not likely to have much that in some small way affects some aspects of the game or event of baseball. Another way to go is to start with one aspect like e.g. Newtonian mechanics, Beer or Decision making and then work your way to the pages that link there. Happy studying. 71.236.23.111 (talk) 23:34, 4 May 2008 (UTC)

Doc Edgerton actually did some work studying baseball physics. Check it out. --98.217.8.46 (talk) 02:03, 5 May 2008 (UTC)

Seems to me that you're looking for Adair's The Physics of Baseball, ISBN 0060084367. -- Coneslayer (talk) 11:45, 5 May 2008 (UTC)

Thus far, physics has been addressed, but the questioner asks for the science of baseball. What about biomechanics, sports medicine, metabolism? This is a different slice of science, but just as relevant to baseball as the physics of a ball trajectory. Nimur (talk) 16:39, 5 May 2008 (UTC)

Water table in natural pond.

Hi there,

I have recently bought a house (Wales, UK) that has a back garden that is on a slope going upwards. At the top there is an old pond that has been left to its own devices for many years. So during my landscaping I syphoned all of the water out of it and cleared the foot of leaves etc from the bottom. To my horror there was no liner, only a clay bottom. The pond is about 3M X 1.5M and roughly 0.5M deep. There are 3 areas in the pond that I sink down deeped into the mud. I left the pond over night and when I visited it in the afternoon the following day the water level was pretty much back to where it originally was. So I have 2 options, get rid completely using some sort of drain or keep the pond. The pond idea sounds very appealing as my old neighbour had a beautiful pond with Koi in it. However, due to the nature of the pond being clay it would be impractical as the fish would cloud the water and the water would clog the filters with clay. So I was wondering if I were to put a lining inside the pond would the weight of the water inside the lining equal the pressure stopping the water from rising?

Many thanks Paul —Preceding unsigned comment added by Bwganllwyd (talk • contribs) 22:19, 4 May 2008 (UTC)

Are you sure the water rose from the ground and it didn't just rain overnight? It seems odd for the water table to be that high, especially at the top of a slope... Either way, you should be fine with a plastic lining - the people at your local gardening centre should be able to advise you further. The water shouldn't push itself up any higher than it would be normally, so as long as your garden isn't flooded, the water in the ground around the pond should still be below ground level. --Tango (talk) 23:40, 4 May 2008 (UTC)

Water tends to go exactly where it wants to go, if the underground dynamics lead water to come out at the top of a hill (which is not impossible), beware of trying to fight it. Generally, a liner won't change the pressure relationship. Also, in my experience, ponds lined with clay tend to be crystal-clear, there is no particular reason that the clay will enter the water column. That said, observe Tango's comment above about the possibility of rain. Franamax (talk) 23:47, 4 May 2008 (UTC)

This sounds more like a spring or a seep. It is difficult to maintain an actual water table at the top of a slope. For a literal waters table, if you add a flexible plastic liner, then the water level will be exactly at the level of the water table. However, since the water table fluctuates, the liner will inevitably displace towards the surface. It would be better to work with nature and take advantage of the natural inflow of water. If you can arrange for an outflow, you will have a nice natural open-loop system with no need for pumps and filters. From your description I suspect that there is a hidden outflow of some sort anyway. -Arch dude (talk) 00:28, 5 May 2008 (UTC)

Hi there, Thanks for the replies so far, the first time I emptied the pond it rained and the pond filled back up, but there is no way that that amount of rain fell. I have since emptied the pond several times without there being any rain and it has still filled up. I have been seeking advice on several sites, here is a link to one of them with some pics on it: http://www.inspectorsjournal.com/Forum/topic.asp?TOPIC_ID=7257

Just to explain the pics, I am excavating land from the bottom to try to level the garden out. The pond is at the top of the garden.

Cheeers Paul —Preceding unsigned comment added by Bwganllwyd (talk • contribs) 04:44, 5 May 2008 (UTC)

Before you put down a pond liner you'd have to find out where your water comes from or what Arch dude says is right. You'll end up with an artificial pond on top of muck and the liner will "float up". I'm no pond expert, but what you took out seems to have been a natural garden pond. They are tricky to get going because you rely on a balanced ecosystem instead of pumps and filters. Things get a lot easier to maintain if you have an inflow like a spring or seep (instead of just rain and surface run-off) which seems to be the case here. That will help with mixing up thewater column and oxygenate the water, see Hypoxia (environmental). Plants provide shade to prevent excessive algae growth. Animals like snails, dragonflies and frogs usually arrive on their own after a while. The clay (or sometimes tile) bottom keeps water from draining and allows only a limited amount to percolate through the ground. [5] The tricky part is that, if you get too much evaporation in summer you may have to top the pond off with tap water and that can damage the eco-system. Natural ponds can get "stinky" at times even if they are perfectly balanced.

What you propose to put in is an artificial garden pond or water garden. "If fish are kept, pumps and filtration devices usually need to be added in order to keep enough oxygen in the water to support them." Pumps and filters will silt up easily in a clay bottom pond. So you need to put in a liner and there's the problem because the water that fills your pond now will no longer be able to get into your pond. Lisa4edit (talk) 16:12, 5 May 2008 (UTC)

Spider

Can someone identify this spider:

Please? –Sidious1701_{(talk • email)} 23:48, 4 May 2008 (UTC)

Do you have a larger picture? I wouldn't be able to identify it with any picture, but I'm not sure anyone will be able to identify it reliably from such a small shot. --Tango (talk) 00:07, 5 May 2008 (UTC)

No, that's the only one I got...sorry. –Sidious1701_{(talk • email)} 01:31, 5 May 2008 (UTC)

Similarly, I don't think I'll be able to identify it, but it might help others if you gave a few details about where the photo was taken, and maybe the time of day. Confusing Manifestation(Say hi!) 03:43, 5 May 2008 (UTC)

I think we can only safely say that it is an Orb-weaver spider.--Lenticel ^(talk) 12:05, 5 May 2008 (UTC)

I found it under a table, it was about sunset, and that's all–Sidious1701_{(talk • email)} 20:51, 5 May 2008 (UTC)

Which country and region was the table in? Graeme Bartlett (talk) 21:36, 5 May 2008 (UTC)

It was in Louisiana, and it was outside.–Sidious1701_{(talk • email)} 00:31, 7 May 2008 (UTC)

Is it like the A. bruennichi image (left) in Argiope article? As Lenticel, an orb weaver, found in warmer areas... Julia Rossi (talk) 09:10, 7 May 2008 (UTC)

I don't know what julia is talking about, I seem to remember louisiana being prety damned warm. --Shaggorama (talk) 09:49, 8 May 2008 (UTC)

Isn't that was Julia's saying? It's an orb weaver that was found in a warm area, so she named a species that fits that description. --Tango (talk) 18:02, 8 May 2008 (UTC)

My bad, misunderstood. retracted. --Shaggorama (talk) 19:46, 8 May 2008 (UTC)