Wikipedia:Reference desk/Archives/Science/2008 August 17

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August 17

sarcodactylus OR sarcodactylis?

I have found that some books give the Latin name for Buddha's hand (fingered) citron as Citrus medica var. sarcodactylus whilst others refer to it as Citrus medica var. sarcodactylis. Can any user please tell me which one is correct. Thank you.Simonschaim (talk) 07:01, 17 August 2008 (UTC)

They appear to be used interchangeably in the scientific literature, though a perusal of Google Scholar seems to suggest that Chinese scientists tend to use sarcodactylis while Western scientists tend to prefer sarcodactylus. Which is correct is likely a matter of opinion, though you could ask a Latin speaker at the Languages desk which is the more grammatically correct "fleshy finger" suffix. Dostioffski (talk) 07:24, 17 August 2008 (UTC)

Thank you. Simonschaim (talk) 07:34, 18 August 2008 (UTC)

Solar mining

I had a hard week and now my mind is wandering off a bit, so excuse me if this question is a tiny bit on the fictional side of science. Imagine that, by methods far beyond or current technology, we could manipulate solar flares to selectively eject some elements and retain others, and on a large scale, too. Would there be enough heavy elements in our sun to build two or three earth-like (in size and composition) planets? Would, on the other side, the depletion of heavy elements alter our sun in a significant way? 93.132.189.68 (talk) 09:33, 17 August 2008 (UTC)

According to Earth#Chemical composition, the Earth is about a third oxygen, a third iron, and a third everything else. According to Sun#Chemical composition, the sun contains about 3000 Earth-masses of oxygen and 200 of iron. We don't have information on the rarer elements (you could try looking up the cited sources), but at a guess, given the superabundance of those two, there's probably enough to get by. I don't know if the loss of a tiny fraction of its heavy elements will have much effect on the sun. Algebraist 11:36, 17 August 2008 (UTC)

Well, great, thank you! I'll just start right away! Don't worry if you see some minor flickering of the sun, it's just me .... well, now, wait, how many d'ya say? 200? Um, I've just cleaned out my attic but I doubt there's room for all of them ... . OK, to be serious again, what would be the densest known stable constellation for earth-sized planets inside the habitable zone? People have thought up things like Dyson spheres, there should be something about stability, too. I think a binary system taking only two planets would be fine, but putting another at the L₄ or L₅ would not be stable enough (I mean, another moon would be a great sight but I'm afraid my insurance policy doesn't cover a planet hitting the earth). Putting a gas giant inside the habitable zone and let a few dozen earth-like planets orbit it should work, but what to do with the others? 93.132.189.68 (talk) 15:50, 17 August 2008 (UTC)

I don't think 2 Earth's would be stable (one on each side of the Sun would be in equilibrium, but the slightest move away from that point would mess it all up and the other planets would cause such a move pretty soon), there are stable patterns for more than 2, though, I remember seeing some Java applets demonstrating them. I'll try and find them. As for the effect on the Sun, see metallicity - I'm not sure there's anything of use there, but it might point you in the right direction. --Tango (talk) 17:07, 17 August 2008 (UTC)

I was thinking of two earths orbiting a common barycenter, each as the other ones moon, like pluto and charon. I need some time to check all the links given by now. 93.132.189.68 (talk) 19:34, 17 August 2008 (UTC)

It's Wikipedia, so we have an article on this. See Klemperer rosette. -Arch dude (talk) 18:16, 17 August 2008 (UTC)

Well, I see a hard-to-spell Klemperer rosette firstly rotates around its common barycenter, not around a star --- I was not planning to put the sun aside. It is not clear from the article if a Klemperer rosette is stable, even less if it would be stable if orbiting (all of the bodies) around a star. 93.132.189.68 (talk) 20:45, 17 August 2008 (UTC)

According to the original paper linked, the rosette (the one with alternating light and heavy planets) is stable whether or not you put a star in the middle. There are some tight restrictions relating the radius of the system to the mass-ratio of the planets. Algebraist 20:53, 17 August 2008 (UTC)

OK, you beat me. I haven't read the large article completely. As I don't know when I'll have the time to do that, I promise not to create those 200 worlds until I have done so. You think I'm a megalomaniac? I hadn't even a chance to tell you about my three major plans with our local multiverses! 93.132.189.68 (talk) 21:18, 17 August 2008 (UTC)

Local multiverses? I'm intrigued! Not only are there multiple multiverses (each, presumably, containing multiple universes), but that's only taking into account the local neighbourhood? Wow! ;) --Tango (talk) 21:32, 17 August 2008 (UTC)

Just make sure our sun is not alive like the one in the Doctor Who episode 42. -- KathrynLybarger (talk) 15:26, 17 August 2008 (UTC)

Bah, I'll just tell it the procedure is good for its health and that the costs are covered by the national health service, no extra payment needed. 93.132.189.68 (talk) 16:08, 17 August 2008 (UTC)

Lower-metallicity stars have lower temperatures (http://nedwww.ipac.caltech.edu/level5/Sept01/Pagel2/Pagel4_3.html). By association, they also have lower luminosities and appear closer to red then to blue. Removing metals from the Sun will change its position on the Hertzsprung-Russell diagram towards the lower right. Oops, I misread the webpage. --Bowlhover (talk) 11:28, 18 August 2008 (UTC)

Doesn't that link say just the opposite? Anyway, I suspect that there are strong selection effects at play here: the oldest stars are also the coolest and the least metal-rich. I doubt that removing (magically and only) the metal from Sol would change its temperature significantly. --Tardis (talk) 16:04, 18 August 2008 (UTC)

Anti-ballistic missile

How effective are these anti-ballistic missile defenses? Are they really capable of intercepting ICBMs with 100% success rate? Otolemur crassicaudatus (talk) 14:22, 17 August 2008 (UTC)

There have been successful tests when the target missile had no countermeasures such as decoy warheads and flew a known path at a known time. Edison (talk) 14:50, 17 August 2008 (UTC)

But those tests have been isolated one-off tests. The chosen US technology is mid-course interception where the ICBM is shot down during its ballistic phase out on the edge of space. The handful of tests that have been done are not statistically significant indications of 100% success, even in those very limited circumstances - and it took a lot of tries before they hit one. The short answer to your question is: Their effectiveness is likely to be minimal against sophisticated ICBM's that could use stealth technology, could launch up to a dozen MIRV's and dozens more decoys. MARV technology might also render interception impossible. They might work against much simpler devices. All of those ideas have been in use in real ICBM's for decades.

Descent-phase ABM's have been used with some success - the "Patriot" missile had some success in the first gulf war - not 100% but it's been through several rounds of improvements since than. Of course you have to position them in large numbers around potential targets - which makes protecting an entire country essentially impossible. But they are "battle tested" - and they exist in reasonable numbers today. For shooting down nuclear weapons, they are not a great solution because the bits of destroyed warhead some showering down into the target zone - kinda like a "dirty bomb". That's better than having a nuclear detonation...but it's not exactly what you'd like to happen!

IMHO, what is needed (and would work a heck of a lot better) is launch-phase interception. In this situation, you catch the ICBM soon after takeoff. It's moving more slowly - it's moving in atmosphere (so it can't change direction quickly) - it can't deploy cheap decoys and it's MIRV/MARV's won't have split off yet. Best of all, the nasty, poisonous pieces of plutonium come raining down on the heads of the people who launched the darned thing rather than "burning up" on reentry - which spreads the incredibly poisonous stuff throughout the worlds atmosphere. I believe that if a ship-mounted ABM technology had been divised rather than following Reygan's crazy "Star Wars" ideas - then in times of international tension, ABM-equipped vessels could be positioned in international waters off the coast of any potential agressor as a way of saying "Don't even think about it". But for countries such as Russia and China which could position their launch sites far from international waters - this too has it's problems.

SteveBaker (talk) 15:53, 17 August 2008 (UTC)

• The claim that "the 'Patriot' missile had some success in the first gulf war" is disputed. See Patriot missile#Success rate vs. accuracy. --Anonymous, 03:56 UTC, August 18, 2008.

The problem with launch-phase interception is that you have pretty much no warning at all. How do you launch an interception missile in time for it to reach the ICBM soon after takeoff? --Tango (talk) 17:34, 17 August 2008 (UTC)

I find it unlikely that vaporizing the amount of plutonium in even a primitive warhead (~15 lbs of Pu) in the upper atmosphere would appreciably damage the health of people. Chernobyl dumped far more poisonous isotopes in far greater quantities into the environment at much lower altitudes and even that had relatively restrained effects (probabilistic increases of cancers, birth defects, etc., but no radiation poisoning other than people at the site itself.) As for ship-mounted ABM, see Aegis Ballistic Missile Defense System. --98.217.8.46 (talk) 17:56, 17 August 2008 (UTC)

You could always go back to the old plan of setting off hundreds of nuclear bombs in a line starting 150 miles west of Ireland and going up north. The plan was to destroy the Ruskie bombs with the electromagnetic pulses and radiation as they went past. And the trade winds would take any fallout over Europe away from America, they're all socialists anyway which is another word for commie. Dmcq (talk) 16:16, 17 August 2008 (UTC)

Of course, that wouldn't help you against SLBMs with flight trajectories other than over-the-pole, anyway. --98.217.8.46 (talk) 17:56, 17 August 2008 (UTC)

The answer is almost certainly no. But the practical effectively is perhaps secondary to the strategic and psychological effectively of having a co-ordinated anti-ballistic missile defense system that might work. The very fact that one exists, however potentially ineffective, could be a sufficient to deter anyone from launching a missile that would require intervention. The threat of MAD as a deterrence strategy so effective during the of the Cold War was deemed ineffective against potentially irrational "rogue" actors with nuclear access, so another strategy was needed. The anti-ballistic missile defense system was the result of this. Dostioffski (talk) 17:49, 17 August 2008 (UTC)

I'll take a little issue with your "history". The current ABM system comes right out of the work done on SDI in the 1980s—it never really stopped(see National Missile Defense). As for whether deterrence is ineffective against "rogue states" (meaning, presumably, North Korea or Iran), there's no evidence yet that it isn't, or that these leaders are willing to sacrifice their own political stability (or lives) for their ideologies (yes, they sabre-rattle, but so do all sides here). Iran is not al-Qaeda, and neither is North Korea. al-Qaeda does not have access to ICBMs (and the likelihood of them getting access is nil—if they are going to go nuclear, they aren't going to use ICBMs). --98.217.8.46 (talk) 18:01, 17 August 2008 (UTC)

I didn't mean to suggest that deterrence is not ineffective against "rogue states" or that the idea of a AMB system was a new one. I was noting that is part of the expressed reasoning for why the strategies used in the Cold War were deemed, by certain administrations, no longer effective and thus why other pipeline strategies became a priority. What we are told by governments, and what there is evidence for, often bear little relation. By the way, I think this reasoning was originally made in relation to former Soviet States. Al-Qaeda and the US were friends back then. Dostioffski (talk) 18:11, 17 August 2008 (UTC)

If you tell me when you plan to break into my house, and through which door or window, and with what tools, I have a good chance of preventing it. Edison (talk) 05:20, 19 August 2008 (UTC)

Yes - but if you tell me exactly how you protected your house - with what alarms and detectors, I have a good chance of breaking in. SteveBaker (talk) 02:13, 20 August 2008 (UTC)

And while you two were telling each other these things as length, I'd be stealing your cars! Or something like that. --98.217.8.46 (talk) 01:10, 21 August 2008 (UTC)

Dockin in orbit

Help! I am in orbit in my lander module having just taken off from the planet's surface. The command module is 100m ahead of me at the same altitude. I need to dock, but if i burn the forward boosters, I will increase my altitude and therefore be out of line. If I fire the retros, I will lag further behind command module. How the hell can I get docked? —Preceding unsigned comment added by 79.76.158.77 (talk) 03:44, 17 August 2008 (UTC)

...This is the Science reference desk, not the Read-Your-Mind-To-Figure-Out-What-The-Heck-You're-Talking-About-Desk =) --mboverload@ 03:48, 17 August 2008 (UTC)

'S ok mb, the question was not addressed at you ;) —Preceding unsigned comment added by 79.76.158.77 (talk) 03:57, 17 August 2008 (UTC)

Engage the autopilot. Algebraist 04:09, 17 August 2008 (UTC)

Auto pilot on shore leave. —Preceding unsigned comment added by 79.76.158.77 (talk) 04:16, 17 August 2008 (UTC)

Actually, you have got that wrong. If you fire your retros you will lose energy and fall to a lower orbit certainly, but you will also accelerate as you fall. In the lower orbit you will be travelling at a faster angular velocity and will start to catch the command module. For circular orbits;

$\omega ^{2}={\frac {GM}{r^{3}}}$

You might want to fire your attitude thrusters also to trim the orbit back to circular. After catching the command module you can now fire the forward thrusters to both bring you to higher orbit and to match velocities with the command module again. This is not professional advice, no liability accepted - if you scrape your spaceship talk to your insurance company, not to me. SpinningSpark 19:38, 17 August 2008 (UTC)

Your Orbital Maneuvering System and Reaction control system should help you do that. If you don't have a OMS/RCS you have no business being in space. Dostioffski (talk) 19:40, 17 August 2008 (UTC)

Why don't you simply harpoon the main module? Or shoot a harpoon backwards, the mass of the harpoon and the length of the rope carefully calculated so that, given the barycenter stays put at the distance with the main module, your lander module will just touch the main module. But be quick to grab the main module for you will be drawn back when the harpoon recoils on its rope. 93.132.189.68 (talk) 19:49, 17 August 2008 (UTC)

So what you're saying is that if you fire your engine in a line directly towards the command module then your orbital speed will increase - and so will the radius of the orbit. That's true. But you're pretty close to your command module - a very gentle nudge in the that direction won't increase your orbital speed by enough to make a significant difference to the radius of your orbit - and a very small change in orbital velocity will allow you to catch up the command module pretty quickly - it's only 100 meters away.

But if I understand what's behind your question - so let's pretend the command module is 100 kilometers away or something. Who says you have to aim your rocket DIRECTLY at the command module? Just rotate your craft until you're aiming a little BELOW the command module and fire your motors. If you time it right, the thrust will push you towards the planet - whilst simultaneously increasing your speed. Assuming you get your math right, the two effects will cancel out just as you arrive at the command module.

If your rotation thrusters were broken or something - and your were strictly only able to fire in a direction that's a tangent to the orbit then you could fire your main engine - let the orbit get a little larger then cut the engine and drift until you're a little ahead and above the command module. Then firse your retros at just the exact right moment and you'll fall behind it and reduce the radius of your orbit and arrive at the perfect spot.

SteveBaker (talk) 23:05, 17 August 2008 (UTC)

We have no rotation thrusters: this is Russian craft -we cannot afford luxuries like you Western capitalists. —Preceding unsigned comment added by 79.76.202.169 (talk) 01:15, 18 August 2008 (UTC)

The other consideration is that it's usually beneficial to minimise fuel consumption. As long as you're not in a hurry, a tiny nudge retro to change your orbit to a lower one, waiting to catch up, and then another tiny nudge to match orbits again will probably use less fuel than any other technique - you can use an arbitrarily small amount of fuel by just allowing it to take an arbitrarily long time to catch up. I'm not really sure what you happen if you thrust forward and slightly down, your logic sounds good - I expect you could do it in such a way as to intercept your destination, but I don't know what would be required to match orbits again, you would be in a completely different orbit. --Tango (talk) 23:25, 17 August 2008 (UTC)

You might ask Neil Armstrong. He was good at this, back in the day. Edison (talk) 05:17, 19 August 2008 (UTC)

Medicine

Please, what is the active ingredient in the prescription drug, Synthroid.

– — … ‘ “ ’ ” ° ″ ′ ≈ ≠ ≤ ≥ ± − × ÷ ← → · §  —Preceding unsigned comment added by 81.252.82.4 (talk) 19:40, 17 August 2008 (UTC) 

Synthroid. Wisdom89 _{(T / ^C)} 19:41, 17 August 2008 (UTC)

Or try www.synthroid.com --Tango (talk) 21:03, 17 August 2008 (UTC)

To paraphrase for those interested: It's a thyroxine analogue. Fribbler (talk) 22:52, 17 August 2008 (UTC)

Light in a time warp

Can light travel faster than the speed of light inside a time warp ? 69.157.227.243 (talk) 21:22, 17 August 2008 (UTC)

If you tell us what a time warp is, we might be able to help you. Algebraist 21:25, 17 August 2008 (UTC)

It's just a jump to the left... DuncanHill (talk) 21:28, 17 August 2008 (UTC)

Good call Duncan. We actually have an article on the sci-fi concept of time warps. Like Algebraist implies, there's no definition clear enough to answer the OP's question. But if this were asked on the Humanities Desk, I'd respond that as many sci-fi authors seem to imagine a time warp (as a tunnel-y sort of wormhole), light would travel at its normal speed locally while inside the time warp, while from a point of view outside the time warp, light (and everything else) would seem to travel faster than the speed of light (that is, back in time... assuming we're talking about the back-in-time kind of time warp). --Allen (talk) 22:19, 17 August 2008 (UTC)

To say this as clearly as possible: There is no such thing as a "time warp". Hence this question is utterly unanswerable. SteveBaker (talk) 22:52, 17 August 2008 (UTC)

Probably not what the OP was thinking of, but a "spacetime wrap" is contained in every black hole's event horizon. Since Einstein's theory of general relativity states matter bends space and light travels in straight lines, the path taken by light indicates the distortions caused by gravity. Light cannot escape from within an event horizon, so it's logical that the space is bent inward and no paths lead to the outside world. For an observer inside the horizon, light doesn't travel faster than usual, but an outside observer would not see light from inside the horizon at all. --Bowlhover (talk) 08:49, 18 August 2008 (UTC)

Olympic dope caught doping

What benefit would Kim Jong Su have gotten from taking propranolol? Clarityfiend (talk) 22:25, 17 August 2008 (UTC)

Our article on the drug says: "Propranolol is often used by musicians and other performers to prevent stage fright." Perhaps he took it to settle his nerves - you don't want your hands shaking when you're aiming a gun. --Tango (talk) 22:29, 17 August 2008 (UTC)

You're pretty much spot on, Tango. Propranolol works by blocking the action of epinephrine (a.k.a. adrenalin). Kim Jong Su competed in the 50 metre pistol event at the 2008 Summer Olympics. This is a game where the effects of adrenalin may not be a good thing, since adrenalin can makes edgy physically and mentally. As you can imagine, in a game of accuracy, this isn't fantastic. So by taking a β-blocker, Kim Jong Su could avoid this effects and have an advantage against other competitors. —Cyclonenim^T@lk? 22:36, 17 August 2008 (UTC)

Additionally This NY Times article says "In competitive rifle shooting, beta blockers are often used to reduce body bounce (caused by the pumping of the abdominal aorta)". That article discusses its effects for prone rifle shooters, but you'd think that similar effects would be felt by upright pistol shots like Kim. -- Finlay McWalter | Talk 22:46, 17 August 2008 (UTC)

Maybe students should be given a dose of propranolol before taking an important exam (especially an oral exam). Then they would not have the excuse, which is sometimes valid, "I knew the answer but I froze up." Andme2 (talk) 23:02, 17 August 2008 (UTC)

I know plenty of students who have taken beta-blockers before exams or, even more commonly, important presentations. They say it works wonders. Plasticup ^T/C 23:12, 17 August 2008 (UTC)

It is frowned upon, though... --Tango (talk) 23:16, 17 August 2008 (UTC)

It's not limited to students. It's widely known – if not widely commented upon – that professional musicians often engage in this sort of off-label use of beta blockers. See for example this page, which describes a survey of a large of number of U.S. symphony orchestra performers. (Few reported using beta blockers all the time, but a large minority took them for auditions and difficult solo performances.) TenOfAllTrades(talk) 18:30, 19 August 2008 (UTC)

Beta blockers seem to limit the max heart rate and stop you getting too excited. Certainly stopped me! Also did tend to reduce nervousness for that reason. Only problem: if you need to get your heart rate up with physical exertion etc, you cant! —Preceding unsigned comment added by 79.76.202.169 (talk) 01:20, 18 August 2008 (UTC)

How is that experienced, subjectively? I'd assume a high heart rate is needed during physical exertion, so do you feel "weak", "easily tired" or something more dramatic? EverGreg (talk) 08:18, 18 August 2008 (UTC)

I used to take propranalol for chronic headaches, and I once tried to ride my bicycle a bit too hard, and I passed out in the middle of the road. I don't remember passing out or falling, just waking up to see the beautiful blue sky and being unsure if I was dreaming. Then people were peering down at me. --Sean 14:17, 18 August 2008 (UTC)

Sedative effect of alcohol

The Sedative effect of alcohol is not explained in the article. Can anyone explain it here?--79.76.202.169 (talk) 23:19, 17 August 2008 (UTC)

Have you read short-term effects of alcohol#Pharmacology? Algebraist 23:26, 17 August 2008 (UTC)

Octopus

If an octopus has eight tentacles, with which one does it make love?--79.76.202.169 (talk) 23:24, 17 August 2008 (UTC)

With the Hectocotylus. Algebraist 23:26, 17 August 2008 (UTC)