Wikipedia:Reference desk/Archives/Science/2008 July 11

= July 11 =

Can I feed Rich tea and other hard biscuits to the larids?
I've been tidying a relative's house up today. She's been in hospital for months and is going to be well enough to come home soon, so I'm getting things ready for her. I went though the cupboards and found lots and lots of out of date biscuits. So, I've got like 20lbs of old biscuits in my house now. They're not mouldy or anything but I'm not gonna be eating them. I was going to feed them to the always hungry seagulls instead of just binning them but I wanted to check here before I do. I know not to feed them anything with chocolate on it but can gulls safely eat hard, dry biscuits like rich teas? I've seen the way they gulp their food and I don't want them to hurt their throats because of me. Thanks a lot. --84.67.208.62 (talk) 00:22, 11 July 2008 (UTC)


 * Please, if you feed them, please feed them in an unpopulated location. Seagulls have a propensity for pooping within close proximity of the hand that feeds them. Also you can soak your biscuits in water. They will be quite happy consuming them. 71.100.1.87 (talk) 01:26, 11 July 2008 (UTC)


 * Translation for Americans: UK "biscuit" = US "cookie". StuRat (talk) 04:55, 11 July 2008 (UTC)
 * UK "biscuit" ≈ US "cookie" AlmostReadytoFly (talk) 11:10, 11 July 2008 (UTC)
 * What I needed a translation for was larid, but luckily WP took me right to the spot. Looked like a typo for Laird, as in the Laird o' Phelps spent Hogmanay/declaring he was sober/counted his feet to prove the fact/and found he had one foot over. MacNiece, I think, or maybe Day Lewis. --Trovatore (talk) 02:07, 12 July 2008 (UTC)

Auditioning loudspeakers - is it a con?
You know when you go to the hi-fi store to choose some new loudspeakers? well when they get you in the listening room with different pairs of speakers, isn't this a con? I mean aren't those other inactive speakers going to suck out some of the sound from the ones you're listening to? —Preceding unsigned comment added by 79.76.184.112 (talk) 01:22, 11 July 2008 (UTC)


 * All surfaces will absorb some sound, and speakers will likely absorb more than most surfaces. So, of course, the acoustics in the sound room won't exactly match your intended room for the speakers, but it's likely still close enough to judge one set of speakers relative to another fairly well. StuRat (talk) 04:51, 11 July 2008 (UTC)


 * The most common "con" is based on the fact that louder sounds better, so if they really want to sell you some specific pair, they play that pair louder than the rest.


 * Atlant (talk) 09:54, 11 July 2008 (UTC)


 * Yeah Surat but what Im particularly thinking is all those bass reflex cabs in the room must suck out some of the bass from the ones your listening to. Right? —Preceding unsigned comment added by 79.76.201.118 (talk) 10:09, 11 July 2008 (UTC)


 * But that would make all the speakers they're trying to sell sound worse, so how is that a "con" ? StuRat (talk) 21:05, 11 July 2008 (UTC)
 * Not necessarily worse. It could make the speakers youre listening to sound less bbomy than they are! —Preceding unsigned comment added by 79.76.238.223 (talk) 23:18, 14 July 2008 (UTC)


 * If the other loudspeakers aren't connected then their effect would be to turn the room into a highly damped one ie like a room with a lot of heavy curtains. Most loudspeakers do have a resonant frequency but they all tend to be heavyily damped. Note: some businesses will have a room for demonstration and only have one set of speakers in at a time - you could request this.
 * Are the tests a con in general - yes - there will be a fairly heavy element of the shop selling you the speaker they want to get rid off.87.102.86.73 (talk) 12:19, 11 July 2008 (UTC)

I have no interest in physics and math
...but because I want to go into a career in computers, so it's pretty much a must. I don't want to seem like I'm blaming someone else for my problem, but really I've never had a teacher "inspire" me to go learn math or physics. They always taught to the test and told us - do this and you'll get the answer. How did you get interest in the subject - is it inborn, or does it come after doing it for a while?

Do you have any words of advice to offer? I know I need to have interest in these subjects to succeed - it's just I don't know how to get it. And I kind of have a fear of math. —Preceding unsigned comment added by Legolas52 (talk • contribs) 03:52, 11 July 2008 (UTC)


 * I got interested in math by my father teaching me stuff at a really young age, and then having inspiring teachers... I guess that's not much help. But I got interested in physics partly by reading pop physics books; you could try that.  Atom: Journey Across the Subatomic Cosmos and A Brief History of Time especially.  Mind you, I didn't get interested enough to actually major in either subject, but I was certainly propelled far enough to get the prereqs I would have needed for a CS degree if I had gotten one of those.  --Allen (talk) 04:36, 11 July 2008 (UTC)


 * My own interest in math and science is inborn. I have always been an objective person, sometimes to the point of being apathetic.  I also found courses involving analytical thinking to be much easier than those that require subjective judgements or pure memorization.


 * I'm curious as to why a computer-related career involving math and physics interests you. Do you just feel comfortable working with computers?  How about a job in web design, database management, or programming, then?  The most difficult part of producing software is software engineering, because a knowledge of computer science is a must to optimize efficiency.  Writing the code itself takes comparatively little effort.


 * As for advice, you don't need to be extremely interested in a subject to do well in it. Understand every topic taught, do all homework, study for all tests, and you should receive a decent mark.  Do not panic on tests or exams; they may seem difficult, but remind yourself that it's nearly impossible for a single evaluation to drastically affect your mark.  --Bowlhover (talk) 05:44, 11 July 2008 (UTC)


 * Yeah, I think the idea that working with computers requires an understanding of math or physics is kind of misguided. That depends a little on what you want to do, of course, but there's a vast field of things you can do without any real knowledge of either. If you're, say, a web designer or a system administrator, being able to do basic arithmetic and understanding that if you put a cup of coffee on top of your monitor, there's some potential energy there that you need to be careful of is probably going to be entirely sufficient. -- Captain Disdain (talk) 08:56, 11 July 2008 (UTC)


 * I agree that you don't need more than basic math skills for a job in the computer field (unless you intend to design computers), and the same for physics. If you would like to find something that might stimulate an interest in physics, I would suggest finding a book that discusses the subject with a sense of wonderment and mystery.  These types of books often turn out to be pseudoscientific pscyhobabble, but they have the desired effect of intriguing readers into learning more about the real science.  Let's face it, pseudoscience is much more interesting to the layman than hard science is.  Once you discover a real interest then you will voluntarily hit the books to learn as much as you can, leading to an understanding of the subject.  Eventually you'll look back and realize how silly those first fantastic ideas were, and have a good laugh.  By that time, though, you'll be hooked - and educated.  At first place more emphasis on whether or not the book interests you than on the qualifications of the author.  As you learn the science you'll learn to seperate the wheat from the chaff.  152.16.16.75 (talk) 10:20, 11 July 2008 (UTC)


 * I never really "got" math until I started writing software to do my linear algebra homework for me. Then I found it a fun and an interesting challenge.  Maybe that could work for you, too.  --Sean 11:30, 11 July 2008 (UTC)

There are great authors out there that can take the esoteric hard sciences and make them more accesible. I'd particularly recommend anything by Carl Sagan. For math, maybe looking into some of the quirky-but-surpisingly-relevant topics like game theory can make the overall topic more interesting. While I've always been a nut for science in general, I only really began to appreciate math & physics when I understood how they provided a framework to explain foundational aspects of biology & chemistry (particularly my area of greatest expertise, pharmacokinetics & pharmacodynamics), and they are vital to the leading edge of new technologies to explore these topics. Check out things like this for other suggestions, and sites like this for more insight. &mdash; Scientizzle 14:59, 11 July 2008 (UTC)


 * I wonder if perhaps the OP means that theres a concern about pre-requisite courses. If this is the case, I'd suggest following a lot of the recommendations above. Find something cool and follow it, Pale Blue Dot by Carl Sagan is an excellent book. Inspiring a love of science is, in my opinion, a lot easier than inspiring a love of math. Even as a physics/chem major with a math minor, math is a tool for me, not something I'm really passionate about. EagleFalconn (talk) 15:07, 11 July 2008 (UTC)
 * Taking this from a rambling and (mostly:) purely educational standpoint, an academic degree is not just a stamp that you can do a certain thing, but that you also know something about its relationship to other things. If really all you want to do it design web pages or be a sysadmin, an undergrad CS degree is often useless overkill...get a trade-school certificate. Take the MS certs (I won't get into their usefulness beyond "HR departments seem to care about them") or some visual-design courses and you know "everyhing you need to know to do that specific task." Of course, you won't know anything about the how or why, or the history or be able to work as well with those who do understand the historical context, or be as able to adapt when there is a paradigm shift or hardware/software quantum-leaps forward or a zillion other buzz-word things happen. There's a big difference between knowing how to do something, and knowing why it's done, how/why it works, etc. Even for a degree in a certain field that requires taking classes in many other fields, maybe even usually some/all of those others won't be interesting on their own. Maybe at least one will be on its own when you take it, and that's great. But more often, later, you'll work on some project in your field and recognize something you learned in that other field, and your job will be easier, your task will make more sense, or you will be able to justify to your employer or customer why your approach is better. In the real world, you have to interact with specialists in many different fields, and if you know something about the ideas and terminology in the ones "near" yours and how your and their fields relate, you will be better able to communicate with them to make your solutions work for them (or intelligently choose what tasks you can delegate to them) and not look like an idiot when you try to fake it with buzz-words and mis-applied ideas. DMacks (talk) 16:14, 13 July 2008 (UTC)

Antimatter into Matter
How would the universe be different if all anti-matter was turned into matter, and all anti-energy was turned into energy ? 69.157.227.80 (talk) 05:12, 11 July 2008 (UTC)
 * All that would happen would be every thing would switch around, e.g. north to south. (I think). Harland1 (t/c) 05:39, 11 July 2008 (UTC)
 * Why? We live in a regime of the universe where the vast majority of particles are matter.  I can't see taht the conversion of all anti-matter into matter would produce this effect.  Jdrewitt (talk) 13:48, 11 July 2008 (UTC)


 * As far as I can tell, if all antimatter and matter were switched (is that what you mean?) nothing would change. Also, I don't think there is any such idea as anti-energy in physics.  --Allen (talk) 05:45, 11 July 2008 (UTC)


 * Actually what makes you so sure that all matter isn't anti-matter? Harland1 (t/c) 06:17, 11 July 2008 (UTC)


 * Because the more abundant substance is termed "matter" and the substance with particles of the opposite electric charge is antimatter. The word "matter" has been used to refer to anything with mass long before antimatter was theorized, according to the etymology given here.  --Bowlhover (talk) 06:38, 11 July 2008 (UTC)


 * I don't think the question is asking what will happen if the two are switched, it is simply asking what would the consequences be if anti-matter became matter. Well for one you wouldn't be able to do Positron annihilation spectroscopy. Jdrewitt (talk) 09:04, 11 July 2008 (UTC)


 * But you would be able to do Electron annihilation spectroscopy. Have a look at C-symmetry & CPT symmetry. I think the Standard Model says that if you swapped every particle for it's antiparticle it would be possible to tell the difference but if you also changed the direction of time and reflected everything then you couldn't. JMiall  ₰  11:28, 11 July 2008 (UTC)


 * No, that wouldn't work either since it would require the existence of positrons for the annihilation event to occur. The question does not ask what the effect would be if the two are switched but simply asks what the effect would be if all antimatter was converted into matter.  i.e. anti-matter would no longer exist since everything would be matter. Jdrewitt (talk) 13:38, 11 July 2008 (UTC)


 * If that's what he was asking, then it would be an illogical question. Because you can't turn matter into antimatter. You can turn energy into antimatter and matter though (producing equal amounts of both). If the question is asking what would happen if the universe was composed of mostly anti-matter instead of matter, I don't think there would be much difference. For example anti-iron looks like regular iron. Anti-earth looks like regular earth. Anti-you looks like regular you. ScienceApe (talk) 01:09, 12 July 2008 (UTC)

(outdent) see CP violation. --Trovatore (talk) 01:22, 12 July 2008 (UTC)

I haerd rumors about this? In 2012, the Earth will be gone?
I heard rumors that the earth will be destroyed in 2012. The person who said the rumors claims a professor at USC predict that the earth will be destroyed in 2012. I don't think so. Is this false? Jet (talk) 05:30, 11 July 2008 (UTC)


 * Probably something related to 2012. --Allen (talk) 05:50, 11 July 2008 (UTC)


 * Well, the same year was recently brought up on the Miscellaneous desk. Are you sure the rumored professor is not, in fact, an alien collaborator?


 * More seriously, though, you might want to employ a bit of common sense. If there was someone with even a shred of credibility making realistic and believable public predictions that the Earth has four years to go, don't you think you would hear something a little more substantial than vague rumors about it? -- Captain Disdain (talk) 11:26, 11 July 2008 (UTC)


 * Never underestimate the ability of conspiracy worriers to feel that matters of massive importance are being totally and successfully hidden from everybody except people like themselves. ;-) --98.217.8.46 (talk) 14:31, 11 July 2008 (UTC)
 * I heard that, besides all the Mayan stuff and whatnot, there'll be an alignment of the planets of our solar system, the sun and the center of the galaxy, or something like that. Since it hasn't happened before in recorded history there's a lot of completely outrageous speculation about what might happen. There's also a computer program that was developed to scan information on the internet to make predictions for stock traders. It supposedly predicted that 'something major' would happen on 9/11/2001 and it also predicted something major for 2012. The thing to remember about both of these is that anyone or anything can speculate about the future. People thought the world would end in 2000. The Mayan stuff and the ridiculous pseudoscience stuff is based on astronomy. The computer thing is based on human activity, which is erratic and hardly readable. My suggestion: worry about stuff you can actually do something about. There's plenty already going on in the world that's scientifically verifiable that can use everyone's help. -LambaJan (talk) 16:07, 11 July 2008 (UTC)


 * People actually thought the world would end in 1000 too. Millenarianism is not a new thing. Using it to generate profit (book sales) is probably not a new thing either. --98.217.8.46 (talk) 21:44, 11 July 2008 (UTC)


 * There has been a somewhat controversial prophesy made about that year on qntm.org. — DanielLC 16:02, 11 July 2008 (UTC)


 * I bet you £100 the world isn't destroyed in 2012. --Tango (talk) 23:14, 11 July 2008 (UTC)


 * Check out Bad Astronomy by Phil Plait. To put it simply, yes, this is a hoax/conspiracy theory based on a lot of nonsense. Expect the mainstream media to be picking up more about this over the next couple years, just like the millenial crap did in 1999. It's a combination of misinterpreting the Mayan calendar and a lot of weird pseudo-science/pseudo-religion books & websites trying to make a buck. &mdash;  The Hand That Feeds You :Bite 13:44, 12 July 2008 (UTC)
 * changed www.badastronomy.com to blogs.discovermagazine.com/badastronomy/ in the above link to get around the spam filter.&mdash;eric 05:32, 15 July 2008 (UTC)

Basically the world has been on the brink of annihilation from the day it was formed. There are a huge variety of such claims all through history, I had found a really good site which listed many apocalypse theories of different cultures. What I would like to know is the psychology of the individual of group which "enjoys" the prospect of total annihilation, anyone got something on that?Bastard Soap (talk) 18:47, 12 July 2008 (UTC)

Hooke's Law
Two questions: 1) On the Hooke's Law page it say that in the equation 'q' = the 'force constant', what is the force constant and how does one find it? 2) And it says that x is the distance that the spring has been stretched or compressed away from the equilibrium position, does this mean x is the difference between the length with no mass applied and the length with mass applied or the total length with mass applied? Thanks very much. Harland1 (t/c) 05:36, 11 July 2008 (UTC)


 * x would be the difference, not the total length. k is the amount of force you have to apply to stretch the spring a unit length.  To find it, just apply a known force to the spring (like hanging a weight from it... the force would be the mass of the weight times g).  Then measure the displacement (x), and divide the force by the displacement (mg/x).  --Allen (talk) 05:59, 11 July 2008 (UTC)


 * (after edit conflict) x is the difference between the length at which the Hookean material applies no force and the length to which it is streched or compressed. Hooke's law postulates that the force applied by a Hookean elastic material, such as a spring, is proportional to the amount it is stretched or compressed. "k" is the number by which a length should be multiplied to calculate the force required to stretch/compress an elastic material by that length. If a spring's k is 30, for example, it would take 30 N to change its length by 1 m.  --Bowlhover (talk) 06:08, 11 July 2008 (UTC)


 * (e.c.)One further thing, I not that great at science, I assume g is always the same? And when you've done that is the number you get F in the Hooke's Law equation, thanks. Harland1 (t/c) 06:10, 11 July 2008 (UTC)


 * Hooke's Law is F=-kx, so multiplying k by -1 by x would give you the force the material applies. F is negative because the force is in the direction opposite to the change in length. --Bowlhover (talk) 06:38, 11 July 2008 (UTC)
 * g depends on only an object's mass and the distance from its centre of gravity, so the changes in Earth's gravity are negligible. Also, for most practical purposes, g can be assumed to be 9.8 m/s² on Earth's surface.


 * Have been doing more thinking. So if I put 100g on a spring. The force constant would be 100x9.80665=980.665. Then divided by the displacement -say 2cm. So you would get 980.665/2=490.3324999999999818 (roughly)? Harland1 (t/c) 06:16, 11 July 2008 (UTC)


 * 100*9.80665 is the force the weight applies on the spring, not the force constant. Also, be careful with the units.  Your force is in gm/s² (g*(m/s²)), where g is "gram".  However, your displacement is in centimetres, so the force constant calculated would be in gm/(cm*s²).  The calculation would be easier if you use the force in Newtons (0.1 * 9.80665) and the change in length in metres (0.02 m).  The force constant would then be in N/m.  --Bowlhover (talk) 06:38, 11 July 2008 (UTC)

(unindent) Thanks very much! Harland1 (t/c) 06:59, 11 July 2008 (UTC)

Infra red lamps
We bought a bathroom heater which use 4 infrared lamps 275Watts each. I want to know how the infrared lamp work and if it will use to much electricityRia erasmus (talk) 10:55, 11 July 2008 (UTC)


 * I anticipate that they will use about 275 Watts each. You might enjoy reading infrared as well.  Dragons flight (talk) 11:04, 11 July 2008 (UTC)


 * The wire inside gets hot like an Incandescent light bulb -but not as hot so it mostly gives out heat and not light - ie it's red-hot not white-hot.87.102.86.73 (talk) 11:13, 11 July 2008 (UTC)


 * (ec) See infrared heater. Basically they are high-powered light bulbs running at a much lower power and temperature than if used for lighting. The filaments in light bulbs is a black body radiator, so if you lower the filament temperature the emission spectrum will shift towards the infra-red end, producing more infra-red and less visible light. --antilivedT 11:19, 11 July 2008 (UTC)


 * Electrical devices use more electricity the more heat they put out, so electrical heating devices of any sort use a relatively large amount of electricity, in this case slightly more than a single bar conventional electric heater for your four lamps. They are a relatively inefficient way of heating a bathroom.--Shantavira|feed me 15:16, 11 July 2008 (UTC)


 * These heaters, like all electrical heating, are almost 100% efficient inside the bathroom, but inefficient (as Shantavira said) because of the energy losses in generation and distribution of the electricity, which is why electrical energy is much more expensive than gas. I use this type of infra-red heater because the convenience makes up for the high running cost (and because the nearest mains gas is six miles away).  The running cost of your heater would be about £0.10 per hour in the UK (depending on your electricity contract)   D b f i r s   16:53, 11 July 2008 (UTC)


 * The only inefficiency in the heater itself would be any light which escapes out the window. All of the rest of the energy used up is converted to heat.  Electricity is more expensive than other sources of energy, like around 3X more than natural gas, so it does get expensive to heat with electricity.  It can actually save money to use an electric space heater instead of turning the house temp up, though, if you only heat the room(s) that are currently occupied, instead of the entire house.  The ideal solution would be to have a system for heating a home with natural gas which allowed the temp to be controlled independently in each room, but the louvres on the average vent make almost no difference.  (They do this intentionally to prevent you from closing all the vents at once, which would be very dangerous.)  It seems to me they could put a simple detector in the system to shut down the furnace if significant back-pressure is detected, though, and give us vents we can actually open and close all the way. StuRat (talk) 20:58, 11 July 2008 (UTC)
 * Electricity is usually more expensive than other sources of energy. There are a few places where this is not true: the Pacific Northwest has enormous amounts of hydropower from the Columbia and other large rivers, while Iceland has abundant geothermal power. There are a few other places with cheap electricity, but I can't remember where they are. --Carnildo (talk) 22:59, 11 July 2008 (UTC)

South Africa has by far the cheapest electricity in the world, which is partly to blame for our current electricity shortages. Which is also why the National Energy Regulator has granted Eskom a 35% increase in tariffs this year. It is literally orders of magnitude cheaper (and still is under the new tariffs) to use electricity for everything rather than gas.  Zun aid  ©  ®  00:20, 12 July 2008 (UTC)

Losing a finger
When somebody severs a finger and doesn't have it re-attached, how long does it take for the ragged, bloody stump to heal and become smooth skin? (I ask for fiction writing purposes.) I realise it might depend on the medical treatment received, so assume it gets disinfected and bandaged and basically taken good care of. 220.235.169.89 (talk) 13:22, 11 July 2008 (UTC)
 * Healing time hovers around the one month mark for a finger amputation. Fribbler (talk) 13:49, 11 July 2008 (UTC)

Myth: darkest night
There is a myth that "the night before dawn is the darkest". Is that true? Why shouldn't midnight be the darkest?--218.102.234.249 (talk) 14:07, 11 July 2008 (UTC)
 * It's not meant to be scientific. It's an idiom, meaning "things always seem worst just before they improve". Fribbler (talk) 14:18, 11 July 2008 (UTC)
 * It might have some historical truth, however. Artificial light sources (the campfire, candles, etc.) would more likely be extinguished in the pre-dawn hours than earlier. Of course, that's probably just trying to force a fit. --Elliskev 15:07, 11 July 2008 (UTC)


 * This question has come up before and should be in the archives (anyone remember)?87.102.86.73 (talk) 15:35, 11 July 2008 (UTC)


 * I thought the saying was "It's always darkest just before it goes pitch black." — DanielLC 15:57, 11 July 2008 (UTC)


 * The darkest night (excluding artificial light) is the equilibrium between sunset and sunrise, but as the time of sunrise and sunset changes every day, midnight would not always be the darkest. Dawn is the twilight before sunrise when the sun's light starts to reach the earth again, so the period just before dawn (ie the the exact time between sunset and sunrise) would be the darkest. Jessica  N10248  16:06, 11 July 2008 (UTC)
 * The times of sunrise and sunset change, but they do so symmetrically, so midnight is always the middle of the night, just as noon is always when the sun is highest (assuming you're using true local time, if you're using civil time it may be a little off if you aren't exactly in the middle of the time zone). Dawn is the beginning of twilight, but that isn't immeadiately after midnight. There are different definitions of twilight for different purposes (see Twilight), but there is usually a period between dusk and dawn by any definition (if you are at high enough latitudes and it's near enough to local summer then it may never get properly dark). --Tango (talk) 17:00, 11 July 2008 (UTC)
 * Note however twilight is very short (although still exists) near the equator where it may only last ~20 minutes. Also the coldest time of day is usually just after dawn Nil Einne (talk) 17:05, 11 July 2008 (UTC)
 * It's not precisely true that the sun is highest at local noon. At local noon, the mean sun is at its highest, but that's not the same as the actual sun, which can be a bit east or west of the mean sun, due to the eccentricity of the earth's orbit, and hence the earth's varying orbital speed.  This variation contributes to the shape of the analemma.  -- Coneslayer (talk) 17:53, 11 July 2008 (UTC)
 * True. What difference does that actually make in terms of time? The Earth's orbit is pretty close to circular, so I would guess it's a few minutes at most. --Tango (talk) 23:03, 11 July 2008 (UTC)
 * From mean sun: Because many of these long or short days occur in succession, the difference builds up to as much as nearly 17 minutes early or a little over 14 minutes late.  That's pretty substantial, on the same order as the effect of one's position within the time zone.  -- Coneslayer (talk) 00:45, 12 July 2008 (UTC)
 * Here are the previous responses to the same question. Somewhat interestingly, the question was posted around the time of 2006's December solstice.  --Bowlhover (talk) 06:58, 12 July 2008 (UTC)


 * People from the European Sothern Observatory told me that the night is really dark if you can see your own shadow due to the light of the milkyway. --Stone (talk) 09:25, 12 July 2008 (UTC)
 * In the southern hemisphere, which points towards the centre of the galaxy, that may well be true. I'm pretty sure it's not true in the northern hemisphere, though. I've never seen the Milky Way as more than a wispy bit a cloud. --Tango (talk) 20:01, 13 July 2008 (UTC)
 * The page Bortle Dark-Sky Scale says of the darkest sky class, "Scorpius and Sagittarius regions of the Milky Way cast obvious shadows on the ground". As I understand it, this darkest class of sky is never seen by most people these days. I'm sure I've never seen it. A few centuries ago, however, essentially everyone saw such a sky now and then. Pfly (talk) 05:25, 14 July 2008 (UTC)


 * Note that according to, the Milky Way can cast shadows even in skies wtih a Bortle scale of 2. Also, even though the centre of the Milky Way lies in Sagittarius and has a negative declination, Sagittarius can seen in much of the northern hemisphere.  --Bowlhover (talk) 08:42, 14 July 2008 (UTC)

Oxidation of potatoes
The other day, I cut a potato in half. I gave half to my dog and put the other half in a Ziploc bag which I then placed in the fridge. The next day, I noticed that the surface of the potato in the bag was starting to turn black. Specifically, the surface created by the slice. He didn't enjoy the potato at all, so the next day I blended up a mixture of wet dog food and additional potatoes. He digs this concoction! What I had left over, I put into a Tupperware-esque container and put that into the fridge for the next day. The surface of that has turned black. More surface area and all, I guess. So is this just harmless oxidation? Dismas |(talk) 15:32, 11 July 2008 (UTC)


 * That, or the potato from Hell.


 * Potatoes undergo both enzymatic and non-enzymatic darkening which is accelerated when the broken surface of potato tissue comes into contact with oxygen. Though yours sounds rather rapid. Perhaps you need another doggie so you can finish the potato in one fell swoop..... - Nunh-huh 17:37, 11 July 2008 (UTC)


 * Well, we have three already and it's just the puppy that needs a bit more fiber in his diet. I'd rather not have to blend a new batch every day, that could get to be a big chore.  We have been discussing throwing some carrots into the mix to pump up their nutrients and make up some of the fiber content....  Thanks for the info...  Gonna go look up enzymatic and non-enzymatic darkening now...  Dismas |(talk) 17:48, 11 July 2008 (UTC)


 * Well, if you're going to moosh the potatoes and Alpo together anyway, why not do it before refrigeration and put it in a more-or-less airtight container? Skip the "store the potato" step. The dog food should stop the air from disfiguring the potatoes. I had a dog that loved beef and rice, if he gets bored of potatoes, and rice stays white. Check out  for some old food science lit on enzymatic darkening. - Nunh-huh 17:56, 11 July 2008 (UTC)


 * I think you misunderstood. I didn't use the half potato in the mush.  I threw that one out into the ditch in the front of the house (I live in the country, so I can do that occasionally).  I used fresh potatoes for the mush.  We might just go with rice...  easier to store, easier to mix together, etc.  Just thought of potatoes for the fiber first instead of rice.  Dismas |(talk) 19:40, 11 July 2008 (UTC)
 * Yep, I misunderstood. Your puppy's lucky you're taking such good care of him.- Nunh-huh 22:32, 11 July 2008 (UTC)


 * I have something you can try. Lemon juice seems to stop the oxidation of apples, to prevent them from turning brown after they are sliced.  Try some on the potato and see if it makes a difference.  If not, you can always just slice off the black area and use the rest. StuRat (talk) 20:43, 11 July 2008 (UTC)


 * Darkening so fast is surprising. What kind of knife were you using? Knifes made from mild steel or iron oxidize very easily on the surface, and then leave a usually harmless black or dark brown deposit on vegetables cut with them (and that will spread out a bit over time).  --Stephan Schulz (talk) 09:35, 12 July 2008 (UTC)


 * Storing the potato under water will also keep the oxidation from happening. Just put the remaining half in a bowl of water, with the potato completely under water, and it should be fine the next day.  And yes, oxidation does happen very fast with potatoes. If I am preparing potatoes, I cut them shortly before I cook them or the oxidation becomes noticeable fairly quickly.PhySusie (talk) 10:39, 12 July 2008 (UTC)


 * For those interested in the mechanism, "Tyrosinase is a copper-containing enzyme present in plant and animal tissues that catalyzes the production of melanin and other pigments from tyrosine by oxidation, as in the blackening of a peeled or sliced potato exposed to air." This reaction requires molecular oxygen, so keeping air from the surface of the potato (say by immersing in water) will stop the reaction. I think low pH (i.e. acid, like lemon juice) slows the reaction, but I can't find confirmation of that at the moment. The speed of the oxidation is not all that surprising - I have seen cut/shredded potatoes turn darker (although not black) after ~1 hr at room temperature. I cannot say for certain (this is not medical advise) but I do not believe that tyrosinase caused darkening is harmful if ingested, just merely unappealing. (And on the topic of medical advise, I would caution you to check with a veterinarian or dog care expert before feeding people food to dogs or other animals. Some foods that are fine to humans (chocolate or grapes, for example) can kill dogs. I don't know about potatoes, but they are in the nightshade family ...) -- 128.104.112.147 (talk) 18:10, 12 July 2008 (UTC)

ELECTRIC CURRENT
electric current moves in a specific direction and with a specific magnitude then why is it so that electric current is a scalar quantity?????please answer soon... —Preceding unsigned comment added by Adrijit sengupta (talk • contribs) 16:04, 11 July 2008 (UTC)


 * Current flowing past a point in a circuit is usually considered as a scalar, but if you take account of the direction, then it can be treated as a vector. See Fleming's left hand rule for example.    D b f i r s   16:45, 11 July 2008 (UTC)


 * The explanation above can be confusing. Consider the amount of charges flowing through a cross-cut in a conductor. In that way the current in that conductor is defined as a scalar (amperes) because there is no direction specified. You may want to be more specific and define current in a point within the conductor. This "current density" in that point is then defined as a vector (amperes/m²). The sum of all the current densities of the points that form a cross-cut then equals the current from the first (scalar) definition. But this last sentence can be hard to understand without knowledge of surface integrals. Hope that was soon enough 87.67.19.134 (talk) 23:11, 11 July 2008 (UTC)


 * Indeed. It can be treated as a vector or a scalar depending on the circumstances. You can't say that it is one or the other, since vectors and scalars are just abstractions that we choose to use as models of real things.  In AC theory, current is often modelled as a rotating vector.  In most other situations, as in a fixed wire, it is more useful to model it as a signed scalar, since the wire is approximately one-dimensional. There's a detailed thread on the subject at Phys-L. --Heron (talk) 17:27, 11 July 2008 (UTC)
 * If we say that an appliance needs a 5 amp fuse or a 13 amp fuse, then we are treating current as a scalar rather than as a vector. I thought of this analogy. You own a piece of land that is a square and is 400 square metres in area. If you describe your land to a garden designer, you say it is a square and you might the area. If you are trying to sell your land to you say it is 400 square metres and you omit the shape. The land is still the land. Its shape and area are both known, but the shape may not be relevant to the question or the area might not be relevant to the question. So when you say there is a current of 5 amps, the direction of the current may be known but it may not be important. If you are just trying to choose the right fuse, you assume that the direction is known and you just need to cite the scalar quantity. Itsmejudith (talk) 20:43, 11 July 2008 (UTC)

growing potatoes.
my english teacher brought up an interesting question in my class. He asked, "how do you grow a potato?" and it occured to me (and the rest of the class) that potatoes do not have seeds, but they have eyes.

i looked this up on the internet, and i am still unsure as to how planting an eye would grow a potato. and btw, what exactly is the eye. is it a different form of a seed? RedHoTriCE (talk) 19:47, 11 July 2008 (UTC)
 * Did you read our article? It answers your question somewhat. Potatoes are usually grown from tubers. Tubers can usually be cut into multiple pieces and each one should be capable of producing a potato provided it contains an eye. These are sometimes called seed tubers or seed potatoes since they are intended to be used to grow new potatoes and not to eat. These should not be confused with real seeds, they are not at all related. Many (but not all) potatoes varieties do produce seeds and they are obviously necessary for crossing to produce new varieties. Seeds could also be used to try and reduce the spread of disease. Nil Einne (talk) 20:00, 11 July 2008 (UTC)
 * Pretty much every first or second grade student that I've ever known has tried or at least heard of this home science project that shows how potatoes grow. Try it out and you'll learn the answers to your questions.  Dismas |(talk) 20:05, 11 July 2008 (UTC)
 * Here's a related topic that might take some of the mystery out of the idea of growing a whole individual from something other than a seed: Totipotency. The article doesn't say it, but plant cells are generally totipotent under the right conditions.  --Allen (talk) 00:49, 12 July 2008 (UTC)
 * Well it's not clear where RedHoTriCE lives. It's possible for example he/she lives somewhere potatoes don't grow Nil Einne (talk) 13:14, 12 July 2008 (UTC)
 * I've bought potatoes and then didn't eat them all for over a month and they started to grow vines on them. Try that and then you'll see. William Ortiz (talk) 23:09, 13 July 2008 (UTC)

Systems engineering
What is the difference between systems engineering and engineering project management? Clover345 (talk) 20:20, 11 July 2008 (UTC)
 * First of all we have an article Systems engineering.
 * Secondly we also have an articel Project management so "engineering project management" would be project management of an engineering project, I think.87.102.86.73 (talk) 22:06, 11 July 2008 (UTC)
 * Those two should help you decide on similarities and differences.87.102.86.73 (talk) 22:08, 11 July 2008 (UTC)
 * Ive already read those 2 articles and they don't really help. Clover345 (talk) 22:20, 11 July 2008 (UTC)
 * So do you think they're the same? or totally different?87.102.86.73 (talk) 22:37, 11 July 2008 (UTC)
 * I'll try to give you a clue "The aim of education in Systems Engineering is to simply make good engineering project managers".87.102.86.73 (talk) 22:53, 11 July 2008 (UTC)
 * Where did that quote come from? Clover345 (talk) 23:30, 11 July 2008 (UTC)
 * From me, I adapted it from Systems_engineering.87.102.86.73 (talk) 23:32, 11 July 2008 (UTC)
 * Thanks. Clover345 (talk) 23:36, 11 July 2008 (UTC)