Wikipedia:Reference desk/Archives/Science/2010 August 22

= August 22 =

Strange shadow
I observed few years ago that when one shadow nears another they start to merge, but before they do they appear to ”reflect” each other. I figured description wouln't make much sense, so I took a picture of shadows casted by my fist and pipe - observe how an extra fist appears to be coming out from the pipe (the shadow also shows a welding on the pipe which was behind my hand). I noticed this ilusion again tonight and since I didn't find any explenation the first time around, I decided to ask here - what exactly causes this ? Xil (talk) 01:14, 22 August 2010 (UTC)
 * I think this would be an example of an Umbra. 99.114.94.169 (talk) 01:39, 22 August 2010 (UTC)
 * I don't think so - as far as I understand umbra is the darker part of shadow, which you can see, but it is not what I want. In case it is hard to see shadows in first pic (I chose it because you can see what is going on with the objects in case placement is important), here is another one which might ilustrate the ilusion itself better Xil  (talk) 02:03, 22 August 2010 (UTC)


 * What you have photographed is an elementary diffraction pattern. Diffraction accounts for many visual anomalies that exist in our daily lives but that we mostly take for granted.  Dolphin  ( t ) 02:19, 22 August 2010 (UTC)
 * I don't think you understand what I am asking. Lightwaves bending around small objects still appears to be related to color of the shadow not the shape and as for ”our daily lives” - I have never noticed this happening anywhere else, I assume it needs certain conditions to happen. If not, please, elaborate how difraction causes this mirrored shadow to appear. In any case I want to know how to replicate this somewhere else Xil  (talk) 10:23, 22 August 2010 (UTC)
 * The region of interest is the overlap of the penumbra or soft gradients at the edges of the shadows. An object produces a penumbra when the light source is larger than a point. The two penumbra of the fist and pipe are due to obscurations of different parts of the distributed light source, which may be uneven. This explains why the umbra grow unevenly as the penumbra merge. I don't expect any diffraction effects where the light is not correlated and the dimensions are many orders of magnitude larger than the light wavelength. Cuddlyable3 (talk) 11:08, 22 August 2010 (UTC)
 * I notice that happening too. When I put my hand in the sunlight coming through a window, the shadow "stretches" when it nears another shadow. --Chemicalinterest (talk) 11:14, 22 August 2010 (UTC)
 * Cuddlyable is correct. The poster who led you to umbra was also on the right track - you're seeing the conversion of penumbra to umbra based on a narrowing of the light source as indicated in the figure. Wnt (talk) 12:23, 22 August 2010 (UTC)
 * I still can't replicate it. I tried nearing my hands to each other under a lamp - the penumbras overlap normaly, no mirroring Xil  (talk) 13:13, 22 August 2010 (UTC)
 * Put one hand closer than the other. You should try (I think) to reach the apex of the lower triangle among the four made between the Sun and the Earth on the umbra diagram.  You can't do that if your hands are at the same distance from the light source.  Also note a broader source like a window will yield more visible results. Wnt (talk) 15:38, 22 August 2010 (UTC)
 * Black drop effect. ~ A H  1 (TCU) 17:46, 22 August 2010 (UTC)
 * My hands don't have atmosphere :) besides that appears to be diffrent kind of streaching. I'm not sure it is clearly visible in pictures I took so I'made another ilustration to avoid confusion Xil  (talk) 18:21, 22 August 2010 (UTC)
 * I don't see an obvious relation to the black drop effect, though Venus' atmosphere may offer a refraction effect that somehow can be compared. For a demonstration, see the crude figure I've added - I've taken the liberty of pushing the others up. (In reference to another thread, a child artist could surely do better...) Wnt (talk) 00:36, 23 August 2010 (UTC)

You're right that your fist doesn't have an atmosphere, which means there's no refraction involved, but diffraction can play a similar role here. Some light passing close by the pipe bends in around it slightly because of diffraction, just as light refracted by Venus' atmosphere is bent toward it. When your fist obscures that light that would pass by the edge of the pipe, it may darken a region of the wall farther in than you would normally expect, making the shadow stretch as it approaches the shadow of the pipe. But I'm not sure if that effect would actually be large enough to be noticeable. You can see it for instance by looking at your computer screen with one eye and moving you finger in front of your eye. The text will be distorted near the edge of your finger. Rckrone (talk) 03:20, 23 August 2010 (UTC)


 * I'm very, very skeptical about the diffraction. Usually diffraction concerns things with a size on the order of a light wave... not on the order of an elbow.  I'm not saying you can't observe diffraction - obviously you always can - it's just not a major effect in this situation. Wnt (talk) 03:55, 23 August 2010 (UTC)


 * The bottom picture shows the explanation, but it doesn't have anything to do with antiumbras. Note that from the purple area, there is no view of any part of the light source.  That would remain true even if you change the light source so that the purple area is in the umbra of both objects rather than the antiumbra of one.  Basically what is happening is that the light in the overlap area is what remains after subtracting the light blocked by each of the objects.  When the objects are close to each other, it's possible for each to subtract more than half of the incoming light.  Because of the nonlinear sensitivity of the eye to light, the brightness of the shadow doesn't give us a good estimate of the amount of light that is being blocked. Looie496 (talk) 03:48, 23 August 2010 (UTC)


 * It's true that the umbra/antumbra position is irrelevant (though the two objects can't be at the same distance from the light). I just painted two dots fairly arbitrarily and that's how the figure came out.  Sorry if that confused you.


 * It's also true that the nonlinear sensitivity has something to do with it (though I think the camera has flattened the curve more than your eye alone). But the effect would be visible with nearly any curve for brightness, I think. Wnt (talk) 03:55, 23 August 2010 (UTC)
 * Guys, I still feel that you are explaining how two shadows overlaping cause there being another dark shadow, not why it is the other way around than the object, because Wnt your diagram shows how shadows overlap causing streching and darkening and Rckrone your picture seems to show shadows streching and forming penumbra between them. BTW the lightsource is fluorescent lamp (sort of like second from above), I think it gives even spread of light, it is positioned above and to side from the object in the scene though Xil  (talk) 12:00, 23 August 2010 (UTC)
 * I'm not sure whether this means my explanation was satisfactory or not. If not, I should repeat: my figure shows the umbra (full shadow) of the top object expanding as the other object approaches.  Note that the region between them receives more light than either shadow, because it is at an angle where it can see more of the light source between the two objects, whereas below, the lower object is completely in front of the light source and blocks quite a bit of the light, and above the two objects overlap and block out all the light. Wnt (talk) 17:47, 24 August 2010 (UTC)

Water
Why is water a pre-requisite for life for every known thing in the world. What's in it that makes it invigorate crops and fuel our body's and how does it work after all its only 2 parts hydrogen and one part oxygen, what so special about that? --Thanks, Hadseys 02:10, 22 August 2010 (UTC)


 * See water, there is an effects on life section. There are many different reasons why water is important, it is considered a universal solvent, meaning many materials easily dissolve in it and allows compounds to react in ways that are required in metabolism such as anabolism and catabolism. Also, it doesn't fuel our bodies, autotrophic organisms require CO2 and water plus an energy source (usually light in the form of photosyntesis) to produce glucose which is then used for energy and leaves the byproducts water and CO2. Water also has a neutral pH. These are just some of the roles it plays, as to why it has the properties it does is because the arangement of the valance electrons in the atoms that water is composed of and the way those elements bond to one another.--74.67.89.61 (talk) 02:35, 22 August 2010 (UTC)


 * Water is special because life originated in water, evolved there, and to this day most living things are made up largely of water. It is a matter only of speculation whether extraterrestrial life might have originated in other solvents - while some speak of the advantages of water for life, it is difficult to say how advantageous it really is by the standards of some other life we've never seen. Wnt (talk) 12:30, 22 August 2010 (UTC)


 * Actually no, water really is special. All the hypothetical types of biochemistry have severe problems that probably make them impossible. Ariel. (talk) 17:16, 22 August 2010 (UTC)


 * That article is interesting, but it is hardly complete. For example, sulfuric acid was the first solvent that came to my mind just now, which is present in abundance on Venus, and there is indeed a reference proposing it  but it is not listed there.  If there's one thing that mankind's little tour of the solar system has proved, it's that you can find a remarkable variety of chemistry by looking at just a few planets formed from the same primordial disk of matter. Wnt (talk) 05:47, 24 August 2010 (UTC)

Spider
Can anyone help identify a spider without a picture? It's body is about the size of the index finder distal phalanx. It's body and legs are hairy. It has about 3 black bands on each leg. It seems to be a reddish/brownish color. The back end of the spider has a black circular spot with 2 yellow dots in it. It is not hiding his fangs as they are massive. It seems to be extremely aggressive. The web is massive. It is spinning it starting from the outside then going inside. I currently reside near Pittsburgh next to a wooded area. I'm mostly concerned if it is poisonous but I'm not going to mess with it either way. I'll have someone else take care of it. :) 74.109.217.103 (talk) 02:36, 22 August 2010 (UTC)
 * After taking a quick look it seems to be a typical Orb-weaver spider. 74.109.217.103 (talk) 02:57, 22 August 2010 (UTC)
 * Could be a European garden spider? 99.114.94.169 (talk) 03:37, 22 August 2010 (UTC)
 * You might like to try this site Spiderzrule. Incidentally, I would suggest your little spider friend is being more defensive than aggressive - unless it came out of the woods chasing you to start with! Richard Avery (talk) 07:21, 22 August 2010 (UTC)
 * According to our article on spider bite, virtually all spiders are venomous (venom is an injected toxin; poison refers to other delivery methods, so spiders are venomous, not poisonous), with only three genera not being able to inject venom. That being said, most spiders are not venomous enough to do you serious damage and would much rather not have any dealing at all with monsters thousands of times their size (i.e. you). Matt Deres (talk) 13:37, 22 August 2010 (UTC)

Dissolved oxygen
Why warm water has less dissolved oxygen?117.193.106.26 (talk) 06:00, 22 August 2010 (UTC)
 * Basically this is Le Chatelier's principle and results from the fact that dissolving oxygen in water is exothermic. This website has a good and fairly non-technical explanation: . I actually had to look up the answer to this question, which is scary considering that I studied a chemistry module at university only 2 years ago... time to dig out my old textbooks for a refresher! Equisetum (talk &#124; email &#124; contributions) 09:16, 22 August 2010 (UTC)
 * Warm water (or soda) contains less carbon dioxide too. You can see when you pop a can of warm soda, it fizzes much more. --Chemicalinterest (talk) 11:11, 22 August 2010 (UTC)
 * The dissolution of gas into fluid tends to be an unstable mixture. Gas particles tend to be light and subject to large changes in energy with typical collisions. Warm water contains more high energy liquid particles which are better capable of bumping gas particles out of the liquid and back into the air. 24.177.120.57 (talk) 14:05, 22 August 2010 (UTC)
 * Hydroxyl interaction between air and water may be affected by temperature. ~ A H  1 (TCU) 17:43, 22 August 2010 (UTC)

Titan's atmosphere
Titan has a pretty dense nitrogenous atmosphere (http://en.wikipedia.org/wiki/Titan_(moon)#Atmosphere). How has it been able to have such a gravitational field, being not heavy or large?Zachilles (talk) 08:01, 22 August 2010 (UTC)


 * Titan has a much weaker gravitational pull than Earth, indeed. However, it is also much further away from the Sun, so it is much colder. If you take a look at the Barometric formula (Equation 2 to be exact), the height at which the density (and pressure) of the atmosphere drops by a given factor -- say, by a factor of 1/2 -- is proportional to the ratio of gravitational pull to atmospheric temperature. This is one of the factors contributing to the atmosphere of Titan being so dense. There are probably others: maybe magnetic field of Saturn offers some protection from the Solar wind, maybe Solar wind is just too weak at those distances, and so on. Besides, Earth's atmosphere could have been much denser if it wasn't lost once already to the impact that split off the Moon, if you believe that hypothesis. --Dr Dima (talk) 09:26, 22 August 2010 (UTC)
 * How directly is the object's mass and distance from the sun related to its atmosphere? Venus has 85% of the volume of the Earth, 81% of the mass and 90% of the surface gravity, and is 70% of Earth's distance from the Sun. Yet the surface is twice Earth's absolute temperature, and the atmospheric pressure is 93 times Earth's. (Yes, I know Venus's atmosphere is mainly CO2, which accounts for the temperature). CS Miller (talk) 19:09, 22 August 2010 (UTC)

Computer science
1. how computer works? how hardware, software, firmware, driver software, cmos bios setup, operating system, inter chip level program etc... are inter linked and works? explain with clear text, flow chart, diagram, animation, example and video-audio?

2. i want to make some own embedded system project. How can i integrate (hardware, software, firmware, driver software, cmos bios setup, operating system, inter chip level program etc...) these things?

3.How software controls and operates hardware with examples? —Preceding unsigned comment added by Pachaimalai (talk • contribs) 11:24, 22 August 2010
 * 90.193.232.65 (talk) 12:44, 22 August 2010 (UTC)
 * You have to be more specific...which type of computer...which hardware...which embedded system.Smallman12q (talk) 13:14, 22 August 2010 (UTC)


 * Well, the question is so broad, I'm not even sure it's homework. But in any case, the best place to start is in the articles: computer; hardware, software, and so on.  We have articles on all of these topic with clear explanations, charts, diagrams, and so on.  After you read the articles, come back with any questions you have, or if anything is still unclear.  Nimur (talk) 16:17, 22 August 2010 (UTC)


 * Also take a look at computer engineering, integrated circuit and CMOS. ~ A H  1 (TCU) 17:39, 22 August 2010 (UTC)


 * To try to answer one part at a time:
 * how computer works? how hardware, software, firmware, driver software, cmos bios setup, operating system, inter chip level program etc... are inter linked and works? -- This is a vast subject, the things you've listed might take a full degree program in Computer Science to adequately explain. The starting point is our computer article.  Start reading there, then follow the links as necessary to broaden the topic from there.
 * i want to make some own embedded system project. -- OK - but if you truly don't have the basics (which seems apparent from Question (1) then you're a long way from being able to do this. If you actually know more than your question (1) implies, then I would recommend you get an Arduino embedded computer and start to learn to program it and build hardware for it.  You can pick up an Arduino computer for around $26 and there are VAST amounts of internet resources you can find to help you with hardware and software that you might wish to create to work with it.
 * How software controls and operates hardware with examples? -- Generally, there are 'special' memory locations inside the computer hardware which are either connected to drive external hardware - or to monitor it. On something like an Arduino computer, you can (for example) flash the LED on the board by writing either a '1' or a '0' to a particular location that the LED circuitry connects to.  Similarly, if you were to connect a switch to one of the specialised pins of the Arduino circuit board, you'd be able to have your software read from some other special memory location and the value that you'd get back might be a '1' if the switch is closed and a '0' if it is not.  On a more complex computer such as the one you'd find in a laptop or a cellphone, the mechanism is basically the same, but the "operating system" software (like "Windows Vista" or "Android") will take care of the details of how that works and allow the application software to talk in higher level terms such as files on disk rather than individual commands to the disk drive motors, etc.
 * SteveBaker (talk) 18:21, 22 August 2010 (UTC)
 * For 1. There are a number of universities that offer joint computer programming and electronic engineering courses. I'd highly recommend them if you are interested in designing your own computer from the CPU (or even logic gates) upwards. CS Miller (talk) 19:19, 22 August 2010 (UTC)
 * For the details of 3. see memory-mapped I/O, direct memory access and interrupt for some specifics. CS Miller (talk) 19:12, 22 August 2010 (UTC)

Instructions for Filtering Water in Urdu Language?
Can the above be found anywhere? Preferably with drawings or photos? It's for PK flood relief workers to pass out to IDPs. Am reading Twit posts about babies being given dirty water to drink. The disease risk is obvious, and basic instructions will help prevent the more serious maladies. Any and all help is appreciated. —Preceding unsigned comment added by Juju31 (talk • contribs) 11:29, 22 August 2010 (UTC)
 * I wonder whether WP:RD/L might be a better place for this Nil Einne (talk) 12:14, 22 August 2010 (UTC)
 * We can file a translation request for water filtration. As you can see from پانی, even the basic articles have poor coverage in Urdu; by comparison to other languages, we don't have many Urdu-speaking Wikipedians.  I wonder if the World Health Organization might be a better resource in this case - they have a lot of information in many different languages.  Here's their Pakistan Office website and their Basic Development Needs program (which includes water quality and sanitation).  You might telephone their office to see if they already have a water-quality brochure that you can help distribute.  Nimur (talk) 16:29, 22 August 2010 (UTC)
 * Indeed one advantage there is it would hopefully be better adapted for the local situation. For example, in Bangladesh a common recommendation is cloth filter of an old sari. This probably isn't such good advice in Pakistan as they aren't so common there (Sari). Nil Einne (talk) 16:57, 22 August 2010 (UTC)

Juju31 here. Thank you for this. I'm emailing WHO PK office to ask what they have. If I get the info, I will repost it here so you can add it. —Preceding unsigned comment added by Juju31 (talk • contribs) 03:01, 23 August 2010 (UTC)

Responding to the above need, Hesperian Foundation has kindly allowed one of their publications as a free download relating to basic care for use by disaster relief workers in Urdi, Sindhi and English languages. Here is the link: http://www.hesperian.org/pakistan.php

Wasn't sure where to post it but wanted to pass this on to you so that the initial question wasn't left hanging. Thanks so very much for all your efforts. Juju31 —Preceding unsigned comment added by Juju31 (talk • contribs) 01:48, 20 September 2010 (UTC)

For Every Human
1. WHAT IS THE OBJECTIVE OF OUR LIFE( FOR HUMANS AS WELL AS A LIVING BEING)? 2. WHAT ARE THE PRINCIPLES OF LIFE? 3. HOW TO LIVE IN LIFE? —Preceding unsigned comment added by Pachaimalai (talk • contribs) 11:33, 22 August 2010 (UTC)
 * See meaning of life. I don't think anyone here (or anywhere) can answer your question. 90.193.232.65 (talk) 12:41, 22 August 2010 (UTC)
 * This is a matter of perspective. For analyzing life, see Life course theory. As for objective...Nihilism argues that life is without objective meaning, purpose, or intrinsic value.Smallman12q (talk) 13:12, 22 August 2010 (UTC)


 * Put another way, probably everyone on here has a different opinion on this, but there is no way at all to distinguish with any reliability a good opinion from a bad one. Certainly no way to scientifically do it. It isn't a science desk question. --Mr.98 (talk) 14:23, 22 August 2010 (UTC)


 * If there was an ideal objective of life for every human, that would be both idealism and a specific ideology. It could just as well be different for everyone. The biological purpose is reproduction, the philosophical approach may be to seek purpose, and the humanistic ideal is humanism and so on. ~ A H  1 (TCU) 17:37, 22 August 2010 (UTC)


 * From a scientific perspective - we (and all other living things) have evolved to pass on our genes to the next generation. Humans (and many other species) also take care of and guide their offspring until they too can pass their genes on.  We do this because evolution favors lifeforms that can do that and rapidly eliminates those who cannot or do not pass on their genes.  SteveBaker (talk) 18:06, 22 August 2010 (UTC)


 * However, human population growth has gotten so out of control that people in poorer countries who once had many children are now having few children. Can purpose evolve? ~ A H  1 (TCU) 18:18, 22 August 2010 (UTC)


 * Passing genes does not mean "reproduce indiscriminately." It means, "make sure your genes survive into the next generation," which might be more ideally done if, say, you only have one child that you invest a lot of resources in, or, say, if you kill off all of your competitors. Evolution is rather "blind" about the means. This is one of the reasons it is not seen as particularly useful in looking for a meaningful sense of "purpose". It just makes clockwork machines of us all. It is not a very satisfying sense of "purpose". --Mr.98 (talk) 22:24, 22 August 2010 (UTC)
 * That's debatable. For those who have a religious "obligation" to fulfill. Genesis 1:28 states to "God blessed them. God said to them, 'Be fertile and become many. Fill the land and conquer it. Dominate the fish of the sea, the birds of the sky, and every beast that walks the land." (or a similar translation). For those whose purpose is to worship god...the act of procreation fulfills that purpose.Smallman12q (talk) 01:49, 23 August 2010 (UTC)
 * Procreation is good but when debating about marriage (Mat. 19:12) Jesus opined that making oneself a eunuch would be preferable for one who can manage it. People should not try this at home - oops oops!.Cuddlyable3 (talk) 14:45, 23 August 2010 (UTC)

Laser Cutting of Metal Sheets
Sometimes after Laser cutting of M.S. Plates, they show the tendency of lifting up by almsot 50 mm - 300 mm. What will be the reason behind this behaviour of M.S. Plates? Which of any mechanical or chemical parameter playing the major role in this performence of Plates? —Preceding unsigned comment added by 220.225.75.226 (talk) 12:05, 22 August 2010 (UTC)

Are you sure you don't mean 300 micrometers? Lifting a steel plate by 300 millimeters is a heck of a lot. I suspect the cause is thermal expansion from the cutting laser. Nimur (talk) 16:39, 22 August 2010 (UTC)

Yes, but there were no substantial faults in the textbooks WE used!
Textbooks in scientific subjects allways have been, and presumably forever will have to be, rewritten time and time again (because the scientific knowledge and understanding grows as time goes by).

Still, a surprising lot of people, more or less consciously, seems to cling to a strange belief, which one occasionally may hear expressed by the claim: Yes, but there were no substantial faults in the textbooks WE used! What I am refering to is the situation where the person seems to fully understand that science has progressed over the years, but seem to think that the textbook that himself or herself used is the full, complete and final truth about the subject, and that IT will stand unchanged forever.

I need some approved (published) research reports, proving that this kind of false belief really do exist. Do you know of any? If so: Could you please help me with some references to it?

P.S. I am familiar with the concept of the Bias blind spot, so that is not what I am looking for here. --Seren-dipper (talk) 17:01, 22 August 2010 (UTC)


 * Not sure about research reports, but many textbooks in the United States promote Intelligent design, or label evolution or global warming as a "controversial" theory. ~ A H  1 (TCU) 17:33, 22 August 2010 (UTC)


 * That is surely interesting but not quite what I am after.Moved clarification up into my original question --Seren-dipper (talk) 18:12, 22 August 2010 (UTC) --Seren-dipper (talk) 17:53, 22 August 2010 (UTC)


 * That seems like a strange position to take. Most people I've met have the opposite experience of discovering that the stuff they were taught from textbooks was wrong. SteveBaker (talk) 18:00, 22 August 2010 (UTC)
 * I fully agree that it is strange! But still I have met quite a few people who seem to think this way :-) --Seren-dipper (talk) 18:12, 22 August 2010 (UTC)


 * Also take a look at lie-to-children. ~ A H  1 (TCU) 18:04, 22 August 2010 (UTC)
 * Also have a look at ignorance, confirmation bias, and the scientific method which describes how theories are corrected/changed as new evidence/interpretations are made.Smallman12q (talk) 20:01, 22 August 2010 (UTC)


 * People often cling to the high value of things that existed when they were young. See nostalgia. I haven't seen that apply to textbooks very much, personally. --Mr.98 (talk) 20:06, 22 August 2010 (UTC)
 * I'm with the others. I know lots of adults who cling to "what they were taught in school" about certain things, but that's in the face of any and every type of evidence (more recent advances in the field, corrected/amended editions of textbooks, more nuanced/specific/mature analysis, etc.). Is it even possible to distinguish textbook "mistake" from "newer knowlege" and "more advanced textbook"? DMacks (talk) 20:38, 22 August 2010 (UTC)


 * This may be off the topic, but I think there are certain systematic biases in science from generation to generation. For example, the capabilities of ancestral organisms and cultures are always underrated.  This is due to a certain religious fanaticism about Occam's Razor.  In the rush to avoid speculation, people will come up with explanations for how, for example, humans came to Australia without building ships, how a dozen phyla came up with eyes from a blind ancestor, how ancient pharmacopoeias included known effective treatments without any conception of a scientific method, and so on. Wnt (talk) 04:09, 23 August 2010 (UTC)
 * Oops - I said "overrated" above, meant underrated. Sorry for confusion. Wnt (talk) 17:53, 23 August 2010 (UTC)
 * Yes I thought that. Your comment didn't seem to make much sense otherwise Nil Einne (talk) 00:57, 24 August 2010 (UTC)
 * To give the next great example: mushroom bodies and the cerebral cortex are both derived from a common ancestral structure. People were too timid to propose that this structure could have existed 600 million years ago, but there it is. Note that it took only two weeks for such a good example to come out.  Wnt (talk) 03:53, 7 September 2010 (UTC)
 * Well, one cannot really tell what is "bias" and what is "brilliant" until one has gotten a little bit more distance. But on the general point that certain types of scientific explanations are appreciated by different generations — something which is a bit different than saying "science improves" — this has been well-studied by historians of science, and bears out to a large degree. It's especially obvious in anything to do with human beings, because we tend to superimpose our unexamined and often unconscious cultural values onto descriptions of human origins and practices. So it's not terribly coincidental, for example, that people looking at human evolution in the 1950s often saw 1950s values being repeated (male hunter, female cooker), or that in the 1960s and 1970s focus on hominid evolution began to look at bonobos and other "non-violent" alternatives, and so on. (These are very broad examples and most are of course a bit more subtle.) I certainly think that the anxiety about Creationism in the United States has led evolutionary biologists to be constantly on the offensive — every new odd species gets to be a "missing link" and so on quite immediately. (This is not to say I endorse Creationism at all, just that the anxiety is rather obvious and culturally and temporally specific.) --Mr.98 (talk) 13:56, 23 August 2010 (UTC)
 * I don't think the 'missing link' thing is simply to do with creationism but also to do with the self-promotion and publicity whether for the researcher or more common the institution they work with that's often common/necessary? in the modern scientific world. 'We found some ancesteral (proto-)lemur' is must less existing then 'WE FOUND THE MISSING LINK!'. It's notable claims are sometimes made by PR departments that the researcher themselves don't really agree with. And you see this in most other areas of science. Journalists of course are all to happy to help. Nil Einne (talk) 14:13, 23 August 2010 (UTC)

Thank you, all, for your replies! (Even though I did not get exactly what I had hoped for, they were still useful to me :-) --Seren-dipper (talk) 00:42, 28 August 2010 (UTC)

Interspecies crying
Hi. It is known that animals of one species, other than humans, often befriend a member of another species (do we have an article on that?). Often, a predatory animal befriends its prey, either domesticated or wild. There have also been reports of domestic animals crying. This often occurs as the animal realises it's about to be killed. My question is, and I thought of this one this morning, are there any documented cases of an animal (other than humans) crying over a member of another species? Thanks. ~ A H  1 (TCU) 17:23, 22 August 2010 (UTC)


 * Emotion in animals has some interesting links...but I think that some of the things you are stating as truth here are far from solidly known facts. Anyway - Koko the gorilla is known to have expressed sadness when her pet cat died - I'm not sure whether she actually shed tears though.  Our article on the cat (All Ball) says that Koko made a sound akin to human crying - but there is no mention of actual tears. SteveBaker (talk) 17:57, 22 August 2010 (UTC)
 * Have a look at crying and this ask yahoo link, this link on crocodile tears. Are you asking if animals shed tears at the loss of another animal, or simply the display sadness/other emotions at the loss/separation.Smallman12q (talk) 20:06, 22 August 2010 (UTC)
 * Mostly the first one, I'm asking whether any animals shed tears during a display of sadness at the loss of another animal of a different species. ~ A H  1 (TCU) 20:37, 22 August 2010 (UTC)
 * This little piece seems to rule out other primates.  Sean.hoyland  - talk 13:56, 23 August 2010 (UTC)
 * I was listening to a PBS story about emotional expression on the radio this morning -- the reporter said that humans are the only animal that sheds tears. Looie496 (talk) 15:48, 23 August 2010 (UTC)
 * ...for emotional reasons, yes. But tears lubricate the eye and eyelids - and they can form for other reasons (allergies, for example).  So I'm sure there are a wide range of animals that "shed tears" - but I could well believe that only humans do it for emotional reasons.  The example of Koko the gorilla (see above) shows that one of the closest animals to humans doesn't produce tears even when they are expressing the precise emotion and vocalization that humans produce.  Unless chimps are known to cry - that's a pretty sure reason to believe that other animals don't do that.  SteveBaker (talk) 22:33, 23 August 2010 (UTC)

Contact lenses
How can I tell if someone is wearing contact lenses, preferably without staring them in the eye for extended periods. Asking them in this context would be too personal and impolite, but I'm curious. 76.228.196.92 (talk) 20:10, 22 August 2010 (UTC)


 * You probably cannot. Contact lenses are pretty discreet and unnoticeable, even if you were to stare the person straight in the eyes for extended periods.  Why not just ask them?  It's not a particularly impolite question.  And, with this individual, you must at least have a suspicion that they wear contacts.  (64.252.34.115 (talk) 22:46, 22 August 2010 (UTC))
 * If you are ever sitting beside the person, this would be the best angle to try see from ihmo. I've spotted people with contacts more then a few times from this angle, in particular if you sit next to someone on a train or bus and they are looking forward. Usually the contact lens isn't perfectly fitted to the cornea and you can see the edge of the contact lens on the surface of the eye. Vespine (talk) 03:54, 23 August 2010 (UTC)

Thistle varieties that spread by root
What varieties of thistle (particularly those known in the Pacific Northwest) are spread by rhizomes or root pieces? I know that Canada Thistle is but that fortunately does not appear to be the more prevalent of the multiple thistle types we are now seeing in our pastures and fields. I simply don't have the time to go down the whole list of thistle varieties and check through multiple references for each to see. Help would be much appreciated. —Preceding unsigned comment added by Crwind (talk • contribs) 20:59, 22 August 2010 (UTC)


 * This says "Extensive rhizomes of Canada thistle make it unique among the thistles." - are you certain that they aren't Cirsium arvense? If you could take a photo and upload it here or elsewhere then someone will probably be able to help. Smartse (talk) 11:45, 23 August 2010(UTC)

Carduus nutans and C. acanthoides are invasive species that can easily overtake pastures. They do not spread by rhizome as far as I know.

what kind of spiders?


What kind of spiders are these? They seem to be known here as banana spiders, but they don't seem to match. Bubba73 (You talkin' to me?), 21:05, 22 August 2010 (UTC)

Click on the box and then Full Resolution. Bubba73 (You talkin' to me?), 21:12, 22 August 2010 (UTC)
 * The first one appears to be a female Argiope aurantia. Deor (talk) 21:44, 22 August 2010 (UTC)
 * And although one can't really see the markings on the second one very well, the distinctive zigzag stabilimentum in the web suggests that the second photo is of a female Argiope aurantia as well. Deor (talk) 03:10, 23 August 2010 (UTC)


 * Yes, they were 15-20 feet from each other, so they were probably the same species (and the leg markings look the same). Bubba73 (You talkin' to me?), 03:13, 23 August 2010 (UTC)


 * Where are they located? What country or region of a country?  Googlemeister (talk) 12:59, 23 August 2010 (UTC)
 * Bubba's user page says that he lives in Georgia (U.S.A.), so I assumed that the spiders also lived there. Deor (talk) 13:17, 23 August 2010 (UTC)
 * Yes, they were making their webs on the outside of a house in coastal Georgia (U.S. state). Bubba73 (You talkin' to me?), 14:19, 23 August 2010 (UTC)

What's in between the dunes?
So, looking at the featured image of the day for August 22, between the sand dunes there's a large quantity of flat-looking gray/white/blue stuff. It looks to me like the surface of a frozen-over lake, or possibly a sky reflection. I don't think either of those makes sense, so what is it? Are there a lot of salt flats in that area, maybe? The NASA page the image came from doesn't give an explanation. --Anonymous, 21:52 UTC, August 22, 2010.


 * best guess is that this is a mirage - a reflection of the sky in trace amounts of water vapor boiling out of the sands and gathering in the troughs between dunes. notice how the effect gradually gets stronger towards the lower right (pretty much what you'd expect to see in a reflection with changing angles of incidences of sunlight).  -- Ludwigs 2  22:07, 22 August 2010 (UTC)


 * The second picture in the Rub' al Khali article appears to show the same feature and is referred to as a "pale gravel plain", which would be a deflation surface covered with rock clasts too big to transport by wind, see Aeolian processes. Mikenorton (talk) 22:10, 22 August 2010 (UTC)


 * According to the description on Wikipedia: "The image, acquired by the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) aboard NASA's Terra satellite, shows dunes as brown with gray regions being the underlying gravel plains." ~ A H  1 (TCU) 22:38, 22 August 2010 (UTC)


 * Here's a close-up of those "gravel plains" from another angle -- I wonder if a better description might not really be "salt flats" though -- anyway, not a mirage. Wikiscient  (talk) 03:08, 23 August 2010 (UTC)


 * Not a salt flat, unlikely these areas get wet at all, they really will be flat areas covered in gravel. Mikenorton (talk) 07:09, 23 August 2010 (UTC)

<- It's a bit hard to tell because it's unclear what we're looking at in terms of ASTER bands in the satellite image. For example, apparently clay and silt rich areas have high reflectance in band 1 (0.520–0.600 µm wavelengths = visible green/yellow) and look blueish.  Sean.hoyland  - talk 07:33, 23 August 2010 (UTC)


 * Originally the Rub' al Khali area was covered in coarse alluvial deposits. When the climate turned arid, aeolian processes took over, reworking all of the finer sediment from the alluvial deposits (mainly sand) into dunes, leaving behind only that which the wind cannot move, gravel and coarser material. However, some ephemeral lake deposits are described in interdune areas, with white calcite-rich layers and some finely stratified silts and clays (but no salt). Mikenorton (talk) 16:35, 23 August 2010 (UTC)


 * Thanks. --Anon, 19:15 UTC, August 23, 2010.
 * Desert pavement?- Jarry1250 [Humorous? Discuss.] 21:19, 23 August 2010 (UTC)
 * Yes that's the term that I'd forgotten, and I've added a picture from the Rub' al Khali of just that. Mikenorton (talk) 11:29, 24 August 2010 (UTC)


 * What's the scale of that NASA image? Would one be able to make out an individual camel for instance?  Sp in ni ng  Spark  15:59, 20 September 2010 (UTC)

Unknown special character
Saw this double-arrow, inequality-like character here (p. 69 and forth), but can't figure out how to render in wiki (digged through Math, Math and Template:Unicode chart Arrows, but found nothing like that). Copying from pdf doesn't help either. Twilight chill t   22:33, 22 August 2010 (UTC)


 * It's in Table 96 of this list of characters and is a form of 'very much greater than', I think. Mikenorton (talk) 22:49, 22 August 2010 (UTC)


 * A single arrow means greater than. (When turned 180 degrees it means less than.)  The double arrow means much greater than.  (When turned 180 degrees it means much less than.)  Dolphin  ( t )'' 01:01, 23 August 2010 (UTC)


 * Copy it from here: Unicode mathematical operators and symbols. Ariel. (talk) 01:48, 23 August 2010 (UTC)