Wikipedia:Reference desk/Archives/Science/2009 January 20

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

January 20

A pore excuse for a question...

Do we have the same pores on our skin all our lives, or do some close up and others develop ? How about those at the nipple which deliver milk in nursing females, do they develop in pregnancy and close up after nursing ? StuRat (talk) 00:48, 20 January 2009 (UTC)

We can't give medical advice, I'm afraid. (You forgot the requisite 'this is not medical advice' disclaimer.) If you are concerned about your pores, please consult a doctor.  :-) 74.137.108.115 (talk) 04:46, 20 January 2009 (UTC)

The pores around the tip of the female nipple are called lactiferous ducts. They grow and proliferate quite significantly during pregnancy, but are present also in non-lactating females. Apocrine sweat glands become functional at puberty, eccrine sweat glands much earlier. A lot of sweat glands are associated with hair follicle, and together they form a functional "pore". The ducts and follicles themselves remain relatively static, but after the sweat duct passes through the dermis it essentially stops, and the sweat drains through clefts between prickle cells, through the stratum corneum on to the surface. This sweat-channel changes all the time as the cornified cells of the epithelium slough off. Rockpocket 05:27, 20 January 2009 (UTC)

Come on, this is clearly an anatomy question. As you'll see if you follow the link from the subject line, pores in the skin are associates with sweat glands. According to my copy of Gray's Anatomy (the 1958 edition, but I don't imagine this has changed), sweat (sudoriferous) glands are formed in the fetus during the 4th month of pregnancy. The breast is in effect "a greatly modified collection of sudoriferous glands" and its structures are also formed before birth. So the answer is yes, you keep the same pores. --Anonymous, 05:20 UTC, January 20/09.

Rockpocket says the "female nipple" has lactiferous ducts. How about the male nipple? Wouldn't it be similar to the nipple of an immature female, and capable of producing milk in such conditions as Gynecomastia or prolactin secreting pituitary tumors? Edison (talk) 19:50, 21 January 2009 (UTC)

Apparently so. Lactiferous ducts develop before the differentiating effects of testosterone, so male nipples have them too. Rockpocket 20:17, 21 January 2009 (UTC)

True color image vs. false color images

is there any difference between true color and false color images? Isn't it right what we see in space is always very different from what we see through satellite iamges. Ex. blue stars in space looks way too blue from what it actually looks, our sun is not as yellow from what it look from space. Mars is not as rust color as it is if we are orbiting around it. Mercury, Venus, and Mars is perfect enough to see clearly orbiting around it, but is Mercury brown or silver, all spacecraft's images is unfortunately wrong, even Mars and jupiter, although color vision is enough for humans, is it pink, orange in space which is shouwn by true color image-spacecraft-it's wrong,wrong,wrong, am I rght. I thought, the amount of light on Saturn is essentially dim,what you expect 100 times dimmer than Earth, Titan will not look pretty tangerine-yellow, they only look like a dim, almost gray sphere when you fly a rocket around it. Europa, is it brown or white, nothing is right, I thught Europa is dark eough to only have little color vision. Whatever SteveBaker, said, I count on him. He's a better scienctist than I am--69.226.46.118 (talk) 01:53, 20 January 2009 (UTC)

I think what you are trying to get at is, "is there any really 'true' color?" In which one can reply: what 'true' and 'false' mean can vary from situation to situation. In one case it can mean, as you indicate, "as if we were not viewing it through Earth's atmosphere", but in another it can mean, "we've represented infrared signals as part of the visible spectrum". --98.217.8.46 (talk) 02:20, 20 January 2009 (UTC)

The diff is that a true color image attempts to match the colors as closely as possible, while a false color image does not. They may decide to color a map based on elevations, for example, instead of the actual colors, in a false color image. StuRat (talk) 02:59, 20 January 2009 (UTC)

I think there are actually three kinds of image out there.

• False color images are nothing like 'reality' - the colors are used to deliberately distort some property of the science data to allow our eyes to see it. So you might be looking at rainbow colors representing (say) temperatures or altitudes or radio emissions. Things which are quite meaningless to our eyes without some false coloring.
• Enhanced images are an effort to give us an idea what the object could look like - perhaps if it were better illuminated or illuminated with more 'normal' colored light. The images we get back from the Mars rovers are kinda like that. The rovers have little color swatches on their bodies whose colors in normal earth lighting are well known. By adjusting the output of the rover cameras to make those color swatches look like they do here on earth, the colors on mars can be related to our normal experience...but those images are still not what our eyes might see if we were really on mars.
• Color approximated images. Very often, the nature of the science that a particular craft needs to do precludes them from taking proper Red/Green/Blue images that we can understand. So it might be that the spacecraft took an image in infra-red, another in ultra-violet and another in (say) sodium-yellow. None of those colors are things that our eyes can see directly - but it's possible to use the data in the other bands to make an estimate for the red/green/blue colors we might really see.

It's debatable what 'should' be shown in these cases - certainly false color can be downright misleading to the untrained eye. Enhanced color is often necessary because we simply can't see anything in many of these cases...and Color-approximated images are a lot more interesting and (arguably) useful than a monochrome image. But as we've discussed before - in many such cases, our eyes would 'really' see almost nothing - it would perhaps be just too dark to see anything.

Should NASA show us black images for far distant moons? That would be the most "realistic" thing - but it's just not useful. The one think I wish is that they would be more clear about exactly what processing they DID do on these images...even if it's just for "the general public". SteveBaker (talk) 03:09, 20 January 2009 (UTC)

Does Saturn count as far distant planet? Uh, it's 100 times dimmer. if you rocket around Saturn, it would look close to black, perhaps just dim gray sphere. humans can barely see Saturn with their own eyes. All spacecraft do is use black-and-white cameras, NASAs just use spectrums/chemicals to fix the image, so it will look better, all those iamges are hopelessly wrong.--69.226.46.118 (talk) 03:25, 20 January 2009 (UTC)

I'm not sure 69.226.46.118 is correct in calling these devices "black-and-white" cameras. Some of them use a variety of techniques for hyperspectral imaging, including a "monochromatic" imaging sensor, with a set of filters for different bands... but isn't that how all cameras / eyes work, anyway? On some level, every color imager is simply a multi-channel intensity imager. Nimur (talk) 03:36, 20 January 2009 (UTC)

The cameras vary - some are indeed a wide-spectrum monochrome camera with various color filters that can be placed in front to select some range of frequencies to be captured. That's not how our eyes work - we genuinely do have four different kinds of sensors - each of which is responsive to the light in a different way. One sees only monochrome - the other three each see one band of frequencies (one each for red, green and blue light). So you're right about many spacecraft cameras - you're wrong about eyes. SteveBaker (talk) 13:36, 20 January 2009 (UTC)

Here are some samples all from NASA. The greens and yellows in the false color image just feel wrong to me. The "true color" image is definitely better, but still noticeably more vibrant than the actual photo. Also, one might note that in both composite images the day/night shading is artificial, and the image was stitched together from many smaller images covering less than a whole globe and taken over several days. Dragons flight (talk) 03:38, 20 January 2009 (UTC)

• 
  False color satellite composite
• 
  "True color" satellite composite
• 
  Astronaut photograph from Apollo 17

• i've watched the news about Mars on January 1, 2009. When spacecraft went on Mars, they took it with black-and-white image from spacecraft, the NASA team review it and revise the color with pink, salmon, orange and brown color. That's not what it will look like if we actually were hanging out on Mars. Spectrum for example use yellow color for sulfur. 3 peoples have been on Moon in 1969, when they went on moon, out in space is black, and they have no light. is the planet brown or gray, nobody can answer it.--69.226.46.118 (talk) 05:54, 20 January 2009 (UTC)
  • The sun provides plenty of light to the Moon; it is gray. You can see this from Earth if you simply look at the Moon. Dragons flight (talk) 06:01, 20 January 2009 (UTC)

(after edit conflict) There is definitely light in space, on the moon, and on other planets. The intensity may vary for a large number of reasons (distance from sun, dust / atmospheric absorption and refraction, insolation angle, etc). But there is definitely light on the moon and elsewhere in the solar system. You might also want to read about Color constancy. And from color, "The color of an object depends on both the physics of the object in its environment and the characteristics of the perceiving eye and brain." However, there is an absolute, quantitative answer about an object's color - you can parameterize its reflection and absorption spectrum. Nimur (talk) 03:22, 21 January 2009 (UTC)

You can certainly scientifically, qualitatively talk about the 'color' of any object by plotting it's spectrum - this is an exact matter with precise and undeniable results. HOWEVER, that doesn't help much in describing "how it would really look" because our eyes don't work by measuring a spectrum and our brains do an unbelievable amount of "image processing" on the data that our eyes produce. What might technically be a source producing such-and-such number of lumens of light in the such-and-such nanometer waveband of the yellow region of the spectrum can still look anything from white to yellow to orange to brown to black to us humans. Worse still, our perception of 'hue' shifts depending on the brightness. Objects look much more blue-ish in dim light than they do in bright light. As our dark-adaptations kick in, the color of a single, unchanging object will shift. How our brains interpret a color depends dramatically on the nature of the colors of objects close-by in our field of view - and the longer we look at an environment that's all of one color, the more we percieve that as "normal" and start to skew that color towards white. If we spent all of our lives living on a reddish planet like Mars, the more we'd start to see 'red' as a neutral color and note the colors of everything else by contrast to red. The last astronauts on the moon (who'd spent days looking at a more or less monochrome world) were blown away by what they said were intensely bright orange rocks at the end of their last moon-walk. They were so blown away by this sudden (and to them) INTENSE color that they came close to running out of suit oxygen while collecting them. In reality, the rocks are pretty subtly tinted - but to color-starved eyes, they looked incredibly intense. So: What some particular image would "really" look like is an incredibly complicated question. Making a set of photographs "look real" is an essentially hopeless task - and you can't rely on your eyes to tell you the "truth" when it comes to color anyway. SteveBaker (talk) 13:36, 20 January 2009 (UTC)

I agree with everything you are saying, but I think it is nonetheless important to keep in mind that some reconstructions are reasonable approximations to photographic images, and other imagery does not achieve (or even want) to do that. As much as psychology and ambient conditions impact perception it is still true that there are right and wrong answers when the goal is to develop something that approximates what humans could see. The things we call "true color" images often want to be approximately photographic, while "false color" images may have many other goals entirely. Dragons flight (talk) 16:05, 20 January 2009 (UTC)

Regarding the false-color earth pictures above, the most amazing thing to me is the "terrain" emphasis. There's a lot of visibility for the terrain of mountain ranges, visually depicted as a shadowing effect, on both the false-color composites; while the Apollo photograph does not really indicate any shadowy terrain. There's an example of a false-color application which may distort the interpretation of the image. Nimur (talk) 06:06, 20 January 2009 (UTC)

"Distort" is a loaded term. Without understanding what you're seeing, yes, you may get a false impression - but if you set up that false color for a very particular reason (like you're looking for subtle undulations in a relatively 'flat' world) - then juicing up the image so that the subtle shadowing becomes more prominent - is a perfectly valid way to extract more useful information from an image. Remember - we don't take these pictures as art for the masses - they are taken to allow scientists and trained image analysis experts to discover new scientific fact about the subjects of these photos. So one man's "distortion" is another mans "enhancement". SteveBaker (talk) 13:36, 20 January 2009 (UTC)

The light from the sun would illuminate Saturn at about the same level as a good office I believe, see lux. Much better than a sitting room at home. So it wouldn't seem dim at all if we were close. Our eyes can accommodate an enormously wide variation in brightness. Dmcq (talk) 18:23, 20 January 2009 (UTC)

Here's a good guide to the brightness of outer planets: According to Apparent magnitude, the full moon has an apparent magnitude of −12.6. I think we would all agree that we can see fairly well under a full moon, when given a few minutes for our eyes to adjust. The same list puts the brightness of the sun when viewed from Neptune as −20. This means that the sun's brightness at Neptune's distance is around 700 times as bright as a full moon on Earth. Given these facts, I'd say that Neptune, and thus any other planet, would be quite bright enough to see comfortably from a spacecraft.-RunningOnBrains 18:52, 20 January 2009 (UTC)

That's an odd way to calculate it...and I'm not even sure it's right because the apparent magnitude of an object is independent of it's area - but the amount of light it casts is not...or is it? Well, it doesn't matter because here is the direct way to calculate it: The Earth is 150 million kilometers from the sun - Neptune is 4550 million kilometers from the sun - because brightness decreases with the inverse square of the distance, the amount of light available on Neptune is 920 times less than on Earth. That's a lot - but (as you say) the eye is pretty sensitive. Our eyes can adjust between brightest and darkest by a factor of about 100:1 - meaning that if you are in a brightly sunlit area and then in an area that has 100x less light, you can see just as well in both cases - and after a few minutes of adaptation, you can't even tell the difference between the two. But Neptune is 920x darker - so it would definitely seem nine times darker than here on earth - even after your eyes had adjusted. However, we can see brightness differences down to around 1/1,000,000th of bright daylight - so we'd certainly be able to see something in the gloom. Furthermore (and more germane to this question) - even if we accept User:Runningonbrains's result - you can see by the light of a full moon - BUT YOU CAN'T SEE COLOR. Everything looks blueish. That's because your 'cone cells' (which are responsible for color perception) don't work in light that dim - they simply shut down - and leave you with only the 'rod cells' which detect brightness across the entire spectrum but without giving any perception of color. So, sure - you'd be able to see on Neptune - but not in color. So this leads us back to the original point: When you see a color photo of Neptune, is that "what it really looks like"? Well, no - because if you were really there - you wouldn't be able to see any color. But it is this very complexity of explanation that reinforces the impossibility of answering this question cleanly. SteveBaker (talk) 20:25, 20 January 2009 (UTC)

Defining magnitude for non-point sources is of only limited use - see Surface brightness. One major correction to your calculations - it wouldn't seem 9 times dimmer, since we perceive light logarithmically, the difference between 1:100 and 1:1000 is 2/3 as bright (or 1.5 times dimmer). --Tango (talk) 22:21, 20 January 2009 (UTC)

Actually - it's not logarithmic - it's a power law - but in any case, we adapt for the difference of a factor 100 - the REMAINING factor of 9 after we run out of adaptation is what we're discussing here. SteveBaker (talk) 01:03, 21 January 2009 (UTC)

If it's not logarithmic, why is the magnitude scale logarithmic? --Tango (talk) 01:11, 21 January 2009 (UTC)

Weber–Fechner law#The case of vision says it's logarithmic... Could you provide a reference for it being a power law? --Tango (talk) 01:13, 21 January 2009 (UTC)

"Misconceptions About Astronomical Magnitudes," E. Schulman and C. V. Cox, American Journal of Physics, Vol. 65, pg. 1003 (1997).

...or you could believe our article Apparent magnitude: "A common misconception is that the logarithmic nature of the scale is because the human eye itself has a logarithmic response. In Pogson's time this was thought to be true (see Weber-Fechner law), but it is now believed that the response is a power law (see Stevens' power law)." - which actually cites that paper. But I have indepenent (WP:OR) verification of that in my studies of dim-light vision as relating to the simulation of night vision using computer graphics. The whole area of dim light perception is very messy...it almost seems like the human body doesn't like people fitting mathematical relations to it! But for sure the astronomical 'magnitude' thing is an ugly mess brought on and perpetuated by poor science and an appalling inattention to appropriate ways to set standards for use into the future. In an age of amazingly precise instruments and computers, astronomers are still talking in terms of brightness scales devised using naked eye astronomy in 300BC! SteveBaker (talk) 14:38, 21 January 2009 (UTC)

So our article on the Weber-Fechner law is incorrect? Could you fix it (and save me having to actually read the paper!)? We have introduced fractional magnitudes since the system was first invented, and have defined in all rather more precisely. If we measured brightness in watts it would all be written in scientific notation and people would only look at the exponent anyway, so why not just use a logarithmic scale? --Tango (talk) 15:47, 21 January 2009 (UTC)

I don't think the rods detect brightness across the entire (cone) spectrum, at least not according to diagrams like this. -- BenRG (talk) 20:32, 21 January 2009 (UTC)

Can you restate If we spent all of our lives living on a reddish planet like Mars, the more we'd start to see 'red' as a neutral color and note the colors of everything else by contrast to red this again? I don't fully understand it Steve. What you said about neptune is same thing about Saturn. i said Saturn is 100 times dimmer, 10 times farther away from sun than Earth. You can still see Saturn the planet but not the color.--69.226.46.118 (talk) 22:33, 20 January 2009 (UTC)

Let me point out an experiment you can do right now that'll illustrate it better than I can explain it. Click on the weird colored US flag to the right here. Open it up so it more or less fills the screen - grab a sheet of white paper. Now, stare at the center of the flag for at least 30 seconds...then hold the white paper up in front of the screen so you're suddenly staring at a white "screen". What happens is that you suddenly see the flag in it's correct colors (red, white and blue). That's because in just 30 seconds your eyes started to 'adapt' to the colors in the weirdly-colored flag - when you suddenly look away, what is white now looks colored. Similarly - if you spent your time staring at red ground and reddish sky on mars - then when you set eyes on a pure white object, it would look pale blue (cyan) because the red receptors in your eyes are sick of seeing red - and the green and blue sensors are struggling hard to see anything at all in that reddish world. When you look at something white, the red receptors are still 'dialled down' and the green and blue receptors are hyper-sensitive - so you see the color 'cyan' (pale greenish-blue). Once again, should photos taken by the Mars rovers show white objects as "true" white - or should it show them as our adapted eyes would see them in "realistic" shades of baby-blue? See Afterimage for a better explanation. SteveBaker (talk) 00:49, 21 January 2009 (UTC)

• I know sky color vs. what the true color of planet in my own eyes are not relevent. The sky on Neptune ro Saturn will not be black until we go right inside the planet's mantle. Above the cloud-tops, the sky wouldn't be black yet, they still scatter some light waves, so the color should be moderate. Between the clouds, the light scatter is different-the sky would be shallow-moderate level there.--69.226.46.118 (talk) 22:46, 20 January 2009 (UTC)

• • What?? I stare at grass everyday, the color is green all the time. i stare at the wooden tables all the time-it is always brown? So what will be the world like, if I stand on Mercury and Venus, especially Venus a world over thick layer of greenhouse heat?--69.226.46.118 (talk) 03:08, 21 January 2009 (UTC)

Because the grass is green and the sky is cyan (blue/green), red objects seem very VERY 'visible' to us - red is a bright color. That's no accident - we're evolved from creatures who looked for ripe fruit in the branches of trees - so being able to spot something red in a sea of green had a huge evolutionary benefit. If you were on mars, you'd hardly notice a red object because the red receptors in your eyes would be exhausted! Dunno about Venus - we don't have enough data from the couple of old Russian probes that landed there (and were promptly destroyed by the atmosphere) decades ago. Mercury has almost no atmosphere. On the dark side the ground would be profoundly black because the only illumination would be the stars (and perhaps venus if it's the right time of the year). It would be like looking out into space from anywhere else in the vacuum of the solar system. On the bright side - well, mercury is 3x closer to the sun than use - so it would be 9x brighter than the sunniest day on earth...well - more even than that because there is no atmosphere to scatter and attenuate the light...so it would be far too bright to see anything at all with the naked eye - so you'd have dark glasses on and now all bets are off because it depends on the nature of the glasses. SteveBaker (talk) 14:38, 21 January 2009 (UTC)

This general subject has been discussed before on the Ref Desk—see Venus and Jupiter's true color for one. This page is interesting. -- BenRG (talk) 20:49, 21 January 2009 (UTC)

Rechargable batteries - the 'S' terminal?

I've noticed that most batteries in mobile phones have three terminals, +ve, -ve, and 'S'. Anyone know what this 'S' terminal is for or how these cells work? I've searched around and tried the Wiki article Rechargable_battery but can't find any mention of this third terminal? —Preceding unsigned comment added by 194.63.116.72 (talk) 10:20, 20 January 2009 (UTC)

It's a guess - but laptop batteries have a pin that enables the charger to sense (hence 'S') the temperature of the battery so that it can be recharged at the maximum rate without destroying it. Presumably there is a thermistor wired between the -ve and 'S' pins. I'm guessing that cellphones have now reached that same level of sophistication. But I don't know for sure...someone else may know better. SteveBaker (talk) 13:14, 20 January 2009 (UTC)

My phone has a T pin (which may concur with SB's suggestion) Nil Einne (talk) 20:25, 21 January 2009 (UTC)

First movie projector for more than one person?

Who invented the first movie projector that could project an image for an audience? Lumiere brothers are sometimes quoted, other sources tell they weren't the first, but fail to mention another name. 82.181.93.226 (talk) 12:09, 20 January 2009 (UTC)

The History of film article mentions Robert W. Paul and Birt Acres as contenders for the title, in addition to Auguste and Louis Lumière. The three projectors were created pretty much the same time. Who exactly ran a first successful test of a projector in his laboratory may be lost in history; Acres appears to have a good claim for the first scheduled demonstration. 88.114.222.252 (talk) 14:16, 20 January 2009 (UTC)

Homo genus

I've been reading about the Homo_(genus) and about the fossil records that have been used to try and establish the history of this Genus, as there is only one presently living species in the genus. My question is how do paleontologists know based of features of a fossil that two specimens actually should fall under different species (which means they are making assumptions about their ability to mate). I understand there is plenty of controversy to which specimens fall under what species and how many species there are, but what is to say that any give one can't mate with any other given one? What establishes that line? What is the scientific reason that two closely related species can't mate? Anythingapplied (talk) 14:43, 20 January 2009 (UTC)

It's definitely a gray area. Obviously species that are very different couldn't mate to produce fertile offspring, but for those which are fairly similar, scientists must use other methods to determine if this was possible. If the two species existed in the same time and place, and they could interbreed, you'd expect to find some fossils of half-breeds. If they were separated by space and/or time, then this method doesn't apply. Assumptions can be made based on how long the two have been apart, as genetic drift tends to happen at a somewhat predictable rate, meaning that a certain amount of time is required to create a distinct species. Another option, if the fossils are recent enough to contain DNA, is to do a genetic analysis. Species with different numbers of chromosomes, for example, are less likely to be able to mate to produce fertile offspring. StuRat (talk) 15:48, 20 January 2009 (UTC)

Paleontologists don't care about mating. Really they don't. When dealing with extinct taxa, these decisions really are all about fossil morphology and whether one group of fossils arising in a particular time and place has quantifiably different characteristics than another group found at a different time and/or place. How big the differences have to be are a matter of debate (see lumpers and splitters), but it is really all about form and seldom ever about mating compatibility. Dragons flight (talk) 15:56, 20 January 2009 (UTC)

Paleontologists don't care about mating ? Is that why there's so few of them ? :-) StuRat (talk) 20:53, 24 January 2009 (UTC)

"Species with different numbers of chromosomes, for example, are less likely to be able to mate to produce fertile offspring". I thought only plants could mate with something that didn't have the exact number of chromosomes? Is this what you meant? or are there other exceptions?

When you (or I) say "species can't mate", what does that mean and why is that scientifically? Suppose I put Hare DNA (46 chromosomes) into my sperm to fertilize an egg. Shouldn't it fertilize just fine? I'm guessing something would start to grow too... it probably just wouldn't live very long, right? Die before birth. Is that what is meant when you say creatures can't mate? I suppose a lot of times it is also physically impossible or the male/female delivery systems are different enough that it wouldn't even get to the fertilization point, but those two obsticles shouldn't apply to closely related species. Anythingapplied (talk) 20:41, 20 January 2009 (UTC)

I didn't say "species can't mate", I said that, if they can't mate to produce fertile offspring, they aren't the same species. It certainly seems unlikely that species with a different number of chromosomes are likely to pass this test, but I'm not willing to say it's completely impossible. Here's a case where a pregnancy occurs, but isn't viable, for sheep-goat hybrids, due to a differing number of chromosomes: [1]. Also, this doesn't mean that all species with the same number of chromosomes can interbreed. You may get a pregnancy that's not viable, like your hare-human example. As for closely related species always being able to mate, that isn't always even true of the large dog/small dog example of the same species, given below. If they do somehow manage to mate, I would expect the combo of a small male and large female would be viable, but the small female/large male combo would not be, as the uterus of the small female would be too small for the litter of medium-sized offspring. Perhaps aborting all but one of the puppies early on and then delivering the surviving puppy by C-section could work, though. You could also do in-vitro fertilization and implant the embryos in a female dog large enough to carry them. StuRat (talk) 14:34, 21 January 2009 (UTC)

(This is in reference to your initial question). Palaeontologists largely don't know when to classify something as being a single species. They can make an educated guess, obviously, but the sheer scarcity of fossils versus the richness of nature makes it a very difficult decision. All the classic dinosaur names people know (triceratops, diplodocus, stegosaurus, etc.) are simply the genus names. If a dinosaur is only known from ten fossils found over thousands of square kilometers, how could you ever know whether they represented different species, different genuses, different ages, different sexes, or even just good ol' natural variation? And even if two skeletons look anatomically identical, what does a term like species even mean if the actual animals lives a hundred thousand years from each other? Think of the dozens (hundreds?) or warbler species extant today. If you laid out the skeletons for each one, perfectly preserved and all in one place for ease of comparison, not even a ornithologist could separate them all out; they'd call them perhaps a half dozen species of one genus and probably still louse it up by conflating a female skeleton or three as being a distinct species. Birds are dinosaurs, so imagine trying to do the same thing, except the skeletons are millions of years old, broken into dozens of pieces, and scattered around the globe. Oh, and each bone is bigger than you can even lift. Matt Deres (talk) 21:28, 20 January 2009 (UTC)

We've discussed this a few times before - it's clear that the quasi-formal definition of "a species" involves the issue of whether a cross-breeding produces viable, fertile offspring that breed true...not just 'offspring'. So a mule is not a species and although crossing a horse and a donkey will reliably produce a living mule - the mule cannot itself breed more mules because it's infertile. Hence horses and donkeys are not the same species. Similar arguments apply to lions and tigers and their crosses the 'ligar' and 'tigon' (yes - we really do have separate articles!). Whether you get a tigon or a ligar depends on whether it was the momma who was the lion or the daddy - but you can't breed tigons or ligars (at least, not reliably). So the issue of whether the egg will be fertilised and become viable or the foetus or the birth or living more than a few weeks...it's all moot. If the offspring doesn't survive and breed true - it's not a species and the two parent species are different too. Contrast that with (say) dogs - a Labrador and a Poodle can be crossed to make a Labradoodle - and if you take two labradoodles and breed them, you get (probably) more labradoodles - but for sure you get live, healthy, fully functional dogs. Hence Labradors and Poodles and Labradoodles are not separate species, they are all the same.

Having said that - there are an enormous number of grey areas - species A can breed with B which can breed with C which can breed with D...but D can't breed with A. Are A,B,C,D all the same species? Tough. I doubt that crossing a Chiuahua with an Irish Wolfhound would produce viable puppies - so which one of them isn't considered to be a dog? So it's all very vague and fuzzy and nasty.

The one CRUCIAL thing you should take away from this is that words like "species" are merely convenient shorthand - they don't represent any "real world" thing - they are just handy words for biologists to toss around. Everyone agrees on what's going on - the underlying mechanisms that make Tigons, Mules and Labradoodles is pretty well understood - we just can't make up our minds what to call the resulting groups of animals. Just as the decision as to whether Pluto is a Planet or not was completely arbitary - so the decision as to whether the Chimpanzee should be renamed "Homo-Pan" or remain "Pan Trogolodytes" is more a matter of religion than of science. (I'm all for the change - mostly because it'll piss off the fundies and the other nutjobs - and I have a mischievious nature!)

SteveBaker (talk) 22:21, 20 January 2009 (UTC)

Naively, you would expect a litter of labradoodle-labradoodle pups to contain 25% Labradors, 25% poodles and 50% labradoodles. In practice, it will be more complicated than that, but you would almost certainly get a litter ranging from predominantly Labrador to predominantly poodle, with most somewhere inbetween. --Tango (talk) 01:20, 21 January 2009 (UTC)

Those ratios would only apply if there was a single gene which determined which breed you get, while there are actually many genes, on different chromosomes. StuRat (talk) 14:09, 21 January 2009 (UTC)

Hence "naively", and the more accurate but less precise "in practice" sentence. --Tango (talk) 14:37, 21 January 2009 (UTC)

von brun's nest

what is von brun's nestDreamoftrust (talk) 15:21, 20 January 2009 (UTC)

Not sure. Could possibly be refering to Von Braun (crater), a crater on the moon. See also Von Braun which shows several other articles which may contain this info... --Jayron32.talk.contribs 15:52, 20 January 2009 (UTC)

It's probably (von) Brunn's nest: [2], given the genre of the question below. Fribbler (talk) 15:58, 20 January 2009 (UTC)

nissle's substance

what is nissle's substanceDreamoftrust (talk) 15:23, 20 January 2009 (UTC)

It's another word for Nissl body. Fribbler (talk) 15:45, 20 January 2009 (UTC)

Is this a lichen or an animal colony?

I couldn't find another way to ask (submit?) for information about the enclosed colony. I couldn't find anything similar in your terrific database. This colony? is on a granite boulder in Truckee, CA at about 6400' elevation. The photos are magnified for better viewing....actual size of the group is about 1 cm across. How can I find out what this is and more information about it? (I can't figure out how to include the images with this query.) Many thanks!76.197.15.28 (talk) 16:03, 20 January 2009 (UTC)

do you have a link? Julia Rossi (talk) 17:40, 20 January 2009 (UTC)

How's this for going out on a reference-desk limb? Without a photo or any specific information at all, I'm guessing slime mold. Deor (talk) 13:08, 21 January 2009 (UTC)

I hope that's with a net! You Daring Deor you. Richard Avery (talk) 14:02, 21 January 2009 (UTC)

MAG 29

What does the MAG stand for in the name of this carbon star? 196.2.124.248 (talk) 19:18, 20 January 2009 (UTC)

Well, the MAG 29 link does no good, as that article is about something completely different. It's just a guess, but could it mean they are in the vicinity of the Magellanic Clouds ? StuRat (talk) 19:38, 20 January 2009 (UTC)

Presumably you are referring to the MAG 29 of this week's Science (journal) article entitled Dust Formation in a Galaxy with Primitive Abundances. For those who do not have access to the full text, here is the abstract. The article cites "...studies with the Infrared Spectrograph (IRS) on the Spitzer Space Telescope of the Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC) and the Fornax Dwarf Spheroidal", and goes on to mention MAG29 in detail, "a carbon star in the direction of the Sculptor Dwarf Spheroidal galaxy with the IRS on Spitzer. The Sculptor Dwarf is a satellite of the Milky Way, with a metallicity only 0.04 that of the Sun. A study of carbon stars in the Galactic Halo detected a candidate, MAG 29, in the field of the Sculptor Dwarf."

It would appear that MAG 29, while not actually located in the Magellanic Cloud, appears in the same region of the sky, and was thus named "MAG 29" incorrectly. However, I'm not particularly familiar with my Dwarf Spheroidals and it's possible that Fornax is on the outskirts of the Magellanic clouds.

This of course brings up the interesting problem of naming a deep sky object, because it takes a fair amount of scientific study to accurately position the object in "3-D", but to do thorough study, you need to locate it in the "2-D" field of view of earth's sky. So a name may be assigned prematurely, as it seems was the case here. Nimur (talk) 03:34, 21 January 2009 (UTC)

In fact, further research (N. Mauron et al.: Halo carbon stars, Astron. Astrophys. 418, 77 (2004), PDF) (I'm deep diving here, bear with me), indicates that the actual location of MAG 29 is not well known (even though it has been observed since at least 1985!) "No radial velocity could be determined by us for #29, and its membership to Sculptor needs further observations to be proven." It makes me a happy scientist when an astrophysicist has enough confidence and integrity to state the degree of uncertainty without embarrassment. It's really really hard to know where things actually are, when they're some 300,000 light years away. Nimur (talk) 03:50, 21 January 2009 (UTC)

Lest the user get the impression that astrophysics is a rough science when it comes to positioning, it might help to point out that the celestial latitude and longitude are always known with great accuracy and it is only the radial distance which chronically is a problem. (see Cosmic distance ladder). Rotational (talk) 05:48, 21 January 2009 (UTC)

Seems to me (and SIMBAD) that the identifier has nothing to do with the Magellanic Clouds (it should be LMC or SMC in that case) but is formed from the initial letters of the names of the first three authors of the discovery paper by Mauron, Azzopardi, Gigoyan & Kendall (2004, linked above). It may have been more polite to include the fourth author as well... --Wrongfilter (talk) 12:21, 22 January 2009 (UTC)

Temperature of a lit cigarette

What temperature does the lit end of a cigarette reach during inhalation? I have a vague memory of hearing that it can be as hot as a blast furnace, but have no idea if this is true, or just something I heard in the pub. DuncanHill (talk) 20:15, 20 January 2009 (UTC)

I guess the parts that glow reddish-orange are closer to 1000 K, and the parts that glow brighter yellowish-orange would be closer to 2000 K temperature or even a bit higher. You may look at the chart here for a rough estimate. --Dr Dima (talk) 20:39, 20 January 2009 (UTC)

So yes, it is definitely in the same ballpark as a typical blast furnace temperature (which is around 2000 K, see e.g. here). --Dr Dima (talk) 20:45, 20 January 2009 (UTC)

Many thanks. DuncanHill (talk) 20:51, 20 January 2009 (UTC)

It glows the same colour as a blast furnace, so it's the same temperature - the colour of thermal radiation is a function of temperature. (There are exceptions, as with any rule, of course - but this isn't one of them!) --Tango (talk) 22:15, 20 January 2009 (UTC)

It is important to note the difference between temperature and thermal energy. A small quantity of mass at high temperature does not have the same total thermal energy as a blast furnace, even if it is at the same temperature. Nimur (talk) 03:38, 21 January 2009 (UTC)

Color of a blackbody object at a certain temperature in the mired scale. Mired number = 1,000,000/temperature in Kelvin

I think I fixed the formatting this time. 152.16.15.23 (talk) 04:05, 21 January 2009 (UTC)

rice in a silo exploding

I heard from somebody that you have to dry out rice before you put it into a silo. I asked why, and they said it was because gravity would make them explode or something like that. They didn't give any more explanation, so I'm coming here. Is this a myth or would that actually happen? flaminglawyer^c 22:06, 20 January 2009 (UTC)

I can't see them being wet with water making them explode... certain oils maybe. Rice in a silo could probably explode, given the right conditions - the surface area is enormous so if it caught fire it would burn extremely quickly, we call burning very quickly "exploding". I would have thought dry rice would burn better. Wet rice may well go rotten and mouldy - not very dramatic, but still undesirable. I can't see what gravity would have to do with any of it, though. --Tango (talk) 22:13, 20 January 2009 (UTC)

Spontaneous combustion hints that dampness might help bacteria in hay to heat up and cause a fire. I suppose it might happen also to rice. The article doesn't say that, though, so I can't say. APL (talk) 22:18, 20 January 2009 (UTC)

Perhaps the drying process removes any part of the grain that would end up as dust in the silo, so has nothing to do with wetness at all. 161.222.160.8 (talk) 23:25, 20 January 2009 (UTC)

Fine dust can and does cause explosions in silos, but wouldn't moistness keep the dust levels down? Apparently "dust removers" (presumably filters of some sort) are used to cut down on the level of fine airborne particles.152.16.15.23 (talk) 01:39, 21 January 2009 (UTC)

Are they really talking about a large scale explosion? At first sight, I'd take this to mean that with a bazillion tons of rice pushing down on the grains at the bottom - they simply wouldn't be structurally strong enough - so they's split and 'pop'. Dried rice is much harder - and therefore more able to resist that pressure without splatting. But I don't really know. Dust explosions are a serious matter - but dry rice has got to be more prone to that than wet stuff. SteveBaker (talk) 00:26, 21 January 2009 (UTC)

Also, dry rice may become wet and expand in the silo. If packed tight enough, this could generate enough pressure to cause a spectacular failure of the silo without heat and/or flames at all. A 40-foot tall structure splitting open violently and spraying chunks of rice across the landscape may cause one to call the event an "explosion" even if there was no fire or no heat. --Jayron32.talk.contribs 00:31, 21 January 2009 (UTC)

What's all this I hear about dust? Is dust easily explodable or something? Why does dust matter? flaminglawyer^c 01:19, 21 January 2009 (UTC)

Dust is highly explosive - flour mills are very dangerous places. It's because of the enormous surface area to volume ratio (which increases reaction rates) - surface area is proportional to the square of diameter, volume to the cube, and the square of a very small number is much bigger than the cube of a very small number. As always, we have an article: Dust explosion. --Tango (talk) 01:28, 21 January 2009 (UTC)

Dust explosions are very dangerous. To put Tango's post into layman's terms - imagine taking a treetrunk and trying to set light to it with a match...you wouldn't succeed. With some effort you could set light to twigs from the exact same tree though. Take a piece of wood the size of a matchstick and it burns pretty easily. Take wood-shavings and they burn quickly and vigorously. Take fine sawdust and it burns so fast that it's an EXPLOSION. The finer the dust the more easily it burns...and as Tango says - it's because the surface area is so large compared to the volume. SteveBaker (talk) 02:04, 21 January 2009 (UTC)

This PDF discuses many causes of silo failure. One thing they note is that moisture can migrate between static particles (the rice in this case) if the moisture is not evenly distributed. Moisture causes the rice to expand. If no rice is being withdrawn for a period of time, upwards expansion is greatly restrained so the pressure is instead focused on the walls of the silo. Failure of the steel hoops which hold the silo together will cause the silo to burst open: sort of like an explosion. A case involving moist corn not being removed over a period of a couple days resulted in five times the normal pressure on the walls of the silo. Additionally, drying the rice will put less stress on the silo walls by reducing the weight. Rice and other grains can be thought of as a fluid of sorts. Hypothetically, moist rice may flow differently than dry rice. Improper or unexpected flow of the grains can cause a silo failure by placing unexpected stress on the silo's structure. 152.16.15.23 (talk) 01:39, 21 January 2009 (UTC)

Wow. You mean I was right?!? That NEVER happens! --Jayron32.talk.contribs 03:13, 21 January 2009 (UTC)

Now that reminds me of a Hornblower story. Hornblower is sailing a prize ship with a cargo of rice. During the action in which the prize is captured, it was holed below the waterline. The sailors patch the holes and man the pumps. Strangely, the pumps are dry. Unknown to Hornblower and his shipmates, the rice is absorbing all the water leaking into the ship. Eventually - the ship starts to break up, and they have to abandon her. Which just goes to shew that I should have been able to answer this question! DuncanHill (talk) 14:56, 21 January 2009 (UTC)

For the record, that's Mr Midshipman Hornblower#Hornblower and the Cargo of Rice. Algebraist 15:35, 21 January 2009 (UTC)

Thanks - and what a sensible title for a story about Hornblower and a cargo of rice it is! I must re-read it. DuncanHill (talk) 15:49, 21 January 2009 (UTC)

I had asked a similar question a while back when Car Talk's weekly puzzler involved the dangerous transportation of rice by ships.

And as for dust explosions, search YouTube for "sawdust cannon" and "non-dairy creamer cannon". Mythbusters did a pretty impressive experiment about it. -- MacAddct1984 ^{(talk • contribs)} 18:03, 21 January 2009 (UTC)

Lycopodium powder (the spores of some clubmoss or other) is an amazingly fine (and therefore highly explosive) powder. It's sometimes used in fireworks because a first charge can disperse the powder outwards and a second can set it off to make a large 'blossom' of (IIRC) yellow flame that appears all at once rather than seeming to spread outwards. Anyway - that and (as the Mythbusters showed) non-dairy creamer are the substances of choice for making large explosions without using anything obviously explosive. SteveBaker (talk) 21:03, 21 January 2009 (UTC)

Aah, but did they try custard powder? I recall an explosion in a custard factory in the 1980's. DuncanHill (talk) 02:32, 22 January 2009 (UTC)

Golden Ratio

I"m confused as to why there's such a fuss made about this...

What's so "aesthetically pleasing" about these various shapes constructed with these ratios?

are the buildings built using the ratio any better? stronger?

are these pieces of music containing little ratio nuggets any more passionate or moving?

I'm not trying to start a fight, i just was wondering if someone could explain to me the point

(by the way Steve Baker--you rock)192.136.22.6 (talk) 23:49, 20 January 2009 (UTC)

You may want to read Golden ratio; additionally this question may be better suited at The mathematics desk. --Jayron32.talk.contribs 23:53, 20 January 2009 (UTC)

The math desk will tell you that it's the "most irrational number" and turns up in a lot of surprising ways, but is not better suited to answer any of these questions. —Tamfang (talk) 06:23, 21 January 2009 (UTC)

There's no evidence that people find it esthetically pleasing and no evidence that it's ever been used in the design of buildings or any other form of art. There are people who see it in everything just like there are people who see Jesus in everything. It has some nice mathematical properties, but no more than many other numbers. I think it does appear in nature, though not in the conch shell, which is the most commonly cited "example". Possibly it appears in Romanesco broccoli (better image here), but don't quote me on that. See "Misconceptions about the Golden Ratio" by George Markowsky. -- BenRG (talk) 12:08, 21 January 2009 (UTC)

It is true that coincidental close approximations to the golden ratio can be found in the ratios of almost any sufficiently numerous set of measurements, and there is no direct evidence to support claims that the golden ratio was used in the design of ancient buildings such as Stonehenge and the Pyramids. However, some architects in modern times have explicitly and deliberately used the golden ratio in their designs and their theories of aesthetics - for example, Le Corbusier used it in the Modulor. Gandalf61 (talk) 12:33, 21 January 2009 (UTC)

I've run into several people who thought that the golden ratio is in every equiangular spiral! Argh. —Tamfang (talk) 06:51, 22 January 2009 (UTC)

There is also a relationship between the golden ratio (technically the golden angle) and the seeds of a sunflower. The spacing of seeds occurs in Fibonacci numbers because (as I understand it) this is a very efficient way of packing the seeds together. -- MacAddct1984 ^{(talk • contribs)} 17:51, 21 January 2009 (UTC)

This has decent coverage about the sunflower. —Tamfang (talk) 06:51, 22 January 2009 (UTC)

"I"m confused as to why there's such a fuss made about this..." Well, the fuss is mostly because it was heavily mentioned in a recent best selling book and, I assume, the movie based on the book. (The Da Vinci Code) APL (talk) 01:23, 22 January 2009 (UTC)

— And because people keep asking about it. B00P (talk) 16:28, 22 January 2009 (UTC)

Nutrition of a Egg whites

The wikipedia article has a nicely broken down nutritional makeup of a whole egg (including the yolks.) However, any such diagram is sadly absent from the wikipedia article regarding egg whites. I was wondering if anybody could obtain the nutritional value of Egg white (therefore a whole egg minus the yolk.) The USDA nutrient database also didn't yield many results, and a google search yielded conflicting reports. Thank you in advance.

http://en.wikipedia.org/wiki/Egg_(food)

(The diagram under nutritional value is perfect, and if one along those lines could be found for egg whites I would greatly appreciate it.) 216.165.25.53 (talk) 23:58, 20 January 2009 (UTC)

Now you have to do some work here because I can't give you a direct link... (USDA Nerds...) Anyway... Begin Here.Next step, type "Egg, white, raw, fresh" into the search field, then ensure "All Food Groups" is selected. Now click submit and then select the radio button next to the search result. Tadaaa! Wish granted! Have a great Wiki-Day! Operator873 (talk) 09:31, 21 January 2009 (UTC)

Here's a direct link to the "raw egg white" page on www.nutritiondata.com: [3]. StuRat (talk) 13:53, 21 January 2009 (UTC)