Wikipedia:Reference desk/Archives/Science/2007 January 14

= January 14 =

Embryonic Stem Cells and the beginning of human life
My reading suggests that after an egg is fertilized in vivo, it is composed of stem cells that continue to divide at least until the egg attaches to the uterine wall. The write up under stem cells says "When given no stimuli for differentiation, ES cells will continue to divide in vitro and each daughter cell will remain pluripotent." The specific question is: Is this also true in vivo and what is the stimuli in vivo that begins the differentiation? The answer I am expecting is that it is something in the process that is initiated following attachment of the egg to the uterus that begins the next stage of embryonic development and if the egg does not attach, it degenerates and gets flushed with the next menstrual cycle.--Billxm 00:23, 14 January 2007 (UTC)
 * Much more is known about early mouse development than early human development, but during early human embryo development the cells start to differentiate before the embryo implants in the uterus. Two types of cells form according to their position in the embryo, Inner cell mass cells and trophectoderm cells. For mice, it is thought that signals from the uterus help the trophectoderm cells differentiate and get ready for implantation. See: Blastocysts don’t go it alone. Extrinsic signals fine-tune the intrinsic developmental program of trophoblast cells. While the cells of the inner cell mass remain as multi-potential stem cells until about the time of implantation, they quickly form two epithelial cells layers, the epiblast and the hypoblast (Wikipedia's short Epiblast article). --JWSchmidt 02:09, 14 January 2007 (UTC)

Metal Working
I want to construct this model gun from sheet metal for laser-tagging purposes. Given that the diameter varies along the length of the gun, how might I accurately fold the metal? And ideas for making the gun handle, which I'd like to construct from the same metal? The blue part is a plastic window. >>gun<< --Username132 (talk) 00:23, 14 January 2007 (UTC)
 * What equipment do you have? It would be quite difficult to fold a sheet of metal to such a small dimension. It would be a lot easier using plastic by using wood to make it first, vacuum form it, use the mold to make the parts our of plastic and stick it all together. —The preceding unsigned comment was added by Antilived (talk • contribs) 04:20, 15 January 2007 (UTC).

If you use very thing sheet metal, you could maybe stretch it around a mold to get the desired shape. A ductile metal like copper would work best. If it's too thick to stretch, you may have to create a cylinder for the middle and two cones at the ends, to approximate the barrel shape. StuRat 04:29, 15 January 2007 (UTC)


 * A prototype could be designed in Autocad, with futuristic design details, then a prototype created with a Fabber look quickly, the article is up for deletion) or by another term, Desktop manufacturing. Such a laser pistol might have more visual and tactile appeal than a simple folded piece of metal. Numerical control machine tools could mill the device out of a metal blank, also working from an Autocad or similar design. Edison 18:20, 15 January 2007 (UTC)

light pollution help
I am doing a science fair project related to light pollution. I plan to zoom in on 'earth at night' maps located on the Internet and count the number of pixels in a certain 'area' (e.g. mid sized city) and see if light pollution naturally occurs in areas where there is population. Unfortunately, few (or no) maps on the Internet are reliable enough for me to look at (because of low res, no state or country boundaries, chance of being Photoshopped to make the image look 'better', etc...) and the process seems too tedious (city boundaries hard to 'distinguish', time in counting pixels, etc...). Can anyone help me, like introduced me to some special software or a good image (ahem...I mean really good, and better than the IDA stuff or the World Atlas of Night Brightness)? And if you can find the latter (an image) please give me a suggestion on how I can make the project less tedious. If you think I should have a new project, please keep it so I don't have to go outside during the nighttime or have to buy too many things. Thank you! —The preceding unsigned comment was added by Member (talk • contribs).


 * You need GIS software to do this right. What you need is a georeferenced image of the night area you want to study -- finding high-resolution ones may require some digging, but with a little Googling I was able to find evidence of 5km resolution images -- and then you need to load it into ESRI's ArcGIS, using an extension called Spatial Analyst.  You define a grid with the cell size equivalent to a pixel in your input image, and then fill each cell with a numerical value based on a color value from the original image (probably whiteness).  Then you define another grid of the same size, filling its cells with population data (which you would pull from, say, the US Census 2000 data, if you are doing this for the US:  note there are a lot of processing steps I'm leaving out).  It would take several iterations to get it right.  Then you can compare the numbers between the two grids and see what you find, most likely by producing a third grid which gives, in each cell, the ratio between the cells in grids 1 and 2; it would be interesting to see the outliers, i.e. what bright areas have little population, and what dark areas are heavily populated, and then to try to figure out what causes them.  Here is an example of a paper I found where an agency has attempted to correlate population with night light  -- go to the very bottom of the page to see the reference.  Do you have a geography lab or computer lab at your school with ArcGIS? (the software is not cheap:  current ArcGIS plus Spatial Analyst will set you back about USD $4000). Antandrus  (talk) 02:44, 14 January 2007 (UTC)

Here's a nice map of the US with states shown:. You can look at a political map for each state and figure out what each city is. StuRat 04:10, 15 January 2007 (UTC)


 * Good find, Stu! If you get a "403 forbidden" error when trying to bring up that image, navigate to it by going here  first, and then clicking on "high res image of USA with state outlines".  Antandrus  (talk) 17:10, 15 January 2007 (UTC)

Shaking a bottle of ice and water
If I have a bottle of ice and water and want to drink the water -- will it help if I violently shake the bottle and splash the ice/water around?


 * Some things to think about:


 * You're putting kinetic energy into the system, and energy = heat. But, some of this energy will escape as sound, bugger all, though. Convection between the bottle and the surrounding air would also increase. However, shaken water is whiter and presumably reflects more light (energy) so in this respect shaking may hinder the melting. Breaking up the lumps of ice into smaller pieces may help by increasing surface area available to melt - also, if you break it up small enough, you can get it out the top and melt it in your mouth or stomach. Holding the bottle to shake it could also have an effect on conduction to the bottle. Your hand is warmer than the surrounding air (presumably) and a better conductor. 121.72.14.221 03:43, 14 January 2007 (UTC)


 * Most of the effects mentioned here are trivial. The most important effect is this: when still water is in contact with ice, it forms a temperature gradient, so the part of the water near the ice is coldest.  By agitating the water you mix the different parts of it, eliminating the temperature gradient. So the water near the ice is a bit warmer.  This means the ice melts a bit faster and so the water is cooled faster.  However, I can't see violent shaking being any more effective than gentle stirring or swirling (you just need to keep the water moving), except that it might break up the ice cubes.  If you're in a hurry to get cold water (and I assume that is what you wanted "help" with), then you should start with small cubes, or better yet crushed ice, in the first place. --Anonymous, January 14, 23:22 (UTC).


 * I find that violent shaking produces small shards of ice, which are most unpleasant to swallow, so I'd just wait, instead. StuRat 03:54, 15 January 2007 (UTC)

Hearing problems
I'm 14 years old but I seem to have hearing problems. I've always had the problem of hearing people talk, but never understanding what they are saying, especially when there is background noise or I am talking on the phone. This is obviously annoying because I either say what 5 times before understanding, or I just nod and say yes, not ever knowing what they just said. I also just listened to these high frequency "mosquito noises" on this website. A teenager like me is supposed to be able to hear from 21.1 khz to 22.4 khz. I can only hear up to 14.9 khz, which is what people 39 and under are supposed to hear! I have never listened to music on earphones very loud for long periods of time and I don't go to loud concerts. However, I did have many ear infections and had to have ear tubes put in when I was young. Is my problem just going to get worse as as I get older? Maybe as far as though I will go deaf? Hopefully this doesn't count as medical advice. Thanks for your responses. :-). Imaninjapiratetalk to me 02:05, 14 January 2007 (UTC)


 * I went partially deaf once due to ear wax in one of my ears and flushing them helped a lot. I used a wax softener and a syringe that came with it to flush out tons of wax. You could also have a nurse do it at a hospital if you're feeling uncertain about it, just make sure your ear is healthy (no very recent or current infections). - O bli (Talk) ? 02:20, 14 January 2007 (UTC)


 * Warm water (not too hot!) works as well as a softener (or even better) and is cheaper and less messy. --Lambiam Talk  11:32, 14 January 2007 (UTC)


 * I would think that getting a pro to look at the problem makes sense: 1. The poor hearing may be fixable (it probably can be improved), and it may be easier to fix than if you waited for say another five years. 2. There may be something you need to be doing - or avoid doing - to prevent it from getting worse. 3. There are some pretty important implications for social activities, sport and career choices. 4. Think of what fun it would be if you could hear all the sounds that your friends do. --Seejyb 04:20, 14 January 2007 (UTC)


 * You think YOU have problems? I'm fifteen and can only just hear the 12khz sound. Vitriol 04:30, 14 January 2007 (UTC)

Stop! Don't panic! Never use the computer to diagnose yourself or others. You didn't go into detail about how you listened to the tones. Unless you have a fantastic computer/audio system, you can't reliably test your hearing. The high frequencies won't get through most speakers. There's a good chance that you don't have a problem, but the only way to make sure is to have your hearing tested by a professional.Bunthorne 06:31, 14 January 2007 (UTC)


 * Hoo rahh!! My professional headphones would :) Sony MDR-7506! But anyway, I'm with Burnthorne. There's a good chance you don't have a problem, although you can go see an ear-ologist if you like. I know my hearing is MUCH worse because of the earwax in my ear. It is normally compacted, and there is seriously a lot of stuff in there. X ['Mac Davis '] (DESK |How's my driving? ) 19:02, 14 January 2007 (UTC)


 * Don't worry too much about the 20Hz to 20Khz statistic for young people, it's just covering the bases of people who are lucky enough to have exceptional hearing. Most of us can't hear over 16Khz by the time we enter double figures. I also doubt the validity of many of these tests because I've performed it on students who, not knowing the capabilities of the human hearing system, confessed to hearing sine waves in excess of 20Khz! Note also that our sensitivity to different frequencies follows general loudness contours and higher frequencies tend to "roll off". —The preceding unsigned comment was added by Magic Window (talk • contribs) 21:57, 14 January 2007 (UTC).


 * Man, that 20Khz maximum for the human ear is just an "average" not something theoretically fixed such as the Chandrasekhar limit, he, he. Some people might have a superior ear than what would be expected. It is very easy to check whether they are lying or not: just make them not see you playing the file and let them say: "Yeah, I do hear it!". By the way, I'm almost 21 and my limit (and my hardware's) is 19,8KHz, which I can hear quite clearly. As for the questioner, I've heard that these problems are better solved the earlier the problem is detected, so the only thing I can say is that if you really think you have an ear problem, go to the doctor :). Good luck to all... PS:Oh, I forgot to say what I wanted to say. I found somewhere in the Internet a group of asthmatic people that claim they can hear frequencies as high as 100Khz "superhuman" ear, which is high enough for them to hear dog whistles and bats flying around. Quite impressive :D --Taraborn 09:16, 19 January 2007 (UTC)

The two possibilities that come to mind to describe being able to hear but not able to distinguish words are:

1) Lack of high frequency hearing, as you suggested may be the problem in your case. I suggest having your hearing tested, and possibly using hearing aides.  They can be small enough to hide within the ear canal, and can selectively amplify certain frequencies.  Parabolic microphones also allow you to hear voices from one direction only, but those are, of course, highly visible.  You might want to get one of those for home use only, if you're embarrassed to use it in public.  I would say the ear infections are likely the cause.  I wouldn't expect your hearing to get much worse until old age, however, but wouldn't expect it to improve, either.

2) Some type of brain damage could also make it difficult to interpret speech, but this doesn't seem to match what you've described. StuRat 02:30, 15 January 2007 (UTC)

hey i am another 14 year old and i had all my friends hear it none of them could hear the noise so mabe they have incorrect data at that site

Also the samples are aliased because of the low sampling rate. Try using audacity, crank the sampling rate all the way to the highest (100k) and generate the tones. --antilivedT 04:32, 15 January 2007 (UTC)


 * I was able to hear the first 4 sounds on my PC, but yours may not play the same frequencies. StuRat 20:32, 20 January 2007 (UTC)

Fire Bottle
What sort of chemicals might these smart kids be using to create the fire in the bottle? Thanks for the help. --72.69.146.116 03:08, 14 January 2007 (UTC)


 * Any sort of "flammable" gas or volatile liquid after evaporating would probably work, but I'm not sure what they're using here.  The trick is to get the ratio of oxygen and the chemical right.  As long as there is no oxygen in the bottle, their won't be ignition until they're mixed outside of the bottle.  But I wouldn't recommend trying it, unless you really know what you're doing. --Cody.Pope 04:15, 14 January 2007 (UTC)


 * It has to be a gas that's heavier than air; many of the common flammable gases, like carbon monoxide, natural gas, and methane, aren't. I'd go for lighter fluid vapour, since it is very accessible.


 * By the way, I think there has to be some oxygen in the bottle. The person holding it squeezed it, and then let go, sucking air in.  --Bowlhover 04:33, 14 January 2007 (UTC)


 * It's almost certainly ethanol alcohol coating the inside of the bottle. Just pour a tiny bit in, shake well, light, then squeeze.     -bmk

Why do cats love fish?
Of course, fish is nutritious. But why is the common stereotype that cats, rather than dogs love fish? Our article on cats says that domestic cats successfully hunt for fish. I have seen many swimming dogs, but never a swimming cat (despite the external link in our article). &mdash; Sebastian 03:31, 14 January 2007 (UTC)
 * Where did these animals evolve? Dogs = wolves from the woods, maybe not many places to practice catching fish. Cats... er... Egypt? You wouldn't think there'd be many fishing holes in a desert. Maybe Africa like lions, there'd be a fair few watering holes to dabble in there. There, how helpful was that! 121.72.14.221 03:50, 14 January 2007 (UTC)
 * actually land mammals (not stuff like whales porpoises etc which have a more fish like body shape and only come onto land occasionally if at all) don't fish by swimming, fishing from outside the water has many advantages: you can move much faster, you don't get anywhere near as wet (and wet tends to lead to cold which is bad) and you are unlikely to be noticed by the fish.


 * also lets not forget that cats have far better claws than dogs (this certainly applies to the domestic variants but i think it applies to thier wild variants as well), maybe dog claws are simply not good enough to get fish out of water. Plugwash 04:07, 14 January 2007 (UTC)


 * Yes, cat's retractable claws are a considerable advantage for fishing from the banks of a pond. This allows them to have claws long enough to spear fish when extended, yet still be able to walk when they are fully retracted. StuRat 02:14, 15 January 2007 (UTC)


 * Thanks, that makes sense! &mdash; Sebastian 04:24, 14 January 2007 (UTC)

Simple microcontroller stepper control
What solutions would you suggest for a simple stepper motor controller? Ideally, the microcontroller should only have to send two bits: the direction and a pulse. The motor controller would then move the motor according to the input.

Most websites recommend the Allegro UCN5804B for this type of application, but it has been discontinued. The replacement (A3967) is unfortunately only available in a SOIC package (which is much harder to prototype).

Do you have any recommandations or suggestions for this project? --Jcmaco 00:59, 16 January 2007 (UTC)


 * After more research, I found that the L297 and L298N can be combined to control bibolar stepper motors just like I was suggesting. The L297 can also act as a translator for unipolar stepper motor control and then use a darlington transistor array to control the motor (driver). --Jcmaco 00:59, 16 January 2007 (UTC)

A PIC microcontroller might do this simple job--Light current 03:51, 14 January 2007 (UTC)
 * it would but you'd still have to build the drive switching cuircuit from scratch. BTW you can buy dip-soic converter boards which you can solder your soic chip to, solder two rows of pins in and then drop into your breadboard or stripboard prototype. Plugwash 03:58, 14 January 2007 (UTC)


 * Google search of "Stepper driver chip" finds: MC3479, NTE1857 .  I don't see anyone selling the old Moto. SAA1042. --Wjbeaty 02:02, 15 January 2007 (UTC)

Why Mercury?
Why mercury is used in a thermometer?Vichu satheesh 04:25, 14 January 2007 (UTC)


 * We use mercury becasue it is a very heat sensitive substance. Compared to other elements, it expands very significantly due to temperature.Rya Min 05:53, 14 January 2007 (UTC)


 * Did you try reading mercury and thermometer?--Shantavira 09:29, 14 January 2007 (UTC)


 * Mercury is also extremely opaque when compared to any other liquid. (Alcohol thermometers require concentrated dye in order to make the alcohol column visible.)  Mercury also does not "wet" the inside of the glass capillary, so it doesn't leave an opaque film behind as it contracts with falling temperature. --67.183.217.169 01:26, 15 January 2007 (UTC)

And, perhaps it's obvious, but you want a substance which is liquid over the entire range of temps you are likely to encounter, and one that won't break down with age or sunlight exposure. StuRat 02:10, 15 January 2007 (UTC)


 * I've wondered, but not found an anwer, to what is used in the far north reaches of Alaska, Canada, Norway, Sweden... When I was in Norway in February, I was stationed on top of a very tall mountain near the northern tip. My mercury thermometer was just a little silverish ball.  Our Norwegian guide told me it was hitting -40, so there's no point in using a thermometer.  Is there a common cold weather thermometer? --Kainaw (talk) 02:53, 15 January 2007 (UTC)


 * The modern solution is to use a digital thermometer with a thermocouple. Another common option is an alcohol thermometer. --Carnildo 21:39, 15 January 2007 (UTC)

In some cultures, a brass monkey is used. Apparently they are very sensitive to extreme cold. FT2 (Talk 09:06, 15 January 2007 (UTC)
 * Mercury-in-glass thermometer says that a mercury-thallium alloy is used to measure temperature between -38 and -61. Rmhermen 00:46, 16 January 2007 (UTC)

manufacture of petorl
hello,

I would like to know the manufacturing process of petrol with more details than the normal one paragrph process. being a chemical engineer and gonna pursue my studies in oil and i would like to have a strong backgroud. waiting for your reply.

thank you for your co-operation.
 * You can start with gasoline and then look at and .  Superm401 - Talk 06:20, 14 January 2007 (UTC)

Perpetual Motion
How is orbit not a perpetual motion device? The object is continuously falling, so therefore gravity should keep accelerating it, right?
 * Yes -- until you actually try to extract any of the energy from it. In an isolated system consisting of two objects orbiting each other gravitationally, the two objects will remain in orbiting motion forever, as long as they are not disturbed. However any attempt to extract useful work from this system would lead to a loss of energy. This would result in the objects slowing down and getting closer to each other, until at some point the objects would collapse together and no more energy would remain to extract. (from Perpetual motion.) --jpgordon&#8711;&#8710;&#8711;&#8710; 06:08, 14 January 2007 (UTC)


 * That's not quite true. Two orbiting bodies will only remain in orbit forever if you're using newtonian gravity.  In GR they slowley get close together.


 * I think this stems mainly from a problem in the conception of perpetual motion. Physicists only use that label for machines that are designed to do work.  Superm401 - Talk 06:21, 14 January 2007 (UTC)

Orbit is a perpetual motion system in the sense that moving through space is perpetual motion. It's not doing work, it's not producing net output of energy, it's just following a no gain/no loss path through space-time. You can see how "perpetual" orbit is, by watching what happens if even small amounts of atmosphere exist in a satellite's orbit. Eventually it will lose velocity, spiral and fall out of orbit. As said above, perpetual motion devices are intended to do some work, for example, to continue to move eternally despite having to offset friction, or to produce some form of net energy output. FT2 (Talk 09:02, 15 January 2007 (UTC)

Forget frogs. How about crabs?
...as a metaphor. A few hundred centimeters up, we spoke about boiling frogs as a metaphor. Another metaphor has been going around for a while (see Crab mentality,, or

Ok, so if you're too lazy to click on the above, in short it is claimed that if there is an open bucket of live crabs, none would be able to escape, since if one tried to climb out, the others would pull it back. I've heard this used as a metaphor for someone who tries to get out of the 'hood, that the other members will do all they can to keep people from bettering themselves.

So, any fisherfolk out there that can vouch for this supposed behavio(u)r of crabs? Bunthorne 07:46, 14 January 2007 (UTC)


 * Only crabby people would ascribe this to the crabs' mentality. A crab trying to claw its way out that is not positioned at the side of the bucket has no other leverage than nearby crabs. Those in the second layer of crabs (second-nearest to the side) will, mindlessly trying to clamber out, attempt to find leverage on the first layer. Because of Newton's third law they pull the crabs in that layer down. And because of Archimedes' Principle, they would have to push them well under water in order to get out themselves. --Lambiam Talk  11:51, 14 January 2007 (UTC)


 * Although it may be fair to say that one crab is completely unconcerned with the welfare of the others. StuRat 02:05, 15 January 2007 (UTC)

physics-infrared photographic optics question
I am a photographer and have been doing infrared film photography since 1987. I was contributing to the Infrared photography article, and I came upon an assertion under the Film Cameras section that I could not confirm and that did not sound correct to me.

"Catadioptric lenses do not require this adjustment because mirrors do not suffer from chromatic aberration".

"This adjustment" refers to the refocus of a camera lens to compensate between visible light focus and infrared light focus. Is this correct? I just wanted to check since I teach infrared photography workshops and this would be good to know definitively. There are other optical assertions under Infrared photography that are so far out of my league I wouldn't know it they are right or wrong, but this one sounded odd. Thanks--Schafphoto 08:12, 14 January 2007 (UTC)schafphoto


 * Well, chromatic aberration happens because lenses are also prisms, and they have dispersion (optics) which splits white light into rainbows.  Mirrors don't do this.   But catadioptric lenses aren't purely mirrors.   Perhaps it would be more accurate to say that the "adjustment" is insignificant because the glass lens in the catadioptric element does not contribute significant chromatic aberration. --Wjbeaty 19:34, 14 January 2007 (UTC)


 * Might I suggest a test ? Since you teach those classes, you could justify buying such a lens for instruction purposes, couldn't you ? StuRat 02:02, 15 January 2007 (UTC)


 * I love this business, always a justification for new equipment. I'm sure i can get my hands on a cat lens somewhere, and if I don't see a red infrared focus index mark, I'll give it a try.--Schafphoto 05:45, 15 January 2007 (UTC)Schafphoto

Can woodpeckers manipulate objects with their feet?
I notice from reading the woodpecker article that some species have zygodactyl feet (i.e. two toes forward and two toes back). Birds in the parrot family also have this configuration and are able to use their claws like hands to manipulate objects. Can woodpeckers do the same? --Kurt Shaped Box 11:46, 14 January 2007 (UTC)


 * From my (limited) experience watching Old World woodpeckers, no. Woodpeckers normally do not perch on branches like parrots do, but rather cling to the bark. That's what piciform zygodactyl feet evolved for in the first place. I presume clinging to the tree trunk makes it much harder to manipulate objects. BTW, birds do not have to have zygodactyl feet to manipulate things. I often see hooded crows using feet to manipulate objects. Cheers, Dr_Dima


 * Interesting. What have you seen the crows do? We have European Magpies, Carrion Crows and the odd Raven around here but I've never actually seen them 'manipulate' anything with their feet - unless you count putting a foot on a piece of food to hold it down whilst eating as 'manipulating'? --Kurt Shaped Box 16:07, 14 January 2007 (UTC)


 * Yes, Kurt, I refer to manipulation ("using claws like hands") in a broad sense of good "foot-beak coordination" like, for example, prying things apart or turning things around to get to the softer or better-tasting parts. Crows are much better skilled than magpies in that respect; but no, crows probably can not hold objects in their feet like parrots do. Crows seem to either press objects against something or hold them with both beak and foot. In retrospect, I understand that you were asking specifically about holding and manipulating objects away from any surface, using foot toes alone. You are right, crows probably can't do that, or at least I never saw them do that. Sorry. Best regards, Dr_Dima

q
what is the actual fullform of Rx in medical sciences?—
 * Are you talking about Medical prescriptions? (check the article) &mdash; Kieff 17:20, 14 January 2007 (UTC)


 * You asked the same question at this Reference desk on December 29, as well as at Yahoo Answers. Were you not happy with the answers given then? If you provide some feedback, perhaps we can fine tune the answer to your needs for next time. --Lambiam Talk  19:32, 15 January 2007 (UTC)

NORTH POLE TO SINGAPORE
how would an animal such as a polar bear adapt to the environment if it was taken fm the northpole and put in singapore??


 * It wouldn't. It would just die. Adapting to a new environment is a slow process that take many generations through many years. &mdash; Kieff 17:16, 14 January 2007 (UTC)

If you mean in a zoo, they would be OK so long as they have some method to prevent overheating, like a nice pool to swim in. In the wild, however, their usual methods of hunting, such as pouncing on seals in their dens through the snow roof, just don't work. They can survive by stealing food from landfills, however, which they often do when their natural hunting methods fail them. StuRat 18:04, 14 January 2007 (UTC)

effect of total silence on human hearing
What are the effects on the human sense of hearing in total silence?Rick42774 14:13, 14 January 2007 (UTC)


 * From 4'33":
 * ''In 1951, Cage visited the anechoic chamber at Harvard University. An anechoic chamber is a room designed in such a way that the walls, ceiling and floor will absorb all sounds made in the room, rather than bouncing them back as echoes. They are also generally sound-proofed. Cage entered the chamber expecting to hear silence, but he wrote later, "I heard two sounds, one high and one low. When I described them to the engineer in charge, he informed me that the high one was my nervous system in operation, the low one my blood in circulation."
 * It's the best I can give you on that topic. &mdash; Kieff 17:13, 14 January 2007 (UTC)

People can often hear their own heart beat in such conditions (when not breathing). StuRat 17:49, 14 January 2007 (UTC)
 * I don't think they could hear their nervous system operating. That's a little out there. Probably something like tinnitus. Just because he's at Harvard doesn't mean his opinion is final. X ['Mac Davis '] (DESK |How's my driving? ) 18:24, 14 January 2007 (UTC)
 * Yes, I'm also skeptical about that bit. &mdash; Kieff 03:01, 15 January 2007 (UTC)

Warning: Speculative comments ahead: - Although science does not have a definitive answer, I wouldn't discard the latter quite so quickly. There are a number of body processes and it's not impossible that some might give rise to the slight sensation of sound, or low level stimulation of the aural nervous or neural systems that might be interpreteted as 'sound' in a completely silent environment. Also I'm incined to not completely discredit the comment of some mystics and meditative practices who comment that the entire body's nature is vibrative, with the solidity an illusion. Obviously at present that would not be considered a scientific observation, at best being hearsay from some people. But Indian meditative practices contain meditation upon internal subtle sounds that might match cage's description. Again, unconfirmed, so take it for whatever it's worth. FT2 (Talk 08:58, 15 January 2007 (UTC)


 * In absence of external stimulus, neurons of human auditory cortex are still firing. Whether one perceives that activity as sound or not is a different question. I am not aware of a definitive answer to that one. Dr_Dima

Working Mechanism-SRE
Can you explain how the recently launched SRE-satellite vehicle by ISRO works and return back to earth without any damage by the viscosity of the air?59.92.82.44 15:32, 14 January 2007 (UTC)

Zebra subspecies identification
I have recently created an edit of Zebra Botswana.jpg for its featured picture attempt, and one of the major problems I have with the image is that the subspecies of Plain's Zebra (at least, I think that's the right species) isn't identified. It seems to match Burchell's Zebra, but I would like a second (and perhaps more knowledgeable) opinion. -- Pharaoh Hound  (talk)  16:19, 14 January 2007 (UTC)
 * Never mind. I've answered my own question (they're Damara Zebras). -- Pharaoh Hound  (talk)  16:15, 15 January 2007 (UTC)

casimir effect and gravity mix up
i was asked a while back and could not answer, so could someone tell me how they knew the casimir effect was caused by the zero point field and not by the gravity between the two plates. i know they did somehow but not how they distinguished this. can anyone help me? curious


 * I would guess because the magnitude of the gravitational effect is known precisely, so any additional attraction is assumed to be due to the Casimir effect. StuRat 17:46, 14 January 2007 (UTC)

how can digital radios auotmatically jump over noisy channels?
Do they compute the spectrum width on the fly with some kinda DFT? tia --Ulisse0 14 January 2007 (UTC)

I think they just feel out where the signal is strong

Pluto
I heard many times that Pluto is not a planet. Why? Sciencefordummies 19:40, 14 January 2007 (UTC)


 * It's now a dwarf planet, namely because it hasn't cleared its neighborhood, and so doesn't meet the new definition for full planethood. You'll want to read 2006 definition of planet for the new definition. Chances are more than likely that they will change it again fairly soon, since it's incredibly lacking (planets must orbit the Sun, for example), but I doubt any new definition will move Pluto back up to planet status. -- Consumed Crustacean (talk) 19:46, 14 January 2007 (UTC)


 * The Devil's Advocate would ask "But isn't a dwarf planet a particular kind of planet, and therefore still a planet?". -- JackofOz 02:25, 15 January 2007 (UTC)


 * But a sea cow is not a cow and a fake Picasso is not a Picasso. --Kjoonlee 03:38, 15 January 2007 (UTC)


 * If we were coming up with a new label for an object that excluded it from the class of things known as "planets", don't you think it would have made a lot of sense to have a title that did not contain the word "planet" anywhere in it? The whole point of that long-winded exercise by the IAU was to define, rigorously, once and for all, which celestial objects are to be known as "planets", and therefore which are to be known by other titles.  Having finally come up with such a definition, to then retain the word "planet" in the title of the things they've just excluded from the definition of "planet" looks like they've been wasting their time.  It looks like: "dwarf" is merely a descriptor, but Pluto is still some kind of planet.  However, according to the new definition, Pluto is no kind of planet at all but something else entirely.  The label "Dwarf planet" spectacularly fails to make that distinction clear, and is doomed to create confusion.  Very woolly thinking indeed on the part of the scientists.  JackofOz 04:25, 15 January 2007 (UTC)


 * There are a lot of problems with the definition. See Definition_of_planet. The language problem you mention is in there. The Solar System exclusivity of the definition annoys me most; why was that overlooked? -- Consumed Crustacean (talk) 04:30, 15 January 2007 (UTC)


 * I'm guessing they spent so much effort on the dwarf planet issue they ended up forgetting about extra-solar planets. &mdash; Kieff 06:27, 15 January 2007 (UTC)


 * I also don't think we should just uncritically accept the ruling of the IAU. I find it incredibly arrogant that they should attempt to promulgate an official definition of "planet". Expert consensus properly evolves, it isn't voted on. I think, just on this principle alone, we should refuse to follow IAU's lead -- slap them down hard, so that the next academic association that considers pulling something like this thinks twice about it. --Trovatore 02:34, 15 January 2007 (UTC)


 * Well, everyone uncritically accepted the ruling of the IAU when they ruled Pluto a planet in the first place, right? --Kainaw (talk) 02:45, 15 January 2007 (UTC)


 * That's because back in 1930 it was more like a "ruling" than meeting any kind of definition. It seemed to be like the other objects known as planets, so the label seemed appropriate.  Nobody bothered to ask the question "What defines a planet?", so there simply was no hard-and-fast definition of "planet" till 2006.  Now there is - which is what all the fuss is about - and Pluto gets the chop.  I wonder if people would have been as up in arms about the new definition of planet if Pluto had continued to be classified as a planet.  JackofOz 03:09, 15 January 2007 (UTC)


 * Probably not. But it would still be wrong. They have no right. There shouldn't be any official definitions in astronomy, any more than there are (thank God!) in mathematics. --Trovatore 03:46, 15 January 2007 (UTC)


 * Why? Astronomy isn't mathematics. This aspect of it could even be compared to taxonomy, and if you start arguing that we should do away with definitions in that then you'll start to get some friction. In any case, there are some conventions in mathematics. One can circumvent any of them by "redefining the rules", as it were, but if such changes are not made explicit then the convention is applied. 2 + 2 = 4. It makes things easier; there's no reason to define the addition operator every single time you use it. That would be obnoxious. Or, if everyone started using a different symbol for something common like addition (or a different classification for Pluto), it would become downright confusing.
 * You can call Pluto anything you want regardless, but you better be sure to qualify exactly what your definition means every single time you use it to differentiate it from the accepted one. -- Consumed Crustacean (talk) 03:58, 15 January 2007 (UTC)
 * Huh? I have nothing against definitions or conventions. I have nothing against accepted definitions or conventions. I have a lot against deciding what's accepted by the vote of some organization (or, for that matter, any other decisional procedure of some organization). Consensus of experts is a factual matter, not one to be decided by some allegedly "official" procedure, but one to be observed by reading the works of experts and seeing if they agree. --Trovatore 06:17, 15 January 2007 (UTC)
 * Huh? How exactly should it have worked? This isn't really much of a factual matter, it's a bunch of semantics. As for agreement: no one had a working definition. In order to be understood (astronomers are not mathematicians thing again) most work published would have simply used the 9 planets, everything else being an asteroid/comet/KBO. There was and still is very little agreement over what the definition should be, so the IAU tried to make it something. Again, no one is forcing you to pay any attention to them, it's just easier if you do, as there was no working definition of planet at all before. I'm getting less coherent. Time to sleep. -- Consumed Crustacean (talk) 06:33, 15 January 2007 (UTC)
 * This is exactly how it should have worked: Someone (let's call him Smith) could have published a definition in a journal article, and stated that the article would use the definition. Then Jones would publish a paper in which he referred to planets "according to the definition of Smith". Then Fernandez and Himmelschein would publish another such paper, and so on, until with time the "definition of Smith" part would be dropped, because it would be understood. Or in the interim, Okikiolu and Park might have published a paper with a competing definition, and perhaps it would have been picked up by more other authors, and eventually become the default, or perhaps remained as a competing definition, with some authors referring to "the definition of Smith" and others to "the definition of Okikiolu and Park", depending on which better fit their specific needs; that would also be a fine outcome. But while a definition might or might not become the default, at no point is it necessary or desirable that it become official. --Trovatore 06:44, 15 January 2007 (UTC)


 * Well, what if the people who publish well over 90% of all of the respectable astronomy papers got together in a long meeting and decided to have a long debate about what they all felt the definition of a planet should be? Oh - wait - that is what happened. --Kainaw (talk) 08:29, 15 January 2007 (UTC)
 * Yeah, and that's a bad way to do it. --Trovatore 08:34, 15 January 2007 (UTC)
 * Also, I seriously doubt that's what happened. 90% of published astronomers were in that meeting? You'd have to prove it. What you mean is, an organization that claims to represent them, just because they happen to be members of it. Sorry, that doesn't cut it. --Trovatore 08:37, 15 January 2007 (UTC)
 * It should be doable to get all the people who publish over 90% of the respectable papers together in a loooong meeting. But wait a second, respectable... We need a definition of "respectable". --Lambiam Talk  19:44, 15 January 2007 (UTC)
 * Possible, conceivably. Desirable? Absolutely not, not for this purpose, anyway. There is no need to have an official definition of "planet". Not just there's no need; it's actively a bad thing. The badness resides not in the definition, but in the officialness. --Trovatore 23:16, 15 January 2007 (UTC)


 * Does that mean that an outcome which might otherwise be acceptable becomes unacceptable because of the manner in which, or the people by whom, it was created? If all you're objecting to is officialness, that's understandable.  But do we need to throw the baby out with the bathwater?  As for there being no definitions in mathematics, how about the square root symbol being defined to mean the positive square root only?  JackofOz 01:54, 16 January 2007 (UTC)
 * Good case study -- let's take that one. That's a universally accepted convention, for good reasons of convenience. It never had to be voted on; no organization ever promulgated it as an official ruling. It wouldn't occur to any mathematical organization that they had the right to rule on it, and of course they're right, they don't have any such right. Too bad the IAU doesn't similarly know its place.
 * When this sort of convention is the consensus view, no vote is needed, nor any other sort of action. It just is the accepted convention. When a standard doesn't come about by genuine consensus, you shouldn't try to force one by having a meeting about it. You should just continue to allow there not to be a standard, and let authors explain themselves if there's a risk of confusion. --Trovatore 03:47, 16 January 2007 (UTC)
 * It seems to me that there already was at least a rough (if unstated) definition of planet. Prior to last year, what would you have said to a suggestion that each of the hundreds of thousands of asteroids was a planet?  Laughable?  Of course.  On what basis would you have laughed?  On the basis that they don't satisfy anyone's concept of what a planet is.  How come Pluto was universally accepted as a planet in 1930 but the asteroids (except Ceres) were never so considered?  Was it just a question of size?  And why was Ceres demoted?  There must have been some reasonable, rational basis for these decisions, not merely the post-jentacular caprice of an anonymous official.  So there always was a notion of what "planet" meant, just not a very clear notion.  Why was that fuzzy, ambiguous, unstated, error-prone notion acceptable to scientists, but a clear, explicit, unambiguous one is not?  JackofOz 04:42, 16 January 2007 (UTC)
 * Sure, there was a rough notion of what a planet was. What would have been wrong with leaving it rough? Anyone who needed a more precise definition for a specific purpose could offer one. If enough people found it useful, it would become the consensus definition. If it didn't, it means that a more precise uniform definition was not in fact needed. --Trovatore 05:31, 16 January 2007 (UTC)
 * The whole debate began with the discovery of Eris. To some, it was the 10th planet, but others maintained it did not fit their concept of planet at all, despite the fact that it was larger than Pluto.  The issue of what a planet is had to be clarified somehow.   You might quibble with the new definition of planet, just as I quibble with the new terminology "dwarf planet", but how can we quibble with the principle of clarity taking the place of fuzziness?  JackofOz 02:22, 17 January 2007 (UTC)
 * Precision, as a general rule, should not exceed accuracy. The real state of affairs is that there is no agreement on whether Eris is a planet. The proper response to that is to keep saying "some consider it a planet, and others don't", until that isn't true anymore. Otherwise it's a false clarity, as if I were to claim there are 6,012,482,173 persons currently alive on Earth. --Trovatore 07:26, 17 January 2007 (UTC)


 * Without jumping topic again to precision, definitions, square roots... Trovatore, it seems to me that you are basing your viewpoint on the "fact" that some group made themselves an authority to define what everyone else should consider a planet. When did that happen?  All I've heard about is the IAU stating that they made a rather precise defintion of a planet for themselves.  If anyone else wants to use it, go right ahead.  Is there a secret concentration camp somewhere for those who don't want to use the IAU's personal definition?  Are you claiming that the IAU isn't allowed to create a definition for themselves - basically making yourself an authority above the IAU to demand what they can and cannot do?  Or, the simplest explanation, are you just trolling? --Kainaw (talk) 07:56, 17 January 2007 (UTC)
 * I wouldn't have any objection to them saying "the IAU definition of 'planet' is thus and so". But that isn't what happened. Take a look at the resolution itself; they never limited it in that sense. Of course my quarrel is at least equally with the way other groups -- textbook writers, newspapers, museums, etc -- have responded, by acting as though they should accept IAU's authority on the matter. Just the same, I think it was unwise of IAU even to attempt to short-circuit the natural process of terminological evolution. So yes, in that sense, I am indeed saying what the IAU should and shouldn't do. --Trovatore 08:40, 17 January 2007 (UTC)

Different Interpretations of color
I have several people about this and they said they have also wondered this, but had no definitive answer. Is the way I see light at 450–495 nm (blue) the same way someone else sees that wavelength light? So if I could see through someone else's eyes would their sky be the way I interpret red? Sorry if this doesn't make any sense, I'm not very good at explaining things. :-). Imaninjapiratetalk to me 20:36, 14 January 2007 (UTC)
 * Not a direct answer to the question, but language plays an important part in colour perception. The Ancient Greeks had no words for colours at all; it simply didn't occur to them to group objects by the quality (which led to some odd translations of Homer's works that claimed that the sky was "bronze", and that sheep, wine, and the sea were all the same "colour"). Different languages divide colours in different ways. For example, the Russians have two words (Синий and Голубой) that in English would both usually be translated as "Blue", but are considered completely distinct in Russian.
 * If you look at Book I of the Iliad, lines 475–482, you find in these lines rosy-fingered (ῥοδοδάκτυλος) Dawn (not by itself a colour perhaps but showing awareness of the same quale in roses and the sky at dawn), and white (λευκὰ) sails. (There is also the (πορφύρεον) sea, which is sometimes translated as blue or purple, but there is doubt that in Homer this is a colour name). Elsewhere spears are reddened with blood, and so on. Strange translations may simply mean that the translators had the wrong idea about the meaning of ancient Greek colour names. --Lambiam Talk  00:50, 15 January 2007 (UTC)


 * Putting language aside, another piece of evidence for different people interpreting colour in different ways comes from questions asked of colour→tone/taste/etc synæsthetes. All perceive colours in different ways. GeeJo (t)⁄(c) &bull; 21:14, 14 January 2007 (UTC)


 * Thats really interesting that they would have no words for colors. Color is such an inherent part of life that you think someone would have mentioned it sometime and made up words for them. Very strange. :-) Imaninjapiratetalk to me 21:52, 14 January 2007 (UTC)


 * Actually, language plays no role in color perception. The ability to perceive and differentiate colors is biochemical, not cognitive.  Language may help in describing color distinctions and whatnot, but there are languages with no color words or words that equate to "light" "dark" and "colorful."  Nevertheless, speakers of such languages have no problem distinguishing colors.  I'd say that since there's no physical reason why color perception would be different from person to person that there's no reason to believe that it is different, especially as drastic as from red to blue.  Æµ§œš¹ [aɪm ˈfɻɛ̃ⁿdˡi] 21:44, 14 January 2007 (UTC)


 * No reason to think that colour perception would be exactly the same. The neural pathways used will more than likely differ from person to person. It doesn't really matter though, and you can't really compare one person to the other; they're just different methods of getting the same information. It's like playing a game of basketball with a green ball versus an orange ball; the game is exactly the same either way, even if the specific mechanisms aren't. (Bad analogy, yes; an AMD versus an Intel CPU maybe?) As for the effect of language, see Sapir–Whorf hypothesis. -- Consumed Crustacean (talk) 21:54, 14 January 2007 (UTC)


 * Some languages, make no distinction between blue and green. Vietnamese only has the word "xanh" for blue-green, but they get around this by saying "xanh da trời" (xahn like the sky) and "xanh lá cây" (xahn like the leaves), so they can see the difference, even if they couldn't always express it. Laïka  21:56, 14 January 2007 (UTC)


 * One example of a language with no colors is Tiv which contrasts pupu (light), ii (dark), and njian (colorful/red). According to Swadesh, people who have little color words are known to describe shadings of color by making analogies with the things around them.  This may be how we've gotten the color words we have today, Semantic change has a great example of the origin of the English word "black." Æµ§œš¹ [aɪm ˈfɻɛ̃ⁿdˡi] 22:05, 14 January 2007 (UTC)


 * IMHO the Sapir–Whorf hypothesis is not very convincing; I'd call it lack of evidence, not proof of effect. --Kjoonlee 03:32, 15 January 2007 (UTC)


 * Yeah, it seems a bit fishy to me as well. The article seemed fairly good at covering both sides, but I skimmed it really quickly. -- Consumed Crustacean (talk) 04:01, 15 January 2007 (UTC)


 * On the subject of language and color, the work of Paul Kay and Brent Berlin is quite enlightening. Different cultures identify different "focal" colors though the line up with more or less the same wavelengths, as these trigger specific chemical reactions in the eyes (we all see focal red as being a distinct form of red because it causes certain nerve cells to fire at their maximums). Though cultures may have more or less focal colors, the focal colors that they choose are all along this sort of physiological spectrum. (If you Google Kay's name, you'll get a lot of papers/interviews etc. which are quite clear). Now this is not the same thing as saying that people experience the same qualia—the same sensation, the same innate understanding—which is quite impossible to prove either way at this point, but there is, at the moment, no good reason to suspect that most people differ along these lines (those with neural or optical "defects" excluded). --24.147.86.187 22:29, 14 January 2007 (UTC)


 * See also Reference desk/faq. --Lambiam Talk  23:54, 14 January 2007 (UTC)

You should read up on tetrachromats. Due to mosaic x-inactivation some women are thought to have tetrachromatic vision. The result is that the resolution of different light frequencies is more acute and therefore more colours can be distinguished. David D. (Talk) 08:44, 15 January 2007 (UTC)
 * In response to this and the OP, I certainly think blue and green are quite contentious. I've often had arguments with my mum, who sees more green, and I see more blue. We can never determine if turquoise is more green or more blue! Even after using a computer to exactly mix the colours, we see the same off ratio, so it's definitely related to photoreceptors rather than perception acquired by experience or any other factors. Sandman30s 09:16, 15 January 2007 (UTC)

What is this bird?
I have no idea what type of bird this is. Bewareofdog 20:47, 14 January 2007 (UTC)


 * Whoa! Look at its eyes! It looks like some sort of vulture but I'm just guessing from the bald head... --Kurt Shaped Box 21:51, 14 January 2007 (UTC)

that bird is ugly —Preceding unsigned comment added by Rya Min (talk • contribs) 18:04, 14 January 2007


 * I think it is a Northern Bald Ibis. --CBD 00:32, 15 January 2007 (UTC)
 * Looks like it is related to the skeksis. Vespine 03:06, 15 January 2007 (UTC)


 * Is it a wird bird or a weird beird? Clarityfiend 03:43, 15 January 2007 (UTC)
 * This is a rare case where a bird went backwards time and did survive. But yes, it looks ugly. -- DLL .. T 17:27, 15 January 2007 (UTC)

The illusion of time
Some of this post will probably contain bogus information, so please correct me

It is my understanding that time is essentially an illusion created by the fact that the universe tends to unfold in a certain direction, i.e. higher entropy. It is possible to go "backwards" in time but the chances of it happening are just so rare that it simply wouldn't happen - every single particle in the universe re-configuring to a previous state is just ridiculously statistically improbable.

But yet if an egg were to fall off a table and shatter on the floor but then by some freak chance reassemble back onto the table in a reverse direction, we wouldn't consider that we were going back in time, just that something very very rare had ocurred.

Put simply, there is no true direction of time we are just so used to it being one way due to the way matter predictably behaves and configures itself? 164.11.204.52 21:48, 14 January 2007 (UTC)


 * Time has quite a lot of information on this sort of thing. -- Consumed Crustacean (talk) 21:56, 14 January 2007 (UTC)


 * (CTU) 7002 yraunaJ 41 ,10:22 klat ojndyh-- (-;  .noitseuq ruoy dnatsrednu t'nod I::


 * If entropy is increasing in one direction of time which you think of as "forward", so that eggs reassemble and jump on the table, then, presumably, that holds for all physical processes, such as the memory of the elpoep populating that epoch. So when an egg "spontaneously" reassembles and jumps on the table, they are not surprised, since they have no memory of the event anymore; it was erased even before the last photons emitted by their eyes reached the egg in a disassembled state. Earlier, before the reassembly, they foresaw that it was going to reassemble, which gave effect to annoyance, especially just before reassembly. At that time they may be a bit surprised, because they foresee that the egg will be lying quite securely on the table, and eggs that jump on the table tend to be position themselves near the edge. What they don't foresee, because they will not be paying attention at the time, is that the egg will roll to the middle of the table, because the table is not quite flat but a bit convex. --Lambiam Talk  01:21, 15 January 2007 (UTC)


 * Also see arrow of time, entropy and introduction to entropy. If the whole universe were to go "backwards" in time then your memories would unravel and you would not notice that it had happened - which indicates that the whole "direction of time" business is subjective, and time itself is an illusion, although a pervasive and useful one. Gandalf61 11:43, 15 January 2007 (UTC)

ORGANS AND THEIR FUNCTIONS
Which organ has the ability to monitor and regulate blood pressure and electrolytes: A. LUNGS B. HEART C. KIDNEY D. SPLEEN —Preceding unsigned comment added by 72.40.72.252 (talk • contribs)


 * Well, first of all, you should do your own homework. I can, however, give you a hint. The answer can be found by reading the introductions to lungs, heart, kidney, and spleen. – ClockworkSoul 23:09, 14 January 2007 (UTC)
 * It can? Blood pressure might be better. BenC7 01:03, 15 January 2007 (UTC)
 * (Fixed link. Hope you don't mind.) --Kjoonlee 03:35, 15 January 2007 (UTC)
 * Thanks. BenC7 06:56, 15 January 2007 (UTC)
 * Well, the multiple choice question was probably meant to have only one correct answer, but it doesn't. The answer the teacher wanted was clearly C. KIDNEY, but you could make a case that B. HEART is also correct, since the heart secretes atrial natriuretic peptide, regulating both sodium and blood pressure. I suppose you might disqualify the answer on the basis of "electrolytes" being plural.... - Nunh-huh 07:54, 16 January 2007 (UTC)

Stars: Supergiants, giants, dwarves and so on
Hello. Okay, the thing is that our Sun currently is a "small" star but later it will become a red giant or supergiant in its final stages of its life. Now my question is, stars such as Antares, Arcturus and Aldebaran that are so huge... is it because they are "by nature" much more massive, big (in volume) and generally cold or are they just stars that are at the end of their lives? Of course some difference in mass between stars must exist, it would be too much of a coincidence if they were aproximately the same. What is what causes these differences? Thanks. --Taraborn 23:54, 14 January 2007 (UTC)


 * Probably the amount of matter available during its creation. --Wirbelwind ヴィルヴェルヴィント (talk) 00:55, 15 January 2007 (UTC)
 * Stars definitely do form at different sizes, it is their size that determines what happens to them. The section of formation and evolution in the star article has lots of info. Vespine 02:43, 15 January 2007 (UTC)


 * Red giants are stars at the end of their lives, while blue giants are inherently large, bright, and hot. Antares, Arcturus, and Aldebaran are all red giants, while Rigel is a blue giant.  So to estimate a star's luminosity, look at its colour.  --Bowlhover 03:14, 15 January 2007 (UTC)


 * Image:Hertzsprung-russel_diagram.png -- Consumed Crustacean (talk) 04:05, 15 January 2007 (UTC)

Stars can have very great difference in mass when they form. That makes sense since mass is just "how much matter came together to make the star"; if it forms in a hydrogen-rich environment or not, for example. The mass is crucial to their fusion cycle, and hence to both the color of their light and also their history and fate. This is my basic understanding of the mechanism, someone more knowledgable may need to correct some of it:

Stars start by burning hydrogen to form helium. When the hydrogen is substantially burned, then ordinarily like most fires when the fuel runs low, the transformation of energy (in this case mass to energy by fusion) slows. The star was held in equilibrium between gravity (that is trying to force it to collapse) and heat production and other stellar processes (that provide pressure against contraction). As the hydrogen cycle slows, the latter reduces, and the star begins to collapse. When things are compressed it often results in a higher temperature (think of using a bicycle pump). If the star is big enough, this will generate enough temperature for helium fusion to occur, and the star will now have a helium burning core, with the hydrogen burning layer outside that. Because helium burns at a higher temperature, this is a hotter core, higher temperature, bluer light, and shorter lived. This can repeat several times for supermassive stars, with silicon, oxygen, and other fusions occuring in different layers. But when iron is being produced the process ends, because iron can't be fused this way - unlike lighter elements, there is no element which iron atoms can fuse to create, which would produce a net release of energy, because Iron is too stable in this sense.

So that's color. The size of a star is determined by mass and core temperature, so different stars and different masses and different stages in their fusion cycles, can have very different sizes. I don't know enough to comment on why and how that works in detail though, but the above I am broadly sure is fairly accurate.

The ultimate fate of a star depends again on the same things. Does it blow off its outer layers, does it collapse and become a nova or supernova or does it just fade once its hydrogen fuel runs out. Again, not sure exactly the details. But hopefully this has helped somewhat on one aspect anyway. FT2 (Talk 08:45, 15 January 2007 (UTC)