Wikipedia:Reference desk/Archives/Science/2007 August 23

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August 23

What is Lanalool?

I see this crazy sounding substance in more and more shampoos and conditioners. What is it? And where does its name come from? --24.249.108.133 03:14, 23 August 2007 (UTC)

Are you sure you spelled that right? Lananool has no ghits.Whoops, mispelled it. Someguy1221 03:20, 23 August 2007 (UTC)

Lanalool does, but I'm still unsure exactly what the diff is between that and linalool. --jpgordon^∇∆∇∆ 03:57, 23 August 2007 (UTC)

I don't know what it's fashionable to put in shampoos these days, but maybe you mean lanolin? --Anonymous, August 23, 2007, 03:50 (UTC).

See Acetylated lanolin alcohol (aka Lanalol). -- MarcoTolo 04:04, 23 August 2007 (UTC)

No, I mean Lanalool. I'm quite familiar with Lanolin, silly. --24.249.108.133 19:40, 23 August 2007 (UTC)

I'm not trying to be obnoxious, but you're sure it's "lanalool"? Linalool (with a i) is "one of the most frequently encountered floral scent compounds".[1] -- MarcoTolo 20:02, 23 August 2007 (UTC)

sun and moon simultaneously visible

When the sun and moon are simultaneously visible, how do they appear to people on the other side of the world?

Literally on the other side of the world, i.e., a full half-rotation away? It would be night time, and a very dark night, as there'd be no moon visible. --jjron 08:39, 23 August 2007 (UTC)

Only half a rotation? What about a full one?  :) --Bowlhover 15:18, 23 August 2007 (UTC)

No! Ignore jjron! If it's dawn for me - then someone on the exact opposite side of the earth will be seeing a sunset. So it is certainly possible. There will be some difference in the relative position of the sun and moon because of parallax. This is most noticable during a solar eclipse. The amount of the eclipse is different depending where you are on the surface of the earth. Some places are seeing the moon precisely aligned with the sun (a total eclipse) - other places nearby (a couple of hundred miles away) see the moon slightly overlayed on the sun (a partial eclipse) - and further away still, a few thousand miles away, the moon is just off to the side of the sun (no eclipse at all). SteveBaker 11:52, 23 August 2007 (UTC)

This is the summertime, so if it's dawn for you in the United States (5:30 a.m.), it would be a hot late-afternoon somewhere in China (5:30 p.m.). But it would be nighttime in Australia at the point exactly half a world away, both in latitude and in longitude. Their time would also be 5:30 p.m. but it's winter for them right now; thus the day is shorter.

The same applies with the Moon, except there's a two-degree paralax error that SteveBaker mentioned. The actual parallax error will be smaller if one observer isn't exactly half a world away from the other. --Bowlhover 15:16, 23 August 2007 (UTC)

No! Oh come on guys - THINK! Forget about summer/winter, day/night, USA/China/Australia, whatever! Just take a near-perfect sphere - hold it up in the light of an object that's a very long way away (like the Sun for example) and you'll see that exactly half of the sphere is illuminated. Take one point that's right on the edge of the shadow - now find the point on the opposite end of a line through the center of the sphere - and guess what? It's right on the edge of the shadow too. PLEASE! Simple geometry! Hence if the sun is rising at one point on the surface of the earth then the sun is setting on the exact opposite point. QED.

Now, you may try to argue that the sun isn't infinitely far away and hence slightly less than half of the sphere of the earth is illuminated by it - but that's not true because the sun isn't an infinitely small dot - it's a large disk. Hence the some fraction of the suns disk is definitely visible from two opposite points on the earth at some point during sunrise/sunset. Now you're going to think to argue that the earth isn't a perfect sphere - but the error is of the order of 20km - 0.3% which isn't going to make enough difference to matter. Additionally, refraction of light through the atmosphere actually bends the suns light somewhat into the dark side of the planet - which prolongs both sunrise and sunset somewhat - so in fact, more than half of the earth can see the sun at any given time. SteveBaker 17:29, 23 August 2007 (UTC)

How did sunrise/sunset come up? haw haw pun. I thought he was asking about when you can see a white "ghost" of the moon in the daylight sky.. the answer would be maybe under the best of circumstances a person on "the other side of the earth" - I don't think he means literally 180 degrees, rather just generally on the dark side - could see a sliver of the moon. See this top down view. http://img212.imageshack.us/img212/1687/moonvz3.png --froth^t 22:17, 23 August 2007 (UTC)

No! Ignore SteveBaker! ;) His answer deals only with the extreme conditions at sunrise and sunset. My original answer, and Froth's answer above, deals with the 98% of the time (I don't want an argument on the exact percentage) when it's not sunrise and sunset. Surely that's what the original questioner meant. The sunrise/sunset issue is simply an addendum to this. --jjron 23:07, 23 August 2007 (UTC)

WHAT!? When did the OP mention that it couldn't happen at dawn? In fact, if the question has meaning, the OP must have been talking about dawn/dusk since it's the only way for it to happen. Then YOU flippantly (and utterly incorrectly) suggested that the OP was asking a stupid question (when in fact, it's a perfectly reasonable question) - when I corrected you, Bolhover claimed I was talking nonsense - so he also had to be corrected. And now you are pathetically trying to change things around to make it sound like your first comment was valid. Froth's answer is also nonsense - the OP specifically said "When the sun and moon are simultaneously visible" - so OP was not talking about anyone on the dark side (duh!). So, my answer (which said - precisely - that people on the exact 'other side of the world' when 'sun and moon are simultaneously visible'...can see the sun and moon in different relations to each other in the sky. I answered the actual question that was asked - not some other question as you guys did - and without invalidating what the OP specifically asked for. What's more, I went the extra mile and corrected your collective errors...and I'm in trouble?!?! Bah!  :-) SteveBaker 00:31, 24 August 2007 (UTC)

Hmmm, OK...

1. Now, who said the original question said it couldn't be at dawn? All I said was that without further clarification the logical assumption is that they're asking about the 98% of the time when it's not sunrise/sunset. Now perhaps they did only want a sunrise/sunset answer, but that's nowhere in the question, and has not been clarified any further.
2. I neither flippantly nor incorrectly said the original question was stupid - you're the only one who's mentioned that.
3. Bowlhover might appreciate you getting his name right.
4. I don't know about other users, but I feel that some of your comments are verging on personal attacks, e.g., saying my answers are pathetic. This is not the first time I've noticed this type of behaviour directed towards other users. I would thank you to desist with these actions.
5. Time to cut down on your tirades, and accept that you're not always right, and don't have a monopoly on giving answers. This is not the SteveBaker Reference Desk, it's the Science Reference Desk. --jjron 09:43, 24 August 2007 (UTC)

Ummm, one can see both sun and moon at other times than just dawn and dusk..... (runs away and hides). DuncanHill 00:36, 24 August 2007 (UTC)

You're completely right DuncanHill. It's only in SteveBaker-land that the moon and sun are only ever both visible at sunrise/sunset ;) . --jjron 08:56, 24 August 2007 (UTC)

Don't forget that special circumstance which allows people to see the Sun and Moon not only at the same time, but also in the same space! At this time, the other side of the world is indeed in a dark night (and generally experiencing quite high tide). Laïka 09:59, 24 August 2007 (UTC)

[edit conflict] SteveBaker must be considering the case where the sun and full moon are simultaneously visible. --Allen 10:02, 24 August 2007 (UTC)

Let me try to summarise:

• Most of the time the Sun is not simultaneously visible from two fixed antipodal locations on the Earth - it will be day at one location and night at the other.
• There are two short periods that are exceptions to this - around sunrise and sunset the Sun (or at least part of its disk) may be simultaneously visible at two antipodal locations.
• Similar considerations apply to the Moon - most of the time it will not be visible simultaneously from two fixed antipodal locations. There may be short periods around moonrise and moonset that are exceptions to this generalisation - although the relative neareness of the Moon to the Earth may rule this out too.
• So the only possible times that the Sun and the Moon could both be simultaneously visible from two fixed antipodal locations (even if only in theory) would be when moonrise or moonset conincide with sunrise or sunset i.e. when the moon is close to conjunction or opposition. Gandalf61 10:37, 24 August 2007 (UTC)

Looking back at OP's question, "When the sun and moon are simultaneously visible, how do they appear to people on the other side of the world?"

I don't think the question is asking when or where would one be able to see both sun and moon at 2 opposite positions are earth. The question asks when you can see both sun and moon at the same time, what does the sky look like at the exact opposite position on earth. Seeing both sun and moon can happen most time of the day. I was able still able to see the moon at around 11:30am in chicago during mid-fall. MOST of the time the opposite side wouldn't see either object. But during early sunrises or late sunsets (given you can still see both moon and sun), the other side may be able to see either one or both sun and moon.192.53.187.183 15:25, 24 August 2007 (UTC)

I agree- gandalf's answer is useful but not what the OP was looking for. If one of the antipodes sees the sun and moon simultaneously, what would the other see? Not, "under what circumstances would two antipodes both see the sun and moon simultaneously" --froth^t 16:24, 26 August 2007 (UTC)

Megapixel equivalent of eye

Had a discussion today about the sensitivity of the human eye versus digital camera sensors, VDUs, photographs, etc. We were trying to work out a megapixel equivalent of the human eye. I reckon I came up with a reasonable solution, my friend reckoned I was hugely underestimating. I won't give our figures at this stage, as I'd be interested to see what others come up with independently. What do you think? --jjron 08:35, 23 August 2007 (UTC)

You might want to check out the article on the Eye#Acuity, since it does cover this. Also, keep in mind that the density of photoreceptors differs in parts of the retina, as well as the type of photoreceptor (rod or cone), so comparing the megapixel resolution of a digital camera (which has a constant density across the whole width) to an eye is bound to have problems. -- JSBillings 11:37, 23 August 2007 (UTC)

There are some subtle issues that make direct comparisons with a digital camera tricky:

• The eye has more resolution in the center of its field of view than the edges.
• The edges of your retinas are more sensitive to motion and less sensitive to colour than the center of the field of view.
• Your eye continually vibrates back and forth so that each "pixel" samples the scene in different places which greatly increases the effective resolution for still scenes - but doesn't help much for moving scenes.
• There is the matter of being able to see brightness changes with maybe 4 to 6 times more precision than colour changes.
• All sorts of strange adaptations happen in low light conditions that trade "image quality" for night vision ability.
• We have a continually variable lens on the front end of the eye. This means that those (however many) pixels are sampling a different amount of the world when we are focussing at long distances than at short distances. Because this adjustment is continual and unconscious, it can result in a perception of higher resolution for things closer to the eye than at long distances.

So you just can't come up with a single meaningful number. Do you count the motion due to the vibration of the eyeball? Well, you should if you were deciding the resolution you should print a photograph (say) - but you probably shouldn't bother when planning a movie theatre that's going to show mostly fast-moving pictures. Should you count the monochrome 'pixels' at the edges of the eye? Well, again - "it depends" - those pixels are really good for attracting your attention to potential dangers sneaking up on you from the sides - but terrible at (say) reading a book. That vibration of the eye to improve resolution tends to vanish when you are extremely tired (or sick or drunk) - which is why you may get blurry vision under those circumstances. Black and white pictures can be seen with much, much better resolution than (say) red and green pictures. Switch your Windows colour scheme to red text on a green background and see how long you can stand it! Red and green are about the same brightness - so only your low-resolution colour sensors are helping you out...which makes vision much more blurry than for black and white text.

The whole question is a bit dubious...there just isn't a 1:1 comparison between our eyes and a digital camera. But if this information is not to to be used to settle an argument (or worse still, to win a bet!), I'd say this: In the flight simulation business (where I used to work) we would consider a graphics display of something like 6000x4000 resolution over a 60 degree arc to be roughly "eye limiting resolution" - ie there is no point in making the display sharper than that because the human eye would be unable to see the improvement. So - very, very roughly, 24Mpixels is about it. However, this is a tremendously variable thing and I wouldn't want to be held to that number under all circumstances. SteveBaker 11:41, 23 August 2007 (UTC)

I say roughly 100-200 MegaPixels. Something like 17320 x 11547 digital camera capturing images at 80 times a second. 202.168.50.40 22:25, 23 August 2007 (UTC)

I'm a bit doubtful about that. Suppose we go with (roughly) a 60 degree field of view...at normal reading distance (say 30cm) you'd be able to resolve an object that is 0.3/17320 = 1.7 x 10^-5 meters across. That's 17 microns - you'd be able to see some of the larger bacterium if your eyes were that good. I don't think so. SteveBaker 00:17, 24 August 2007 (UTC)

Hmmm, well the width of human hair ranges from 18 to 180 µm, with an average value of about 80 µm. I personally have no problem seeing a normal human hair from 30cm. Now I may not be able to resolve the very smallest/thinnest ones at that distance, but it's certainly not as absurd as you are trying to suggest. --jjron 08:30, 24 August 2007 (UTC)

Firstly, how do yo know you can see the finest hairs? After all, if you can't see them you won't know they are there! People have very, very fine hairs on some parts of the body. Maybe you can only see the thicker ones. 180um is no problem - you can see that with just 1Mpixel. Are you telling me you can see bacteria? I'm saying that 24Mpixels is reasonable and 100 to 200Mpixels is not. 24Mpixels is only 4x the 'area' resolution of 100Mpixels - just half the linear resolution. So I wouldn't be so surprised if you could see a 34um hair - but I'm pretty darned certain you can't see a single bacterium at 5cm - let alone 30cm. SteveBaker 18:18, 24 August 2007 (UTC)

OK, thanks for answers given so far (no kidding there's lots of complexities to it, I never said the sensitivity of the eye could be directly stated in megapixels; and get down off your high horse, whoever it is that's up on it...sheesh! It's a thought exercise for crying out loud. I thought my original question was pretty clear on that.). Anyway, for the record the answer I proposed was just over 100 megapixels per eye, based essentially on the number of photoreceptor cells. My friend thought it would be more likely in the gigapixel range. Since then though I have also noticed the article on the optic nerve says that the nerve itself contains only 1.2 million nerve fibres, indicating that the retina preprocesses the image before sending it to the brain. This would probably impact the effective sensitivity, i.e., what would get to the brain would not actually be the maximum possible figure that the eye could theoretically detect. Therefore my figure may be too high for the reality of the situation, and what our brain can actually detect may be closer to the figure given by SteveBaker from his practical experience, or possibly even less. Any other thoughts still welcome. --jjron 08:29, 24 August 2007 (UTC)

The optic nerve doesn't transmit pixels - or anything remotely like pixels. It's sending higher level things like "There is a vertical line 20% across from the left and it's moving at such-and-such speed" - the idea that our brain is fed a bunch of pixels is very far from the truth. Hence, you can't deduce anything whatever about resolution from examining the number of nerve fibres. (And even if it was sending pixels - I'd point out that my antenna connects to my TV with just two "fibres" - video and ground - that tells you nothing whatever about its resolution!) SteveBaker 18:18, 24 August 2007 (UTC)

Just noticed this in the eye article - equivalent resolution. Interesting. One calculation gives 81 megapixels, but goes onto to say that the area of sharp vision gained from the fovea is closer to just 1 megapixel. --jjron 08:42, 24 August 2007 (UTC)

Yes, it's an interesting question and odly - one I too was recently thinking about - I wanted to know how many megapixels an EVF would need to be as good as or better than the viewfinder in a SLR - i got 10,000 x 10,000 to be better - 100Mpixels - so I would agree with the 81megapixels figure above .87.102.79.29 13:12, 24 August 2007 (UTC)

where is the sun in google sky?

hi, on google earth "sky" mode.... I cant find the sun (it hasnt gone out has it?)

also how old are the pictures of earth and how often are they updated?

TIA —Preceding unsigned comment added by 91.105.76.65 (talk • contribs) 7:47, 23 August 2007

The images used in Google Sky were collected from telescope images, which don't include the sun. Like the images in Google Earth, they aren't "live" images, but come from archives of images collected by different agencies around the globe, some more frequent than others. Google answers the question of the age of the images in their Help section. -- JSBillings 14:19, 23 August 2007 (UTC)

Now that I think of it, I'm surprised that Google hasn't included high-resolution imagery of the Sun in it's Google Sky, with the option of turning it off. After all, it is a star in our sky. Maybe I'll suggest it. -- JSBillings 14:23, 23 August 2007 (UTC)

Why don't telescope images include the sun?! My telescope can view the sun jus-- I CAN'T SEE!!! AUUUUGGGGGH! :) --Mdwyer 05:15, 24 August 2007 (UTC)

They do have telescope images. They were mostly taken during sun elcipse to get rid of the intense glare. I'm sure it can also be done with some sort of filter though...

Recovering wet electronics

If the interior of a simple electronic is wet, should I dry it until it works again, or slightly longer to ensure no additional water remains? I'm keeping a previously-wet (still wet?) device warm right now with a hair blower even though it became functional half an hour ago. --Bowlhover 14:54, 23 August 2007 (UTC)

Water will rarely destroy electronic devices when there is no electricity running through them. However, it can leave corrosive and/or conductive deposits on the electronics when it dries. For that reason, you should dry the electronics and then clean them (I use rubbing alcohol). -- Kainaw^(what?) 14:58, 23 August 2007 (UTC)

You should probably avoid using a hair dryer to keep the device warm, since it'd probably produce a static charge, plus, heating the electronics can damage the components. Try a normal table fan. -- JSBillings 15:50, 23 August 2007 (UTC)

It sounds like this ship has sailed, but if it happens again, you shouldn't even attempt to turn the device back on until it is completely dry. kmccoy (talk) 16:56, 23 August 2007 (UTC)

Yep - exactly. The best procedure is:

1. Turn off the power, pull out the batteries - as fast as possible! Seconds count!
2. Dab off as much of the liquid as you can with something absorbant like a paper towel. Don't wipe it because you'll spread water from wet areas into dry areas.
3. If the liquid has 'stuff' in it (like a sugary drink for example) - then you may need to wash the stuff off. If so, use distilled water - not tap water. Don't use any detergent or soap...just plain water...and definitely don't used bottled mineral water (the minerals are what we're trying to avoid by using distilled water).
4. Leave it to dry SLOWLY - don't apply heat - don't blow air over it. You'll want to keep it somewhere not too cold - but don't deliberately heat it up.
5. Only after many days - when it's UTTERLY dry - in all the little nooks and crannies - try turning it back on again.
6. If it totally doesn't work - you can try using some of that oily stuff they sell in car parts stores for displacing water from car electrical systems. I've never had any luck with it - but some people claim it worked for them. Definitely a last resort though.

It's a crap shoot though - sometimes it survives - othertimes not. My favorite keyboard died of a diet coke overdose and couldn't be revived - my inkjet printer works just fine after a friends child dumped about a half pint of sticky orange juice inside! I'd never have believed it would still work after I had to pull out soggy paper - and re-wash with fresh, distilled water several times to get rid of the stickiness that pervaded every crevice of that mechanism! SteveBaker 20:01, 23 August 2007 (UTC)

Nobody actually said why to wait until there is no possibility of a drop of water remaining before starting it. The reason is that a drop of water can create an arc and short-circuit the electronics, which will likely cause permanent damage. StuRat 21:18, 23 August 2007 (UTC)

It's not just arcs. What you're really trying to avoid by instantly removing all power and batteries is the movement of ions. For example, you don't want to see all those nasty little chloride ions (from salts) migrating into the guts of the electronics where they'll rapidly murder everything.

It's on this point that I disagree with one bit of SteveBaker's advice: once I'd rinsed away any sticky stuff, I'd use mild heat and/or plenty of air motion to try to dry the circuitry as rapidly as possible. But keep mindful of the idea of mild; lots of electronics won't think well of you above 70°C (the top end of the "commercial" temperature range).

And yes, like so many of you, I rescued something. In my case, it was a TV that was given a drink of egg nog one New Year's Eve; I ended up mechanically removing a lot of the congealed nog the next day.

Atlant 23:10, 23 August 2007 (UTC)

Further to Steve's advice, while I agree that distilled water would be better than tap water to wash away a drink, I'd certainly do it with tap water if I had nothing else available. If the drink dries up in place, it will surely produce more residue than the tap water. --Anonymous, August 23, 22:10 (UTC).

The main reason to chop the power ASAP is because the water connects bits of electronics to other bits of electronics in ways that they were never designed to be connected! Who knows what that might do? Lots of chips are very sensitive to (for example) being driven with negative voltages. Shorting out the power supply ought to just blow a fuse - but these days, fuses cost money - so cheap power supplies are designed to just fail instead. Shorting out a resistor could result in too many volts going to the next device along the chain. Shorting a capacitor could shove a huge spike of current through something down the line - or cause the capacitor to discharge a stored charge suddenly, which might well wreck it. It's unlikely you could get to the power switch fast enough to stop any of those things happening where the circuits are already wet - but water spreads out fairly slowly so if you can cut the juice within just a few seconds, you are definitely improving your chances. The reason to prefer distilled water is that it's less corrosive than water with minerals in it - and also it doesn't conduct electricity anywhere near as well (although you aren't going to turn the thing back on until it's utterly dry - so maybe that doesn't matter. You need to avoid applying a lot of heat to the electronics as they dry because warm water is more corrosive than cold water - and most electronics don't like being overheated (eg with a hair drier). SteveBaker 17:48, 24 August 2007 (UTC)

This thread has prompted me to innovate Dweller's Ref Desk thread of the week award, and I hereby give the inaugural award to those who contributed here. Congratulations. --Dweller 13:00, 24 August 2007 (UTC)

What? No cookies? No barnstar-of-refdesk-goodness? No massive cash prizes? Not even a teeny-tiny penguin to put in the top-right corner of your user page? Where's the incentive here?! :-) SteveBaker 17:36, 24 August 2007 (UTC)

First, shake off any loose drips, then leave to drain (on a draining board) for say 30 mins. If you have a switched on dehumidifier, place the electronics in front of its output and leave there for for 24 hrs. After this time it should be safe for you to reapply power to the circuit. If you have an A/C unit set to dry/cool, this should also work. I have performed this on circuit boards from a TV. Worked perfectly afterwards (the picture ,however, was not noticeably cleaner)--88.109.139.255 18:43, 25 August 2007 (UTC)

The Federal Puke Ray: How does it work?

The government is working on something called a puke ray. http://www.theregister.co.uk/2007/07/27/dhs_chunder_cutlass/ The article claims it just uses light. Anyone know any more about it? I would like to try to build my own. Juanita Hodges 21:29, 23 August 2007 (UTC)

Mythbusters claimed an infrasonic beam could affect the intestines of a person. It did not work when they built it. It would work by shaking the contents loose! Graeme Bartlett 22:35, 23 August 2007 (UTC)

Wasn't there some research done (by the Soviets?) at some point into creating a 'gay beam' and a 'make them shit their pants' beam? --Kurt Shaped Box 22:39, 23 August 2007 (UTC)

I seem to recall the KLF getting hold of some American experimental kit and exploding a cow using sound waves some time ago. DuncanHill 22:43, 23 August 2007 (UTC)

Brown note? Capuchin 06:36, 24 August 2007 (UTC)

On a more serious note, I see we have a Less-lethal weapons article, with some interesting links from the see also section. DuncanHill 22:50, 23 August 2007 (UTC)

• I would guess that one way to do it would be with microwaves: since they (when focused right & all that) heat up water molecules, they should be able to cause serious damage to a gastrointestinal system. --M@rēino 23:01, 23 August 2007 (UTC)

How come it's a "federal" puke ray? I think each state should have its own. ◄Zahakiel► 23:10, 23 August 2007 (UTC)

How absurd. Next you'll be suggesting that each individual state administration should be privy to the records of the CIA's dream-stealing psychoelectronic satellites and the recordings from the microdot cameras hidden in that eye on the back of a dollar bill... --Kurt Shaped Box 23:22, 23 August 2007 (UTC)

Say, are you running for president on 08? ◄Zahakiel► 23:32, 23 August 2007 (UTC)

The news article appeared to claim it was by light, not sound. My neighbors' car stereos already are a sonic attack that cause me so much pain and naseau I nearly puke, but the article said this was with light. Juanita Hodges 01:10, 24 August 2007 (UTC)

Could they be showing the victim sickening images? Also a flashing light at a customized rate around 15 Hertz could cause some interesting effect on people including epileptic fits. Graeme Bartlett 11:47, 24 August 2007 (UTC)

I thought it might be flashing. They did claim there was this specific frequency they hit that did bad things. The TV, computer monitor stuff, etc. is all just red, green, blue stuff and maybe blacks and whites. The sun and light bulbs are all white-yellow variations usually. So it could be a specific frequency of light people don't see. Juanita Hodges 18:11, 24 August 2007 (UTC)

Remember the Sick Sticks in Minority Report? One touch and you'd lose your lunch! I could see a nausea induced weapon if it upset your inner ear and made you dizzy (like sea sickness). Not sure how lights would make you sick unless you were wearing VR goggles and your environment was spinning out of control --24.249.108.133 20:46, 27 August 2007 (UTC)

Which animals sweat?

Horses and humans perspire. Dogs and pigs don't (much). Is there some common thread or selective pressure that makes some animals sweat and others not? Which other animals sweat? Thanks! --Sean 23:11, 23 August 2007 (UTC)

The body surface-to-mass ratio might have a hand in that. If the animal is too large to efficiently siphon off heat, the skin is as good a place as any to get rid of the excess. ◄Zahakiel► 23:19, 23 August 2007 (UTC)

There was an article on sweat not long ago in the New York Times Science section titled "sweatology" or something like that. The basic drift of it as I understood it is that humans are actually pretty unique in this regard, and our copious, full-body sweat glands are among the reasons we can tolerate so many climates. One of the other interesting facts in the article is that while human internal temperatures can regularly be lowered without too much ill effect (hypothermia, but there are some professions where that occurs all the time), but if you raise the internal temperature by just a few degrees you get delusional and often quickly die. Ergo the importance of sweat glands, etc. --24.147.86.187 23:42, 23 August 2007 (UTC)

The lack of thick body hair on humans makes sweating work better. The question should really be why horses sweat. It does seem to cause them problems, as a horse that runs hard in cold weather gets soaked with sweat, then gets cold when it stops running. Perhaps being bred by humans has increased their tendency to sweat, as humans are likely to ride them hard (for which sweating helps to keep them cool) and then keep them warm (say in a barn with a blanket on them) and provide water. Thus, those which sweat profusely were more likely to survive with humans than they would on their own. StuRat 00:24, 24 August 2007 (UTC)

That happens with humans too - they always tell you that in arctic conditions, it's essential not to over-exert yourself to the point where you start to sweat because the moment you stop exercising, you die. SteveBaker 15:22, 24 August 2007 (UTC)

The article Sweat says that "Primates and horses have armpits that sweat similarly to those of humans." -- WikiCheng | Talk 06:15, 24 August 2007 (UTC)

One source states pigs can only sweat 3% the volume we can. Bendž|Ť 08:08, 24 August 2007 (UTC)