Wikipedia:Reference desk/Archives/Science/2008 June 16

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June 16

Course of the moon in the sky

From the chair I habitually sit in to watch tv, I can sometimes see the moon in the small area of sky visible through an uncurtained window in the room. I've noticed, when visible, that night after night it moves across the sky in the same direction, but each night it gets lower (or higher, I forget which). And when I see it, it always seems to be a full moon. My questions please 1) Is there a diagram anywhere that shows how the moon moves across the sky, and how this changes night after night? 2) Does the full moon tend to go through the same part of the sky each month? Or can it be anywhere? Thanks 80.0.111.219 (talk) 01:15, 16 June 2008 (UTC)

Most star charts should show the course of the moon - I find http://www.heavens-above.com/ very good, it shows the location of the moon at any date and time you give it (although I don't think it can give comparisons between different times on one chart - you should be able to find a chart that will, though). It will go along pretty much the same course each month, relative to the background stars (there are a few very small changes, but probably nothing noticeable to the human eye over the scale of quite a few years). --Tango (talk) 01:36, 16 June 2008 (UTC)

Thanks, but as I cannot see any stars due to light pollution, it is the course of the moon compared to my fixed view that interests me. 80.2.202.167 (talk) 22:40, 18 June 2008 (UTC)

Stellarium is an excellent sky chart program. Also, YourSky may be a little more user-friendly. --Russoc4 (talk) 02:59, 16 June 2008 (UTC)

For the second part of the question, the moon roughly follows the path of the sun (the ecliptic) as do the planets. However, the ecliptic moves around relative to the observer because of the rotation of the earth. The result is that the moon is lower in the sky in the summer and higher in the winter (unlike the sun), but of course it always rises in the east, culminates in the south (if you live in the northern hemisphere) and sets in the west. The full moon is always opposite the sun, so it will always rise at sunset and appear in the eastern sky in the evening.--Shantavira|^{feed me} 05:58, 16 June 2008 (UTC)

Thanks. So the moon keeps revolving over the same part of the sky, apart from the seasonal tilt, if its full or not? I expect the raising or lowering of the track of the moon must be due to its gradually changing position each night as it revolves around the earth every lunar month. Or have I got it wrong - it a lunar month the time the moon takes to go arounsd the earth, or just the time between full moons, or are these the same? Are there any parts of the sky the moon will never appear in, such as near the star Polaris? 80.2.203.46 (talk) 11:24, 16 June 2008 (UTC)

See Lunar month - there are different definitions. The time it takes to go around the Earth with respect to the background stars is the "sidereal" month, the time between consecutive full moons is "synodic" month, and is just over 2 days longer, due to the Earth orbiting the Sun. The course of the moon relative to the background stars is pretty constant (what phase it will have at each point varies depending on the time of year), and it will always be near the ecliptic. So, it will never go anywhere near Polaris, you're correct. --Tango (talk) 15:26, 16 June 2008 (UTC)

Let's amplify the bit about "the course of the moon relative to the background stars is pretty constant". The plane of the Earth's orbit around the Sun is called the ecliptic. The Moon orbits the Earth in a plane that is inclined by just over 5° relative to the ecliptic, but the direction of this 5° inclination changes, rotating in a cycle 18.6 years long. This change is a type of precession. So if on a certain date the Moon passes in front of a certain star, then if you wait for that date 9 years later and wait for the Moon to get to the same part of its orbit, it may miss that star by as much as 10°. Within a person's lifetime this cycle will happen several times and so the Moon may be seen anywhere within a band of sky 10° wide, relative to the stars, centered on the ecliptic plane.

(The ecliptic is itself inclined at about 23.5° relative to the Earth's equator, and this inclination also precesses on a much slower cycle of about 26,000 years. This motion changes which star is the North Star, for instance. So over thousands of years, the Sun may be seen anywhere in a band about 47° wide and the Moon anywhere in a band about 57° wide, both bands centered on the plane of the Earth's equator.)

One more thing. The intersections of the Moon's orbital plane and the ecliptic determine when solar and lunar eclipses happen. If the Moon happens to be full when it's near the intersection of its orbit with the ecliptic plane, then there is a lunar eclipse. If it's new, there is a solar eclipse. In each case if it's very near the point of intersection, the eclipse is total or annular; if not so near, it's partial. Thus there are "eclipse seasons" about twice a year when a lunar and solar eclipse may happen two weeks apart, and the rest of the year no eclipses are possible. For example, according to Fred Espenak's excellent eclipse web site, the eclipses for 2008 are:

• 2008 Feb 07: Annular Solar Eclipse
• 2008 Feb 21: Total Lunar Eclipse
• 2008 Aug 01: Total Solar Eclipse
• 2008 Aug 16: Partial Lunar Eclipse

The precessional changes in the Moon's orbit mean that the eclipse seasons shift a bit earlier each year. By 2010 they will be in December/January and June/July. After 9 years they will have cycled halfway around and will be in February and August again.

--Anonymous, 22:06 and 22:15 UTC, June 16, 2008.

Hi. Also, the moon tends to rise and set an hour later one day than the last. The full moon will tend to be highest at around midnight, with cresent moons closer in apparent position to the sun. If the moon's cresent forms a C or backwards D, the cresent is becoming smaller ("croaking" or waning), and usually appears in the morning. If the cresent is a D or backwards C, it is growing and usually appears in the evening. If the moon is appearing late at night, usually it will generally be higher in the winter than in the summer, and vice versa if it appears in daytime. Hope this helps. Thanks. ~AH1^(TCU) 22:26, 16 June 2008 (UTC)

The part about C and D shapes would be applicable if you're in the Northern Hemisphere, but reversed in the Southern. --Anon, 17:45 UTC, June 17.

Using very short people as astronauts

If people half average height and one eighth average weight (assuming all dimensions halved) were used as astronauts, could the size of space rockets be reduced proprtionately, so you'd only need a rocket an eighth the usual size? Hence saving a lot of money. 80.0.111.219 (talk) 01:23, 16 June 2008 (UTC)

You could probably make some savings, but nowhere near 7/8. Most of the (non-fuel) weight of the rocket is the engines, structure, whatever is needed for the mission, life support systems, etc. The astronauts are a minute portion of the total mass and you can't just scale down everything else. Making something smaller generally costs a lot more, more than you would save on fuel. It may not even be possible to make some things smaller - they have to be a certain size to do their job. --Tango (talk) 01:30, 16 June 2008 (UTC)

I don't agree. If the stated assumption was correct, that you could have astronauts that weighed 1/8th as much, then you could possibly make a rocket to launch them that would weigh 1/8th (or very close to 1/8th) as much. Let's discuss each of the items Tango listed:

1) Life support systems: I'd expect a person with 1/8th the mass to use around 1/8th the amount of oxygen, produce around 1/8th the amount of carbon dioxide to scrub, urine to process, and feces. It would be reasonable, then, to say that the equipment needed to process these reduced quantities could be reduced accordingly.

2) Structure: The structure can be reduced in proportion to the contents.

3) Engines: They can also be reduced in proportion to the mass they need to lift.

4) "Whatever is needed for the mission": This gets a bit tricky. Some items can't be reduced at all, like the Hubble Telescope, as reducing the diameter of a telescope reduces it's light gathering power. So, if launching the Hubble was the mission, you're out of luck here. However, if the mission was to observe the changes that occur in astronauts in space, then all the equipment, like the treadmill and blood pressure cuff, could also be reduced accordingly. It would depend entirely on the mission whether the items could be scaled down.

Sure, all those things can be reduced, but can they be reduced proportionally? I doubt it. At least, not without a massive increase in cost. --Tango (talk) 15:19, 16 June 2008 (UTC)

Does a model train cost massively more than a full-sized train ? Only when you reach a certain threshhold of "smallness" does cost go up. Half scale wouldn't normally hit that threshold, with the exception of some electronics that are difficult to reduce further in scale as they are already at the minimum size possible using current technology. Also note that many half-scale items already exist, designed for children, like clothes and chairs, so could be purchased "off-the-shelf" for little money. StuRat (talk) 18:15, 16 June 2008 (UTC)

Note, however, that a person half as tall isn't really going to weigh 1/8th as much, since they wouldn't be 1/2 as wide and 1/2 as thick. Dwarves always look "stout" precisely because the reduction in height is not matched by a corresponding reduction in other dimensions. Their heads, for example, tend to be very close to the size of average-sized people's heads. StuRat (talk) 02:00, 16 June 2008 (UTC)

Thanks. The second-ever satellite had a dog in it, which would not have weighed much compared with a human. I do not know what the rocket size was compared to the first astronauts, although the dog-rocket may have been designed with the capacity to lift humans in mind. 80.2.203.46 (talk) 11:09, 16 June 2008 (UTC)

In the infancy of the space age, pre-astronauts and cosmonauts, right after Sputnik, Hugh Walters wrote Blast Off at Woomera (1957), ("Blast off at 0300" in the U.S.) about a moon rocket launched by the "United Nations Exploration Agency" which carried 17 year old Chris Godfrey, an English boy who was only 4 feet 10 1/2 inches tall, making the whole spacecraft able to launch with less booster power than for a 6 foot test pilot. Woomera Australia was the launch site. Walters was a member of the British Interplanetary Society and tried to keep the science accurate. Pretty good juvie sci-fi. Edison (talk) 19:03, 16 June 2008 (UTC)

So how big a rocket would you need to launch a hamster, ant, or bacteria into space? 80.2.207.210 (talk) 20:23, 16 June 2008 (UTC)

There has to be a point of dimishing returns as you make the rocket smaller.I can't picture a rocket the size of a pencil (or toothpick) getting into space at all, even with nanotechnology used to make the pumps, servos, etc. Why does it seem a rocket must be a certain minimum size (V2 or larger) to reach orbit? Edison (talk) 03:16, 17 June 2008 (UTC)

Wind resistance. Cross-sectional area (and to a first approximation, wind resistance) increases as the square of size; available thrust increases as the cube. --Carnildo (talk) 21:27, 17 June 2008 (UTC)

also, alot of fuel needs to be carried along. tiny rocket = tiny fuel volume. Doesn't get you far. --Shaggorama (talk) 05:41, 18 June 2008 (UTC)

Blue skin on a Budgerigar's nose

By what process does the skin on the nose of a male budgerigar become blue? Does it involve an accumulation of copper compounds beneath the surface? I always wondered about that. —Preceding unsigned comment added by 90.242.157.1 (talk) 01:45, 16 June 2008 (UTC)

No. There is no known blue pigment in birds (in fact, blue pigment is extremely rare in the entire animal kingdom with only two species of fish known to have cyanophores). While the basis of the blue colour in male budgerigar cere has not been studied specifically, the way blue colour is generated in birds is well known. In birds (and indeed, in mammals) blue is generated by coherent light scattering: specifically by hexagonally organized arrays of collagen fibers in the dermis. Underneath the fibres are melanocytes (black/brown melanin containing pigment cells) that gives the base colour. The fibres on top create the colour by scattering the light, which effectively "skews" the base colour to our eyes. There is a very nice scientific review of blue colouration in animals: [1] Rockpocket 05:17, 17 June 2008 (UTC)

want to know how to figure out isotope half life

using diagnostic or therapeutic methods of a very old dead like mummy —Preceding unsigned comment added by 70.234.104.170 (talk) 02:35, 16 June 2008 (UTC) only info i have is c14 for isotope and a half life of 5730yrs —Preceding unsigned comment added by 70.234.104.170 (talk) 02:37, 16 June 2008 (UTC)

Have you read our article on radiometric dating? It explains the general concepts, including Carbon-14 dating. — Lomn 03:20, 16 June 2008 (UTC)

Natural sleeping position

I've heard that in the late Middle Ages it became the custom to sleep sitting up. Could it be that how we sleep is determined by culture? 217.168.0.72 (talk) 04:21, 16 June 2008 (UTC)

I understand that in a castle for example, most people did not have bedrooms or beds but slept in the great hall with lots of other people. Hence the sitting up, perhaps because it was crowded and the floor not very nice to lie on (old food, dog-do, spit, vermin etc). Nobody recorded what the peasants did. Monks seemed to have their own beds as far as I am aware. 80.2.203.46 (talk) 11:15, 16 June 2008 (UTC)

OP: Where did you hear that? Wierd. I think there's more to it than culture. I can't speak for everyone, but I find it difficult to sleep sitting up unless I'm watching TV or being lectured, and even then my body tends to find its way downward. I think it's pretty natural to want to sleep lying down; allegedly the impulse was strong enough to kill John Merrick (of course, it's been suggested that his desire to sleep reclining may have been due largely to social pressure). Physiologically, it may have something to do with the increased activity of the brain during sleep: it takes less effort to pump blood to the brain if the head is level with the heart. It's worth noting that many animals also lie down or curl up on the ground to sleep. --Shaggorama (talk) 05:51, 18 June 2008 (UTC)

special relativity

shanu 09:00, 16 June 2008 (UTC) Suppose two twins A, B are on a platform near earth. C is another person of same age but his platform is near mars. B travels from earth to mars. When B starts his journey, all the persons start their clock. when B reaches on platform of C, C should expect that B should measure less time(due to time dilation)then him. But if we see the situation from B^,s reference frame, A and C have done journey. Therefore he expects C measures less time. But B and C both cannot measure less time! How can we resolve this contradiction?

Have you read the Twins paradox article ? SpinningSpark 09:22, 16 June 2008 (UTC)

I know abot twin paradox. But in that excuse is given that one person is 'accelarating'. but in this all are in inertial frames(non-accelarating). Thus we cannot apply this excuse. —Preceding unsigned comment added by Rohit max (talk • contribs) 09:40, 16 June 2008 (UTC)

B and C do both observe the other to have measured less time. There's no contradiction unless B actually slows down to be in C's frame at the end, in which case he's been accelerating and the symmetry breaks. Algebraist 10:04, 16 June 2008 (UTC)

There is no objective "now" in special relativity. The result depends on which point of reference A and C where using to synchronize their clocks. If everyone starts their clocks at the same time from A and C's perspective, then when B gets to C, C's clock will be ahead, but from B's perspective, that's just because C started his too early. Get it? — DanielLC 14:40, 16 June 2008 (UTC)

How does a canon work?

hai friends, can u please tell me as to how a canon, which were being used in wars in olden days, works? And what was/is there inside the iron ball? Bye. Kvees. —Preceding unsigned comment added by 59.178.100.105 (talk) 09:02, 16 June 2008 (UTC)

Take a look at our cannon article. Early cannons did not have any explosive inside the ball. It was solid iron, or even stone in some very old ones. They did damage purely through their kinetic energy. The explosive (gunpowder) is packed into the cannon barrel and propels the cannonball forward under the high pressure caused by the restricted space. It was many centuries after they were invented before the ammunition started to be packed with explosives, compare shrapnel shell with case-shot and canister shot. Don't try this at home. SpinningSpark 09:39, 16 June 2008 (UTC)

There was also hot shot, where a solid cannon ball was heated first, so it would start a fire when it hit the target. The earliest cannons were fired by holding a torch against a small hole in the end so the gunpowder would detonate. There was also the precursor to the handgun, the hand cannon, which was a small, portable cannon. StuRat (talk) 13:13, 16 June 2008 (UTC)

And of course, from the hand cannons came muskets. Or something. But they're the same concept, more or less. --Wirbelwindヴィルヴェルヴィント (talk) 20:40, 16 June 2008 (UTC)

Noble Gases

Can noble gases form compounds under extreme conditions of temprature and pressure? If yes how? —Preceding unsigned comment added by Rohit max (talk • contribs) 10:12, 16 June 2008 (UTC)

Noble gas compound 193.190.253.149 (talk) 10:21, 16 June 2008 (UTC)

Notably, Xenon hexafluoride and Xenon trioxide.

Atlant (talk) 13:36, 16 June 2008 (UTC)

Autism

Does autism affect the age that one lives to? Interactive Fiction Expert/Talk to me 10:40, 14 June 2008 (UTC)

No, not much and not directly. It can affect how one lives their life and make certain causes of death more likely because of their choices but as a disease it will not kill you. Regards, CycloneNimrod ^talk?_contribs? 11:43, 14 June 2008 (UTC)

(edit conflict) Autism absolutely effects the age one lives to. As CycloneNimrod has pointed out, autism does not kill directly, but life expectancy is significantly decreased for autistics [2]. Significant death factors include high susceptibility to accidents, respiratory distress and seizures [3] indicating that in a way the condition does often cause the demise of the individual.

Moreoever, I disagree with the claim that autism is a disease; it is better described as a condition, or disorder: autism is a developmental problem that appears to be genetic[4], it is generally not believed to be caused by external vectors except in the case of factors that increase the chances of birth defects[5]. --Shaggorama (talk) 06:40, 15 June 2008 (UTC)

I'd have to disagree, autism is certainly a disease. Reading the article 'disease' will give you a good reason why. Mental disorders are classed as diseases and although autism is congenital, that does not stop it being a disease. It's a common misconception that diseases have to be contagious, that is not the case. Regards, CycloneNimrod ^talk?_contribs? 14:36, 15 June 2008 (UTC)

Many people would disagree with classifying autism as a disease, or even as a disorder. Condition tends to be more accepted. Of course, there are all sorts of things that some people consider 'mental disorders' and hence diseases which other people consider at most a 'condition' if not normal variation. To say it is 'certainly a disease' is to pick a side in an often contentious debate. 79.66.60.129 (talk) 16:52, 15 June 2008 (UTC)

A disease is defined as "The term 'disease' refers to any abnormal condition of an organism that impairs function." according to Wikipedia, or for other sources try this one: "A condition of the body in which there is incorrect function due to heredity, infection, diet, or environment." or this one "a general term describing a morbid condition which can be defined by objective, physical signs (e.g. hypertension), subjective symptoms or mental phobias, disorder of function (e.g. biochemical abnormality), or disorders of structure (anatomic or pathological change).". Autism is certainly a disease, whether you wish to class it as something as as well is your choice, but it honestly does fit the criteria since autism is an impairment of human functioning. Regards, CycloneNimrod ^talk?_contribs? 17:37, 15 June 2008 (UTC)

I am not a doctor, but I seem to recall that the term "disease" used to only apply to conditions caused by an external organism (ie. bacteria, virus, etc.). That was a much cleaner distinction. The definitions cited above make anything short of physical injury a disease. — The Hand That Feeds You:^Bite 18:04, 15 June 2008 (UTC)

Strictly speaking anything which impairs human function (whether it be a congenital condition, by virus, bacteria etc) is a disease. Condition refers to a state of being, disease means that something is wrong. Look at any dictionary definition you like (assuming its credible) and you'll come up with the same findings. Google 'Define:disease'. Regards, CycloneNimrod ^talk?_contribs? 19:20, 15 June 2008 (UTC)

Talk about opening up a can of worms! Well, after poking around a little at the medline plus dictionary maintained by the US National Library of Medicine, it looks like the problem we've uncovered here is that there isn't any clear distinction between the terms "condition," "disorder," and "disease," although there seems to be a pseudo-consensus here on their meanings relative to each other. For posterity sake, here are the Library of Medicine definitions:

• Disease: an impairment of the normal state of the living animal or plant body or one of its parts that interrupts or modifies the performance of the vital functions, is typically manifested by distinguishing signs and symptoms, and is a response to environmental factors (as malnutrition, industrial hazards, or climate), to specific infective agents (as worms, bacteria, or viruses), to inherent defects of the organism (as genetic anomalies), or to combinations of these factors
• Disorder: an abnormal physical or mental condition
• Condition: a usually defective state of health <a serious heart condition>

By these definitions, it appears to me that autism satisfies the conditions for all three of these. Really I don't think there's a clear difference between these terms, at least not as they are formally defined, although there are more articulated differences in their use. --Shaggorama (talk) 21:50, 15 June 2008 (UTC)

Well, the question I'm really asking is "who is the oldest autistic person ever and how old did they live to?". Interactive Fiction Expert/Talk to me 10:18, 16 June 2008 (UTC)

I think the best answer is 'no one knows'. I don't know if anyone even keeps track of these sort of things and someone's medical conditions is usually consider private. Plus there are obviously many many autistic people who were never identified as being autistic. See for example, people speculated to have been autistic. Nil Einne (talk) 10:59, 16 June 2008 (UTC)

So you're saying cancer and heart disease and diabetes and sickle cell anaemia and rickets and gout are not diseases? Because all our articles describe these as diseases as I suspect would most doctors... Nil Einne (talk)

My point exactly :) Regards, CycloneNimrod ^talk?_contribs? 13:54, 16 June 2008 (UTC)

I really don't want to get into this, as it's an ongoing political debate between various parties, but which word you use to describe various 'conditions', such as being on the autistic spectrum or showing a sexual preference for people of your own gender, is not as straightforward as some have suggested above. Assuming that it is is likely to cause problems if you find yourself discussing these issues with anyone they apply to. If you read the various definitions above, you will notice that some assumptions are necessary to apply these definitions to the situations. I'm not trying to change the mind of anyone who has made theirs up, and I'm not going to discuss this further as I don't think it will be productive or what the desk is for, but I felt I needed to put this here to help people avoid putting their foot in it in certain situations. 79.66.45.237 (talk) 14:50, 16 June 2008 (UTC)

Well I understand why some people dislike the characterisation of autism as a disease, the fact remains, disease are clearly not only things caused by an infective agent, at least I suspect in the eyes of the vast majority of the worlds population Nil Einne (talk) 16:07, 16 June 2008 (UTC)

Nobody was suggesting they are; I think you have missed the point :) 79.66.45.237 (talk) 17:06, 16 June 2008 (UTC)

<outdent> "I am not a doctor, but I seem to recall that the term "disease" used to only apply to conditions caused by an external organism (ie. bacteria, virus, etc.)." That is exactly what somebody was suggesting. Regards, CycloneNimrod ^talk?_contribs? 17:11, 16 June 2008 (UTC)

Yeah, I was just about to go back and edit my last comment because some people do seem to have said that. Sorry about that. None-the-less, my last comment was merely meant to suggest that that is not at all the point when it comes to labelling something like being on the autistic spectrum as a disease. But there we go. 79.66.45.237 (talk) 17:14, 16 June 2008 (UTC)

Except it is entirely the point! It is an impairment of human mental function, this means it is a disease whether you like how that comes across or not. You can call it a disorder, that fits too, or a condition, that also works, but it is a disease. I don't see how anyone can disagree with that since it fits the very definition of disease. Regards, CycloneNimrod ^talk?_contribs? 17:46, 16 June 2008 (UTC)

Oh good Lord. 'Impairment', 'defective', and you don't see the issue? Never mind. Change is slow and there are many people in the world. 79.66.45.237 (talk) 18:59, 16 June 2008 (UTC)

It is not my job to censor the truth. Autism is a defect and causes impairment, there is absolutely no denying that. You can be more sensitive if you wish and call it a disorder or condition, but anything you use will still imply that an autistic person has something different from the norm. I hope to be a doctor and I have no intention of telling anyone that they can't live up to be as good as anyone else but it is the truth that autism is a disease. Regards, CycloneNimrod ^talk?_contribs? 19:55, 16 June 2008 (UTC)

Different from the norm is not the same as defective or diseased or impaired. A gay person is someone different from the norm, and when they live in a society that treats it as a disease it reduces their quality of life. That doesn't make it a disease. Having an exceptionally high IQ is different from the norm, and can reduce someone's chances of 'success' in life. It can impair their ability to interact with others. Doesn't make it a disease. Having an exceptionally low IQ is different from the norm and can make someone's life harder and shorter. Doesn't make it a disease. Certainly you would not expect to see 'high IQ' and 'low IQ' listed as diseases. Being a long way along the autistic spectrum certainly is a disadvantage in terms of achieving success in life and interacting with others, and different from the norm, but it doesn't make autism a disease. Given you are fairly smart, and particularly if you are hoping to be a doctor, I would have expected this to be blindingly obvious. 79.66.45.237 (talk) 22:35, 16 June 2008 (UTC)

You are right to an extent. Someone with an exceptionally high or low IQ is not diseased, however, if there is a cause behind that IQ then they may very well be diseased. Mental retardation is listed as a disease and it features a low IQ. A high IQ wouldn't be classed as a disease because, even if it doesn't allow perhaps as good social interaction with others, biologically it makes little difference. Autism on the other hand consists of signs and symptoms, again read the article, and is often in the forefront of the news about research in trying to find a cure. This word cure alone means that it is classed as a disease by the medical profession because it is looking to be fixed. I do see it as blindingly obvious that different to the norm is distinct from being a disease, otherwise all of us would be diseased, but different to the norm BIOLOGICALLY and with signs and symptoms, that is a disease. Regards, CycloneNimrod ^talk?_contribs? 10:58, 17 June 2008 (UTC)

Allright guys, this has gone on long enough. I'm going to reiterate my previous comment: the terms disease, condition, and disorder are ambiguous relative to each other although we do not use them itnerchangeably. Per definition alcohol intoxication could be considered a disease, but that's just stupid. At low levels, it certainly causes significant impairment, but we don't even consider it poisoning. I think the deal is that once one of these three terms is applied to an ailment it becomes convention and sticks. Beyond that, there seems ot be a bit of "I know it when I see it" attitude towards them. That's it. No clear distinctions. --Shaggorama (talk) 06:03, 18 June 2008 (UTC)

Now that I can trust I will write nothing else, I will put this link here. Sociological_and_cultural_aspects_of_autism. 79.66.85.219 (talk) 11:56, 19 June 2008 (UTC)

Ants in my Car

There are ants in my car and I see them every single time I get in my car, near the dash and near the passenger and driver side doors. I assure you there are no food or traces thereof in my car. Nor water. My car is clean and I don't eat in it. How in the heck are they surviving? What could they possibly be eating in order to survive. It's creeping me out! --Anthonygiroux (talk) 13:38, 16 June 2008 (UTC)

They could be eating paper, glue, insulation, etc. This could be quite dangerous as they could distract you while driving and cause an accident. I suggest a bug bomb, which should work well in such an enclosed area. Let the car air out and drive with the windows down after use. StuRat (talk) 18:08, 16 June 2008 (UTC)

Driving Ms Smokesalot

Yesterday I was driving with my cousin who is quite a serious smoker. He was in the front passenger seat and I was driving - nobody in the back. What would be the best way to ensure that I breath as less smoke as possible? It was too cold to open the windows more than three quarters of the way up. But I did notice that when my window was slightly less opened than his, there was a significant difference. Does that make sense? When my window was closed and his open it was - as expected - really bad. Surprisingly, the fan on plus the back windows open didn't make much of a difference. We were travelling at about 110km/h and it wasn't very windy outside. Zain Ebrahim (talk) 13:55, 16 June 2008 (UTC)

Well, the easiest way to breathe the least smoke is to ask your cousin to butt out in your car. If you're too ashamed of your selfish interest in clean lungs, then you can make an appeal to greed—tell her that you don't allow smoking in the car because you're trying to preserve its resale value.

If you're not comfortable with being honest and sticking up for yourself – or your cousin isn't polite enough to delay her smoke – then you're just going to have to fiddle with the windows and vents until you find something tolerable. Airflow inside a moving car is probably a chaotic system that will be sensitively dependent on the position of the windows and vent blowers, as well as on vehicle speed and the presence of any crosswinds. TenOfAllTrades(talk) 14:25, 16 June 2008 (UTC)

I agree with ToAT's first point. Also presuming it was your car, I suggest you reconsider in the future whether he is allowed to travel in it or at least extract a promise before you take him in the future not to smoke. I understand this can be difficult in a family situation but remember it is your car, and your health! Nil Einne (talk) 16:03, 16 June 2008 (UTC)

(ec) Sounds to me as if this is a demonstration of Bernoulli's principle. The air moving relative to the car causes low pressure outside. So smoke tends to get sucked out the window. But if your window is open slightly less, the vacuum on your cousin's side is greater than on your side allowing a smooth flow of air away from you. On the other hand, closing your window or opening it fully is likely to cause turbulence inside. By the way, you refer to your cousin as "he" but the title of the question is "Ms". Is your cousin confused? SpinningSpark 14:33, 16 June 2008 (UTC)

Lol - he's not. The title was a (lame) "play" on Driving Miss Daisy. Thanks for the answers, Zain Ebrahim (talk) 15:33, 16 June 2008 (UTC)

Did you mean "Driving Over Miss Daisy"? Maybe you should see the movie "My Cousin Smokey". I think the easiest way to keep the cousin from making everybody's life miserable is to lock him up in the car's trunk. -- Toytoy (talk) 16:03, 16 June 2008 (UTC)

Second what Spark said. Make sure your window is open less than your cousin's so that airflow will tend away from you, if your cousin's is open less than the smoke will blow toward you and confound your efforts. Another method that may work is turning on the fan of your air conditioner (the air conditioner itself does not need to be on) and cracking your windows (perhaps 1 inch or so). This will create a positive pressure situation inside your car that may force the air out directly without creating much of a cross breeze. EagleFalconn (talk) 15:50, 16 June 2008 (UTC)

I would NEVER allow anyone to smoke in my car. I'd even make them go air the smoke out of their stinky clothes before allowing them in my vehicle. However, if you insist on tolerating this assault on your health and senses, I suggest you crank up the heat to allow you to open the windows further. Either that or get an antique car with a rumble seat for Mr Stinky. StuRat (talk) 18:02, 16 June 2008 (UTC)

You can always negotiate pit stops for him to smoke, but personally, even when I was a smoker, I never smoked in the car, and didn't let anyone else either. --Wirbelwindヴィルヴェルヴィント (talk) 20:35, 16 June 2008 (UTC)

As a current smoker (not proud of it), I would abide by any rules set down by the driver. Family or otherwise. If they said "no smoking" then grand, I wouldn't find it offensive at all to be asked to refrain. So I think you should just ask him; smokers are very accomodating people :-) I would never smoke in anyone's car unless they invited me to (window open, naturally) do so. (but if somebody asked me to air out my clothes before getting into the car, then I'd reconsider my travelling company; sorry StuRat ;-) ). Fribbler (talk) 01:07, 17 June 2008 (UTC)

Speculative probe

Given our current knowledge and allowing for the development of not too hard to reach technology (say in the next 10 or 20 years), how long would it take for an unmanned probe to reach a star 50 light years away? 200.127.59.151 (talk) 17:20, 16 June 2008 (UTC)

A hell of a lot longer than 50 years, that's all I can say. Regards, CycloneNimrod ^talk?_contribs? 17:44, 16 June 2008 (UTC)

I can imagine spaceships with linear particle accelerator drives and nuclear reactors for power that could approach the speed of light, maybe in the 20 year time frame. Those would take a bit over 50 years to make the trip there, and over 100 to send back pics and data. However, I don't expect the desire for short-term return on investments to disappear by then, so I doubt if anyone would pay for a mission with no benefits during their lifetime. A visit to a closer star, say Proxima Centauri, might be more realistic in that time frame, though, with pics and data coming back in a dozen or so years. I agree that such ships would be unmanned. StuRat (talk) 17:51, 16 June 2008 (UTC)

A bit? Surely taken the fact that approaching the speed of light is still likely to be quite far off (otherwise relativity is going to come into play, no?) suggests it's more then a bit? 70 years seems more realistic to me. And where did you get the 100 to send pics and data? Surely the probe is not going to wait for a signal from earth before it sends data? Nil Einne (talk) 18:29, 16 June 2008 (UTC)

I think he was saying that it would take over 50 years to get there and it would take over another 50 years for the data to get back. Zain Ebrahim (talk) 19:17, 16 June 2008 (UTC)

Dreamer. To get a 50 lb (22 kg) mass to half the speed of light requires the energy equivalent of the entire output of 1 GW reactor summed over 15 years. For scale, 1 GW is about the electricity consumption of a little less than 1 million households. No matter what you are imagining, there is no way that foreseeable technology will be able to compress power generation enough to allow near light speed travel for useful masses. Dragons flight (talk) 18:49, 16 June 2008 (UTC)

P.S. The fastest spacecraft ever launched reached 0.02% of the speed of light ... by diving straight at the sun. Dragons flight (talk) 19:22, 16 June 2008 (UTC)

Let's try a little thought experiment. Let's assume for the sake of argument we can launch a probe now (2008) that can reach 10% lightspeed. This means it will take 500 years (2508) to reach it's destination. But in fifty years time we might well have increased that speed to 20% lightspeed - which means a probe launched fifty years later (2058) will arrive before the first (2308) and so on and so forth. Add in the fact that the rate of technological process is accerlerating I'm sure you can see the problem. It's only worth sending such a probe if it can reach the destination faster than we can supercede the speed of it with the next generation of probes. It's the same paradox that renders a generation ship useless. Exxolon (talk) 19:10, 16 June 2008 (UTC)

That assumes a 100% chance a faster technology will be developed. You can't wait 50 years because something better may come along, because then you'd just end up not going. 192.45.72.26 (talk) 20:39, 16 June 2008 (UTC)

But isn't that precisely the problem? No one is going to spend billion or trillions developing a rocket to go somewhere when they resonably expect someone else in 50 years time will develop a rocket that will beat them to the punch. Nil Einne (talk) 01:44, 17 June 2008 (UTC)

The basic formulae are in the article Relativistic rocket. With ²³⁵U fission fragments the I_sp is 0.04 c (and if you stop the fragments and convert the energy to light or use it for accelerating particles to higher speeds, things will get worse). For a single-staged 0.5 c spaceship you need a mass ratio of 920483, which is of course not realistic. Icek (talk) 21:05, 16 June 2008 (UTC)

Don't know about advanced technology, but I'll just note that for current technology the record for fastest man-made object is one of the Helios probes, launched in the '70s, which clock in at 70.2 km/s. At that rate of speed, they would reach the 50ly mark in a tad over 210,000 years. Voyager 1 is the man-made object with the largest absolute velocity away from the sun, at 17.1 km/s. At this rate, it would take a bit more than 875,000 years to make 50ly out. -- 128.104.112.147 (talk) 23:13, 17 June 2008 (UTC)

Helios was the fastest, but accelerated mainly by sun's gravity - doing the math you'll get a speed of about 24 km/s at its aphelion (at about 1 AU, i.e. at Earth's distance from the sun), which means that it needed only about 6 km/s of hyperbolic excess velocity with respect to Earth (Earth is traveling at about 30 km/s). New Horizons was directly launched into a solar system escape trajectory, for which you need more than 12 km/s hyperbolic excess with respect to Earth (sqrt(2) * 30 km/s - 30 km/s, you should be able to find all the formulas in Orbital mechanics), setting a record for the velocity gained by initial rocket propulsion. The solar hyperbolic excess velocities of the 4 Pioneer and Voyager probes are nevertheless larger than New Horizons', because they gained more speed from their encounters with Jovian planets. The solar hyperbolic excess velocity (v_∞ for short) of New Horizons was 12.56 km/s before the Jupiter encounter (according to this source). Assuming that we want a probe with well-tested technology to leave the solar system as fast as possible, we can assume the 12.56 km/s initial v_∞ and a swing-by at Jupiter and Saturn (I think we don't want to wait for more planets "lining up" ideally, that would last to long). The initial eccentricity would be 1.178, leading to an angle of 77° with the orbit of Jupiter (assumed to be circular). The probe's speed would be 22.3 km/s at Jupiter, and relative to Jupiter (itself at 13.1 km/s) the speed would be 23.2 km/s. This velocity vector is rotated to be parallel to Jupiter's direction of motion by an optimal swing-by, and the departure speed from Jupiter would thus be 36.3 km/s, with the new v_∞ = 31.3 km/s. The new eccentricity would be 5.743, leading to an angle of nearly 85° with an assumed circular orbit of Saturn. The speed at Saturn would be 34.1 km/s, the relative velocity 34.6 km/s, the outgoing velocity 44.2 km/s and the new (and final) v_∞ = 42.1 km/s. Icek (talk) 16:24, 19 June 2008 (UTC)

Which, if I've done the sum right, would take about 30,000 years to reach the nearest star. I think rockets are out of the question! You need something which can maintain thrust for a long time, like an ion drive to get even close to interstellar velocities. --Tango (talk) 16:43, 19 June 2008 (UTC)

No, doing all the acceleration close to massive objects would be better, because you get more v_∞ for the same Δv, but the higher specific impulse of ion drives would help. Icek (talk) 17:06, 19 June 2008 (UTC)

If you could get the same cumulative thrust as an ion drive gets over the span of years all at once, then great, but I don't know of any way to do that. --Tango (talk) 19:02, 19 June 2008 (UTC)

Another problem with ion thrusters is that they need much power, so you'd need many RTGs, adding mass to the spacecraft (I assume a low mission lifetime here compared to the actual travel time to another star). If we assume that with inner solar system gravity assists similar to the ones the Cassini probe used you could get the 42.1 km/s v_∞ after Saturn for a larger probe (Cassini was about 5600 kg), and you have sufficient power and the ion thruster of SMART-1 (or maybe several of them) with an exhaust velocity of about 16 km/s and you have 2/3 of the probe's mass being xenon propellant, and, for simplicity, the ion thruster acceleration is mainly done far from the sun, so that the Δv can be (as a reasonable approximation) simply added to the v_∞, then you get nearly 60 km/s. Not much for interstellar travel, but at least more than 3.5 times the v_∞ of Voyager 1. Icek (talk) 21:27, 20 June 2008 (UTC)

Theory of disease

As I understand germ theory is the basis on which the modern medicinal treatment is done. What are the theories which form the basis of other systems of health care for example Unani, Ayurvedic, homeopathy etc. Thanks--Shahab (talk) 17:46, 16 June 2008 (UTC)

I would tend to argue that in modern medical practice, the guiding principles are those of evidence-based medicine, rather than simply the germ theory. While many ailments are caused by germs (bacteria and viruses, mostly), modern medicine also includes treatments for diseases and conditions not brought on by pathogenic organisms. (Cancer, for instance, is the result of genetic mutation, which in turn may be caused by environmental factors, lifestyle choices, infectious disease, or bad luck. Alzheimer's disease is linked to the accumulation of naturally-occuring proteins in the brain. A number of autoimmune diseases drive the body's immune system to attack healthy tissues and organs.)

Evidence-based medicine employs the scientific method to develop and evaluate medical treatments. The germ theory of disease in an important part of evidence-based medicine's foundation, as specific germs have been identified through controlled scientific experiments as the causative agents for a number of diseases. TenOfAllTrades(talk) 18:10, 16 June 2008 (UTC)

You might want to read the articles on Chiropractic, homeopathy, ayurvedic, Traditional Chinese medicine and others listed at Category:Alternative medical systems to gain an understanding of how their followers believe they work. 79.66.45.237 (talk) 18:56, 16 June 2008 (UTC)

One of the core principles you need to understand when investigating alternative medical theories is that they often have different approaches to understanding and even defining human anatomy and disease (such as new age chakra theory or TCM meridian theory). In some cases, they may even implement verification methods that don't overlap with the scientific method; historically, chinese medicine relies much more strongly on induction from dogmatic principles than deduction from empirical evidence (not to say it is entirely unempirical). --Shaggorama (talk) 06:10, 18 June 2008 (UTC)

Germ theory is certainly not the "basis on which modern medicinal treatment" is conducted. It describes the 19th century discovery that certain diseases are caused by infectious microorganisms. Many others are not, and germ theory has nothing to do with the many thousands of diseases that are caused by other factors such as injury, genetic defects, poisoning, etc. See our disease article for more exaples of diseases unrelated to microorganisms. Dalembert (talk) 20:36, 18 June 2008 (UTC)

HIV+ People who don't develop the AIDS Virus

I think I read some story somewhere that a large group of women in Southern Africa who were HIV+ for decades but never developed AIDS. They also did not take any medicines or any of the sort to treat the HIV status. It was speculated that these women are either naturally immune to this virus or they contracted a type of HIV virus that can't do any damage. Has anyone heard of this story and where can I find it? --Anthonygiroux (talk) 19:05, 16 June 2008 (UTC)

If the the above is true, could that mean that some people are naturally (meaning born with) an immunity to some viral diseases? --Anthonygiroux (talk) 19:05, 16 June 2008 (UTC)

There are people with a natural genetic resistance to the AIDS virus. To be overly simplistic, the virus plugs into certain cells in the body to replicate itself. In a minority of people, the socket on those cells is slightly different, but not enough to inhibit the normal function of those cells. That slight difference in the socket means that the virus isn't able to plug into them and cannot replicate. Because this is genetic, the chance of spreading this from parents to children is much higher than a child sporadically forming the mutation. Therefore, finding a group of genetically related people with the same mutation is not abnormal. As for your specific question, the women were from Nairobi. So, googling for "Nairobi women hiv aids" should turn up the articles you want. -- kainaw™ 19:41, 16 June 2008 (UTC)

Just to be clear, HIV *is* the AIDS virus. AIDS is a syndrome, not one disease. --70.167.58.6 (talk) 19:48, 16 June 2008 (UTC)

As I understand it, those with an immunity to bubonic plague also have partial immunity to AIDS. Since Europe was decimated by the Plague over centuries, many of those Europeans who survived passed on at least a partial immunity. This might be one factor to explain why AIDS is so widespread in Africa, but not in Europe. Based on the large portion of people dying in Africa, I'd expect to see an increased level of immunity soon among the survivors, just like in Europe. StuRat (talk) 20:47, 16 June 2008 (UTC)

I don't understand how the "partial" immunity would work. I may have misunderstood Kainaw but if the socket is different then it's different. How could one be partially immune? Zain Ebrahim (talk) 20:57, 16 June 2008 (UTC)

There's a group of people who appear to be natural carriers of HIV: they can get infected with the virus, but even after 20+ years, it hasn't developed into AIDS. --Carnildo (talk) 22:34, 16 June 2008 (UTC)

I think the wording "natural carriers" could be misconstrued - it's not a "typhoid mary" situation, they just seem to have an inborn relative resistance to HIV disease progression. The majority in cohorts of these long-term non-progressors eventually suffer disease progression and require treatment, for reasons that are currently being studied intently. There is a group of "elite suppressors" who have viral levels below the limit of commercial assays, but even some of these people eventually develop higher levels of viremia and have CD4 depletion. Scray (talk) 02:17, 17 June 2008 (UTC)

To better understand this, I suggest you read HIV#The clinical course of infection. As was described earlier, AIDS is a condition that can result from HIV infection. It is possible to be HIV+ and be asymptomatic. Basically, once you have the virus in your body, your immune system is constantly undergoing a tug-of-war with the viral population: CD4 T-cells vs. virus particles. If the balance shifts too far towards the virus, then it overcomes your body's immune capabilities and effectively destroys your immune system. Then you have AIDS: a lethal susceptibility to opportunistic diseases which your body could otherwise handle with a normal immune system, which HIV annihilated. --Shaggorama (talk) 06:23, 18 June 2008 (UTC)

Archaeopteryx / dromaeosaur scaly muzzle?

I've been wondering about this for a while. Archaeopteryx and dromaeosaurs in general are depicted with scaly muzzles. 90% of the time their muzzles are described as scaly, and the other 10% of the time they are described as having horny beaks, which is incorrect. Fossils like Archaeopteryx and Sinornithosaurus show that at least part of the muzzle was featherless, and the skulls show anchor points for some kind of lips, but is there a specific reason for assuming that these lips were scaly in particular, as opposed to smooth skin or something else? I know one could look at the taxonomic relationships and logically assume that since Archaeopteryx/dromaeosaurs were intermediate between theropods and birds, and did not have beaks yet, they probably still had scaly theropod lips, but is there any reason other than that? Have they found skin impressions, or is there some feature of the bones in the snout that implies scaly skin in particular? 70.212.190.196 (talk) 20:58, 16 June 2008 (UTC)

First, the presence of lips is still debated, and I'd say a majority of researchers prefer a lipless, bird/crocodile arrangement, or only very simple lips that only partially cover the top of the teeth (anything more would be problematic in species where the teeth protrude past the bottom of the lower jaw, like tyrannosaurs). I also wouldn't say it's incorrect that they had some kind of horny beak, there's no evidence one way or the other right now for most species. As far as I know, there are no skin impressions from the very end of the snout known. This would require a really, exceptionally well-preserved specimen, as skin impressions usually lie at the margin of the body, not on top of the bones themselves, and whatever integument theropods had on their heads, it apparently didn't protrude enough to leave a mark (or wasn't noticed and was destroyed in preparation, as has happened to some portions of the Archaeopteryx feather impressions).

So to answer your question, no, there's no reason to think the snouts were scaly, they very well could have had naked skin, or been completely covered in feathers. Sinornithosaurus, as you pointed out, had a feathered snout save for (apparently) the very tip, but that could just as well be a preservation artifact. Based on living analogues, in my opinion, scale-less snouts would probably be more likely. Many birds have naked skin between the beak and start of feathers, despite retaining scales on the feet. Not sure if this would hold for fingers as well, I wonder if hoatzin chicks have feathers, scales, or naked skin on their fingers... Dinoguy2 (talk) 04:24, 18 June 2008 (UTC)

This is a really helpful reply, thank you. I didn't mean real thick lips, just the sort of thin covering that keeps the gums from showing. I guess I could have said "snout", but I was trying to find some word that would denote the non-fuzzy portion. As for fingers, I don't know about hoatzins, but emus and baby cathartids have semi-naked, semi-fuzzy/feathery fingers, so I can imagine hoatzins would be the same. 75.208.3.255 (talk) 04:58, 18 June 2008 (UTC)

dogs and cats

Why do dogs (and cats) tend to sleep with their butts near your (and each others) head? —Preceding unsigned comment added by 69.77.185.91 (talk) 21:09, 16 June 2008 (UTC)

I'd say it's just that they lack the taboo we have on doing that. Therefore, they will sleep in any random orientation with regards to one another and/or you. You probably don't take much notice unless one has it's butt in someone's face. This draws our attention, since it's unusual. So, that's what we remember. StuRat (talk) 03:32, 17 June 2008 (UTC)

Yes, I'd say it's more a result of memory bias, or a specific individual difference of the dog(s)/cat(s) in question. --Mark PEA (talk) 20:08, 17 June 2008 (UTC)

Any possibility that this is a deliberate group act so that they face out away from you (thus being able to look out for danger or better able on being disturbed to do so). ? David Ruben ^Talk 00:23, 18 June 2008 (UTC)

Or because they dislike human breath. Dogs certainly seem to, at least. 75.208.3.255 (talk) 04:02, 18 June 2008 (UTC)

Dog: "Geez, what's with your breath ? It smells like flouride, as if you've never even licked your butt or privates or even eaten any decaying road-kill. Do you need me to show you how ?" StuRat (talk) 13:27, 18 June 2008 (UTC)

My cat always sleeps facing me, and if I turn away she immediately moves around to my face again. Jessica - N10248 (talk) 18:02, 20 June 2008 (UTC)

Hot humid wet vs. Dry desert climate, overheating which more dangerous on the human body

Once, I was taught in high school biology that for a human, a hot climate but with high humidity (ie. tropical wet climate) is more dangerous than a similarly dry one, because humans can't sweat and overheat more easily, while, in the dry climate, the water can evaporate, cooling you off. But I argued that always thought that it would be the contrary, the desert clime makes you lose water faster, and its sun is stronger. With all health affects considered, which is more dangerous for a human being, especially for travelling long distances or strenous exercise, risk collapsing and death? —Preceding unsigned comment added by 192.30.202.21 (talk) 23:54, 16 June 2008 (UTC)

I live in a hot and humid place and I think the humidity problem is more of an irritant (it makes you feel greasy and uncomfortably warm) rather than a problem.--Lenticel ^(talk) 00:17, 17 June 2008 (UTC)

I have lived in hot-dry (Twentynine Palms, CA) and hot-humid (Charleston, SC). I haven't heard of many deaths from overheating in the hot-humid environment, but I heard of many deaths in the hot-dry environment. This could easily be because of population. If you overheat in a hot-humid city, someone will notice. If you overheat in the desert, you could be there for weeks before you are found. -- kainaw™ 00:50, 17 June 2008 (UTC)

(EC) I agree with Lenticel. With a hot & humid place, you very easily feel uncomfortable. The difficulty your body has in sweating can also make an equivalent temperature seem hotter. 'More dangerous' seems unnecessarily broad and will surely depend on your situation. If you have lots of electrolytically balanced water then a humid place is likely to be more of a problem on the whole. If you have little water then a dry place is more likely to be a problem. Both of these are presuming we are talking about similar temperatures and that you know what you are doing, i.e. you don't take too much water. Clearly a 30C humid place is rather different from a 45C dry place. In any case, if you are smart enough to pace yourself properly, don't overexert yourself and ensure you have sufficient practice for whatever you are attempting, I suspect the likelihood of death is low. For references, see Craig Barrett (athlete) who for some strange reason was seen as a hero in NZ after he collapsed during the 1998 Commonwealth Games (in Kuala Lumpur, therefore a hot and humid place), although IMHO he was really just an idiot. I've seen various suggestions he was close to death, I don't know how true it is but it wouldn't surprise me if it was. Obviously the chance of him dying given that he was taking part in the Commonwealth Games and would have had access to excellent medical care is very low but I think it does emphasise what happens when you are stupid and push yourself too hard (he was 6 minutes ahead of the person behind him when he collapsed, so it's not as if he had to go that hard) in a situation you presumuably haven't practice enough for; and potentially do other stupid things (the article suggests the was drinking pure water and probably suffered from water intoxication). Nil Einne (talk) 01:24, 17 June 2008 (UTC)

If you're in a hot place (low or high humidity), you're going to sweat a lot. It's what your body does to try to cool you down. If you don't have copious amounts of fresh water to drink, you're going to get dehydrated, which can lead to health problems real quick. If you're exercising, it's worse, because you're generating that much more metabolic heat that you have to get rid of.

If the humidity is high, your sweat doesn't evaporate as well, so doesn't cool you as well, so it's easier to overheat, and that can lead to health problems, too. Plus, of course, the stickiness makes you way uncomfortable.

If the humidity is high and you don't have any water, you're going to be sticky and uncomfortable on top of being seriously overheated on top of being dehydrated. Triply bad news.

Me, I'd much rather be in a hot, dry place than a hot, humid place. Your sweat cools you very well when it's dry. If you've got water, you won't get dehydrated. If you've got sun protection, you won't get sunburned.

(I fondly remember summers at my grandparents' house in Palm Springs, which is where my dad grew up after they moved from, as it happens, Twentynine Palms. So I know what Kainaw's talking about. I've also lived in St. Louis, and I absolutely hated it.)

When I hear about people dying in heat waves, my impression (contrary to Kainaw's above) is that it tends to be in humid, inland, non-desert climates. You hear about the old and the infirm being relocated to public places where there's good air conditioning, because that can be the only way to survive under hot and humid conditions. When there's a heat wave in (say) Phoenix, Arizona, on the other hand, I suspect that what's most important is just to stay in the shade, drink lots of water, avoid exerting yourself, and maybe fan yourself gently to goose the evaporative process that little bit further. I don't think people are nearly as prone to heat-related death in the absence of air conditioning in Phoenix as they are in Chicago or St. Louis. So I'm inclined to think that, everything else being equal, humid heat is more dangerous than dry heat.

If a desert climate is more "dangerous" overall I think it's because there's less likely to be water, and there's less likely to be shade. But I wouldn't say it's dangerous because of losing water faster there, because as I said, you sweat just as much when it's humid. (The difference is that when it's dry, your sweat evaporates immediately and cools you as it's supposed to. In the desert, you hardly realize you're sweating profusely -- which can, it's true, make it easier to forget to drink enough water to rehydrate yourself. Oh, and you can remember your name, 'cause there ain't no one for to give you no pain. :-) ) —Steve Summit (talk) 01:13, 17 June 2008 (UTC)

Obviously it depends on your situation and thus to compare the two one must eliminate other variables. In a typical house with no air conditioning in a city with plenty of water a person would be at more risk of heat stroke in a humid climate as the body will over heat more. In the same situation but without water I am unsure of the relative rates of water loss, more evaporation does not necessary mean more sweat. It would be impossible to comment on whether it is 'safer' to be lost in the wilderness in dry climate vs a humid one without going into specifics such as; avaliablity of water (you can't claim there is more potable water in humid climates); shade; actual temperature; actual humidity etc--Shniken1 (talk) 01:47, 17 June 2008 (UTC)

There would definitely be more water loss from breathing etc, although the quantity lost is probably small enough that it is insignificant Nil Einne (talk) 01:52, 17 June 2008 (UTC)

That's a very good point, and I'm not sure it's insignificant. —Steve Summit (talk) 02:08, 17 June 2008 (UTC)

A couple points:

1) Our sweat glands are rather stupid: They don't seem to know that if it's 100% humidity out there's no point in sweating as it will just drip in your eyes instead of evaporating. Therefore, you can lose a lot of water by sweating, even in humid climates.

2) Being uncomfortable is a good thing: In that it causes you to take actions to cool yourself, like taking a cool bath. If high humidity makes you uncomfortable earlier, that may convince you to act before it's too late. StuRat (talk) 03:29, 17 June 2008 (UTC)