Wikipedia:Reference desk/Archives/Science/2009 December 2

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December 2

several questions

Here are two questions I that keep popping into mind and I have not had the chance to ask.

1. If you release a 100 pound mass from a geostationary orbit will it still be attracted to the Earth at the speed of 32 feet per second per second and if not what speed?

2. If you vibrate a magnet will it send out a magnetic wave at the frequency of vibration and if so will this magnetic wave in turn produce an electrical wave?

71.100.160.161 (talk) 00:13, 2 December 2009 (UTC)

For question 1, you need to specify at what height you are dropping from. The acceleration due to gravity should be (roughly) uniform at any given height, but will decrease with distance from the earth. However, if you drop such a weight from a geostationary orbit, it will not sink towards the ground; rather it will remain exactly where you let go of it, since it is in free fall with you when you release it, so unless you push it, it will remain in free fall right next to you. If you push it, it will move at whatever speed and whatever direction it was going when it left contact with your hand.

For question 2, electromagnetic waves are not seperable, they basically move together, orthogonal to each other. See this picture:

--Jayron32 00:29, 2 December 2009 (UTC)

(ec) If you release something while in orbit that something will also be in orbit and won't fall at all. If something started out at the altitude of geostationary orbit but with no horizontal momentum, then it would fall at a little under 1 foot per second per second (at first - it would increase as the object got closer to the Earth). Geostationary orbit is at about 36,000km above the centre of the Earth and the surface is about 6,000km above the centre. That's a factor of 6 different and, since gravity follows an inverse square law, that results in a factor of 36 difference between the gravitational acceleration. --Tango (talk) 00:29, 2 December 2009 (UTC)

For question 2, Jayron32, are you implying that if you move a magnet you make light (radio)? I guess it makes sense, since if you move a charge (electron in a wire) it makes light. Can you shake a magnet at kilohertz speeds? Ariel. (talk) 02:32, 2 December 2009 (UTC)

The OP implied that. I said nothing of the sort. I was dodging the question by merely noting that "magnetic" and "electric" waves cannot exist in isolation from each other; they are two sides to the same coin. His question is unanswerable as written because it presupposes something which is not true (the seperate nature of "electric" and "magnetic" waves). --Jayron32 05:02, 2 December 2009 (UTC)

"Fields and waves" was far from my strong point in school, but altering the current flow in a set of coils can create a rotating magnetic field, as was established by Nikola Tesla. Similarly, vibrating a magnet would cause induced voltage in a nearby coil, similar to varying current in a parallel coil. At least so far as "near field" effects are concerned, a moving magnet or a varying current in a wire or coil could have the same effect. Not so clear on antenna effects and radiated field. Electromagnetic waves have no lower frequency, and a charged particle or a magnet vibrating at 1 Hz or 100 Hz or 1000 Hz or 10 KHz should create an electromagnetic field, though at a lower frequency than what we usually consider "radio." Clearly a little horseshoe or bar magnet from the dime store, or a ceramic refrigerator magnet would fly apart or come loose from the moving thing if you attempted to rotate or vibrate it at megahertz radio frequencies, or microwave frequencies, or light frequencies. That is a material science problem and unrelated to the underlying physics. It should be possible to use a sound transducer to move a little neodymium magnet back and forth at 20 KHz, which is toward the upper end of the Very low frequency radio band (3Hz to 30KHz). I have doubts about the moving magnet acting as an efficient antenna or the actual emitted power. Edison (talk) 17:57, 2 December 2009 (UTC)

Evolution

http://www.jesus-is-savior.com/Evolution%20Hoax/devilution.htm

Is this a joke, or is that person serious? --70.250.212.43 (talk) 00:35, 2 December 2009 (UTC)

Sadly, he's probably serious. It doesn't make him correct, but I would fathom that the author of that bullshit actually believes it. --Jayron32 00:43, 2 December 2009 (UTC)

On the internet, if it looks crazy, it probably is. Hooray for democratization of communication channels—for every nut, a megaphone! --Mr.98 (talk) 01:48, 2 December 2009 (UTC)

It can sometimes be difficult to tell if a site or person is being serious or intended in as satire or parody. (Many people think Edward Current's work on Youtube is genuine/serious for example.) However that site appears to be genuine, I can find numerous discussions of it an evidentally it has had hosting problems Nil Einne (talk) 02:13, 2 December 2009 (UTC)

I'm beginning to be able to tell that a site is junk just by looking at the fonts, colors and centering of text on the page! It's truly incredible. Look at almost any site on perpetual motion, crystal healing, moon-landing conspiracies or anything like that - they all have the same basic look - primary colors, too many font sizes, centered text and pages that scroll on for dozens of screenfulls. It gets to the point where you don't even need to read the words anymore! SteveBaker (talk) 02:20, 2 December 2009 (UTC)

It's true that really amateurish/crazy sites stand out (e.g. Time Cube) in their embrace of vernacular web design... but looking good doesn't mean the content is any more sensible. Answers in Genesis has a wonderfully professional-looking site... but it's still full of junk. Looking bad doesn't necessarily mean that you're a crackpot, but I think most non-crackpots recognize that looking like a crackpot does not get their message across and change it. I think people who are 100% crackpots probably can't tell the difference. --Mr.98 (talk) 02:46, 2 December 2009 (UTC)

Mr.98, you only say that because you've been educated stupid by evil academia. :) A Quest For Knowledge (talk) 03:59, 3 December 2009 (UTC)

"primary colors, too many font sizes, centered text and pages that scroll on for dozens of screenfulls". Just like Daniel Brandt... Fences&Windows 03:31, 2 December 2009 (UTC)

Check out http://www.islamdenouncesterrorism.com/darwinism_materialism.html; it's even more ridiculous! They blame evolution for every societal problem since Darwin. Even things before Darwin are blamed on "Darwinism's" "materialistic roots". ----J4\/4 <talk> 17:58, 2 December 2009 (UTC)

The general principle of "If you sling enough mud - some of it will stick." definitely applies here! SteveBaker (talk) 19:28, 2 December 2009 (UTC)

I love a good comedy ;-). Falconus^{p t c} 21:15, 2 December 2009 (UTC)

There are lots of crazy sites out, and yes, some people really believe this crap. What gets me is that they think we're the naive ones. Add WP:FTN to your watchlist to get a sampling of the craziness. A Quest For Knowledge (talk) 05:01, 3 December 2009 (UTC)

BTW, we really could use some watchful eyes on the Fringe theory noticeboard, especially from editors knowledgeable about science. The fringe theorests were having a field day with the Climatic Research Unit e-mail hacking incident until we had to lock down the page. A lot of the time, it's hard to keep up with them because there are so many. A Quest For Knowledge (talk) 05:25, 3 December 2009 (UTC)

*wonders if anyone else thought of this Fringe when they first saw that board mentioned, and wondered how it managed to get so bad that we needed an entire noticeboard for one tv show...* :P J.delanoy^gabs_adds 05:42, 3 December 2009 (UTC)

The original link isn't nearly as funny as this one [1] where he claims that America is already communist (and so is every other Western democracy in the world). DJ Clayworth (talk) 20:25, 4 December 2009 (UTC)

greater permittivity than a vacuum?

Is it possible that there is something, perhaps an effected area of space such as in a pre-particle, (an area of space after the Big Band but before any particle has formed) where permittivity is greater than in a vacuum, allowing a particle to form? 71.100.160.161 (talk) 01:41, 2 December 2009 (UTC)

By Big Band, I assume you mean the big bang? Quantum mechanics states that even a vaccum has energy, so an absence of energy may indicate lower mass or permeability, but how the universe formed in the first place is probably beyond our scope of knowledge. ~AH1^(TCU) 02:35, 2 December 2009 (UTC)

By "vaccum," I assume you mean Vacuum. Edison (talk) 06:36, 2 December 2009 (UTC)

I assume that maximum permittivity is for a vacuum is determined by use of a perfect vacuum which would offer greater permittivity than a partial vacuum, So yes, is there the possibility of greater permittivity than a perfect vacuum such as an area in space so small it is too small to contain anything? 71.100.160.161 (talk) 15:39, 2 December 2009 (UTC)

I don't think this is an appropriate forum. There are several physics forums on the internet where you can discuss new theories and questions that are beyond the current scientific knowledge, but here our answear can merely be that no, there are no evidence nor generally accepted theories describing something like what you propose. (Which of course can be something exciting from one point of view :-) EverGreg (talk) 12:09, 2 December 2009 (UTC)

Such a variation has been proposed (published version requires payment) as an explanation for the Pioneer anomaly, but is far from being accepted. SpinningSpark 12:52, 2 December 2009 (UTC)

What's the permittivity of the space between two Casimir plates? --Tango (talk) 15:15, 2 December 2009 (UTC)

The same as a vacuum, the plates attract each other with an electromagnetic force. The difference is due to the plates. Graeme Bartlett (talk) 20:21, 2 December 2009 (UTC)

2,3-Dihydropyran as a protecting group

How do you take it off? I know you take it off with acid, but how do you guarantee that you get your actual alcohol back, with high yield? I would imagine the protected group might cleave in acid several ways ... John Riemann Soong (talk) 01:42, 2 December 2009 (UTC)

There are no guarantees in chemistry. You have to do the actual experiment using the actual reactants (and often screen several different times, temperatures, acids, reactant ratios, solvents, etc.) to find "what works best for intended reaction with minimum of unintended reactions". One reason there are so many different protocols for doing reactions is that every substrate is different, and (unlike in textbooks) every little thing may matter and may matter in totally unexpected ways. And the reason there are so many different protecting groups is because different substrates may have different sensitivies to various specific chemicals. Again, Nature is cleverer than the total of every journal article ACS has ever published.It's called research because you have to search over and over and over to find how to actually perform what seemed like an obvious and easy proposed idea:) DMacks (talk) 02:14, 2 December 2009 (UTC)

Well "guarantee" is a relative term. My prof mentioned it as a protecting group and now I am following up on it. According to design, is the ring oxygen supposed to be protonated sometimes? Or is the ring geometry making the ring oxygen act like an ethoxy oxygen on an anomeric carbon? Basically I'm worried the protected group will hydrolyse the wrong way. John Riemann Soong (talk) 02:29, 2 December 2009 (UTC)

In the real world, it doesn't matter which of the O is protonated first during acid-catalyzed hydrolysis deprotection. The acetal will fall apart either way, and eventually the ROH (deprotected alcohol) will detach—the product of acid-catalyzed hydrolysis of an acetal is ROH, R'OH, RCHO and you just happen to have "R' and R attached to the same molecular chain). On paper (i.e, not tied to the real world) you can do any and every possibility until you get to the one your prof wants:) But seriously, the reactions are reversible, and conditions are chosen to push towards the desired product by kinetics, thermodynamics, or concentration effects, etc. DMacks (talk) 21:14, 2 December 2009 (UTC)

Well I was wondering if the acetal cleaves (the non-product oxygen leaves), how is the product alkoxide ever supposed to leave? (It will create a primary carbocation...) John Riemann Soong (talk) 15:08, 4 December 2009 (UTC)

You asked about the "wrong way" cleavage and about whether it mattered which O gets protonated. I said (and you should know from learning about acid-catalyzed acetal hydrolysis) that both H get protonated eventually. And that it's not a primary carbocation, but is actually an oxonium-carbonyl (in resonance terms, the lone-pair on the "other" still-attached oxygen stabilizes the C⁺ attached to it (the original anomeric position). Once you protonate one oxygen, the whole hydrolysis reaction continues (and the other oxygen can come off under either acidic or basic conditions...hemi-acetals are not stable at all). DMacks (talk) 17:29, 4 December 2009 (UTC)

Also I have a question regarding the synthesis posted in that article. Do you dehydrate with alumina in neutral conditions? Is there a carbocation rearrangement involved? John Riemann Soong (talk) 01:50, 2 December 2009 (UTC)

Typhoon Nida

Hi. Please refer to the discussion topic I posted on Talk:2009 Pacific typhoon season. I am not forum shopping, just trying to incite quicker discussion. This seems a little disturbing, and the weather for the past few days has been unpredictable (just one example is that we've had black ice for the past two mornings). Thanks. ~AH1^(TCU) 02:43, 2 December 2009 (UTC)

If you wish to avoid accusations of "forum shopping" - then you need to ask us a specific question that you're unable to answer for yourself with the resources you have at hand. SteveBaker (talk) 12:46, 2 December 2009 (UTC)

Is the super typhoon responsible for all these ocean temperature changes, will this enhance El Nino, and could the pool of warm water actually cut of the Humboldt Current? ~AH1^(TCU) 00:32, 4 December 2009 (UTC)

ring opening/closure, reaction rates and entropy

I've been trying to organise the overload of reactions depending on some special entropy-reducing quality of rings or where two substituents are held in a conformed position next to each other ... can I get this straight:

Assuming enthalpy of the reaction is near zero (e.g. esterification <___---> hydrolysis), ring-closure reactions are slightly disfavoured (e.g. K will be a little less than 1) because of reduction in entropy. (Unless there is some weird effect where closure might actually relieve strain and increase the rotational degrees of freedom?) However, being in a ring will catalyse the reaction e.g. make both forward and reverse reactions faster.

Take the phthalic anhydride and pthalic acid. The enthalpy of forming the anhydride is positive (and the reduction in entropy hurts it further), but however kinetically, the rates of hydrolysis and anhydride-formation are both increased cuz of the ring effect. Distillation of water and heat will define the equilibrium point, but the ring proximity thing will make both reverse and forward reactions faster? I'm trying to frame this in terms of thermodynamics. John Riemann Soong (talk) 02:45, 2 December 2009 (UTC)

Speed at which levels of melanin in humans adapt to UV light

As I understand it, the varying levels of melanin in humans (and thus varying skin tones, and so forth) are believed to have evolved at least partly in response to differing levels of ultraviolet light — the high levels of UV light in equatorial areas prompt retention of melanin, while in places closer to the poles, there's less UV light and thus not so much melanin is kept. (I'm setting aside other contributing factors like diet, for now.) My question is: how quickly would changes in UV light be reflected in melanin? That is, if a group migrated from one place to another, how long would it take before there were noticeable changes in melanin levels (setting aside other factors) as a result? I don't expect this is the sort of thing that can be determined with any precision, but even rough figures would help. Ten thousand years? A hundred thousand? -- 203.97.105.173 (talk) 03:02, 2 December 2009 (UTC)

I recall being told that it would take ~10,000 years for black to go to white or vice versa. Dragons flight (talk) 03:05, 2 December 2009 (UTC)

To slightly side-step the question, some research suggests that light skin in Europe may have evolved as recently as 5,500 years ago:[2] Fences&Windows 03:28, 2 December 2009 (UTC)

In modern times, it may be never. Since everyone pretty much lives indoors now, theres little reproductive pressure to favor one skin tone over another, so there is little reason to suppose any such changes will occur in the future. Furthermore, there is little genetic isolation anymore, so there is little reason to believe that an isolated population would develop such uniform traits among themselves. --Jayron32 04:59, 2 December 2009 (UTC)

Jayron, you should come out sometime and enjoy the outdoors. Everyone does not pretty much live indoors. Your second point stands. Dauto (talk) 06:07, 2 December 2009 (UTC)

Do you work outside? Most don't anymore. --Tardis (talk) 15:59, 2 December 2009 (UTC)

Woman wearing a bikini

Who said anything about work? Dauto (talk) 01:42, 3 December 2009 (UTC)

Evolution can run pretty quickly when the genetic basis for the change is already in the population and the environmental change makes a significant dent in the ability of less useful genes to be passed on. It's likely that the genes for different skin colors are present in the general population - so if the UV levels changed suddenly and started to cause a dramatic change in birth rates and survivability then evolution might happen very rapidly. But that second point is the issue here. The disadvantage to light skinned people in sunny places or dark skinned people in less sunny places just isn't that dramatic. If there is only (let's say) a 1% chance of someone being so seriously disadvantaged by inappropriate skin tone that they failed to reproduce - then the rate of evolutionary change will be fairly slow. But if 90% of people with the wrong skin tone died before reaching child-bearing age - then we'd evolve in not too many generations. I don't know what the case was as mankind migrated around the world - or what it is today - but my gut feel is that this would be on the slower end of the scale in the past and essentially non-existant today in a technological world of sunblock, indoor living, clothing and vitamin Evitamin D(sorry!) supplements that allow anyone to live successfully in any climatic conditions. SteveBaker (talk) 12:44, 2 December 2009 (UTC)

That concept that skin tone evolution has stoped because we all live indoors, use cloth and sunblock and vitamin E (That last one is probabily irrelevant anyways) doesn't hold water. Those factors will make us evolve towards a lighter skin tone instead of a darker one. evolution still happens. 169.139.217.79 (talk) 15:54, 2 December 2009 (UTC)

Why would they make us evolve towards a lighter skin tone at all? What is the reproductive pressure to do so? Do darker-skinned people reproduce less effectively when they wear sunscreen and clothes and work in offices? The idea that people's skintone will change just because their environment changes smacks of Lamarckism, a thoroughly disproven idea. --Jayron32 18:56, 2 December 2009 (UTC)

People with dark skin tones at high latitudes do have an increased risk of rickets, but it is fairly minimal. --Tango (talk) 19:01, 2 December 2009 (UTC)

It's minimal in a modern world with good nutrition, vitamin-D supplements in milk and decent medical care - but when darker skinned people started to migrate into Northern Eurasia - none of those benefits were present - and that would have been enough of a problem to reduce reproductive success - and hence evolutionary benefit for people with lighter skin tones. The need to wear clothing as protection from the colder climate (thereby covering up yet more skin and making vitamin D production still less effective) probably added to the problem. Within enough generations - voila - lighter skin color. The benefit must have been substantial enough to offset the costs in terms of skin cancers and such caused by having a lighter skin on sunny days in the summer...which also isn't such a big deal in a modern world with people staying indoors much more and having clothing and sunblock. SteveBaker (talk) 19:23, 2 December 2009 (UTC)

Sorry, yes, I meant in the modern world. --Tango (talk) 19:43, 2 December 2009 (UTC)

Surely you mean vitamin D? --Tardis (talk) 15:59, 2 December 2009 (UTC)

Yes - I do, sorry! Vitamin D is produced in the skin when exposed to sunlight. Light skinned people need very little exposure to the sun each day to make all the Vitamin D they need. But dark skinned people who live in the extreme North or South of the planet - or in places where there is dense cloud cover for extended periods - don't absorb enough sunlight to make sufficient quantities of this vitamin - and that (presumably) is the main reason for the evolution of lighter skin colours as humans migrated away from the tropics. However, in our modern civilisation - this problem is easily overcome by eating an appropriate diet or (in extreme cases) taking vitamin supplements. Hence, there is unlikely to be any evolutionary pressure for lighter skin to continue to evolve in modern times. SteveBaker (talk) 19:15, 2 December 2009 (UTC)

Actually, there is a considerable body of opinion that vitamin-D deficiency (less serious than that needed to cause rickets) is a widespread problem even among light-skinned people. I remember this being in the news when I lived in Canada, where obviously it would be more of an issue than at my current California latitude.

The experts can't seem to agree on whether to recommend oral supplementation, partly because D, as a fat-soluble vitamin, is possible to overdose on. (Experts don't trust people much, as a general rule.) In any case I took D supplements during the Canadian winter. --Trovatore (talk) 02:02, 3 December 2009 (UTC)

Since going outdoors might involve disconnection from the internet and Wikipedia, could this be fatal?Trevor Loughlin (talk) 12:49, 2 December 2009 (UTC)

Wikipedia does not offer medical advice. Of course, if disconnecting yourself from Wikipedia could be fatal, we can hardly suggest that you go see a doctor either. Do you have an iPhone? --Tardis (talk) 15:59, 2 December 2009 (UTC)

The article Human skin color has a bit about all this. One gene which only arose between 5 and 12 thousand years ago accounts for about a third of the difference between black Africans and white Europeans. The previous ones in all likelihood spread even faster as they would have had a greater effect. So about 20 thousand years for most of the change would probably be quite reasonable. As to the amount of difference needed for genetic advantage to take effect I've read that a real advantage as little as one in a thousand will eventually spread throughout a population and not get swamped by random factors. This is why it always interesting to ask about possible advantages in some harmful genetic disease or predisposition to it to account for its existence. Dmcq (talk) 09:20, 3 December 2009 (UTC)

Thanks for all the answers. -- 203.97.105.173 (talk) 21:58, 5 December 2009 (UTC)

vitamin c chart at bottom of vitamin c article.

Is it possible to include kale in the vitamin c chart at the bottom of the vitamin c article? —Preceding unsigned comment added by 97.96.127.130 (talk) 10:13, 2 December 2009 (UTC)

Yes, it is possible. Be bold! Red Act (talk) 10:21, 2 December 2009 (UTC)

Remember to include your source for the information. SpinningSpark 10:25, 2 December 2009 (UTC)

You can get the vitamin c content for kale from the first of the three references cited for the table. If you get a value from that source, there's no need to cite a reference specifically for the new kale line that you add to the chart. All you need to do is add a new line in the table for kale, using the value you found in the reference. Red Act (talk) 10:36, 2 December 2009 (UTC)

GIS + ray-tracing algorithms = traffic noise estimation

I've put this here rather than in the Computing section as I think it is more likely to catch the eye of the appropriate people. I'd like to write a freeware program to predict the amount of traffic noise at various distances from busy roads, and display it in noise-intensity contours. Are there any freely available relevant algorithms or programming code that I could use rather than starting from scratch? Or does a free program already exist? The use of ray-tracing for sound rather than light was discussed in an earlier question on this page. Thanks. 89.242.106.49 (talk) 15:30, 2 December 2009 (UTC)

I see an immediate problem with this. First, assume that the entire world is perfectly flat - no trees, houses, fences, hills, etc... Noise is easily measured by the distance to traffic source(s) -- some places may get noise from more than one road. You can use something like Google Traffic to measure traffic density and simply reduce the noise the further from the road you get. Now, what if there is a large solid fence next to the road to block the noise? No online mapping service will map the fence. What if there is a large hill? You will need to overlay an elevation map to reduce sound quicker when going uphill. So, it seems to me that the first step is to create a map that has proper elevation based on land (hills/trees) and manmade objects (fences/buildings). Then, you can work on getting traffic data. -- kainaw™ 18:40, 2 December 2009 (UTC)

Please! I do have at least a double digit IQ and I'm well aware of all that already thanks. 89.242.106.49 (talk) 20:00, 2 December 2009 (UTC)

I think you may be making a mistake in fixating on ray tracing. That's an appropriate way to handle optical rendering - but it may not be the best way for audio. I would expect some kind of wave-front model to be better at handling your problems. As I explained in answer to your previous question on the computing desk - ray tracers (for light) presume light travels in straight lines without diffraction. If you employ that technique for audio then if the simulated microphone doesn't have "line of sight" to the cars on your virtual road - then it'll hear silence. But we know that in reality, a small rise in the ground does very little to cut out the noise of a nearby road (although it easily blocks 100% of the light coming from it!) - so you know, without doing very much deep thinking, that the problem you're trying to solve isn't a good fit for a classic raytracing solution. I typed "acoustics" into the search box at http://www.sourceforge.net (probably the largest repository of OpenSourced software in the world) and came up with several possible hits. One is FOAC - which claims to be: "software for calculating acoustic field by finite difference time domain method( FDTD )". It appears to be a plugin for Matlab. In the FOAC forums, there was a list of other opensourced acoustic packages: HERE. The language they use is completely foreign to a graphics guy like me - so I guess you just hit the limit of my expertise. Good luck! SteveBaker (talk) 18:53, 2 December 2009 (UTC)

I repeat my comment given to the previous poster. While a very simple program would suit settings in the countryside in a flat landscape - and that would be useful to many people including myself - a program suitable for an urban area would need to take into account reflecting off surfaces such as walls and being absorbed by other things such as vegetation as well. For an urban area I would need something which is capable of dealing with the equivalent of large scale maps that include buildings, and ideally being able to add ray-tracing capabilities to it. Doing it as a flat 2d plan would be the simplest case, but in some instances the differing elevetations would matter also. 89.242.106.49 (talk) 20:00, 2 December 2009 (UTC)

If you are going to start from scratch you will need something like Uniform theory of diffraction. I studied Geometric theory of diffraction before, and the formula's were huge, each filling up one complete page. This will account for waves of sound diffracting around obstacles. It will vary with frequency. Graeme Bartlett (talk) 20:10, 2 December 2009 (UTC)

A complex forumula may not be a problem, particularly if you can put it in a subroutine. 92.29.36.113 (talk) 23:37, 2 December 2009 (UTC)

El nino

Will it bring more snow to North Texas than usual?Accdude92 (talk to me!) (sign) 17:19, 2 December 2009 (UTC)

Take a look at NOAA's weekly El Niño status report -- the last few slides give an overview of the effects of El Niño on precipitation across the USA. Looie496 (talk) 17:53, 2 December 2009 (UTC)

I don't know whether El Nino caused it - but North Texas had some snow last night - and that's "more than usual" for early December. SteveBaker (talk) 18:22, 2 December 2009 (UTC)

There is a giant Gulf low currently in the Midwest, formed from a combination of at least five different low pressure systems, and it is travelling extremely fast. It looks to be worse than the 1993 Storm of the Century for those on the East Coast of the US and Southern Ontario, because the storm is drawing air and moisture from the Gulf of Mexico, the East Pacific, and the Caribbean, while the cold Arctic air extends to Hudson Bay and the northern reaches of Nunavut. Yesterday by this time, the low was still three separate systems, one in the Gulf later to acquire a classic tornado signature, another near New Mexico that resembled a hurricane on land, and yet another that was a cold front near the coast of Texas. Meanwhile in the western Pacific, Typhoon Nida recently weakened from a category five to a category one, but when it weakened to a category four it was perhaps briefly larger than Tip. Now a second system is starting to form behind Nida in the gap in the Subtropical High that the storm created. The warmest pool of water is now in the Central Pacific, and the Humboldt current is becoming choked by this warm pool as it moves east. Currently all the warmest water in the West Pacific is south of the equator. This could bring an early and extra boost to El Nino. Already, the warmer water in the south Eastern Pacific is affecting temperatures in the Gulf and Caribbean, and this was likely enhanced by the warmer water temperatures. Off Brazil, a zone of 26C+ water extends almost to Uruguay, and this is what happened in March of 2004 when Cyclone Catarina formed. ~AH1^(TCU) 23:42, 2 December 2009 (UTC)

Ok but what does that mean for North texas? More snow?Accdude92 (talk to me!) (sign) 14:02, 3 December 2009 (UTC)

This link seems to show more snow arriving in north Texas in the next week, probably two storms. ~AH1^(TCU) 00:30, 4 December 2009 (UTC)

Children on Wikipedia

I have a six year old daughter who I want to start using Wikipedia as a reference. However I'm afraid she'll click a few links and suddenly be staring at pictures I wouldn't want her to see for several more years. I believe this is a legitimate concern, for example, it only takes 3 clicks to go from Man to Human sexuality to Bondage (BDSM) where there's quite pornographic material. There must be near infinite similar examples. Is there a children's version she could use (not the Simple English wiki, I would like her to develop her vocabulary)? TheFutureAwaits (talk) 18:39, 2 December 2009 (UTC)

There are third-party ports of Wikipedia which have stripped out all of the "naughty bits". These are not actively edited versions of Wikipedia, so often they are not entirely as up-to-date as Wikipedia itself is, but if you are more concerned with protecting your children from pornographic material (a VERY legitimate concern) than it may be worth it to be dealing with a slightly out-of-date version of Wikipedia which has been cleaned up for the kids. Wikipedia for Schools is the one I recommend for others. Good luck! --Jayron32 18:52, 2 December 2009 (UTC)

A child of six shouldn't be left alone with an Internet connected computer - regardless of which site she uses. The way to have kids get the best out of the Internet (and Wikipedia) is to keep the computer in whatever room your family hangs out in - and for parent and child to surf together - just like you'd read a book together or (hopefully) watch TV together. Any of those things could potentially expose your kid to stuff you don't think is appropriate - so these activities need to be a "family time" kind of thing. That being the case - you can use Wikipedia with complete safety - with YOU deciding what's appropriate and not some anonymous (and fallible) Wikipedia-clone maker. If something difficult needs explaining - you are there to explain it. The computer is not a child-minder and shouldn't be treated as such. More importantly - you can also direct your child towards interesting/useful/appropriate things - not just away from inappropriate material - no amount of censorship of the content will help you there! A 6 year old is not able to make the connections that you can make - to find answers in an online encyclopedia that you can find. SteveBaker (talk) 19:39, 2 December 2009 (UTC)

I find it rather offensive that you're telling me how to raise my child. I simply asked if there was a children's version which Jayron was helpful in providing. It's a lot to assume I'm letting her on the internet unsupervised. It's good to know other people treat the issue with concern but please don't assume I neglect my children. TheFutureAwaits (talk) 19:57, 2 December 2009 (UTC)

I'm actually more concerned with truth than whether you might find it offensive or not. If you are supervising her then what do you have to worry about? Just use regular Wikipedia. What am I to assume from the nature of your question? The best way to increase her vocabulary is to read to her. When a kid doesn't understand a word - they just skip over it and guess the meaning (often incorrectly). SteveBaker (talk)

The suggestion to surf together is a pretty common answer to questions like yours. I don't think you should get offended, it's a good suggestion. It's not that anyone thinks you are negligent or that they're trying to tell you how to raise your child, it's just the fact that the internet, by it's very nature, is only a couple links away from content you might not want your kids to see. -- JSBillings 20:23, 2 December 2009 (UTC)

I had this problem a while back with a sequence which went Tudors>>Anne Boleyn>>Incest (which then was the wikilinked crime on her death warrant). If you do want to avoid being online at all the Schools Wikipedia also comes as a free download which we will mail you without charge if needed (yes, me). It is less popular compared to Wikipedia but a lot of schools intranets load it. As said it is currently mainly March 2008 content and Obama is still only a senator (there will be a big update in Q1 2010). --BozMo talk 20:38, 2 December 2009 (UTC)

It doesn't help the original poster, but I've experimented with creating filtered subsets of Wikipedia using categories and keywords to choose what material to exclude. My impression is that I can actually do a pretty good job at this. Not as good as hand-checking for obvious reasons, but the result I'd hope for would be a much larger collection of "good" articles while excluding most of what people find objectionable. I've thought about trying to finish this early next year. Dragons flight (talk) 20:48, 2 December 2009 (UTC)

Unfortunately, Wikipedia culture is such that we demand that our readers accept our "anything goes" policy as a price of using Wikipedia. You'll never get any prior warning of what the next click will bring you to; that's just not the way we roll here. However, Openmoko's Wikireader is a portable device for reading a static version of Wikipedia offline, and advertises itself as having parental controls. It might be the solution to the original questioner's problem (since Wikipedia resolutely refuses to provide a solution). - Nunh-huh 21:22, 2 December 2009 (UTC)

The wikireader parental controls are just a keyword based filter as I understand it. Dragons flight (talk) 22:29, 2 December 2009 (UTC)

We did make a request yonks ago for a hidden tag of "unsuitable for young children" be included in content so that a reader could switch it on or off but the community is for some reason extremely hostile to any concept of censorship. --BozMo talk 22:34, 2 December 2009 (UTC)

One problem is defining what is and is not "unsuitable for young children" on an international site. E.g. Europeans are pretty relaxed about children seeing non-sexualized female toplessness, but get an accidental 2-second "wardrobe malfunction" on US television, and you won't hear the end of it for months. -- 128.104.112.95 (talk) 23:09, 2 December 2009 (UTC)

Parental supervision while small children read Wikipedia is advisable, since a vandal can introduce any content into all but the few protected articles at any time, or can substitute an extremely obscene image for another image, with it typically taking several minutes or several days for articles few are watching to get reverted to the good version. Wikipedia is not censored, and content you might think inappropriate for a small child is only a couple of clicks away. Children doing unsupervised websurfing are also likely to be stalked by pedophiles. A School-appropriate version of Wikipedia as mentioned above would be useful, with staleness being the main problem. Edison (talk) 23:29, 2 December 2009 (UTC)

Lets not be silly children unsupervised websurfing are not 'likely' to be stalked by pedophiles. That is a ridiculous comment. They are clearly at more risk than when supervised with an adult, but the risk itself is still extremely low. 194.221.133.226 (talk) 10:13, 3 December 2009 (UTC)

I'd say the child is more at risk when they are supervised by an adult -- for every child molested by a pedophile they met over the internet, several thousand are molested by their parents. --Carnildo (talk) 02:40, 5 December 2009 (UTC)

You can get a huge reduction in simple vandalism by not serving any page unless it is at least a few hours old without further editing. That's another kind of automated filter one can use when collecting good versions. Dragons flight (talk) 23:41, 2 December 2009 (UTC)

The main trouble is that it's difficult for anyone else to anticipate exactly which images you would find unsuitable for your child, without knowing you or your child. One option is Internet filtering software, such as CyberSitter or NetNanny, which you can configure to suit your particular concerns. A conservative option is to turn off images altogether and browse text only. Dcoetzee 23:51, 2 December 2009 (UTC)

Exactly - there are widely differing opinions between parents about what is or is not appropriate at a whole range of ages. It's quite unreasonable to expect one filtered source to be appropriate for all parent's requirements, for all children (they are all different you know?!) over a wide range of ages. Then, we have three MILLION articles - nobody, no organisation, can possibly have checked them all. So we're left with some flaky keyword-based thing - which can't figure out what's in photos anyway. That will exclude some appropriate articles and fail to exclude some noxious ones. I simply don't believe this can work. But in any case - leaving a 6 year old alone with an internet-connected computer is just not reasonable. I'm sorry our OP objects - but it's true. Work with your kid - both you and she will be better off as result. SteveBaker (talk) 00:39, 3 December 2009 (UTC)

With keyword-based filters you also have the problem of the unmentionable British town. -- 128.104.112.95 (talk) 22:44, 3 December 2009 (UTC)

Buying the latest edition of Worldbook or just taking your child to the closest public library to read about things in that or similar encyclopedias is another great idea. Edison (talk) 00:24, 3 December 2009 (UTC)

Another question about visual phenomena...

When I close my eye and push hard on it, I see weird psychedelic greyness, like a swirly tunnel with RGB dots. What's that called?--Editor510 ^{drop us a line, mate} 18:52, 2 December 2009 (UTC)

Not sure that is a good thing to do, but I am no eye doctor... Googlemeister (talk) 19:47, 2 December 2009 (UTC)

Phosphene#Mechanical stimulation -- Finlay McWalter • Talk 19:48, 2 December 2009 (UTC)

Thank you, Finlay. Googlemeister, I asked for an answer, not medical advice. Keep that in mind for next time.--Editor510 ^{drop us a line, mate} 20:08, 2 December 2009 (UTC)

I guess this is a situation exemplifying the statement "There are no stupid questions... " Well, I am sure you can fill in the rest. Googlemeister (talk) 21:04, 2 December 2009 (UTC)

"...There are only stupid people who quote trite clichès and leave off the end for others to fill in themselves."--Jayron32 21:18, 3 December 2009 (UTC)

why do i feel hotter after a bath?

It gets cold where I live and I have no central heating. The house feels cold and the fire seems to not do much, however after a hot bath in the evening the house seems to be 50% hotter than it was. Is it my core temperature or something? —Preceding unsigned comment added by 89.242.173.139 (talk) 19:14, 2 December 2009 (UTC)

There's probably a couple of things at work here. First, to point out the obvious, after a hot shower or bath you are warmer. People typically have an internal temperature of about 37C, but it's much cooler than that at your extremities (feet, hands) and, to a lesser extent, any part of you exposed to the environment (i.e. your skin). A hot bath can raise the temperature of your extremities, making you feel warmer overall. Your core temperature changes very little except under rather uncomfortable extremes such as hyperthermia, so I doubt you've affected your core temp more than a tiny amount. The benefit to having your extremities warmed (to me) is that they stop acting like heat sinks for the rest of the body. Cold feet, by themselves, are no big deal, but on some chilly days it almost feels like they're draining the heat right out of you. When you add heat energy to your feet through hot water, rather than through your own efforts, it seems like you get paid twice - your feet are warm and you haven't had to freeze your hands (or your partner's back!) to do it. Matt Deres (talk) 21:33, 2 December 2009 (UTC)

Your temperature-detection equipment is in your skin; a hot bath raises the temperature of your skin, so there you are. As an aside, a simple fireplace will often cause a net heat loss in your house. You want some kind of wood stove or fireplace insert to make the fire put off more heat than it sucks up the chimney. --Sean 17:27, 3 December 2009 (UTC)

That point about fireplaces causing a net heat loss sounds bogus to me. Dauto (talk) 16:35, 4 December 2009 (UTC)

That's the common reaction, but it's true: a fireplace is very inefficient at transferring heat to the surrounding environment. Effectively all the hot gasses generated by the fire go up the chimney, most of the radiant heat is wasted heating up the fireplace bricks, and the room-temperature oxygen used up by the fire is replaced by sucking cold air in from the outside. --Carnildo (talk) 02:46, 5 December 2009 (UTC)

Children aargh

Ok, so I cannot always answer my offspring's question, here is one: "If you exclude a primary colour such as blue from the visual experience of a baby through to childhood we have been told they will not develop the ability to see and process that colour mentally, which I understand, but what if you exclude a secondary colour whilst allowing the separated components into their world: will their brain mix the colours and develop the secondary colour (say, green) via dreams etc or will they not develop a capacity to "see" the secondary colour in cognitive terms". Oh dear. Any help? --BozMo talk 20:43, 2 December 2009 (UTC)

Who said that excluding a primary color will prevent a child from being able to see it? I'm just curious, because I haven't heard that, and I am wondering how they managed to test it. Falconus^{p t c} 21:11, 2 December 2009 (UTC)

Who said it in this case was a biology teacher so it could be suspect although I suspect "see and process" should be taken together. There is lots of stuff around about lazy eyes and some eye conditions do selectively filter frequencies/colours so "testing it" I assumed was more "observing it" --BozMo talk 21:17, 2 December 2009 (UTC)

Firstly, green is a primary colour (it's additive or psychological primary colours that are relevant here and green is in both those groups, subtractive primary colours, which don't include green, are only relevant to painters). Secondly, could you provide a reference for your initial assertion? I'm not sure what would happen if you someone doesn't see a particular colour during their childhood. Under the opponent process theory, we perceive colour along two axes red-green and blue-yellow. I don't think you could exclude red, say, without also excluding green. That would mean you reduce colour to one axis. If the brain doesn't form the ability to see the other axis (and I don't know if it would or not) then you would essentially be colour blind (red-green colour blind or blue-yellow colour blind depending on which axis you exclude). If you exclude a secondary colour, it might be similar to the situation described in Opponent process#Reddish green and yellowish blue (which is about creating new secondary colours). In that case, people described it as a new colour that they couldn't recognise, but some were able to describe it as a combination of colours they knew. It would be reasonable to assume showing someone a secondary colour which is new to them would have a similar effect. --Tango (talk) 21:13, 2 December 2009 (UTC)

That's helpful thanks, and good enough I hope to keep my daughter thoughtful for a couple of hours. --BozMo talk 21:19, 2 December 2009 (UTC)

Google: Mancuso Hauswirth "color blindness" "hard-wired".—eric 01:21, 3 December 2009 (UTC)

Christmas lights

What is it that makes new-fangled LED Christmas lights look so harsh and cold, while old-fashioned incandescent Christmas lights look more warm? Something about the narrowness of their spectrum, prior life experience of them, or something else? - Nunh-huh 21:16, 2 December 2009 (UTC)

I expect it is the narrowness of the spectrum. --Tango (talk) 21:18, 2 December 2009 (UTC)

Color_temperature? --77.22.37.20 (talk) 21:37, 2 December 2009 (UTC)

I think it's because most LEDs are clear while the larger, older lights are usually frosted to an extent. If you've ever bought the wrong type of (regular) light bulb for your home, the difference should be immediately obvious. ~ Amory (u • t • c) 21:45, 2 December 2009 (UTC)

I suspect the answer is along the lines of what User:Tango said. Incandescent Christmas lights work by emitting white light, which is composed of all visible wavelengths, and then filtering it through a colored glass so that it appears colored, but light from the whole spectrum still gets through. LED lights, on the other hand, actually produce light of only one certain color, in a very narrow spectrum. It's this narrow spectrum that you're seeing as "harsh." Mildly Mad^T_C 21:53, 2 December 2009 (UTC)

I think the color temperature is a good answer, as 77.22.37.20 suggested. The retina is not a good spectrum analyzer to determine what wavelengths are present. The size of the source may also be a factor, since most incandescent Christmas bulbs are much larger than their LED rivals. Edison (talk) 23:21, 2 December 2009 (UTC)

It may also be that LEDs are typically strobed to work at maximum efficiency - i.e. they flash on and off very rapidly. This should be faster than the eye can detect, but may still cause an effect of harshness. You can check whether they flash by moving them quickly - you should be able to see the flashes that way. --Phil Holmes (talk) 09:48, 3 December 2009 (UTC)

I thought the strobing is due to plug-in LEDs running off AC current causing flickering at 50 or 60 Hz. I've never noticed the flickering when they operate under DC power. -- Flyguy649 ^talk 15:45, 3 December 2009 (UTC)

If you simply power an LED from a DC source, you're right - they don't strobe. However, LEDs are much more efficient at high currents, but running them continuously at such a current would make them too bright and probably too hot and they would fail. So the solution is to run them at high current for a short time, turn them off to let them cool and then switch them on again. So if you're a commercial manufacturer wanting to make your LEDs as efficient as possible, that's how you power them - and hence the strobing. Nothing to do with AC or DC. --Phil Holmes (talk) 10:00, 4 December 2009 (UTC)

Strobing LEDs definitely makes it look unnatural. If you slide your eyes quickly across a string of such lights you get a weird 'digital looking' trail instead of a smooth blur like you would with an incandescent

If you're thinking of white Christmas lights, then a big part of the issue is the actual color of the lights. They're not quite white. "White" incandescent tree lights are slightly yellowish which we mentally associate with warmth, candles, etc. Most "white" LED lights are actually slightly blue, maybe not enough that you notice consciously, but subconsciously you associate them with coldness, and metal, and artificial light sources. APL (talk) 16:47, 3 December 2009 (UTC)

Since most "white" LED's are typically ultraviolet LED's used to excite a phosphor coating - they could presumably fix that by reducing the amount of blue phosphor in the coating. However, because LED Xmas lights are not a vast market for white LED manufacturers - there isn't enough volume to justify making special off-white ones. I suspect that this will happen though - it's such a joy to have a string of lights actually work reliably after they've been pulled off a tree - stored in a garden shed for 340 days and then dumped back onto the tree again...when the prices fall by just a little more, the incandescent kind will go the way of the Dodo. I made my first set of LED Xmas lights myself - back before there were any that you could buy. I used 50 bi-color red/green LED's which can show any color in the red/orange/yellow/green range - all of which seem pretty Xmassy. They are still working - but the big DC power supply it takes to run them is a pain to deal with...so now I have store-bought ones. SteveBaker (talk) 18:39, 3 December 2009 (UTC)

But going through each bulb on a series circuit testing each one to see where the loose one is is part of Christmas tradition! --Tango (talk) 18:48, 3 December 2009 (UTC)

They'd better hurry up before our old lights need replacing: the decorations section of shops is horrible this year with the strings of strobing LEDs. Is it too much to ask for something that either flashes slowly or stays on? I'd even take a cold white if they at least avoided the headache-inducing throb. Or, instead of trying to be 'tasteful', they could just release strings of coloured LEDs: aren't the red ones cheaper? But either way, they have to stop that strobing. 86.166.148.95 (talk) 01:37, 4 December 2009 (UTC)

which element most toxic?

Which pure element is the most toxic if ingested? Natural elements only, don't worry about stuff heavier then Uranium. Is it arsenic? Googlemeister (talk) 21:41, 2 December 2009 (UTC)

How much and in what form are we talking about here? Chlorine gas is up there, but if you could figure out how to do it I imagine elemental Fluorine would be far worse. ~ Amory (u • t • c) 21:51, 2 December 2009 (UTC)

Well assume the natural state of the element at STP. So whereas drinking liquid helium would probably kill you, swallowing a bit of helium gas would not be lethal, so it is not that helium is naturally toxic. Googlemeister (talk) 21:56, 2 December 2009 (UTC)

Beryllium, Plutonium, Mercury, Arsenic, Cadmium are all pretty nasty.[3] Fences&Windows 22:27, 2 December 2009 (UTC)

But of lot of those are not as toxic as their salts, many of the heavy metals won't dissolve much in stomach acid, and small amounts will pass right through. Therefore one should consider things like sodium, potassium, bromine - not that you would ever be able to swallow them!  Ronhjones  ^(Talk) 22:35, 2 December 2009 (UTC)

Polonium isn't great - it was used to kill Alexander Litvinenko in the UK a couple of years ago. Brammers (talk) 23:15, 2 December 2009 (UTC)

But it didn't kill him via chemical toxicity, but by radiation. Polonium (any isotope) is so radioactive that there is probably no experiment that can measure its chemical toxicity, which is negligible in comparison. --Trovatore (talk) 00:28, 3 December 2009 (UTC)

Right... and if you are allowed to pick non-stable elements, you can find some reeeaaaallly nasty ones, albeit they have very short half-lives. Whether you count these as "natural elements" of course relies on different definitions of "natural". --Mr.98 (talk) 03:25, 3 December 2009 (UTC)

My objection was to the word "toxic". Radioactives will kill you, but they're not toxic, any more than a bullet is. Toxicity is a chemical property. --Trovatore (talk) 10:36, 3 December 2009 (UTC)

Hmm while I'm not disagreeing with you our article does toxic Nil Einne (talk) 15:30, 3 December 2009 (UTC)

I think toxicity means a bit more than you are claiming it does ("chemical toxicity" is one sub-variant of "toxicity"). I am fairly sure that highly radioactive substances are classed as highly toxic (ergo, Polonium#Toxicity). Where things get trickier are weakly radioactive but long-living substances (like, say, plutonium), which are not very acutely toxic (you will not keel over dead if you are exposed to it) but have long-term carcinogenic risks (you will get lung cancer in some number of years if you inhale a lot of it). --Mr.98 (talk) 17:51, 3 December 2009 (UTC)

Plutonium is toxic in addition to being radioactive, because it's a heavy metal. Not very toxic, though; supposedly about as toxic as caffeine.

I really think it's a misuse of the term to call radioactive substances "toxic" as a function of their radioactivity. Litvinenko wasn't poisoned, he was irradiated. Outcome is the same, of course, but it's a different thing. For that matter it strikes me as a bit off to call things poisons just because they are very acid or very alkaline — those are chemical properties but shading into physical ones. --Trovatore (talk) 21:01, 3 December 2009 (UTC)

I think toxicity is concerned less with mechanism than it is with measurements like LD50, which makes sense to me (otherwise you start getting into a lot of hair-splitting when all you really want to know is will it kill me quick). I find a basic benchmark for thinking about what toxicity means is, "what would make a good poison?" I think hair-splitting is useful when talking about acute toxicity or not (again, the radioactivity question, but for different substances), but not further down than that. --Mr.98 (talk) 14:34, 4 December 2009 (UTC)

I think beryllium (by far) is the most toxic element. The term you are looking for LD50. Try googling for LD50 and the names of some potential elements. I checked those that Fences posted, and beryllium easily beat the others. Also you have to distinguish between ingestion and inhalation (and injection possibly). Different things have different toxicity depending on the route of administration. Ariel. (talk) 01:23, 3 December 2009 (UTC)

Isaac Asimov's 1954 short story 'Sucker Bait' hinges on the realisation (by a non-specialist polymath whom Asimov terms a "mnemonic") that a higher than usual level of beryllium in the crust of a recently discovered planet is responsible for the death of its first colonists. 87.81.230.195 (talk) 14:10, 3 December 2009 (UTC)

Are you sure? In our article on Beryllium...

Ingestion

Swallowing beryllium has not been reported to cause effects in humans because very little beryllium is absorbed from the stomach and intestines. Harmful effects have sometimes been seen in animals ingesting beryllium.[41]

Googlemeister (talk) 16:20, 3 December 2009 (UTC)

Did you read the rest of the long toxicity section in the article? --Mr.98 (talk) 17:46, 3 December 2009 (UTC)

I admit, I only skimmed the rest since my question specifically was referring to ingestion and not inhalation or skin contact. Googlemeister (talk) 19:18, 3 December 2009 (UTC)

The most toxic element is anti-matter. Ingesting even 1/1000 gram of anti-matter is fatal. 139.130.57.34 (talk) 20:55, 3 December 2009 (UTC)

Possibly, but I don't see how you are going to get the antimatter (we will use antihydrogen since technically antimatter is not it's own element) into your mouth to swallow it before it annihilates. Googlemeister (talk) 21:14, 3 December 2009 (UTC)

This is not toxicity; this is vaporization. --Trovatore (talk) 21:17, 3 December 2009 (UTC)

--Jayron32 21:14, 3 December 2009 (UTC)

Solar panels

If you used a big magnifying glass to focus the sun's energy on one spot of a solar panel, could you therefore have a smaller panel while producing the same amount of power? What about a concave mirror? Dismas|^(talk) 22:15, 2 December 2009 (UTC)

Yes and yes. People often use reflectors and similar but there is a geometric problem that the sun moves so you have to move them or accept limited effectiveness. I have 11m2 of solar panel (water heating) on my roof plus a similar area of reflectors. It roughly doubles the measured output when the sun is in the correct position but not all day long. --BozMo talk 22:19, 2 December 2009 (UTC)

At some degree of concentration the solar energy would destroy the photovoltaic panel segment it was focussed on, like setting a piece of paper on fire with a magnifying lens. There is clearly a limit on the amount of concentration a panel can tolerate, and a maximum on the electricity it can generate. Edison (talk) 23:18, 2 December 2009 (UTC)

There's also a safety issue, as concentrating too much light can start fires, blind people, or burn them. Also, the "giant lens" might very well cost more than just having more solar cells. StuRat (talk) 07:16, 3 December 2009 (UTC)

A giant reflector is a lot easier to make than a giant lens, which is why this Australian company chose to use those instead. --antilived^{T | C | G} 10:31, 3 December 2009 (UTC)

On a related note, focussed sunlight is used to run concentrating solar power stations; there the sunlight generates heat to run a turbine (rather than using a solar panel). -- Finlay McWalter • Talk 01:34, 3 December 2009 (UTC)

Solar cell efficiency is directly related to temperature, the more you heat up a solar cell the less efficient it gets. A clever idea I saw on a tv show recently had like a raft of solar cells with large reflectors floating on water (like a lake or something) so as to dissipate the heat. Vespine (talk) 05:44, 4 December 2009 (UTC)

Even better, you can get solar cells combined with solar water heaters that keep the cells relatively cool and supply warm water as well. Mikenorton (talk) 23:42, 4 December 2009 (UTC)