Wikipedia:Reference desk/Archives/Science/2007 August 18

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

August 18

Strange creature ID needed...

I've had this pic on my HD for ages (can't even remember where I found it now). What the heck is this strange-looking fat green beastie anyway? --Kurt Shaped Box 00:05, 18 August 2007 (UTC)

There's something vaguely terrapin-like about it, for what it's worth. DuncanHill 00:09, 18 August 2007 (UTC)

I remember posting a link to it on usenet once and the general consensus there was that it was a photoshopped image created from several different animals. I dunno. --Kurt Shaped Box 00:11, 18 August 2007 (UTC)

Whoah, that's a weird picture. My guess is it's an armadillo giving birth. OK, I'm still perplexed. It looks not entirely unlike an armadillo, but where are the ears? If it really were a new baby, you should see the mother's tail. --Reuben 00:28, 18 August 2007 (UTC)

Cantor's giant turtle. They are super rare and live in Southeast Asia. Plug the name into Google Images for more. --24.147.86.187 01:00, 18 August 2007 (UTC)

I've looked. The CGT looks too skinny. --Kurt Shaped Box 01:11, 18 August 2007 (UTC)

What about the related Pelochelys bibroni? Looks a little "bulk-ier" (another image here). -- MarcoTolo 02:10, 18 August 2007 (UTC)

"Too skinny" does not seem to be a valid argument to me. The turtle on your picture sits on a pillow on a floor mat, i.e. it seems to be kept as a pet by someone. Maybe this someone has fed it too much and now it's overweight? Simon A. 08:20, 18 August 2007 (UTC)

I agree with 24.147 that it is probably Cantor's giant soft-shelled turtle (Pelochelys cantorii). Some of the images from a google image search look very close (and just as fat) as Kurt's image.--Eriastrum 17:49, 18 August 2007 (UTC)

Yeah, you may be right. Searching for the scientific name results in more hits. If it's not that particular species, it's pretty damn close. Thanks. --Kurt Shaped Box 19:39, 18 August 2007 (UTC)

Maybe Pelodiscus sinensis, too. Anyway, definitely in the Trionychidae family — what strange looking animals!

Speculation

This may be a stupid question, but here it goes anyway. Say if u bent a rod, I am wondering if the length of the smaller arc of the bent rod would be the same or shorter than the original length of the rod, even if there is only a tiny difference.

Shorter (slightly). The inside of the rod has to compress for it to bend. The outside of the rod has to stretch, so thats longer. See bimetallic strip for an interesting corollary of this principle.--SpectrumAnalyser 02:01, 18 August 2007 (UTC)

Not necessarily - we could imagine a material that would not compress easily but which might have no problem stretching. In that case the inner length would remain the same - and the outside would stretch a lot. Conversely, a material that is easily compressible - but hard to stretch (foam rubber for example), all of the change would be on the inside of the curve and the outside would stay the same length. I guess most materials will both squash and stretch to some degree - but it's not at all obvious that this is universally true. I think the nature of the material matters here. SteveBaker 14:40, 18 August 2007 (UTC)

That would require the stretching to be infinitely harder than compressing, or vice versa. I think it is possible to make a structure where the whole thing stretches or compresses when bent, but that is about the structure, not the material. — Daniel 18:25, 18 August 2007 (UTC)

If you look at a bent metal rod you can usually see little folds on the inside of the bend where the metal has pushed out to compensate for the shorter length. You can sometimes also discern stretching on the outside. Note that heating it allows the metal lattice to realign better, which is why metals bent more professionally, say by a blacksmith, don't suffer these problems. A good thing to try is bending a painted rod - the paint will usually crack or fall off where the length changes, but stay pretty much OK where the length hasn't changed. --jjron 04:43, 19 August 2007 (UTC)

Dreaming

A question above about dreams prompted this question from me, which I have always wondered about. If there is a fact that I personally do not know in real life, is it at all possible for me to have a dream of that fact ... or is that simply impossible on some level (physically / mentally / cognitively / consciously / subconsciously / whatever)? For example, in real life, I can't speak a word of Japanese. In one of my dreams, would I be able to speak fluent Japanese? For example, in real life, I do not know the square root of 378 (or the middle name of Tom Cruise). If I were asked those questions in one of my dreams, would I be able to correctly answer them? Thanks. (Joseph A. Spadaro 01:56, 18 August 2007 (UTC))

You may dream that you know the fact or answer or speak the language, but it is probably wrong. If you remembered what the answer was and checked it out in the waking world you will find out. It is possible that the answer is correct, and it may come from a part of your memory that you have never otherwise been able to recall. Or it could be a message from God, or if you are unlucky from a demon! Graeme Bartlett 02:24, 18 August 2007 (UTC)

I have found myself utterly convinced I knew and understood something that I actually did not. This was real life, unfortunately...So no, I don't see a reason you couldn't have the same feeling in a dream. Someguy1221 10:15, 18 August 2007 (UTC)

In a dream, I'm often convinced I know something, only to find out that I know the truth and it isn't what I thought it was while sleeping. Being convinced that an illogical event is happening while viewing it as logical is a common feature of dreams; even if you accidentally stumble upon the middle name of Tom Cruise, you'll have a hard time convincing me God did it. --Bowlhover 16:15, 18 August 2007 (UTC)

There is a theory that a great deal of learning happens while asleep, by reviewing recent activities and doing "batch processing" to figure things out that weren't apparent "in the heat of battle". For example, if a dog has tried to bite you before, but only when you are wearing a backpack, you might figure this out while asleep. Of course, the idea is that this new knowledge is to be transferred to the waking portion of the brain for future use, so the sleeping brain would only have additional knowledge for a short period.

If you had asked the more general question "can part of your brain know something that another part doesn't", then the answer is yes, at least in the case of multiple personality disorder. That is, one personality can have knowledge or skills that another can't access. However, this knowledge or these skills still have to come from somewhere, such as study or practice. It isn't possible for someone to know something (like Tom Cruise's middle name) without having learned it first. StuRat 20:15, 18 August 2007 (UTC)

Dark energy

Is the energy that is required to keep the Universe expanding simply dark energy? --M1ss1ontomars2k4 02:46, 18 August 2007 (UTC)

No, Dark energy, it it had sufficient density would cause the universe to contract. However it will not clump together by gravity as does other normal matter or dark matter, and so will tend to smooth out the universe. It moves too fast to settle down! Graeme Bartlett 03:44, 18 August 2007 (UTC)

Not quite right; at least in the simplest picture, where dark energy is a vacuum energy or cosmological constant, a greater density of dark energy would make the universe expand faster. It has an equation of state with negative pressure. --Reuben 06:01, 18 August 2007 (UTC)

The increase or decrease in the universe's scale factor $a(t)$ is governed by a differential equation

${\frac {da}{dt}}=H_{o}{\sqrt {\Omega _{m_{o}}a^{-1}+\Omega _{r_{o}}a^{-2}+\Omega _{v_{o}}a^{2}+(1-\Omega _{tot})}}$

where $\Omega _{m_{o}},\Omega _{r_{o}},\Omega _{v_{o}}$ are the present-day matter (ordinary and dark), radiation (CMBR), and vacuum (dark energy) densities respectively. (I cribbed this from Ned Wright, and it should probably go in FLRW, since it's much more convenient than the form that's there now.) So you can see that if $\Omega _{tot}\leq 1$, as it appears to be, then $da/dt$ will always be positive and the universe will keep expanding, regardless of the dark energy density. However, as a increases, the dark energy term will get larger while the other two density terms will get smaller, so eventually the expansion will be essentially driven by the dark energy alone. At that point the equation reduces to ${\frac {da}{dt}}=H_{o}{\sqrt {\Omega _{v_{o}}}}a$, which describes exponential growth. -- BenRG 18:55, 18 August 2007 (UTC)

What kind of squirrel is this?

I photographed a squirrel. It may be an Eastern Gray Squirrel, but I'm not sure. It was at the Blank Park Zoo in Des Moines, Iowa, though it wasn't part of an exhibit. grendel|khan 03:48, 18 August 2007 (UTC)

From the location (Iowa) I would expect it to be a fox squirrel. It's back does appear to be a bit more gray than usual, but that's probably still within the normal variation. StuRat 20:02, 18 August 2007 (UTC)

Hmmm, it's possible (even if not especially likely), that it could have escaped from an exhibit. --jjron 04:46, 19 August 2007 (UTC)

Holy crap that's the functionally extinct Eastern Grey Fox Squirrel called Sucop. Sucop is last female of her species and our zoo lost her just before we attempted to breed her with the last male, Ekaf! -- Blank Park Zoo 11:53, 19 August 2007 (UTC)

Comedians. Comedians are everywhere. —The preceding quasi-signed comment was added by Ummit (talk • contribs) 14:29, 19 August 2007 (UTC)

Who was Ed Hummel?

All I know is that his name (or part of it) turns up in the name of many hybridised succulent plants. There are also many references like ".. a Hummel hybrid .." on the Internet,. It seems like everyone knows one or more of the plants he produced, but these is no biographical information which I can find. I would like to know where he lived and worked, his birth & death dates, and if remotely possible, to find a list of the plant hybrids he produced. Thankyou 211.27.210.31 04:46, 18 August 2007 (UTC)

Ed Hummel, hybridist, of Hummel's Exotic Gardens, Carlsbad, California. See here. Xn4 01:18, 19 August 2007 (UTC)

Thank you very much for the information, not only was it just what I wanted, but it lead me to a resource I had not seen before. Would it be possible to add Ed Hummel to the Hummel disambeguination (Sp?) page? 211.26.60.17 02:09, 24 August 2007 (UTC)

pitcher plant

How do pitcher plants pollinate if they eat the pollinator? Clem 05:57, 18 August 2007 (UTC)

The "pitcher" of the pitcher plant is a modified leaf, not the flower. Thus the pitcher digests the body of whatever critter falls inside for additional nutrition. The flower is a separate structure that does not "eat" the pollinator. The flowers are usually held much higher than the pitchers, and the insect that pollinates the flower is often a different type of insect than that that provides food. The different types of carnivorous plants have varied mechanisms to prevent eating the pollinator.--Eriastrum 15:45, 18 August 2007 (UTC)

Transdermal Deca Durabolin

I know there is both testosterone gel and cream (also injections), but is it possible to have transdermal deca durabolin? Why or why not?

Stovetops

Why do hotplates not cause electrocution? How are they insulated, considering that most saucepans are made of metal?

The heating element is inside the hotplate - and is surrounded by an insulator - the metal (if present) on the outside does not carry any current.87.102.92.28 12:23, 18 August 2007 (UTC)

The insulator is some sort of temperature resistant inorganic solid.87.102.92.28 12:24, 18 August 2007 (UTC)

See heating element.--Shantavira|^{feed me} 13:09, 18 August 2007 (UTC)

Magnetic property of Hydrogen .

Is hydrogen diamagnetic ? 203.112.222.101 did not sign.

Yes it is repelled by a magnet. But only weakly. You may be able to exceed the gravity force with fields about 16 Tesla. as is evidenced by the frog levitation experiment. pyrolytic graphite and bismuth have a stronger diamagnetic reaction. Graeme Bartlett 15:41, 18 August 2007 (UTC)

Why doesn't air conduct current?

We all know that air doesnot conduct current.But why is it so?Air has numerous ions and electrons which is essential for conduction.Why the current cannot be passed through air molecules?--117.97.35.39 14:49, 18 August 2007 (UTC)

Lack of free electrons. See also breakdown voltage and electrical breakdown - the molecules in air need to be ionised first.87.102.92.28 14:55, 18 August 2007 (UTC)

The vast majority of 'air' is made up of empty space (vacuum), of the remainder most is in the form of unconducting uncharged molecules such as nitrogen.87.102.92.28 14:56, 18 August 2007 (UTC)

The original questioner mentions "numerous" ions. The issue at hand is "how numerous?" At sea level, "not much", or less than 0.002%. That's not enough to conduct current. Nimur 15:14, 18 August 2007 (UTC)

A quick run through the Saha equation for oxygen, using a room temperature of 298K, atmospheric pressure, and the ionization energy for dioxygen given at dioxygenyl and a generous value of 10 or so for the ratio $g_{1} \over g_{0}$ that I don't know, gives me a fractional ionization of the order $10^{-101}$. Away from thunderstorms and cosmic rays, then, there's a very good chance that all the times the troposphere has ever had even one such ion measure much less than a second. --Tardis 20:10, 20 August 2007 (UTC)

Anyone who has ever seen an electrical storm knows that air does conduct current, it's just a question of how well. It's a relatively poor electrical conductor, because, as already stated, it has few free electrons. StuRat 19:53, 18 August 2007 (UTC)

Could one say that air is a semiconductor, which requires a very high voltage before it conducts (lightning), thus being binary (conducts a lot or nothing at all), just the way we use semiconductors? Sorry, I barely know what I'm talking about here. DirkvdM 08:34, 19 August 2007 (UTC)

I do not believe that air can properly be called a semiconductor: "a solid whose electrical conductivity is in between that of a conductor and that of an insulator." Edison 18:16, 19 August 2007 (UTC)

That "binary" conduction mode feature would not be the mark of a semiconductor. This process is called dielectric breakdown, and is not the same physical process as semiconductor operation. Nimur 19:14, 19 August 2007 (UTC)

When I was a schoolboy I found that a burning flame would conduct a current - why? 80.2.200.132 10:07, 26 August 2007 (UTC)

bush height

how does a bush/shrub know how high it has to grow?

My guess is genetics, but sometimes it goes wrong. I used to have a 3.5m high Mexican Orange Blossom (Choisya ternata) which all the gardening books say grows to 2.5m.--TrogWoolley 17:14, 18 August 2007 (UTC)

In the same way your body knows when to stop growing: combination of genes and environment. A number of genes interact to determine the size range and organism can maintain. Then environmental factors (like health, competition, access to nutrients, food, water etc) will determine where in that range the organism will reach. Rockpocket 23:21, 18 August 2007 (UTC)

Absorbtion rate through skin

Whats the highest possible absorbption rate through the skin for medicine?

I'd say it's pretty much instantaneous for some tiny molecules. Of course, most meds will be much larger molecules, so will be absorbed much more slowly, if at all. StuRat 19:48, 18 August 2007 (UTC)

[1] and Absorption (skin) might be useful. Nil Einne 11:44, 19 August 2007 (UTC)

Chagos Trench

What is Chagos Trench? By searching the internet, you get a answer like underwater canyon. But what it is in a plate tectonics context? The name implies it is one of oceanic trenches, but I think it is not.

Search Google with "directly from the trends of this ancient transform fault" and you get search result "directly from the trends of this ancient transform fault (the Chagos Trench and the. Mauritius Trench). For our purposes, the two determinations agree well ..."

Here an expert says he does not know anything about Chagos Trench.

Maybe someone could write an article with references?

--Pasixxxx 18:59, 18 August 2007 (UTC)

So, there are red, green and now blue laser pointers...

Anyone have any idea when violet laser pens will be on the market? --Kurt Shaped Box 19:52, 18 August 2007 (UTC)

I would expect there to be multi-colored ones first. With red, green, and blue, you can create any color. So, by allowing a person to adjust the intensity of each laser (inside one small case), you can produce any color you like. -- Kainaw^(what?) 21:39, 18 August 2007 (UTC)

How would you/would you be able to get yellow from that, as a matter of interest? --Kurt Shaped Box 21:52, 18 August 2007 (UTC)

In the RGB color model, yellow is a mix of full red, full green, and no blue. --24.147.86.187 22:15, 18 August 2007 (UTC)

this page has an interesting discussion of violet laser diodes that currently exist; apparently they have a tendency to make things nearby fluoresce (like a black light), which isn't that surprising. In practice it means that getting a pure violet waevlength out of a laser might be difficult, though maybe a mixing of multiple wavelengths as Kainaw suggests would work. --24.147.86.187 22:18, 18 August 2007 (UTC)

But then the whole point about lasers is lost: it is not monochromatic any more. --antilived^{T | C | G} 02:28, 19 August 2007 (UTC)

The whole point of a laser isn't its monochromaticness, it's the fact that it produces a largely coherent beam of light, that remains highly focused long enough to reach whatever powerpoint presenation you're aiming it at.--172.163.113.245 12:04, 19 August 2007 (UTC)

Or wherever you want your cat to run to... ;) --Kurt Shaped Box 16:25, 19 August 2007 (UTC)

Lasers were never monochromatic to begin with :-p (don't believe everything they tell you!) Someguy1221 20:05, 19 August 2007 (UTC)

On the subject of yellow: there's nothing stopping a single wavelength from appearing yellow: that's what rainbows do, after all. The primary colors aren't physics, but rather physiology: the number of them isn't even fixed. See dichromacy, tetrachromacy, etc. That we can make a yellow-looking laser beam in two different ways (finding a single yellow emitter or mixing a red and a green — although the result will not be coherent, exactly) is evidence that our color vision simplifies what's really there. --Tardis 17:48, 20 August 2007 (UTC)

How do I determine the age of an adult female budgerigar?

She's been used for breeding before, so she is definitely an adult bird. Is there any way of telling roughly how many years old she is?

See here. Xn4 00:55, 19 August 2007 (UTC)

IOW, unless she's wearing a leg ring, there's no way of knowing for certain how old she is, now that she's an adult bird. An 18-month old blue budgie (for instance) will look the same as an 18 year old blue budgie. I had a bird that lived 'till his late teens (poss. early 20s) and the only way that I knew he was old was because I knew how long he'd been with me and I knew that he had 'stiff' wings and a tendency to sleep a bit more, compared to how he used to be (his flock members would make an effort to feed him too - which I thought was lovely). I'm actually struggling to think of *any* bird that shows outward signs of ageing. --Kurt Shaped Box 05:58, 19 August 2007 (UTC)

Are you sure someone didn't acidentally kill the bird and replace it? Nil Einne 11:37, 19 August 2007 (UTC)

Na. This was definitely the same bird - unless someone was smart enough to find another bird with identical markings and demeanour and teach him to say exactly the same phrases... :) --Kurt Shaped Box 16:28, 19 August 2007 (UTC)

KSB- "I'm actually struggling to think of *any* bird that shows outward signs of ageing. See [2] for some specifics/examples. 38.112.225.84 05:47, 20 August 2007 (UTC)

Odd vision problem

Being a Wikipedia and RD veteran, there's no need to remind me of our rules about medical advice. I'm well aware of that, and I'm about to leave to check this with a doctor.

But a few hours ago I started to have this odd vision artifact. It's like a bad printing offset. I already ruled out the possibility of it being my computer monitor, as it follows the tilt of my head and I'm seeing it in books as well. What I first saw was a ghost image below letters, but I noticed it everywhere. Looking more into it, I decided to make a little experiment with each color, and each eye individually, using vertical and horizontal lines. The results puzzled me, since it looks like a freaky computer hardware problem. This is how it looks like, for both eyes (it's worse on the left one):

Anything red has a copy directly below. The green has a bit both up and down, but mostly up, and the blue colors leak up. This gives a weird colored ghost image at the top and bottom of things, and the ghost images are RGB-specific (magenta has two ghost images, a red below and a blue above). The distance is not constant and wobbles a bit. I've never heard of anything like this, and it looks kinda serious, so I'm checking it out with a professional already. Either way, I trust the power of the distributed knowledge of Wikipedians to take a guess of what this could possibly be. Have any of you ever heard of anything like it? I'm thinking it may be a chromatic aberration in my eyes. It makes a lot of sense, but in both eyes, at the same time, exactly the same way, and all of sudden? It's odd, but who knows?

Anyway, I'll be back later. Cheers! — Kieff | Talk 22:31, 18 August 2007 (UTC)

Hope it's nothing serious, man. I know that I have suffer from really weird visual artifacts myself when I have a migraine coming on. The first time it ever happened to me, I thought that I was going blind. --Kurt Shaped Box 22:41, 18 August 2007 (UTC)

I stared at those the longest time, thinking that the top and bottom examples looked identical, before I figured out the faint duplication. That's how bad my vision is. Absolutely not offering any medical advice, but you did not say if you wore glasses or if you had been tested for astigmatism. Hope your opthamologist/optometrist can help you. Edison 22:45, 18 August 2007 (UTC)

No, I don't wear glasses, and I've tested my vision last November with good results. — Kieff | Talk 04:41, 19 August 2007 (UTC)

You sure that it's not just a monitor issue? I had to give mine a wipe (didn't realize that it was covered in that much tar - heh) in order to see what Kieff was talking about... --Kurt Shaped Box 22:48, 18 August 2007 (UTC)

Yes, I already ruled out that possibility completely. — Kieff | Talk 04:41, 19 August 2007 (UTC)

I have astigmatism and it looks VERY like what you describe. You've said you are seeking professional advice, so of course - listen to your medical professional not to us! DuncanHill 23:11, 18 August 2007 (UTC)

Monitors with separate control electronics for each color (such as separate electron guns in a CRT sometimes have misalignments like you've shown. Are you sure this isn't a monitor problem? Nimur 23:19, 18 August 2007 (UTC)

Yes, I already ruled out that possibility completely. — Kieff | Talk 04:41, 19 August 2007 (UTC)

(Inappropriate medical comment removed here) There is something called a migraine aura, which can affect vision. A really bad migraine while your driving could be bad. You might want to think about having someone else drive you. --S.dedalus 23:29, 18 August 2007 (UTC)

I sometimes get auras, but do not get migraines. DuncanHill 01:16, 19 August 2007 (UTC)

Yeah, that happened to a friend of mine too. It must be rather surprising when it happens. --S.dedalus 05:02, 19 August 2007 (UTC)

No, I don't suffer from migraines. — Kieff | Talk 04:41, 19 August 2007 (UTC)

One can suffer from auras without migraines, or without ever having head a migraine headache before. It's called a "silent migraine" (somstimes known as "migraine sans migraine"). It's incredibly annoying, especially when you don't know what it is. They usually pass in under an hour.

The visual artifacts you're experiencing certainly sound related to migraine but I'd guess you'd have a really bad headache and other symptoms before or when that developed. As always see your doctor, or in this case an optician as well for professional, advice but I'd like to know if these symptoms are only at short distances. Whether it's short distances or not, if you're over 40 it could be related to a sudden decline in contrast sensitivity (fairly common), astigmatism as Duncan said, a specific symptom of macular degeneration problem or at a push cataracts especially if you've noticed any other problems in vision. If you've recently been light headed, had blackouts or had a knock to the noggin there are a number of possibilities, but by being smart and seeing the doc soon you should be able to sort it out before it becomes serious. Let us know how you are, all the best xx --82.12.235.69 01:55, 19 August 2007 (UTC)

I'm 21, and those things look quite unlikely. In fact, those problems you mentioned were ruled out by the doctor I visited. — Kieff | Talk 04:41, 19 August 2007 (UTC)

'Headacheless migraines' are definitely possible. Not sure if they're rare or not but I suffer from them occasionally. I get the 'auras', sickness and the 'unworldly feeling' - but no pain. One time, this was also followed by going completely numb down the right-hand side of my body and having trouble speaking. I honestly thought that I was having a stroke. *Very* scary stuff. --Kurt Shaped Box 05:12, 19 August 2007 (UTC)

Guys - this business of amateur medical diagnosis has to stop. I'm taking this to the talk page - I want to get an admin patrolling this group and handing out short term bans to people who break the rules. You are telling our OP that his symptoms are nothing important. If that causes him to fail to seek medical advice and this turns out to be symptoms of some terrible disease which maybe is fatal if not attended to (not that I particularly think it is - I just don't know) - then life insurance companies will come after you and you will get into deeper trouble than you can possibly imagine. This behavior has to stop. SteveBaker 02:57, 19 August 2007 (UTC)

I agree with you, but like I said, I'm well aware of this and I'm not gonna take medical advice from anyone here. That'd be a pretty stupid thing to do. All I wanted by asking this question is to probe the knowledge of various Wikipedians to see if anyone has ever heard of anything like this before, because I haven't. — Kieff | Talk 04:41, 19 August 2007 (UTC)

Well people, I went to the doctor and he's also totally puzzled. My eyes seem normal, my vision is nearly perfect, so he says, so none of this should be happening, as far as he knows, and as far as my eyes are concerned. I'll be back there during the week to discuss this with someone specialized in corneas to see if there's anything worth checking out, and also for further tests. I wonder if the effect will vanish by then, but either way, it seems to be an interesting case to study. Like he said, it could end up being a neurological thing, but that's still pretty odd. Anyway, thanks for the comments. — Kieff | Talk 04:41, 19 August 2007 (UTC)

Someone already mentioned it, but I have to say it again: Check out astigmatism. The difference in deflection could be caused by the difference in frequency. I believe one corrects astigmatism by using a lens with a bit of prism shape to it. This would seem to suggest that colors separating might be a normal symptom of astigmatism. At the very least, my astigmatism seems worse for red light sources (stoplights and brake lights) than other colors. --Mdwyer 05:37, 19 August 2007 (UTC)

Maybe, but I think they would have noticed that when they tested my vision, not only last night but also last year when I did some tests as well. They'd have to be pretty incompetent to miss that, I suppose. But I'll ask later this week. — Kieff | Talk 07:36, 19 August 2007 (UTC)

Is it still doing it? --Kurt Shaped Box 11:11, 19 August 2007 (UTC)

• Just make sure you ultimately see an opthalmologist - has more training than an optician or optometrist. Furthermore you can look at kerataconus (sp?) which is (rather scary) when your eyeball changes shape and starts to form a bit of a cone (pointed) which distorts vision - I believe the article has an example of the vision distortion. The other oddity is that your results seem to depend on colour - which is linked to the cones and rods at the back of the eye - but to my little knowledge that should not show double-vision on certain colours - or halo affect on certain colours. Try do some more experimentations for your own purposes - Do you have any known vision problems? Do you wear glasses or contacts? Do you suffer from dry eyes, short-sightedness, far-sightedness, etc. Does the problem change or appear differently depending on - angle, - distance, if you squint (lower your lids a bit). Test your self for colour deficiency. Please keep us posted, this is rather interesting.

Rfwoolf 15:03, 19 August 2007 (UTC)

Could you possibly have the beginnings of cataracts? I developed cataracts in both of my eyes and I started to get faint double images that eventually developed (over a period of a couple of years) into triple images of almost equal brightness. The images were offset by only a very small distance, so that the effect was that of double margins on one or two sides of an image. Once I got lens implants, this effect disappeared entirely, of course. I have never had migraine headaches, but once I had an aura that lasted a few hours--it was utterly terrifying because I had no idea what it was--thought I was having a detached retina! It took the form of a jagged C-shaped form that flashed and glittered. It was as if my vision was on a mirror that was shattered. I immediately went to my eye doctor who was able to tell me it was a migraine aura. Oddly it only happened once, and it was not accompanied by a headache. The human visual system is indeed a complex, bizarre thing!--Eriastrum 15:54, 19 August 2007 (UTC)

If I look from inside a room out of a window during daylight, I usually notice coloured stripes at the border of the window -- blue ones on one side and red ones on the other side. I've always assumed this to be a normal effect of some diffraction off a dark-light boundary, but it never occured to me that it might be a chromatic aberration in the eyes instead of a Fraunhofer diffraction at the object. But now I wonder: does everybody sees this or not? Simon A. 21:00, 19 August 2007 (UTC)

If I look at dark-light boundaries to one side of my field of vision, I get color fringes, which I eventually realized are due to chromatic aberration in my (fairly strong) glasses. Not diffraction, which wouldn't be strong enough to see in that situation. But this is not a separated image like the original poster describes. --Anon, August 19, 2007, 22:08 (UTC).

Kieff, you didn't mention it, but I assume you conducted your experiments without wearing any eyeglasses or contact lenses, right? I ask this because I've notice that polycarbonate eyeglass lenses have very noticeable prismatic effects away from their "central vision". I first noticed this at night where some decorative purple lamps on trucks were refracted into very separate blue and red images, but once you know the effect is there, it can be seen in a lot of circumstances.

Atlant 13:32, 20 August 2007 (UTC)