Science desk
< April 6	<< Mar \| April \| May >>	April 8 >

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

April 7[edit]

Butterfly ID[edit]

As I think I already mentioned, when I was in Nashville for the eclipse, I had seen many fairly large (but not gigantic -- 3-4 inches estimated wingspan) black butterflies which I had later identified (with the help of this ref desk) as Limenitis arthemis -- but I've been thinking since then, maybe a few of them (specifically, a few of the larger ones) might have actually been Battus philenor? The thing is, though, I didn't see any of them up close except fleetingly -- while I did more or less like them (except that they sometimes startled me by flying out from behind me), I did not go so far as to chase after them for a closer look (I had other stuff to do, and besides, I didn't want to unexpectedly run into some abomination like Papilio glaucus, which is also fairly common over there, and which, as I think I mentioned, scares me a great deal). So, my question is: are there any ways to tell between L. arthemis and B. philenor without having to look up close? 2601:646:8A01:B180:A1CD:5991:622F:4D99 (talk) 02:44, 7 April 2021 (UTC)[reply]

From what I can tell from the following sources, the most obvious visual difference is the "swallow-tail" on Battus philenor (poisonous) vs. Limenitis arthemis (mimic, non-poisonous).

"red-spotted purple - Limenitis (Basilarchia) arthemis astyanax". entnemdept.ufl.edu. University of Florica.
"pipevine swallowtail - Battus philenor". entnemdept.ufl.edu. Univerwsity of Florida.

--107.15.157.44 (talk) 20:25, 7 April 2021 (UTC)[reply]

I was aware of that, but the tails of B. philenor are very short and stubby, and therefore cannot be seen from a distance (as opposed to those of, say, Papilio troilus, which are longer and therefore can be seen from some distance away). 2601:646:8A01:B180:2198:6375:D4D0:9B6 (talk) 05:02, 8 April 2021 (UTC)[reply]

I'm not myself familiar with them (being in Europe), but they may noticeably differ in the overall impression of their colour, size and movements, which are collectively referred to by naturalists using a term whose Wikipedia article the system will not let me link to. (My earlier replies were auto-blocked as "unconstructive" – I have submitted a 'false hit' report.) You can find the article by searching on "(birding)" preceded by" zziJ" backwards. {The poster formerly known as 87.81.230.195} 2.219.35.136 (talk) 16:28, 8 April 2021 (UTC)[reply]

I'm thinking along the lines of movements -- the color is the same for both (I checked), and while B. philenor can be much bigger at the upper end of the range than either L. arthemis or P. troilus (and possibly big enough to scare me due to size alone, which is not the case for the other 2), the lower half of its size range overlaps almost perfectly with both of them. I did, however, find one possible way to tell them apart in the article about Papilio troilus -- it says that this species (and other Papilionidae as well, therefore presumably also B. philenor) continue to flutter their wings (slowly) while at rest -- so might that be a way to tell them apart from L. arthemis? 2601:646:8A01:B180:50CC:A800:928E:97F9 (talk) 03:28, 9 April 2021 (UTC)[reply]

Which eclipse? (You've linked to a disambiguation page, so I can't tell.) The reason I ask is because the flight times of the two species (i.e. when adults are on the wing) might help here if you're talking about a February eclipse. MeegsC (talk) 08:19, 13 April 2021 (UTC)[reply]

The one in August -- AFAIK the February one was not visible from Nashville -- so presumably both species would still be flying. 2601:646:8A01:B180:E8C8:7695:1C0E:E994 (talk) 03:03, 14 April 2021 (UTC)[reply]

Evident bias in climate change page[edit]

I intended to use Wikipedia as a resource for an article on climate change. As I wanted all sides of the debate, I looked for the views of MIT's head climatologist, Prof. Richard Lindzen (now retired), because he has a clear and concise way of explaining his position. But Prof Lindzen was omitted.

When I failed to find Lindzen's name, I perused the list of scientists in the index. It appears that only those scientists and organizations that believe human carbon dioxide emissions will cause what used to be called 'runaway global warming' (since changed to 'climate change') are the only views available to Wikipedia readers.

It would greatly enhance the credibility of Wikipedia if readers could see all points of view on the subject. If the views of skeptics of runaway global warming are wrong, readers will quickly see that. But by censoring the conclusion of any scientist who questions the hypothesis that rising CO2 will trigger runaway global warming, Wikipedia becomes a promoter of failed predictions. As such and given time, it will forfeit credibility.

There has been much discussion recently about critical thinking. But a basic requirement of critical thinking tends to be ignored: the thinker(s) must be exposed to all available information, irregardless of the source. When that requirement is met, the thinker(s) invariably arrive at the best possible conclusion under the circumstances. On the other hand, partial information produces erroneous conclusions. The fact that Wikipedia omits available information is not debatable. The question, rather, is: Why was information omitted?

The public climate change debate is a case in point. By censoring views that question the consensus, eventually public opinion will be at odds with Wikipedia's belief that human carbon dioxide emissions are causing catastrophic climate change, since it is clear through real world observation that the predicted catastrophic effects are not occurring as hypothesized. For example, the reigning hypothesis states that when carbon dioxide rises at current rates, it will cause global temperatures to rise more than 2°C, with catastrophic effects.

During the past century CO2 has risen steadily. It is now more than 50% higher than it was less than a century ago. But the planet's temperature is not accelerating upward, as is repeatedly hypothesized. Thus, the central hypothesis is falsified, vindicating scientists skeptical of that hypothesis.

My question: Why is the failure of the CO2=AGW hypothesis being completely ignored? And why are skeptical scientists like Dr. Lindzen omitted from the discussion? That certainly appears to be deliberate, as is ignoring the fact that the central hypothesis in the climate change discussion has been decisively falsified, by the only Authority that truly matters; Planet Earth.

What about this, Wikipedia? Why are only half the scientists opinions — those who predict catastrophic climate change — seen by readers? Where are the views and opinions of the scientists vindicated by empirical measurements, showing that rising CO2 does not have the hypothesized global warming effect? Nephora (talk) 04:57, 7 April 2021 (UTC)[reply]

See Richard Lindzen. Johnuniq (talk) 05:08, 7 April 2021 (UTC)[reply]

There is no scientific debate on climate change. All scientists agree on all the main points, there's only discussion about the details. We have observed enough climate change to see it matches the models that were designed in the 1980s. There are however people with vested interests in the status quo who want a debate, because as long as politicians debate, nothing happens. And enough politicians live in a fact-free world to make this work.

There are regional differences in climate change, so it may be that you live in a place where it doesn't get warmer/dryer/wetter/windier. Where I live (western Europe), climate change is quite obvious. Over the past 30 years, average temperature in the Netherlands has increased by about 1.1°C near the coast, a bit more inland. At my own weather station, the hottest and coldest days of the year have become 5°C warmer over the past 25 years. The polar regions are even more extreme. Climate change caused by CO₂ emission is very real and we've only seen the beginning. PiusImpavidus (talk) 08:52, 7 April 2021 (UTC)[reply]

Perhaps we should have a List of (notable) climate change sceptics, such as Freeman Dyson and Frederick Seitz, which might group them according to their relevant scientific backgrounds (or lack thereof, such as for Michael Crichton and Josef Joffe). The fact remains that among scientists climate change scepticism is a marginal viewpoint, and reporting specifically on Lindzen's contrarianism in the main article will fall afoul of WP:UNDUE. --Lambiam 09:20, 7 April 2021 (UTC)[reply]

Doesn't this discussion belong more/ also at Talk:Climate change? Thanks. Martinevans123 (talk) 09:35, 7 April 2021 (UTC)[reply]

@Lambiam: we did have such a list. After ?8 AfDs and several name changes it was deleted as a result of Wikipedia:Articles for deletion/List of scientists who disagree with the scientific consensus on global warming. Whether to include a particular scientist was one of the several contentious areas of discussion for a variety of reasons including BLP, what counts as a disagreement (if you read the statements of a lot of people considered sceptics, they're often a lot more nuanced than the media present and not always clearly opposed the the consensus) and how to deal with people who are deceased especially after a long time along with old views from people who are still alive when we have no clarity if they still hold that view (a scientist should be continually evaluation their position based on the latest evidence, while it may be unlikely Seitz would have changed their mind now, we cannot know). The outcome of the AfD doesn't preclude making a new list restricted to climate scientists, but frankly despite some on and off involvement in that list in that years and never AFAIR !voting delete, I'm not sure it would be a good idea. In any case, both people you mentioned would be precluded from such a list, although the person the OP mentioned wouldn't automatically be. Nil Einne (talk) 07:03, 8 April 2021 (UTC)[reply]

I see. Climatology is a very multidisciplinary science, combining aspects of the disciplines of geology, physics, physical chemistry, thermodynamics, atmospherology, data collection and calibration, mathematical modelling, numerical mathematics, and statistics, to name a few, so I can also imagine endless debates on whether a given individual scientist is "truly" a climate scientist. That may be harder to reach consensus on than whether a notable person has publicly expressed scepticism regarding the IPCC conclusions. --Lambiam 08:25, 8 April 2021 (UTC)[reply]

@Nephora: I rather doubt that you can be convinced to change your views. To convince us to change the article, it is not enough to say that a different viewpoint exists, it must also reflect a significant view among the scientific community. The possible lines of argument go thusly:

A significant fraction of scientists with relevant training disagree with the mainstream view. If so, you must prove it. Please read through the voluminous archives at the climate change pages though, others have tried before.
The mainstream view is dominant only because dissenters are censored (refused access to journals, jobs in universities etc.). Too bad! Wikipedia does not accomodate fringe views just because they might be right (as they sometimes are). We follow the sources; it is the only way to be the least wrong possible on aggregate even if it means going very wrong in specific cases.
Wikipedia:Neutral_point_of_view#Due_and_undue_weight is bad policy and should be changed. Well, you can try, but I would not be on you getting a consensus to change it enough that climate change ends up being presented as contested.

Side note: you say that when [someone is] exposed to all available information, irregardless of the source, [they] invariably arrive at the best possible conclusion under the circumstances. I must inform you that in developed countries with free elections, 90+% of voters have access to internet (which is all that is required to "be exposed to all available information"), yet having 90+% of the vote going to the same party or candidate is fairly rare. People are limited in their time/willingness to slog through vast amounts of information, as well as in their skill/ability to sort out which information is good and which is not. If "access to information" was enough, Wikipedia would have no reason to exist at all (anything that is sourced can be read directly at the source, and the rest is dubious anyway). Tigraan^{Click here to contact me} 15:55, 7 April 2021 (UTC)[reply]

@Nephora: a flaw in your thesis is its not "only half the scientists opinions". In reality it's only a small number who dispute the basic tenets of climate change. (I don't think your description of the basic tenets is particularly accurate and I'm not saying this applies to Lindzen's views in particular, but that's an aside.) Per WP:NPOV, "representing fairly, proportionately, and, as far as possible, without editorial bias, all the significant views that have been published by reliable sources on a topic". Fringe theories are minimal covered because that's proportionality, be it fringe theories of evolution (e.g. intelligent design), of vaccines (e.g. that they cause autism), of vitamin supplementation (e.g. of the benefits of megadoses of vitamin C), of the age of the earth and universe, of the existence of crytid animals or that intelligent aliens have visited the earth, or yes of climate change. Nil Einne (talk) 06:50, 8 April 2021 (UTC)[reply]

Need I remind anyone that back in the day, the heliocentric theory was dismissed as "fringe"? 2601:646:8A01:B180:50CC:A800:928E:97F9 (talk) 03:39, 9 April 2021 (UTC)[reply]

If someone has scientific evidence which will actually disprove the current consensus on climate change, they're welcome to present it, just as Copernicus presented evidence and a mathematical model which essentially disproved geocentrism. If your only point is "this one theory was wrong once, therefore CLIMATE CHANGE IS A SOCIALIST CONSPIRACY HOAX," well, that's neither interesting nor useful in a context outside the conservative echo chamber. NorthBySouthBaranof (talk) 04:01, 9 April 2021 (UTC)[reply]

Would the recent blizzard in Texas (including in the south part of the state, which is an area that had never seen below-freezing temperatures before in recorded history) not disprove the current models of climate change, and show that the earth is actually cooling and not warming??? 2601:646:8A01:B180:AC5D:E140:5F1F:C128 (talk) 06:58, 9 April 2021 (UTC)[reply]

No, it only proves that Texas isn't warming rapidly, but, as stated above, there are regional differences. The increased greenhouse effect warms the Arctic, causing the snow to melt, which lowers the albedo of the ground and sea, which causes even more warming. Of all parts of the world, the Arctic warms up fastest. This increase in temperature lowers the density of the air, lowering air pressure near the surface and changing wind patterns. In the US this leads to more north-westerly winds, which can cause local cooling in winter. In Europe on the other hand, the shifting wind patterns give more westerly winds in winter, leading to higher temperatures. The net effect is warming. PiusImpavidus (talk) 08:45, 9 April 2021 (UTC)[reply]

Ironically, the California-based IP hopper lives in a state which has seen massive wildfires in recent years, which are attributed in part to climate change. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:52, 9 April 2021 (UTC)[reply]

"Attributed" is the key word here -- and since User:PiusImpavidus has previously raised the issue of vested interests, I must mention that the California Dumbocraps have a very strong vested interest in blaming these on climate change, in order to distract the public from their own mismanagement of the state forests (which was the main cause of the fires)! 2601:646:8A01:B180:D4F2:624F:65AE:D676 (talk) 11:03, 9 April 2021 (UTC)[reply]

And Republicans in general have a very strong vested interest in denying climate change. Likewise the Catholic hierarchy of the middle ages had a very strong vested interest in adhering to the geocentric universe model. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:14, 9 April 2021 (UTC)[reply]

Be that as it may, your own map shows a warming trend everywhere in the USA, but only California had seen such a major epidemic of wildfires -- therefore, climate change cannot be the main cause of the fires, else the other states would've had them too! 2601:646:8A01:B180:61E7:2573:6DB5:7BC (talk) 04:07, 10 April 2021 (UTC)[reply]

The idea that "only California" has seen increasing wildfires is so ill-informed and wrongheaded as to render everything else you say meaningless. See these statistics for Idaho, for example. Anyone who pays attention to wildfire in the United States recognizes that it is on the rise across the West. Colorado had by far its worst wildfire season in recorded history last year. NorthBySouthBaranof (talk) 04:16, 10 April 2021 (UTC)[reply]

Wildfires are strongly correlated with a Mediterranean climate. Such a climate is found for example near Adelaide and Perth in Australia, in Greece, southern France and Portugal in Europe and in California, USA, and those places are all known for their frequent wildfires. This is because the winters are wet enough to get lush plantlife and the summers are hot and dry enough to turn that plantlife into good fuel. When summers get even hotter and drier with climate change, the plants become even better fuel. An increase in wildfires is most noticeable in areas where they were already common. In places where wildfires were very rare, like the Namib Desert or Greenland, they will remain rare, even when it gets warmer.

Now note that the map above only shows the change in yearly average temperature. It doesn't show change in precipitation. In places where a rise in temperature goes together with an increase in precipitation, in particular in summer, you won't get an increase in wildfires. Also note that there's an increase in wildfires in other parts of the world too, like Canada or Siberia.

Of course, mismanagement plays a role too. Spain and Portugal suffer from non-native plant species like eucalyptus, which is more flammable than the native oak (and also a poor match to local fauna). PiusImpavidus (talk) 10:50, 10 April 2021 (UTC)[reply]

There are only 70,000 acres of state forest in California. By comparison, federal agencies manage 19 million acres of California forestland. Who are you trying to blame again, and who was president for the last four years? Moreover, it is incredibly simplistic to claim that the simple solution to wildfires is to "manage" the forests more, by which I assume you mean to say, cut down more trees. For one, commercial logging *increases* fire risk in the medium term, because it leaves behind a ton of worthless slash which is tinder for a conflagration. Again, (Personal attack removed) What is needed is a combination of thinning and increased use of prescribed fire - which requires funding. But Trump consistently proposed slashing the Forest Service budget. NorthBySouthBaranof (talk) 04:16, 10 April 2021 (UTC)[reply]

On the contrary, I know perfectly well what I'm talking about, it's (Personal attack removed) And yes, the solution to wildfires is in fact to thin the forests by cutting down dead and diseased trees and clearing undergrowth (and, where a whole patch of forest is dead, as was the case around Lake Arrowhead for example, then clear-cutting may be the way to go) and, where needed, use prescribed fire -- so what you said here makes no sense, what you said here is "cutting down trees is wrong but we need to cut down trees"! And this has nothing to do with who was President, this has everything to do with the wildfires being caused by tree-huggers preventing proper forest management and not by climate change! 2601:646:8A01:B180:703F:3EEF:DFE6:14AC (talk) 11:50, 10 April 2021 (UTC)[reply]

Environmental groups are not generally against prescribed burning and appropriate non-commercial thinning projects to deal with the legacy of fire suppression. What they are against is large-scale commercial logging and roadbuilding under the guise of "thinning." And of course it matters who is president - Joe Biden has proposed a 16% increase in funding for the Department of Agriculture, in part to increase the pace and scale of forest thinning and restoration projects. One president wanted to cut the budget and lay off thousands of people who do the work in the national forests, and the other president wants to hire thousands of people to do more work in the national forests. Pretty clear which one is interested in results rather than rhetoric. NorthBySouthBaranof (talk) 12:57, 10 April 2021 (UTC)[reply]

(Personal attack removed) ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:49, 10 April 2021 (UTC)[reply]

I have NEVER claimed that the earth is flat (either in this thread or in any other on Wikipedia), so YOU WILL TAKE BACK YOUR COMMENT RIGHT NOW!!! (Personal attack removed) 2601:646:8A01:B180:9538:C20F:64A4:27B5 (talk) 07:54, 11 April 2021 (UTC)[reply]

There's no "stalking" involved. Check any of your "contrib" pages and you'll see a "Geolocate" item. That is public information. And since your IP is constantly changing, there's no way to verify whether or not you've ever claimed that the earth is flat, or that the Apollo moon landings didn't happen, or that JFK was the victim of a gigantic conspiracy, etc., etc. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:59, 11 April 2021 (UTC)[reply]

And by the way, if you are Nephora (talk · contribs), then you should edit under that name and not edit while logged out. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:24, 11 April 2021 (UTC)[reply]

2601: Part of editing here means you accept that your contributions will be publicly viewable. If you don't like that, Wikipedia isn't the place for you. While it's unacceptable to use someone's contribution history to WP:Wikihound, simply viewing someone's contribution history is not wikihounding. Commenting on it can sometimes be a problem but nothing in this thread seems to rise to the level where it is. If you edit with an account, your IP information is hidden, and so people will only know what you chose to reveal about yourself. If you chose to edit with an IP, you need to accept that people can check your IP details such as apparent geolocation and ISP information. Again it mostly your choice. (Editing with both an account and an IP or multiple accounts can be problematic. You need to take care not to violate WP:SOCK.) Nil Einne (talk) 07:25, 12 April 2021 (UTC)[reply]

For the record, I'm NOT User:Nephora -- (Personal attack removed)2601:646:8A01:B180:88E9:8893:7854:D497 (talk) 10:11, 12 April 2021 (UTC)[reply]

There's no way to verify that, unless you were to list every IP you've ever edited under. ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:04, 12 April 2021 (UTC)[reply]

2601: I have no idea why Baseball Bugs said that but you've already stated you never said that so people can read your denial and BB has provided no evidence to the contrary. With that, I suggest you just drop it now since BB often says silly things and frankly even despite WP:NPA this is not the sort of thing that that is ever going to result in sanction. Notably, I really don't think you want us looking into you history since when we do, we find stuff like this [1] where you openly admit to occasional disruption. I see very few edits outside the RD from your most recent IP range so hopefully you stopped with your disruption, but either way your edit history doesn't seem to be the sort you want to advertise as you're effectively doing by making such a big deal over it. Nil Einne (talk) 12:07, 12 April 2021 (UTC)[reply]

If you did want to talk about your edit history, I seem to recall you were once writing a book which involved the US military invading Canada for a medical evacuation from some remote Canadian location for someone who was dying because they didn't trust the Canadians since they don't care about people or something. I think terrorism or nuclear terrorism was also involved. Did you even publish that book? I understand for privacy reasons you might not be willing to talk about it much but I am curious if you and if you did how successful it was. Nil Einne (talk) 13:42, 12 April 2021 (UTC)[reply]

I found what I was thinking of. For clarity I was referring to the novel you mentioned here Wikipedia:Reference desk/Archives/Miscellaneous/2013 September 28#Lifesaving medal. You seem to have moved on to saving people from North Korea prison camps Wikipedia:Reference desk/Archives/Science/2019 April 11#Flight planning so I guess that Canadian novel is done? BTW, I'm not sure if you ever finished the North Korean one but since I noticed no one ever addresses the point, while delayed release are a real thing, I think you'll still struggle to find one where you can guarantee a release in precisely 100 hours. At most, perhaps you can have high confidence that nothing will happen for 100 hours, but you wouldn't be particularly surprised if it also takes 120 hours. Even then 100 hour sounds way too long to me, I doubt with our current level of understanding and technology that anyone can really develop any implant where they can be confident nothing will happen for 100 hours. And it's even less likely if you need to be able to implant these in different organs. Nil Einne (talk) 16:25, 12 April 2021 (UTC)[reply]

I have nothing to be ashamed of as regards my edit history -- the vast majority of my edits have in fact been constructive, and your characterization of my history is nothing more than blatant cherry picking! (Not to mention that you completely ignore the context for the edit you linked above -- the context was that I had just been slapped with a completely unjust, politically motivated 1-year ban on a fabricated charge of WP:NOTHERE because I had called a terrorist a terrorist -- a ban which was therefore an act of terrorism per US law -- and I was trying to demonstrate that nothing in my edit history could possibly be construed as WP:NOTHERE!) Also, your description of my Canadian novel is likewise a total distortion of what it was actually about, but that's a completely separate issue! 2601:646:8A01:B180:E8C8:7695:1C0E:E994 (talk) 03:01, 14 April 2021 (UTC)[reply]

Where did you call someone a terrorist? ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:39, 14 April 2021 (UTC)[reply]

2601: Precisely. See Wikipedia:Why Wikipedia cannot claim the Earth is not flat#Wikipedia's role as a reference work. If Wikipedia has been around at the time when the heliocentric theory was fringe then we would have correctly reported it as fringe and given it limited coverage in proportion to its acceptance. As this changed, our coverage would change. We don't even have to go that far back. Under 40 years ago, the idea that Helicobacter pylori or any bacterium was a significant cause of peptic ulcer disease was either a fringe theory or really probably no theory. Yet by the time Wikipedia had started in 2000, this was no longer the case. Indeed see the first versions in 2002-2003 [2] [3]. Although I can't be bothered thinking of any specific examples, I'm sure you can find articles which when they were created in 2000 or whatever are quite different from now, because our understanding has evolved. I mean obviously anything COVID-19 related has changed a bit in just over a year, but I'm thinking of stuff which has been around for a while so our current understanding would if not be considered fringe at least be considered a fairly minority view in circa 2000. TL;DR what you describe is a feature not a bug of Wikipedia. Nil Einne (talk) 07:17, 12 April 2021 (UTC)[reply]

Also important is to present bullshit as bullshit. NPOV is about presenting information as it is, not introducing false balance by trying to imply that genuine experimentally verified scientific information is somehow equally balanced with complete nonsense. --Jayron 32 13:20, 8 April 2021 (UTC)[reply]

Arguing with anonymous strangers on the Internet[edit]

"Arguing with anonymous strangers on the Internet is a sucker's game because they almost always turn out to be -- or to be indistinguishable from -- self-righteous sixteen-year-olds possessing infinite amounts of free time." --Neil Stephenson, Cryptonomicon

I'm just saying. --Guy Macon (talk) 15:23, 12 April 2021 (UTC)[reply]

Why a grey spot around white colour looks darker?[edit]

I've read in a book (not in English) in past that when one put a grey spot around white colour, then this spot looks darker compared to a case in which you put this spot on a background of black that then it looks brighter. The book used this picture (it states that all of the grey in this illustration is with the same tone! But we can see that those grey around the black, looks darker. It claims that it a visual effect, but no more explanation. Can you please tell me where can I read about its scientific explanation from the aspect of physical / optical point? ThePupil (talk) 11:20, 7 April 2021 (UTC)[reply]

Your brain has a process called color constancy whereby it tries to correct for lighting effects when interpreting the color of an object; though the actual quantitative color of light bouncing off an object can vary dramatically depending on the lighting conditions, your brain "corrects" for these differences so that a green apple looks consistently green even when shown in dim light, in bright light, in sunlight, under different kinds of light bulbs, etc. This is, of course, a necessary thing: you wouldn't want to think the object itself fundamentally changed merely because the light falling on it did. However, optical illusions can play with this mental process, and turn it on its head. These sorts of color illusions are numerous (see also Checker shadow illusion for example). Much of this is due to the fact that most of your color perception is not a physical, but rather a psychological effect (known as a qualia). You don't see the full gamut of colors. You basically three colors, because your eyes have only three kinds of color receptors, cone cells, which are sensitive at different regions of the visible spectrum. When you see a color, it is because your brain has processed these three inputs into a color. You can even see non-spectral colors, which literally do not exist on the spectrum, things like magenta. Your perception of color is highly influenced by how your brain processes these inputs, and that processing is also complexly tied to other things so even things like context (i.e. the color constancy effect) can change how you see color. --Jayron 32 11:44, 7 April 2021 (UTC)[reply]

@JayronThank you! Can I ask why do we consider it as a consistency while it's changed? Can it explain why a white spot/ stain on a white skin looks less white than the same stain is on a black skin? (the white becomes looking 'less white' on a white skin. In past I'd expect opposite!) --ThePupil (talk) 19:06, 7 April 2021 (UTC)[reply]

I downloaded the picture and trimmed away all the solid black bands, and the items on the right have slightly darker dots than the other two. Possibly an issue with the scanning process? (There are also variances in the sharpness of the dots.) ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:27, 7 April 2021 (UTC)[reply]

Honestly, I have no idea. I just wrote what I read. Also, since I didn't believe it as well, I went to Paint of Windows and tried to do an experiment by myself and draw more or less the same, and the results were a little bit different, but still, I asked a few people what looks darker, and everyone pointed towards those who were surrounded with black. If you can try this experience as well, I'll be thankful.--ThePupil (talk) 18:55, 7 April 2021 (UTC)[reply]

I have created an idealized version of the image using solid grey (RGB hex triplet #808080) instead of a halftone dot raster. Judge for yourselves, here. --Lambiam 21:08, 7 April 2021 (UTC)[reply]

To me, the ones on the right side look absolutely darker. If it's one tone in all of them, then that's amazing. ThePupil (talk) 11:08, 8 April 2021 (UTC)[reply]

I ran the same test I did earlier, on Lambiam's version, and it works. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:34, 8 April 2021 (UTC)[reply]