Wikipedia:Reference desk/Archives/Science/2019 July 8

Science desk
< July 7	<< Jun | July | Aug >>	July 9 >

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.

July 8

Speed of Light - Formation of images

We can see light via our eyes either directly or if it reflected off from the object.

Sunlight reaches earth.jpg Sunlight takes an average of 8 min and 20 sec to reach the earth. The speed of the light is 299,792 kilometers per second.

The sun is 109 times bigger than the earth. It radiates light in all direction. Earth receives a very small fraction (less 1% of the sunlight - guess). We are unable to see the rest of the sun lights as it fall in the space-like region and their direction of traveling keep them away further in the space-like region of light-cone - true. Therefore

How come we are able to see the full image of the sun when more than 99% of the sunlight doesn’t even fall on the earth (falls away into the space-like region of the light cone)? No reflections involve either – And the same is applied to the stars, galaxies, and image of the BH, etc.

Would the interference of light rays from these cones nullify the formation of shadows on earth? — Preceding unsigned comment added by Eclectic Eccentric Kamikaze (talk • contribs) 03:56, 8 July 2019 (UTC)

For an accurate idea of how the Sun emits light, you must keep in mind that rays of light do not only emit perpendicular to its surface (as if it had a smooth surface anyway). Every point on the surface of the sun is emitting light in every outward direction. We can see the whole of the sun because for each part of it that we can look at, some light rays are being emitted from that part toward our direction. Someguy1221 (talk) 04:01, 8 July 2019 (UTC)

1)far less than 1%. More like surface of the Earth disc / area of a sphere which radius is the sun-earth distance πR²/4πD², were R=6,371 and D=149,598,023. That is, less than 0.5 e-9 (half a billionth)

2)well, because that the definition of an image. Why would you need to see all the light emitted/reflected? a small fraction will do, as evidenced by the possibility to get image by photographing, when the collected light comes a fraction of a second. And it apply just as well to a computer screen or a chair in front of you. Gem fr (talk) 06:42, 8 July 2019 (UTC)

3)interference have requirement, which are explained here; Wave_interference#Light_source_requirements. These are not met as far as the sun is concerned. To be more precise, they are met by a so small fraction of the sunlight, that we cannot see any difference. Gem fr (talk) 06:42, 8 July 2019 (UTC)

Not a satisfactory answer (to me) but still, it's not 100% guarantee that we would get the same amount of light especially its distribution throughout the year when the earth orbit around the sun, therefore, shouldn’t the sun change its shape with the passage of time? — Preceding unsigned comment added by Eclectic Eccentric Kamikaze (talk • contribs) 04:47, 8 July 2019 (UTC)

in fact we DON'T get the same amount of light throughout the year when the earth orbit around the sun. The so called solar constant is not really a constant, as physicists define them. Gem fr (talk) 06:42, 8 July 2019 (UTC)

If you're talking about the sun changing shape due to perspective, no for two reasons: A) The sun is approximately a sphere, and so its projection is a circle from any distance; B) the distance from the Earth to the Sun does not change that much over the course of the year, only a few percent. I think you need a better idea of your own idea. Make another diagram, but trace every light ray that reaches your earth-bound observer from the sun. Try to figure out what that means, and then come back here if you still have questions. (Okay, not literally every light ray, but get the whole range of angles from which they will reach your observer.) Someguy1221 (talk) 21:37, 8 July 2019 (UTC)

It’s just a tentative diagram for the purpose of understanding only. I’m talking about the same image and appearance of the sun, which is like disc over the period of time. No problem with light rays fall directly on earth but it is the intensity, distribution etc of the rest of the sunlight or rays especially coming from the edges at angle that fall on earth and finally reach our eyes over the course of time which are not constant but changes due to rough surface of sun as you said. Please disregard the earth-sun distance. Anyway, thanks and I appreciate all replies. — Preceding unsigned comment added by Eclectic Eccentric Kamikaze (talk • contribs) 23:30, 8 July 2019 (UTC) For more simplicity, the dark spots (spots from where we don’t receive light rays) on the surface of the sun should increase if we see away from the center of the sun. Since the surface of the sun is not smooth therefore these dark spots should also change their position on the surface of the sun with the passage of time. Similarly, light rays that fall on earth at an angle would nullify shadows either fully or partially due to their cancellation effect. I’m not sure if we are on the same page but this is my thinking, which may be wrong, and again thanks. — Preceding unsigned comment added by Eclectic Eccentric Kamikaze (talk • contribs) 01:21, 9 July 2019 (UTC)

Hi Eclectic. I'm actually not clear on what you are thinking. That's why I suggested drawing a more complete diagram of your thoughts. Words can only convey so much. Someguy1221 (talk) 01:50, 9 July 2019 (UTC)

What darks spots? The sun is extremely bright. Sunspots only look sort of dark because they emit less light than their surroundings. But if you want a clearer idea of what's happening, you could make yourself a pinhole projector like folks often do during eclipses. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:15, 9 July 2019 (UTC)

Like my fellow Wikipedians above, I (speaking as an ex-astronomer) do not find your attempts to describe your thoughts at all clear, but with reference to your last entry you might find the article Limb darkening relevant. I suspect, however, that you have some fundamental misunderstandings about how light behaves, in which case a careful study of the material in at least the opening paragraph of Geometrical optics might help. {The poster formerly known as 87.81.230.195} 2.122.177.55 (talk) 02:22, 10 July 2019 (UTC)

As the first responder said, the surface of the sun is not smooth. it emits light rays in many possible different directions but it can’t emit light rays from the same spot in all directions at the same time as shown in figure - Right

Roughness of the surface area of the sun changes every moment. Similarly, roughness on the surface of sun is not uniform but varies vertically as well as longitudinally in all directions every moment all over the surface area of the sun.

So there are chances that some spots on the surface of sun don’t send light rays towards earth at some moments.

No light from these specific spots towards earth means no images of these spots on image of sun on earth

No image means – these spots are *dark (just like if we close our eyes) however they are ON and OFF depend upon the formation and deformation of the roughness of the surface with time and location of the earth in its orbit.

Portion “A” of the figure shows the surface area of the sun from where earth receives sunrays directly – straight, though at an angle because of the expansion of cone at every moment formed by two adjacent rays – This central part (Portion “A”) is the brightest part of the image of sun. Theoretically one light ray is perpendicular to the earth at noon if both the earth and the sun are perfect spheres. Rest of the light rays fall on earth at an angle.

The chances of the light rays that emit around the central portion A and at the edge or near edge of the sun (disc type) are low to fall on earth as compared to the light rays that emit at or near the centre of sun /disc.

Similarly, an earth can be seen from different faces (NEWS) of the sun when it orbits around the sun therefore difference in roughness means both the seen (emit light towards earth) and unseen (emit light but not towards earth) spots change their positions on the surface of the image of sun w.r.t to the earth, time and earth’s location in orbit. This makes the image of the sun sometimes dark, sometimes darker sometimes brighter but less bright as compared to the brightest central portion of the sun/disc as we receive less light to zero amount of light rays from this portion.

If aforesaid is true then the overall image of sun (disc-like) is brightest at center. Brighter to darker with dark spots may be sited around the brightest central portion toward the edge at any particular moment. i know none of you would agree but this my personal perception of the roughness of the sun as you said. — Preceding unsigned comment added by Eclectic Eccentric Kamikaze (talk • contribs) 01:14, 13 July 2019 (UTC)

The combined view of the figure (Top, North, South, NE and SE) shows there is always light from all thses direction from sun at any point on earth during day time when we see the full image of the sun which cancel the shadows either fully, partially or not at all on earth depend upon the light falling from those views. Again my personal perception about the roughness of sun if true. — Preceding unsigned comment added by Eclectic Eccentric Kamikaze (talk • contribs)

The key thing to recognize is that the roughness of the sun is not relevant the directions in which it radiates light. Every individual atom in the sun emits light in all directions - light is not emitted only orthogonally to some fuzzy "surface". The sun's angular diameter of ~0.5° is insufficient to obliterate most shadows on the scale of humans on earth. During a solar eclipse, the blurry edge of the shadow in which a partial eclipse is visible is much larger than the area of complete totality. VQuakr (talk) 13:10, 16 July 2019 (UTC)

Liquid Glass

I was told by a trained Stain Glass Window maker that during his tutelage he was taught that glass in its natural room temperature state is in fact a liquid. Though this is a little known fact. The reason this was taught to him was that he would need to measure any glass he had created and to in-lay it with the thickest side pointing up once installed. This would allow the glass to flow, though very slowly, over hundreds of years to be thicker at the bottom. If laid the other way around with the thickest side down, the glass would last a much lower amount of time. What truth is there in this please? Is glass at room temperature a liquid, which flows to fill any container it is in, albeit be slowly. In line with this, where is the cut off point for a liquid to be termed and considered a liquid, how long should it take to fill a contain or flow? Like mud, it can be made to fill a container but can also be made to stand on its own. Thanks Anton 81.131.40.58 (talk) 13:42, 8 July 2019 (UTC)

It's not true. "The notion that glass flows to an appreciable extent over extended periods of time is not supported by empirical research or theoretical analysis". Please see Glass#Behavior_of_antique_glass.--Shantavira|^{feed me} 13:53, 8 July 2019 (UTC)

(edit conflict) :Glass is an amorphous solid; the "cathedral glass flow" (liquid glass) theory and contradictory evidence is discussed here: Glass #Behavior of antique glass. However, according to Philip Warren Anderson: "The deepest and most interesting unsolved problem in solid state theory is probably the theory of the nature of glass and the glass transition." —2606:A000:1126:28D:48F3:EC22:BDAE:8519 (talk) 14:09, 8 July 2019 (UTC)

"Liquid glass" is also listed at List of common misconceptions#Materials science. Tigraan^{Click here to contact me} 15:55, 8 July 2019 (UTC)

It is not wrong to consider amorphous solids (including glass) to be liquid-like, since they share traits: Structure of liquids and glasses.

I recommend Viscosity#Amorphous_materials and Viscosity#In_solids. here is an interesting quote

many "solids" (even granite) will flow like liquids, albeit very slowly, even under arbitrarily small stress. Such materials are therefore best described as possessing both elasticity (reaction to deformation) and viscosity (reaction to rate of deformation); that is, being viscoelastic.

Yes, even granite will flow (which will help understand the wonderful fit of old stone wall, btw)

Gem fr (talk) 14:49, 8 July 2019 (UTC)

So will metals. One of the few things that actually behaves like we imagine a solid should behave is a crystal. SinisterLefty (talk) 03:13, 9 July 2019 (UTC)

@SinisterLefty: Please define "crystal", because most metals are crystals (mono- or polycrystals) by the scientific definition of the term (they show a periodic arrangement of atoms at the microscopic scale). Tigraan^{Click here to contact me} 11:54, 9 July 2019 (UTC)

Let's try "single-cell crystals with ionic bonds or covalent bonds (so not metallic bonds)". I may need to refine that further, but I think that's the general idea. It's generally between the cells in multi-celled crystals where the deformation occurs. SinisterLefty (talk) 13:45, 9 July 2019 (UTC)

Just as an aside, back in 2007 a full professor of chemistry lecturing me and the other students in my 3rd year chemistry major cohort regurgitated the "glass is a super cooled liquid at room temperature" line citing the flow of centuries old stained glass windows in cathedrals. I already knew at the time that it was a discredited pop-sci notion. After class I pointed him to the refs on the wikipedia page which explained it was wrong. He steadfastly maintained that it was a fact. This was in a physical chemistry class at a major Australian university. 202.155.85.18 (talk) 01:33, 11 July 2019 (UTC)

Most effective spending on the environment

Are there serious (science-based!) cross-disciplin recommendations about how to most effectively spend money on the environment? Essentially like GiveWell, but for the environment?

I read a few years back in the news that a groups of scientists (?!) was annually (?!) asked how to best spend a considerable amount of money (100 billion??)... but I don't find it anymore. Anything of that sort or related recommendations.

(Obviously any such recommendation would need to seriously debate what they consider "the environment" and what their ultimate goal is - e.g., species protection, combatting global warming, etc. ... but I don't even know where to start looking. All I seem to find are some internet discussions or unsourced gut feelings of well-meaning people. Nothing scientific yet...)

Thanks. Thanks. Thanks for answering (talk) 13:50, 8 July 2019 (UTC)

Please see the work of Professor Bjorn Lomborg You can youtube some of his talks which can be as short as 20 minutes wherre he will cover this topic. Anton 81.131.40.58 (talk) 14:07, 8 July 2019 (UTC)

yes, there are. Lots, actually.

Economically speaking, environment is just a special case of common good (economics) and externality, fields that attracts tons of researchers. Especially when it comes to the so sexy environment. So we have ecological economics, environmental economics, List of environmental economics journals...

Now, as you pointed out, it all depends on the value you bestow to "the environment". An economist can tell you how much it would cost you to do something that the environment take care of (eg: cost of disposing a dead animal, while a vulture will do it for free), that is, price the service of the environment (and some cost if it changes so that it doesn't provide the service anymore); or, the other way round, how much you will benefit from some change (ex: benefits if the Northwest Passage opened). He also can tell you what can be achieved for a given price (eg: what happens if a carbon tax is levied). But he cannot put a price on the existence of a panorama, a swamp, or an insect specie.

So there is no single most effectively spend money on the environment: this will depends on the value the economist uses.

There are, however, lots of least effectively spend money on the environment. Energiewende in Germany for instance (I don't link to our wikipedia article, absolutely unreliable on such highly politicized subject swarmed by militants).

Gem fr (talk) 15:40, 8 July 2019 (UTC)

Re An economist...cannot put a price on the existence of a panorama, a swamp, or an insect specie. Actually he can, by doing carefully worded surveys that ask how much the respondent is willing to pay to keep the panarama etc., and then extrapolating to the whole population and to future generations as well. But of course it's very difficult to elicit responses that are accurate. Loraof (talk) 13:14, 10 July 2019 (UTC)

Looks like to a public worker joke: How do you know if a bridge is to be build over a river? You count the number of people actually swimming across in a year, and multiply by a reasonable estimate of toll and lifetime of the bridge. If the result is more than the cost of building, you do. Gem fr (talk) 17:22, 10 July 2019 (UTC)

Well, you could look at ferry crossings, and what people pay there, but you'd also need to look at people using nearby bridges who would switch to the new one, and perhaps people who opted not to cross the river who would if a local bridge existed. SinisterLefty (talk) 21:31, 10 July 2019 (UTC)

In the case of the swamp, the value is likely negative to those who live there. That is, they are a NIMBY issue. "Lush wetland habitats" sound nice, unless you have to smell swamp gas and battle mosquitoes every day. And finding your dog missing and his leash hanging out of the mouth of an alligator doesn't make locals love swamps much, either. SinisterLefty (talk) 15:33, 10 July 2019 (UTC)

Evidence are that legislations are enacted, and guards paid, so that swamps keep ruining the property, health and life of those living near them, however... So somehow people (most of them NOT living near a swamp, for sure) are very eager to pay for this result. Gem fr (talk) 17:22, 10 July 2019 (UTC)

Coastal swamps do provide environmental benefits, like limiting hurricane damage, so the best solution there is to just ban people from moving there, or, if already there, to provide economic incentives for them to move inland. SinisterLefty (talk) 21:34, 10 July 2019 (UTC)

One thing to be aware of is greenwashing. Spending money on things like "clean coal", for example. SinisterLefty (talk) 03:09, 9 July 2019 (UTC)

I was just thinking I should have mentioned greenwashing (which includes basically ALL that is fashionable and costly, such like renewable energy -- wind, solar --, electric vehicles, recycling, switching back from plastic bottle to glass, etc. Real green is cheap, because it needs as few material, and as few transformation of the material, as possible. Of course all that is cheap is not green; but nothing expensive is). Good that you did Gem fr (talk) 06:40, 9 July 2019 (UTC)

Thanks, but I think most of the items you listed do make sense, at least in some cases. Solar and wind power, for example, make sense where sunlight and wind are strong and consistent, and other sources of power are expensive, such as isolated locations. Electric vehicles could make sense where air pollution is unbearable, like some cities in China. Recycling of lead-acid car batteries makes sense. Glass bottles make sense if you clean and reuse them, like I do.

But, yes, there is a lot of greenwashing, too. Looking at electric vehicles, for example, we have to consider the entire life cycle of the vehicle and batteries, not just "tailpipe emissions". And if electricity in your area comes from burning coal, that's not an improvement over gasoline. I'm also worried that old electric vehicles maybe be junked just because the batteries are weak and replacing them would cost more than the vehicle is worth. SinisterLefty (talk) 07:40, 9 July 2019 (UTC)

Right. Instead of "green", we should talk about "greener". Indeed, in a few case solar and wind are cheaper and greener than, say, coal, but in most case they are not (still; they will eventually, I think), but anyway they never are green. Nothing really is. Gem fr (talk) 10:01, 9 July 2019 (UTC)

To be more specific, my (2 cents worth) understanding of the recommendation are that ... you should just read pigovian tax/pigovian subsidies (and related links) that basically sum up all the issues on the matter Gem fr (talk) 11:23, 9 July 2019 (UTC)

a groups of scientists (?!) was annually (?!) asked how to best spend a considerable amount of money – It sounds like you're thinking of the Copenhagen Consensus. Adrian J. Hunter^{(talk•contribs)} 12:00, 9 July 2019 (UTC)

Thanks for all the input!! Yes, interesting how economics play in. And yes, it seems I (mis)remembered the Copenhagen Consensus.
At the same time, I'm still not much closer to an answer: After all, I'm not a politician or millionaire (neither can I enact taxes nor do I have the money for huge research programs or arming ships for marine cloud whitening), so if I just wanted to donate some modest amount of money, I'd still be no closer to knowing where to donate to actually have a good impact on "the" environment. Whether it's about climate change, about having poison-free habitats, about species preservation or whatever - is there really no reasonable comparison as to where money actually matters more? Any ideas where to start looking for scientifically / economically sound answers? --Thanks for answering (talk) 20:56, 11 July 2019 (UTC)

Kudos to you for actually putting thought into how to maximise donation effectiveness. Picking the right charity can radically change how far every dollar goes, and the world would be a vastly better place if everyone did that. It's a pity that GiveWell and the broader Effective altruism movement tend to consider environmental charities as out-of-scope. I don't have a great answer for you, but this article, though a few years old, may be of interest. Adrian J. Hunter^{(talk•contribs)} 01:36, 13 July 2019 (UTC)

Scop.

Hello,

I have encountered an abbreviation in Wikipedia for which I cannot locate any definition. I am nearly positive that it must be something basic that everyone knows that I don't! I am referring to a listing for Scientific nomenclature. Please see this entry, https://en.wikipedia.org/wiki/Coryloideae. In the first sentence on the second line you will see, "...extant genera - Corylus L., Ostryopsis Decne., Carpinus L., and Ostrya Scop." What on earth does "Scop." mean? It is not the species. It is not the sub-genus, I don't think. It is a bad abbreviation for "subclade," if that is what it is! I've searched Wikipedia and the general web. Help, please. Thank you. Bjb2466 (talk) 15:16, 8 July 2019 (UTC)

Apparently, it's an abbreviation of Scopoli; see here. Dbfirs 15:26, 8 July 2019 (UTC)

Just as, in the same passage, "L." is an abbreviation of (Carolus) Linnaeus, the Latin form of the surname of Karl Linné, and "Decne." is a similar abbreviation of (the Latin form of?) Joseph Decaisne's surname. In the fullest form of Binomial nomenclature, the name (or a recognised abbreviation thereof) is added to show who first scientifically named and described the species in question. "Scop." indicates Giovanni Antonio Scopoli aka Johannes Antonius Scopolius. {The poster formerly known as 87.81.230.195} 2.122.177.55 (talk) 15:46, 8 July 2019 (UTC)

Is there a Wikipedia article that tells us this stuff? If so, I couldn't find it, and there's nothing useful at Scop.--Shantavira|^{feed me} 08:12, 9 July 2019 (UTC)

Author citation (botany). Mikenorton (talk) 08:48, 9 July 2019 (UTC)

Scop (disambiguation) fixed Gem fr (talk) 09:45, 9 July 2019 (UTC)

Thanks. It's actually all at List of botanists by author abbreviation (It would be a major task to disambiguate all of them. There are a lot!)--Shantavira|^{feed me} 10:14, 9 July 2019 (UTC)

There's also List of authors of names published under the ICZN, which includes all (hopefully) of the above plus biologists. {The poster formerly known as 87.81.230.195} 2.122.177.55 (talk) 17:42, 9 July 2019 (UTC)

I think this task is just impossible. But so was the writing of wikipedia, after all. So, step by step...Gem fr (talk) 10:23, 9 July 2019 (UTC)