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.
I have seen that in Canada and Russia, Jet engine snow blowers are deployed. I wish to incorporate details regarding the pro's and con's of this design in relevant articles. Evidently it is of value, being used in snow-heavy countries. Especially of interest are the fuel efficiency and work rate of both designs. Zarnivop (talk) 00:31, 4 October 2014 (UTC)[reply]
Recently jet powered snow blowers have made their way to America and are being seen more and more in areas where large amounts of snow needs to be removed, areas such as airports and railways. Jet Engine blowers first were used in Russia and Canada in the 1960’s as the large amounts of snow fall were becoming problematic for their train tracks and road ways. The jet engine allowed them to melt the snow on the tracks and clear the roads quickly. It came to the USA through the MBTA (Boston Transportation Authorities) for this same purpose. [1]. Where a traditional snow blower is most commonly a light-duty single stage machine run on gasoline or diesel fuel reaching maximum horse power on large scale machines of 1,000 (746 kW), jet engine machines start at around 1,500 horsepower gas-turbine engine and run off of jet-fuel. [2] . In contrast, traditional snow blowers are either electric or gasoline powered and hand-held on small machines, but can be mounted to vehicles in bigger machines and diesel powered. These blowers use a 2-stage machine that sucks snow up and out of the discharge shoot. Blowers can either move snow out of the way and into another area, or it can be dispensed into a truck and removed.
The pros to the new jet engine you have seen more recently is that gas turbine engines have great power-to-weight ratio meaning that the amount of energy you get out of the engine compared to the weight of the engine itself is good. It also is generally a smaller engine than the reciprocating one but with the same amount of power. It can move more snow than a traditional snow blower and the benefit of being able to melt the snow instead of just move it is favorable. The con’s to this new jet engine is that it is monumentally more expensive. Designing and manufacturing gas turbines is tough from both the engineering and material standpoint. It also uses more fuel when idling [3] . If your purpose is to use one for personal usage, the traditional snow blower would in my opinion be more practical. If your desire Is to use it industrially and need to more or remove large amount of snow quickly, the jet engine snow blower is much more effective if you can afford the engine
In the latest Astronomy magazine, there is an article: "How astronomers measure the cosmos." It contains a highlight: "Waves - similar those made by rocks falling into a pond - undulated through the early universe at nearly 60 present of the speed of light." I consider it's impossible. I checked the article "the speed of sound," they have a section on speed of sound in plasma but it is impossible for me to make calculations because many parameters are unknown. --AboutFace 22 (talk) 01:29, 4 October 2014 (UTC)[reply]
Honestly I don't know what does and doesn't count as "plasma", given that quark-gluon plasma is called plasma, but in any case the passage that AboutFace quoted doesn't say anything about plasma. I think it can only be referring to the speed of sound in a relativistic gas. There's always a frontier of knowledge where we're forced to guess/hypothesize, but this isn't anywhere near that; the physics of this era is well understood (by real cosmologists, not by me) since it's described by low-energy physics. Gravitational waves have nothing to do with this thread. -- BenRG (talk) 23:57, 4 October 2014 (UTC)[reply]
The term "plasma" is being used rather loosely, and I think it is serving in this thread to side-track from the basic concept that is being considered. As BenRG has indicated, in the early universe, in particular the radiation-dominated universe, essentially all radiation and matter propagated at a speed indistinguishable from the speed of light, but also interacted without travelling far. This gave rise to a fluid that had readily determined properties, including compressibility, density etc., and this would have led to a readily and precisely calculated velocity of propagation of pressure waves. In a gas, the speed of sound is a large fraction of the typical speed of the gas particles, and it is not strange that the same is true for pressure waves in a fluid of highly relativistic particles. —Quondum03:48, 6 October 2014 (UTC)[reply]
Its about a natural phenomen of surface patterns which occur on sweetwaterlakes during rain (absence of wind). It is supposed to be a phenomen of thermodynamics. By searching "lake" "rain" "surface patterns" some hints came about this. The patterns sometimes look like this[1] (found there: [2]) or like this [3] Can anyone here provide further explanations please? --2.200.38.86 (talk) 07:52, 4 October 2014 (UTC)[reply]
Likely simply caused because many lakes consist of multiple waterparts, that differ in composition of elements. This is very common in lakes that contain one or multiple springs but can have multiple other reasons. In that case this is simply related to physics in sense of differences in material properties, like we know well from other "water mixtures" like in the comparrison of sweet- and saltwater. --Kharon (talk) 11:22, 4 October 2014 (UTC)[reply]
Yet, it's not obvious, if not upwelling / streams could provide for an explanation (by different behavior of raindrop-caused waves spreading) without regard to surfactants .. --217.84.101.211 (talk) 13:34, 4 October 2014 (UTC)[reply]
The last link gives some good explanations. I'd go with the theory of a thin layer of oil. Note that this doesn't necessarily mean industrial pollution. Many oils are naturally produced, say from decaying dead fish in the lakes (just the normal amount, not a massive die-off). If it was upwelling, you'd expect to see "lumps" on the water surface where this occurs (in the center of the clear spots). To test my oil theory, look at the lake surface on a calm, sunny day, and look for the characteristic rainbow patterns in the oil. StuRat (talk) 13:45, 4 October 2014 (UTC)[reply]
There is no oil on this lakes. I guess it is a mixture of temperature changes and viscosity changes (see Viscosity#Water) caused by the different waterparameters which come along with the rainwater. It takes some time to mix this different "water qualitys". 109.40.80.188 (talk) 04:55, 5 October 2014 (UTC)[reply]
Block (periodic table) says, "Helium is placed next to hydrogen instead of on top of neon because it is part of the s2 group," and it doesn't mention helium again. And yet the purpose of that change, seems to be a defining feature of the subject (blocks), and it's probably widespread common knowledge... therefore requiring little citation, so please edit that section to add a sentence explaining why helium is put beside hydrogen, thanks, ~ R.T.G09:22, 4 October 2014 (UTC)[reply]
What do you mean? "Helium is placed next to hydrogen instead of on top of neon because it is part of the s2 group" is as simple an explanation as you can get, there is no other reason. Plasmic Physics (talk) 10:54, 4 October 2014 (UTC)[reply]
I suppose the sentence could be made redundantly specific - "Helium is placed next to hydrogen, which is part of the s1 group, instead of on top of neon, which is part of the pz2 group, because helium is part of the s2 group". However, as I said, it is redundant, since it is implied. Plasmic Physics (talk) 11:17, 4 October 2014 (UTC)[reply]
Rewriting the sentence in this way, is like saying "in the cutlery drawer, this fork is placed with that fork, which is in the fork compartment, instead of that knife which is in the knife compartment, because this fork is a fork and not a knife." As you can see, it is awkward, and unnecessary. Plasmic Physics (talk) 11:36, 4 October 2014 (UTC)[reply]
Yes @PrimeHunter:. It currently says blah is a part of blah without saying anything about what blah is, except for labelling one of them a significant basic element (special block type) of the topic (block). There are no supporting links or anything. It's a total blank. Without explanation, it says something similar to what this image does without explanation. This image depicts a complex area of mathematics.~ R.T.G14:29, 4 October 2014 (UTC)[reply]
You're right, this article is terribly written. There should be more discussion of the meaning and similarities between various elements on the same block. And perhaps images of what different s, p, d, etc. orbitals look like, alá Atomic orbital. There is also no explanation as to why s, p, d, and f are named that way. Shocking and tragic--you are entirely right. -- Mac Davis (talk) 15:02, 4 October 2014 (UTC)[reply]
Someone has removed the clarification tags with words something like, "because it is in the s2 group, as it has a 1s2 configuration". But you could have said, "it has a 124790bz configuration," and we would still not know what it means to be configured in that way. (spiritual isn't it)
How about if I ask, without using code numbers please explain, what constitutes membership of the group coded s2 and its special floating nature? ("special floating" is the assumption that hydrogens movement is a special movement) Try explaining it like for your five year old sibling with words like floaty bits, not to have them pass a test and navigate the index of a masters degree text book, but just to have them understand how one thing is like another, and how categorising them unusually has value... Note: describing the number s2 as constituted by 1s2 will result a further query. We need to know in the practical sense, what is the physical characteristic this unusual block treatment categorises? ~ R.T.G15:58, 4 October 2014 (UTC)[reply]
Gosh, doesn't the link to electron configuration help? I have no clue what you are talking about at all. What is "floating nature"? What is "special floating"? What is "hydrogens movement"? I'm sorry but I don't think we can give an introductory-level course in chemistry in every article. Links mean that if you didn't understand something, you can go read what it is about.
As for what s2 means here: I took that very term out, because nobody uses it. I instead wrote that it is in the s-block (which I linked) because it had a 1s2electron configuration (which I also linked). But maybe the "1s2" scares you away (strange, because it's defined in the links, but OK). So now I write instead "Helium is placed next to hydrogen instead of on top of neon because it is in the s-block, having its outer (and only) electrons in the 1s atomic orbital."
If this really still doesn't help you, I doubt the article will be able to without straying too far off its subject matter into that of other articles. But since this is the Ref Desk, here's my valiant explanation attempt. Atoms are composed of a cloud of negatively charged electrons, bound by electromagnetism to the positively charged nucleus, consisting of protons and neutrons. These electrons can be thought of as existing in electron shells and subshells (orbitals), each at different energy levels: lower-energy orbitals fill first. Hydrogen and helium are in the first row in the periodic table and are filling up the first shell of electrons. Unlike all the others, this shell only has an s orbital, which can hold two electrons: one spin-up, one spin-down. (Also, this spin doesn't mean that the electrons are literally spinning in opposite directions. It's intrinsic to the electrons, and not an extrinsic artifact of rotation.)
The highest-energy electrons (which give the atom's chemical personality) exist in the highest-energy orbitals. For the main-group elements – groups 1, 2, and 12–18 – these are the outermost s and p orbitals. The s orbitals can hold two electrons; p, six electrons. So each atom wants to get a full octet of outer-shell electrons. The noble gases already have this octet, and so are happy and chemically unreactive.
Helium has two electrons in its outermost shell (the first one). However, this shell is exceptional and doesn't have p orbitals, so that helium actually has a complete complement of outer electrons. So it is happy and chemically unreactive, like the noble gases; thus it is usually placed with them in periodic tables, because it better reflects the chemistry.
However, if we need to insist on making the blocks primary – categorizing by what kind of orbital (s, p, d, or f) the differentiating electron (the one added from the previous element) is in – then helium must go in group 2 next to hydrogen, above the alkaline earth metals which have two electrons in their outermost shell (not full for these metals!). Chemists normally strongly criticize this arrangement, because it is completely ridiculous when you think about chemistry: helium behaves nothing like the alkaline earth metals. But it makes sense if all you are interested is the electronic structure of the helium atom, which is the very reason why you would want to think of blocks in the first place.
The lack of a 1p orbital has profound consequences for the chemistry of the first two elements, hydrogen and helium. From lithium onwards periodicity is more well-behaved.
As a further example to illustrate the problem: hydrogen has one electron, that goes in the 1s orbital. The 1s orbital can accomodate one more electron. Hence hydrogen can either lose its lone electron or gain one. In the former case it behaves like the alkali metals, which have one electron in their outermost shell: in the latter case it behaves like the halogens, which have seven. But it is quite different from either of them because hydrogen has a half-filled shell, not an almost empty one or an almost full one, and so neither group is an especially good fit for hydrogen's properties. Indeed, if any element could be said to have a chemistry sui generis, it's hydrogen because it's small (when it loses its only electron, it becomes a bare nucleus, about a thousand times smaller than any other ions in the periodic table) and it's got a strange electron configuration unlike any other element (precisely because there is no 1p). So we have another case where the block placement (above lithium) doesn't really do complete justice to the chemistry of the element.
For hydrogen the block placement is the best we've got, so we stick with it. For helium the place above neon fits much better and so when blocks are not an issue it is moved there.
P.S. The length it took me to tell the whole story from the beginning and try to be as simple as possible is precisely why it's not really covered in detail in the article. I would perhaps include a short paragraph about why chemical properties don't follow what block placement would predict for H and He, but no more (this is more stuff for period 1 element). Double sharp (talk) 16:53, 4 October 2014 (UTC)[reply]
It doesn't scare me at all, but if your sentence is to say, by use of "1s atomic orbital", that their electrons orbit every second, it doesn't actually say that. ~ R.T.G17:08, 4 October 2014 (UTC)[reply]
And I appreciate that you may be wracking your brains about it and that you've thought hard to write such a full page of text, but even you seem to think one sentence could do it.. ~ R.T.G17:11, 4 October 2014 (UTC)[reply]
Yes, because various links to other articles should give the basic information, if you need it. I would probably just write a paragraph, saying that the first shell has no p orbital and then go briefly into the chemical properties of H and He, and then note that for the purpose of accentuating the blocks H and He have been put in places that reflect their electron configuration well, but not their chemistry. Double sharp (talk) 03:52, 5 October 2014 (UTC)[reply]
By "special floating" I mean specifically in the context of appearing in the periodic table. When I tried to read up, I found there were various positions of displaying hydrogen, none of them explained very clearly. ~ R.T.G17:19, 4 October 2014 (UTC)[reply]
Did you ever look at Alkali metal#Hydrogen? It attempts to give an explanation. The usual placements are group 1 (above Li, to conform with its s1 configuration), group 17 (above F, because like the halogens, it needs one more electron to complete its shell), group 14 (above C, because like the carbon group, it has a half-filled shell), and floating around at the top (because none of these placements fit H's chemistry very well, unfortunately). You sometimes see He floating around as well because its s2 configuration doesn't tally well with its noble-gas chemistry; but almost always the electron configuration is ignored and it goes over Ne. Double sharp (talk) 03:52, 5 October 2014 (UTC)[reply]
Electrons are arranged around atomic nuclei is specific patterns called atomic orbitals. Each orbital can be characterized by the amount of energy it has and the distribution of angular momentum associated with it. An "s" orbital is one that has no orbital angular momentum, and the "1" orbital is the orbital level with the lowest total energy. So "1s" means the lowest energy state where the electron has no orbital angular momentum. As it turns out, two electrons can fit in an "s" orbital. We label these "s1" and "s2". We can directly measure the electron configuration of helium and observe that it's outermost electron is in the "1s2" orbital (i.e. lowest energy, no orbital angular momentum, second electron). Other atoms that are similar include beryllium, whose outermost electron is "2s2" (i.e. second lowest energy, no orbital angular momentum, second electron), magnesium which is "3s2", and calcium which is "4s2", etc. Hence some people would suggest that helium should be placed above beryllium in the periodic table (i.e. group 2). Behaviorally though, helium is a non-reactive nobel gas, which is why it is traditionally placed above neon. Does that help? Dragons flight (talk) 18:13, 4 October 2014 (UTC)[reply]
Yes, I understand now that the grouping is related to something like the density, and something to do with the direction of momentum (I thought it was something like that). And Double sharps second edit has further improved the section. I don't understand it well enough to write a paper on it, but an explanation, even if it is verbiose, is still an explanation. Thanks for all the response o/ ~ R.T.G19:12, 4 October 2014 (UTC)[reply]
Should helium be next to hydrogen in this diagram? I think it would be better to put it in column 18, its location in every other periodic table I can remember seeing in my life (even the one at the top of this article), while keeping it red to indicate that it's in the s block, and change the explanatory text to something like "hydrogen and helium are counted as s block members because of their electron structure, though they have chemical properties quite unlike those of other s-block elements." It would be nice to put hydrogen in a spot of its own, too, instead of in column 1, but I'm not sure where it would fit. -- BenRG (talk) 00:26, 5 October 2014 (UTC)[reply]
Agree with you on He, but not on H: short of floating it, group 1 is really the best place, I think. The closest relation to H among the elements seems to be Li. First of all, metallic hydrogen behaves like an alkali metal. Secondly, like hydrogen, lithium can form lithium bonds (analogous to hydrogen bonds). Lastly, H can replace Li in some molecular crystal structures: here's an example. Double sharp (talk) 04:07, 5 October 2014 (UTC)[reply]
Valence atomic energy levels for thallium and eka-thallium (the latter predicted)
I think it would be neat to see a graphic diagram that models the orbitals as "bands", sort of like the conduction band of a metal. For some reason that I don't really understand, it just happens that every time an electron finally has enough energy to enter a higher angular momentum, that "band" of energies (e.g. the first f orbital) works out to be just above some higher-energy s orbital. As a result, elements stack up neatly on the right edge of the table ... except for helium, where the p orbital wasn't introduced yet. To be sure, the energies of these "bands" would depend on the nuclear charge, but I think it should be simply proportional. The bands would overlap, slightly, in some transition metals where the different types of orbitals fill at the same time. Wnt (talk) 15:09, 5 October 2014 (UTC)[reply]
Kind of, but it should go from, say, 1s to 7s, being denominated not in fixed energies but in proportion to energy per nuclear charge, and generated by taking data from a wide variety of atoms of different masses. Of course, there is some imprecision in how they would align, so the 'bands' would be broader of necessity; I'm not sure how much broader. Wnt (talk) 01:25, 7 October 2014 (UTC)[reply]
I found myself wondering whether it is possible to increase the moment of inertia of something chemically, or at least give something like that as an effect. You can do that by redistributing mass within an object, and can seem more or less to do so by precession with a gyrostat, but can you do this at the molecular level?
To begin with, I edited some data at molecular gyroscope - if anyone would like to look over that article you might do the world a service. :) I get the impression that a truly freely rotating phenyl ring tethered at either end could move its atoms in excess of 100 m/s simply due to thermal energy.
I think that counter-rotating flywheels should cancel one another's precession, therefore having no effect on the apparent moment of inertia. I also assume that's why one big flywheel has more effect than many little ones, because if you picture their edges being right next to each other, they're moving in opposite directions except at the outer edge of the whole group.
I think that a rotating molecule with an unknown state ought to act like a pair of counter-rotating flywheels.
Question: is it possible to create a group, molecule, or portion of a molecule that has a half-integral angular momentum (like an electron's spin, but at some stronger level on a larger scale), so that it cannot be measured to have zero angular momentum?
Would such an molecule/portion thereof resist rotation if its angular momentum is observed?
Could you rotate it without thereby observing its angular momentum?
If you have a block of something containing many small molecular flywheels, is it possible to use some vaguely NMR-like approach to knock them all into spinning the same way, so that it works like a gyrostat? How long could that last?
Is it conceivably possible to make a very large near frictionless flywheel at the molecular level using carbon nanotubes, either by putting many concentrically and/or by having ions fly around in the empty space in the middle?
Hello, as your first action was not to add the article to DYK, I have added it...[4], it is just big enough, hope that's alright. ~ R.T.G16:48, 4 October 2014 (UTC)[reply]
I need a current source of a few mA (for a project) that can be switched on and off very quickly (10s of ns). Cant think how to do it fast using normal curent source circuits. Any thoughts?--86.182.55.229 (talk) 19:28, 4 October 2014 (UTC)[reply]
A simple MOSFET circuit, perhaps with some extra components to reduce the Miller effect, should be OK. See, for example, the second circuit on this page. The diode provides a path for the "on" charge to get to the FET's gate, and the transistor a path to remove it. You might even get away with just a resistor between the pulse source and the gate, if your load isn't very reactive. Tevildo (talk) 20:59, 4 October 2014 (UTC)[reply]
It would depend somewhat on the required characteristics as a current source. If you mean something that produces a current that is essentially independent of the voltage on the load, a MOSFET switched fully on will not be suitable, but could act as a fast switch in series with a source that accurately controls the current. Another option might be to use MOSFETs as a switch to route current from a current source either through or around the load. A BJT common emitter circuit can serve as the current source, with MOSFETs giving the rapid switching. —Quondum21:38, 4 October 2014 (UTC)[reply]
This is a good point. If current regulation is important, I would recommend putting the MOSFET in parallel with the load, after the constant-current source. When the MOSFET is on, the current will flow through it and the load will be off - with the MOSFET off, the current will flow through the load. This will give better current regulation than switching the current source itself on and off. Tevildo (talk) 18:46, 5 October 2014 (UTC)[reply]
All of these are group V, but I don't see either of these two grouped with Mononegavirales. They all produce antisense RNA that is transcribed by RNA-dependent RNA polymerase, so there is no potential for ordinary DNA rearrangements. Of course, RNA can be spliced, e.g. trans-splicing, but these viruses aren't normally spliced. Maybe you could melt the partially transcribed strand off one virus, anneal it to the other virus at some little stretch of homology (something akin to strand transfer, and continue transcription, but ... the likelihood of annealing to the wrong RNA when the right one is present, and not even annealing nonspecifically intramolecularly to the same RNA but instead to a whole different RNA ... it seems hard for me to picture. Now, this is biology, nothing is impossible; there are many very low probability events that could happen like reverse transcription by some third virus, but I think you'd be waiting a very long time indeed for any hopeful monster to emerge out of this union, unless of course someone gave it some help. Wnt (talk) 21:21, 4 October 2014 (UTC)[reply]
Seriously? Group V is about as relevant as saying that chapter 5 of one book can be melded with chapter V of another. Is there an actual question here? μηδείς (talk) 02:02, 5 October 2014 (UTC)[reply]
@Medeis: I'm a bit confused by your response; I wasn't asking the question. To explain though, group V means that the sense directions of both genomes are the same, so it would be conceivable to splice two genes somewhere within their CDSes to add a protein sequence from one virus into the other. I don't deny it's a very very unlikely event. Actually I don't know much about very long time-scale evolution of viruses - my feeling is that it would be much more affected by "hopeful monster" phenomena than evolution of more complex life, making such improbable phenomena potentially relevant on multimillion-year time scales, but I don't know that. Wnt (talk) 03:28, 6 October 2014 (UTC)[reply]
Perhaps the misunderstanding is mine. I read you as suggesting that some subtype five of these viruses might be cross-spliceable because of their internal subtypes. The Lassa virus article does not, for example, describe it as belonging to any overarching type V of some larger family, if that's the case the culpa is mea. μηδείς (talk) 17:30, 6 October 2014 (UTC)[reply]
It seems like there's a lot of uncertainty about viral evolution and origin, interspersed with more than a few learned academicians talking out their asses, but there are some interesting data, e.g. here's a neat paper where someone finds a group of circoviruses containing a capsid that had previously been known only in RNA viruses. They take this as an indication that yes, viruses do some really perverted things with each other when we're not looking. But it is still a current research task to try to work out the origin and relationships of the group V viruses. Wnt (talk) 19:39, 6 October 2014 (UTC)[reply]
Is there any way that the length of a contrail can be measured. I have read the contrail pages but find no answer to this question. wsccj8 — Preceding unsigned comment added by 66.74.2.32 (talk) 21:40, 4 October 2014 (UTC)[reply]
You could make an assumption about its height, say 40,000 feet, measure angles from the vertical to its start and finish, and do some basic trigonometry. HiLo48 (talk) 22:06, 4 October 2014 (UTC)[reply]
Chemtrails are the belief that Contrails are being used by the government...or the lizard people...or Microsoft...to spread brain-altering chemicals/diseases/tranquilizers into the air by introducing them into jet fuel. They are indeed a bunch of nonsense.
Contrails, on the other hand, are simply the result of the water produced when burning hydrocarbons in the jet fuel condensing in the cold air at altitude. Nothing particularly amazing or startling about that. SteveBaker (talk) 05:04, 5 October 2014 (UTC)[reply]
Oh, yes, I know that contrails exist. But I have only heard about chemtrails from occasional conspiracy theorists on the radio (I've never come acrost it in print) and thought they were saying contrails, and blaming them for changing the weather or as evidence of a government spy program, or whatever. μηδείς (talk) 16:51, 5 October 2014 (UTC)[reply]
Ah - well, contrails (sans conspiracy theories) do indeed change the weather - according to mainstream science. The strongest evidence for that came in an abrupt daytime temperature rise and nighttime fall across the USA in the three days after the 9/11 attacks when all aircraft were grounded. Many climatologists studied this effect and much has been written about it in serious journals. The consensus is that the temperature extremes moved by two degrees C over those three days!
Chemtrails (which some of the crazies claim are just chemicals injected into regular contrails and others claim are some other, similar phenomenon) are just conspiracy theories. SteveBaker (talk) 00:03, 6 October 2014 (UTC)[reply]
As HiLo48 mentioned, assumptions need to be made, and even with careful triangulation, the best one can hope for is an estimate. For one thing, the beginning of the contrail will have drifted more than the end of the contrail; for another, with long contrails at high altitude, one would need to take Earth's curvature into account. —71.20.250.51 (talk) 04:13, 5 October 2014 (UTC)[reply]
I've certainly seen contrails covering a 60 degree swath of sky - so the contrail is probably around the same length as the altitude of the aircraft...so with contrails forming at altitudes between 8,000 and 16,000 meters - we can deduce that the length of the contrail could be 8 to 16 km (5 to 10 miles). But there are huge error-bars on this math - the contrail doesn't end suddenly, it just gets more and more faint and dispersed - I'm sure the speed of the aircraft and how much thrust it's using are all variables here. SteveBaker (talk) 05:04, 5 October 2014 (UTC)[reply]
Another way to measure them is to see the length of their shadow on the ground. If you have an aerial photo, or satellite image, you should be able to see the contrail or its shadow and measure it off. Graeme Bartlett (talk) 11:34, 5 October 2014 (UTC)[reply]
Aerial photos are taken from relatively low altitude...way below the height where contrails are being formed. So you don't see contrails in aerial photos - and although you might conceivably see their shadows, those are hard to spot on the ground because they are so tenuous.
Satellite photos do show contrails, however - and a sufficiently high altitude satellite with a narrow field-camera ought to get what we need to get a rough measurement. This NASA photo shows a bunch of contrails over the western USA - and in the infra-red image on the right, you can see contrails that cover distances comparable to the width of Northern California - so they must be around 150 to 200 miles long. However, that's in infrared - and it's been 'enhanced', so perhaps the contrail itself wouldn't have been visible over it's entire length when seen from the ground.
Now we get into the ikky part of "How much of the contrail should we measure?" - should we ask how much is visible to the naked eye from ground level - or how much is measurable with scientific instruments from orbit? - or how much is theoretically present? All of those will generate different answers.
A 100 mile contrail would stretch from horizon to horizon. If you look at one of my favorite websites: http://1000skies.com/fullpanos/index.htm (this is a company that sells gorgeous photos of the entire sky) - you can see quite a few contrails - but I don't see any that cross the entire sky. So clearly, the 1000skies cameras can't detect the full 200 mile contrails that NASA are seeing in the infrared. My math (above) suggests that a 'typical' 60-degrees-of-the-sky contrail is 5 to 10 miles long - not 100 to 200 miles as the NASA result shows.
Bottom line here is that because contrails diffuse very gradually over hundreds of miles, there is never a concrete point where you can say "that's the end" - so you can't measure the length without some formal definition like "less than one gram of ice crystals per cubic meter of air".
So we can't really come up with any kind of reasonable answer to the OP's question.
This may or may not be related to the question, but here's the truth on chemtrails: http://www.rsc.org/chemistryworld/2012/05/ultra-low-sulfur-jet-fuel-radar . Basically, there is no upper limit on the amount of sulfur in jet fuel. Captains of industry, whose intelligences exceed ours by the same margin by which a man's exceeds an ant's, have weighed the evidence and chosen jet fuel higher in sulfur than ever, though the exact amount is not given to us to know; we should not speculate that this is geoengineering because it is not for us to know the motives of the gods. The benefit is a 25% lower fuel cost for airplanes, so cheaper tickets! And a small delay in global warming. The cost is a mere 1000-4000 deaths annually from the air pollution, probably less than a Trade Center a year. This is the way of sinister conspiracies -- people talk about them breathlessly, disbelieve them because they're too outlandish or malignant, then finally you find them all neatly written down in a book somewhere and people wouldn't think of trying to change it. Wnt (talk) 14:52, 5 October 2014 (UTC)[reply]
Contrails are water vapor. 1000-4000 deaths a year from pollutants is not good, but it's a relatively low rate. Meanwhile, 5 million a year die voluntarily from tobacco usage.[5] How many World Trade Centers does that make? ←Baseball BugsWhat's up, Doc?carrots→ 15:22, 5 October 2014 (UTC)[reply]
In actual fact, piston aviation engines use avgas that contains lead to prevent engine knocking, particularly with the high compression ratios that are needed for flight at high altitudes. Jets use, well, jet fuel... because their engines are totally unlike the engines you find in automobiles. Trying to explain the thermodynamics or stoichiometry of aviation engines - let alone the environmental impact of trace elements in the fuel - is literally rocket science, so I'd avoid jumping to hasty conclusions. Nimur (talk) 21:34, 5 October 2014 (UTC)[reply]
Next time I see a contrail I'll try to keep my eye on a specific feature of it from as soon as possible after it is created by the aircraft, and then time how long I judge it to be visible, and then do work out how far the plane has flown in that time, and assume that's the length. But I won't post the answer here because it would be original research.Hayttom16:02, 5 October 2014 (UTC)— Preceding unsigned comment added by Hayttom (talk • contribs) [reply]
You can post original research here, just not in the article. But your original research could be used to look for acceptable sources that square with your research, and that info could be used in the article. ←Baseball BugsWhat's up, Doc?carrots→ 16:28, 5 October 2014 (UTC)[reply]
These kind of statistics are easily taken out of context to make them sound terrifying. It's not like an additional 1000-4000 otherwise perfectly healthy people in the prime of their life, who would otherwise live another 50 years, just drop dead because of the jet fuel we use. Vespine (talk) 00:36, 7 October 2014 (UTC)[reply]
Actually, Vespine, that might be what it's the equivalent of. Obviously Wnt's penchant for overblown conspiracy-theory phrasing doesn't help make his argument (and honestly, I can't tell any more if he does it sincerely or ironically). If you make a billion people just a tiny bit less healthy, then you might get a thousand who would otherwise live for decades more, and instead tip them over into a cascade of inflammation that leads to cancer or heart disease and death. A stimulus that kills one in a million people would cause more than 7000 deaths if everyone on Earth were exposed to it. Yes, it's butterfly effect stuff; we can't predict which 7000 it would be out of 7 billions— but that doesn't mean that the effect isn't real. (It's a popular dodge among polluters of all stripes—since the effect is small on a per-person basis, and identifying specific victims is difficult or impossible, there's little incentive to ameliorate problems.) TenOfAllTrades(talk) 03:09, 7 October 2014 (UTC)[reply]
![[1]](http://i.imgur.com/BEmP5Qn.jpg){kind=link}
