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December 23

Stars in winter

While the internet is full of statements that stars are brighter in winter and that this season is good for observation, I've noticed that the typical grey cloud cover, often before snowfalls or drizzle (at least in the Northern Hemisphere), precludes observing any stars at all. Unless one assumes clear cloudless nights in winter are more frequent than precipitation cloud cover? 212.180.235.46 (talk) 11:14, 23 December 2020 (UTC)[reply]

Where does anyone say stars are brighter in winter? The brightness of the vast majority of stars is relatively stable. Winter is good for observation simply because the hours of darkness are longer, and the sun goes further beneath the horizon, so the chances of a clear dark sky are much higher. Clouds can block the view of the sky at any time of year.--Shantavira|^{feed me} 13:32, 23 December 2020 (UTC)[reply]

Cold air is able to hold less moisture than warm air. The sky can be hazy in the winter, but when you get a cold snap you get really clear air and good viewing. Assuming you live in a place where atmospheric moisture is an issue.

And there is the way the Northern Hemisphere faces relative to the center of the galaxy which makes the night sky seem clearer in the winter. 85.76.79.191 (talk) 13:43, 23 December 2020 (UTC)[reply]

The Sagittarian Milky Way (where the center of the galaxy is) is still in a summer constellation everywhere. The geographic latitude makes the summer and southern sky more impressive in like the Outback than the northernmost deserts but the secondary Orion Arm is the closest galactic arm to Earth (we are slightly inside it in some interpretations) which causes the winter sky to have the highest concentration of objectively bright stars, the majorness of the summer sky's arm cannot compensate for its distance and it has many dim stars and fewer bright ones. Buttloads of stars. In the mid-northern hemisphere and light pollution where many astronomy writers live this bilateralness is emphasized to the eye. You can't even see the Milky Way anymore where many people live, so you can't tell that it's better in the summer, or at least the summer Milky Way is dim and unimpressive, that happens in some suburbs. Even most farmland does not show the Milky Way to its full potential (the unresolved summer side of the galaxy, which looks like veined marble in the remotest wilderness even at 40°N) Sagittarian Milky Way (talk) 14:45, 23 December 2020 (UTC)[reply]

The common wisdom, which seems to have been contorted, is that the astronomical seeing is better in winter (or more precisely, on nights with cold and dry atmospheric conditions). A key insight is that the atmosphere needs to be cold and dry - and stable - "all the way to the top." This is categorically not identical to a "cloudless night" - in fact, there are plenty of conditions that are considered "clear sky" that would be absolutely awful for star viewing, casual or otherwise. A great example would be moist, humid, warm, and turbulent air, common to the summer months in many parts of Earth.

Additionally, there are more dark hours per unit-of-time when Earth is so tilted that we call it "winter."

Whether the weather or climate in your geographic area meets these criteria will obviously vary; but in many places on Earth where optical astronomy is practiced, the winter months are the better months for seeing stars.

Nimur (talk) 17:22, 23 December 2020 (UTC)[reply]

Another interesting tidbit is the clearest sky can also be turbulent and the humidest sky can also be calm. If the stars twinkle a lot that is because the air is not stable and you're seeing the turbulence with the naked eye, if the air is dry it looks awesome though making people think it'd be great for a telescope when it's really just clear. If it's hazy but non-turbulent like a temperature inversion it looks horrible to the eye but good for bright small things in a telescope. Also I would like to note that astronomical seeing properly refers only to turbulence while dry clean air vs humid and/or polluted is called transparency.Sagittarian Milky Way (talk) 18:17, 23 December 2020 (UTC)[reply]

I would guess that the major factor is the one highlighted by Shantavira. If the sun does not go 18° below the horizon it's not properly dark. See Twilight#Astronomical twilight. 82.13.210.231 (talk) 17:35, 23 December 2020 (UTC)[reply]

At 40N and a place at the nominal longitude of its time zone it gets this dark at 10:36 daylight time on the latest day of the year, at Arctic circle minus <18 degrees (such as anywhere in your IP country of UK) there's one to many nights a year that never get this dark. Experimenters in the Egyptian desert stopped seeing twilight with the naked eye at 15 to 16 degrees though. In New York City 13 degrees is about as dark as it ever gets and there's always more than 4 hours below 18 degrees. Earth's tilt changes slowly so during Stonehenge times the twilight was even worse. Sagittarian Milky Way (talk) 17:55, 23 December 2020 (UTC)[reply]

December 24

vaccine injection

I had what I think was an an MMR vaccine as a kid. Instead of a needle they used some kind of compressed air sprayer. Apparently a jet of vaccine droplets is shot into the person's arm at high enough speed that it goes through the skin without needing a needle. Therefore they were able to do a room full of kids in what seemed like just a few minutes.

1) what is that thing called, and 2) could they use it for covid vaccine, maybe after they get that vaccine a little bit more nailed down? Thanks. 2602:24A:DE47:BB20:50DE:F402:42A6:A17D (talk) 01:46, 24 December 2020 (UTC)[reply]

The thing is a jet injector. DuncanHill (talk) 01:55, 24 December 2020 (UTC)[reply]

Apparently it's being considered; hypodermic needles are cheaper but more prone to cause accidental injury and there are other pros and cons; see PREPARING FOR MASS VACCINATION (Oct. 2020). Alansplodge (talk) 15:54, 24 December 2020 (UTC)[reply]

Not to mention painful as a hypodermic needle can only make the incision as fast as a human can do it then stop at an acceptable geometry. Then the medicine is given at lower miles per hour and non-simultaneous with the piercing and retrieving the device irritates the wound significantly more than just taking the jet injector. In a jet injector the medicine is moving faster than the human throwing speed record probably and you aim before you pierce so it feels much better. As we want the first vaccination categories vaccinated first (even if they have a high "pain-per-neuron-cut ratio") and there won't be herd immunity till enough persons in later categories get immune this is an important consideration. Sagittarian Milky Way (talk) 17:40, 24 December 2020 (UTC)[reply]

I really don't think the physical speed of the movement of molecules in the vaccine into the injection site is the biggest factor in how rapidly vaccines can be delivered to a population. In fact, I highly doubt it is a factor at all. That's ignoring the fact that the issue right now in getting to herd immunity isn't the speed of delivery per dose, rather, it's actually having enough doses to deliver. --OuroborosCobra (talk) 18:20, 24 December 2020 (UTC)[reply]

It helps how much it hurts which can mildly affect how many high risk of coronadeath people die if there's no hypospray and some people on the high pain-per-neuron-cut end of the bell curve decide to just skip the injection and wait many months for herd immunity instead. I do note that I'm high pain sensitivity and intramuscular injections are too quick to hurt bad if they insert and retrieve at enough inches per second, and the actual injecting is bearable (your mileage may vary), this is why blood drawing especially some drawers is horrible as they have a tiny target. So if pain is a consideration make sure they don't rack up the inserting milliseconds like how the ones who do that probably would if they had to do their own shoulder or butt. Sagittarian Milky Way (talk) 18:48, 24 December 2020 (UTC)[reply]

Does the covid vaccine use a bigger needle (or anything like that) compared to other injections, blood draws, etc.? I've had several of those and they haven't ever hurt much in a purely physical way. It's always been enough to just look in a different direction and think about something else while they stick the needle in. Vaccines often have post-injection side effects for a day or so, that (if you experience them) will be way more annoying than the momentary needle prick of the injection itself, but are themselves no big deal except in some rare acute (allergic reaction) cases. 2601:648:8202:96B0:0:0:0:313A (talk) 01:59, 25 December 2020 (UTC)[reply]

Forgot about that, annoying day+ long vaccine ache. I really do not understand heroin addicts, if I had to inject myself without anesthetic that often I wouldn't live long before suicide. Sagittarian Milky Way (talk) 02:49, 25 December 2020 (UTC)[reply]

Note that the link I posted above doesn't mention anything about jet injectors being quicker, but does say that the patient doesn't have to be particularly compliant, which is a big advantage where children are concerned (wriggling while there's a needle in your arm is obviously problematic). Also that a smaller dose might be needed because the agent is delivered into the skin layer: "The dermis and epidermis of human skin are rich in antigen-presenting cells. As such, focusing the delivery of vaccines to these layers – rather than to muscle or subcutaneous tissue – should be more efficient, inducing protective immune responses with smaller amounts of vaccine antigen". However, that would require more research to determine. Alansplodge (talk)

If a smaller dose can be used that would be a big ameliorator for the manufacturing bottleneck and probably not make the site so sore. Sagittarian Milky Way (talk) 14:26, 25 December 2020 (UTC)[reply]

Plutonium tetroxide

My research indicates at least two reported observations of plutonium(VIII) oxide (PuO
₄), though I am not 100% confident that these findings are definitive. The resources where I found such indicia were:

Zaitsevskii et al. (2013). J. Chem. Phys. 139 (3): 034307. (citing an empirical study in 2011 that I could not access.)
Kiselev et al. (2014). Radiochimica Acta 102 (3).

–LaundryPizza03 (d c̄) 02:06, 24 December 2020 (UTC)[reply]

Is there a question? --174.95.161.129 (talk) 07:39, 24 December 2020 (UTC)[reply]

Presumably the implied question is whether this warrants a mention in the section Plutonium#Compounds and chemistry, which only goes up to Pu(VII). The 2005 article "Experimental data points to the existence of plutonium(VIII) in alkaline solutions" sounds rather tentative, but the 2014 article "A spectrophotometric study of the reduction of Pu(VIII) and Pu(VII) in alkaline solutions" with the same first author (also the corresponding author of Kiselev et al. (2014), mentioned above) has a more definitive ring. The talk page of the Plutonium article may be a more appropriate place to signal this, but I think we'd like to see more independent confirmation. --Lambiam 09:14, 24 December 2020 (UTC)[reply]

Some past reports of Pu(VIII) were debunked by Shilov et al. in 2017, though some of the papers above are not mentioned in the cites. So I would use caution and not include it. That said, Shilov et al. allow that Pu(VIII) and Am(VIII) might be reachable through other means, so maybe one day we will get to have an update. Double sharp (talk) 09:22, 24 December 2020 (UTC)[reply]

Are any elements in the even longer 8th row predicted to be able to form neutral compounds above VIII in the brief moments before radioactive decay? Sagittarian Milky Way (talk) 17:12, 26 December 2020 (UTC)[reply]

Your first article is a modelling study and predicts Pu(VIII) will be unstable. The article itself has been cited 17 times.

This article [1] says, "In neutral chemical compounds, the highest known oxidation state of all elements in the Periodic Table is +VIII. While PuO₄ is viewed as an exotic Pu(+VIII) complex, we have shown here that no stable electronic homologue of octavalent RuO₄ and OsO₄ exists for PuO₄, even though Pu has the same number of eight valence electrons as Ru and Os."

This article [2] says, "Metal tetraoxygen molecules (MO₄, M = Fe, Ru, Os, Hs, Sm, Pu) of all metal atoms M with eight valence electrons are theoretically studied using density functional and correlated wave function approaches. The heavier d-block elements Ru, Os, Hs are confirmed to form stable tetraoxides of Td symmetry in 1A1 electronic states with empty metal d⁰ valence shell and closed-shell O^2– ligands, while the 3d-, 4f-, and 5f-elements Fe, Sm, and Pu prefer partial occupation of their valence shells and peroxide or superoxide ligands at lower symmetry structures with various spin couplings."

Your second article has been cited six times. It says, "The existence of Pu(VIII) was shown in alkaline solutions and in nonpolar solvents (CCl₄ and CHCl₃) on the ground of such experimental facts like extraction of plutonium species, obtained by means of ozonization of Pu(VI) alkaline solutions into CCl₄ and CHCl₃; volatility of Pu compounds out of aqueous alkaline solutions, and the mentioned solvents."

This article [3] suggests the existence of Pu(VIII) in alkaline media, and has been cited 32 times.

It would certainly be worth mentioning something about all of this, with citations, for at least the following reasons. 1: Since Pu's lighter d-block chum, Os, can reach VIII, it's interesting to speculate if Pu could follow suit; 2: Such references provide a great starting point for students or researchers; 3: As a reader, those are the same sources you might want to find, or look up again, in future.

At the least you could say something like, "Claims for Pu(VIII) have been reported [ref 1, ref 2 etc] but remain unconfirmed in light of the expected instability of this state. [ref 3, ref 4 etc]." From my limited reading of the sources it looks like Pu(VIII) in aqueous solution is expected to be more achievable than e.g. PuO₄. --- Sandbh (talk) 00:33, 27 December 2020 (UTC)[reply]

How to plot magnetic field lines around a metal?

Imagine I want to simulate the magnetic field lines of a magnet when there is a metal nearby, how could I do this? I've searched, but all I find is the usual dipole plot. For reference: https://www.kjmagnetics.com/blog.asp?p=shielding-materials, https://www.kjmagnetics.com/magneticfield.asp https://www.kjmagnetics.com/blog.asp?p=block-or-extend If you know a software that's awesome, but if you also can derive a formula to simulate it, that's great too. I'd like to plot https://physics.stackexchange.com/questions/464272/magnetic-field-gradient-of-a-ring-magnet Thanks Sistemx (talk) 20:26, 24 December 2020 (UTC)[reply]

You could ask K&J Magnetics, Inc. about the particular FEA (Finite Element Analysis) software they mention at your second link. Wikipedia offers a List of finite element software packages. I can't give any specific recommendation but here is a review of 7 popular programs. 84.209.119.241 (talk) 23:09, 24 December 2020 (UTC)[reply]

December 25

fastest way to chlll a bottle of champagne

You have a bottle of champagne at room temperature and you want to chill it to serving temperature (I guess that is a few degrees celsius), then pop the cork and serve it the usual way. Normally you do that with an ice bucket but that can take an hour or so. Can anyone suggest a faster way? Note that you have to chill the unopened bottle before popping the cork: you can't pour the champagne through a heat exchanging coil or anything like that. Putting the bottle in e.g. liquid nitrogen doesn't sound like a good idea because of freezing, shattering, etc.

You can use fancy lab equipment if you want, including large amounts of electricity, if that helps. I'm imagining something like a subfreezing liquid bath or cold air blast, combine with gently rocking or turning the bottle to spread the cold evenly through the liquid inside.

Just wondering--thanks. 2601:648:8202:96B0:0:0:0:313A (talk) 00:00, 25 December 2020 (UTC)[reply]

There are a bunch of kitchen/wine-store devices for this. One common method is to use a liquid cooling bath (water or glycol at 0 °C or slightly below, better heat transfer than air) and to rotate the bottle (presumably this helps mix the beverage to get better cooling throughout rather than only edge-inwards). I'm not sure spinning a champagne bottle is good for the bubbliness though. DMacks (talk) 00:07, 25 December 2020 (UTC)[reply]

Fan forced cooling is a solution some shops I know use. HiLo48 (talk) 00:14, 25 December 2020 (UTC)[reply]

If you have a freezer, wrapping the bottle in a wet towel and placing it in the freezer may work faster. There is a serious risk, though, that undercooled champagne will freeze instantly in the bottle the moment the cork is popped, thereby spoiling it, so this is not recommended. Adding cool water (close to 0 °C; can be pre-cooled) to the ice in an ice bucket speeds up the heat transfer; keep stirring and adding ice as it melts. Splintered ice works better than ice cubes. Adding some salt to the water makes the ice melt faster, lowering the temperature. --Lambiam 14:30, 25 December 2020 (UTC)[reply]

Anecdotally, I can attest that Lambiam's freezer + wet paper towel/washcloth method is probably your best option at home. Works like a charm. Temerarius (talk) 20:33, 26 December 2020 (UTC)[reply]

I did some experiments with a digital thermometer equipped with a probe through a wine bottle cork about ten years ago. This was regular wine not Champagne. The fastest chilling I achieved was by putting the bottle in a bucket of ice and then filling the bucket with cold salt water. The most convenient way that I use quite frequently is to put the bottle into the bin of ice cubes that my freezer makes automatically. Cullen³²⁸ Let's discuss it 18:32, 29 December 2020 (UTC)[reply]

December 26

Comparison of RNA vaccines and RNA viruses

How do they compare? Can the former reproduce, at least to some degree, once inside the human body? Some of the latter cause cancer, how can we discard that the former also won't? Is their mechanism of action similar? Both articles might improve with a sub-section around these issues. --Bumptump (talk) 14:40, 26 December 2020 (UTC)[reply]

You should read the respective articles. Ruslik_Zero 17:16, 26 December 2020 (UTC)[reply]

Always a good idea, but do they address the specific questions posed by the OP? --Lambiam 23:36, 26 December 2020 (UTC)[reply]

As implied above, the articles need more content regarding these questions. Ruslik should read the respective articles to see by himself. --Bumptump (talk) 23:51, 26 December 2020 (UTC)[reply]

The last two paragraphs in 'Mechanism' section answer all your questions. Ruslik_Zero 20:23, 27 December 2020 (UTC)[reply]

They describe how the vaccine is intended to work. They do not contain an assurance that no RNA replication can take place. If they somehow imply this, well, then this implication is rather... implicit. I can understand that people want to be sure that this cannot happen. Assurances by scientists saying, "trust us, nothing can go wrong", are probably not an effective approach. Note also that until November 27 the lead stated that the cells are "reprogrammed" by injecting the vaccine, which was not helpful. --Lambiam 23:52, 27 December 2020 (UTC)[reply]

Sure, some scientists can have trouble communicating to the general public because they tend to forget not everyone has their level of background knowledge. An RNA vaccine would have to include an RNA-dependent polymerase or something like a retrotransposon to even hypothetically get a cell to make copies of the RNA. "Typically", gene information only moves one-way in cells, DNA to RNA to protein. Free RNA is rapidly broken down by cells. The central challenge of RNA vaccine development has been actually getting the RNA to persist in a cell long enough to get translated, which was done with the modRNA technique (which is on the Main Page today), selectively modifying the RNA so it's more resistant to degradation but still able to get translated by ribosomes. --47.152.93.24 (talk) 02:14, 28 December 2020 (UTC)[reply]

And some respondents here can have trouble communicating with questioners, dismissing reasonable questions as if they display an unconscionable ignorance and this reference desk has no raison d'être other than to belittle questioners. --Lambiam 12:15, 28 December 2020 (UTC)[reply]

The intent of existing RNA vaccines is to get the RNA into your cells and get it translated by ribosomes into the protein it codes for. Whether that counts as "reproduction" is up to you. This is where we run up against human language being vague. Viruses themselves are just nucleic acid and proteins in a package, and don't do anything outside of a cell, which is why many people don't consider them really "alive". Oncoviruses can cause cancer by trying to insert their genes into the cell's DNA or by otherwise messing with gene transcription and regulation. Doing the former requires enzymes to splice the viral genes into the cell's DNA (retroviruses use a reverse transcriptase). The latter could potentially be caused by just RNA, but it'd probably have to be complex RNA encoding things like ribozymes. This could potentially be used to treat cancer or other diseases as well. But for producing immunity to a disease, the vaccine will generally only contain genes for antigens to elicit an immune response against them. The RNA vaccines for COVID-19 just contain the gene for the viral "spike protein" that binds to cells to infect them. --47.152.93.24 (talk) 03:21, 27 December 2020 (UTC)[reply]

December 28

Covid-19 vs. Spanish Flu, who would win?

Spanish flu had far more fatalities, but that has to be at least in part because treatment possibilities were a lot worse then. There were no ventilators, no antibiotics or antivirals, etc. Like if you compared a mass shooting (50 people struck by bullets, say) in 1918 to one in 2020, the 2020 one would have far higher survival rate because of blood transfusions and antibiotics (making wounded people much less likely to die of infections), even given identical guns for both shootings. You couldn't conclude that the 1918 guns were deadlier.

So is there a reasonable way to compare the virulence of a Covid-19 infection to a Spanish Flu one, given comparable levels of treatment? Similarly, what about the transmissibility? Any idea how the comparison would end up? Thanks. 2601:648:8202:96B0:0:0:0:313A (talk) 00:30, 28 December 2020 (UTC)[reply]

Sociology and epidemiology and psychology and it's just a flu bro people (1918 had them too) are too complex to know for sure without controlled time travel trials of many permutations of years, Covid, Spanish flu (only one per timeline) and patient zero events. Pick lots of different plausible people to be patient zeros and see what happens. To research who are plausible patient zeros start out with using your time machine to find out who was the real patient zero and how did he get it? Did he eat a bat or got bit by one or bit the head off or raped it or what? Find out how easy it is to become patient zero from each method (i.e. what kind of bat eating mishap, can you get it from kissing, how often do humans kiss bats vs drink bat blood vs touch it with an open wound vs breathe bat germs vs..), find out how much viral load you get by the different methods and where the precursor virus lived and things like that and develop a non-distorting unbiased distribution of patient zero events. Like an electron cloud of patient zeros, an electron cloud for each year and germ combination. Account for bat phenotypes too and so on to make sure you replicate the butterfly effect just right instead of favoring one result or the other by choosing to make the bat sneeze at millisecond 3 instead of 10 too often or making the average human a bat zoosadist too rarely or too often or whatever without knowing the real odds. That would be playing God instead of just finding out which virus is worse in an apples-to-apples comparison. Also this trial's unethical.^{[citation needed]} Sagittarian Milky Way (talk) 00:47, 28 December 2020 (UTC)[reply]

On second thought maybe it is simpler to just make the random mutation dice non-deterministic in the progenitor virus species or strain instead of "it's deterministic cause it already happened" and let the patient zero chips do whatever happens. Repeat till you get many epidemics of each type and make a graph of ppm of Earth killed by badness percentile and see which looks worse. Sagittarian Milky Way (talk) 01:38, 28 December 2020 (UTC)[reply]

Hard to give a reference for this one, but it may be possible to say something useful.

First, Spanish flu hit at the worst time imaginable, which must be part of the reason why it's so infamous: right at the end of World War 1. Millions of soldiers were travelling around the world, spreading the virus, millions had been breathing diluted poison gas for a few years and even in European countries that stayed neutral, trade disruptions led to food and fuel shortages, so people were in a pretty bad condition.

I've read in newspapers and seen on tv news that about 10% of covid patients who end up in hospital in my small western European country die within a few weeks. At the same time, only about 0.2% of all people who get infected die, which means that about 98% recovers without significant treatment (although note that some patients die without ever getting to hospital, but those are the people who were expected to die anyway, even if they hadn't had covid). Those number seem to match with numbers reported for excess deaths and some signs of saturation, indicating that in some areas everybody has already been infected. If covid had struck in 1923, those 98% would have recovered too. It appears that Spanish flu mortality was higher than 2%. In the early 20th century, the population was younger, suffered less from welfare diseases (like obesity) and was more used to infections (which keep your immune system in shape), so was less sensitive to covid (but also to some extend to flu). And back then, it was considered normal that elderly people would die of pneumonia.

All combined, I guess that if covid had struck in 1923 (when the effects of WW1 were waning off), hardly anyone would have noticed. And maybe it did, as there are several coronaviruses that now only cause a common cold, but when first appearing would have been as unknown to our immune system as the current virus is now. But if Spanish flu hadn't struck in the aftermath of WW1, it wouldn't have been as bad as it came to be.

Note that I'm not a virologist or epidemiologist, although my understanding of history and statistics isn't worse than theirs. PiusImpavidus (talk) 10:54, 28 December 2020 (UTC)[reply]

The Spanish flu killed the strong immune systems, usually the young not the old. Sagittarian Milky Way (talk) 15:18, 28 December 2020 (UTC)[reply]

If the Spanish flu had struck in 1923 instead of 1918, it might have been a mere blip on the radar (but note that the similar 2009 swine flu pandemic was recognized as an outbreak in Mexico well before it became a pandemic). I am not convinced that this would also have been so for COVID-19, if only because of the suddenness of the transition from mild symptoms to a life-threatening situation as well as the long-lasting effects experienced by some recovered patients. I think there are too many unknowns to compare the respective virulences in a 1918 what if scenario. --Lambiam 12:48, 28 December 2020 (UTC)[reply]

Perhaps worth reminding everyone that although it's commonly referred to as "Spanish flu," epidemiologists are fairly sure that it didn't originate in Spain, nor was it particularly prevalent there. Because many of the countries in which it first spread were in the the throes of WW1, their newspapers were censored to avoid damaging morale: Spain was neutral in the war, so Spanish newspapers freely reported the disease's progress in Spain, leading to a false impression that it had appeared there first. {The poster formerly known as 87.81.230.195} 2.122.56.237 (talk) 14:39, 28 December 2020 (UTC)[reply]

Kansas flu or Chinese flu? Sagittarian Milky Way (talk) 15:18, 28 December 2020 (UTC)[reply]

How does Gravitational waves discovery useful in daily life?

How does Gravitational waves discovery useful in daily life? This discovery made three people won nobel prize in 2017. Rizosome (talk) 15:47, 28 December 2020 (UTC)[reply]

To make sure there aren't hostile aliens communicating to each other with gravitational waves, at least waves above our detection limit. Maybe they'd use gravitational waves or neutrinos cause they're hard to detect. If many more gravitational waves than is plausibly a natural frequency occur with no natural explanation that may be bad, especially if they appear to coding for something. Like evenly distributed small gaps of no gravitational waves when graphed by some aspects which would be ambiguous bits or trits or tetracontaits or whatever. So ruling that out is comforting in addition to the astrophysical knowledge gained. Sagittarian Milky Way (talk) 16:23, 28 December 2020 (UTC)[reply]

There is no need for it to be useful, see basic research. Fgf10 (talk) 16:45, 28 December 2020 (UTC)[reply]
The winners of the Nobel Prize must have conferred a great "benefit to humankind". It is not further defined how to make that determination. --Lambiam 00:35, 29 December 2020 (UTC)[reply]

Knowledge itself is a great benefit. Fgf10 (talk) 09:20, 29 December 2020 (UTC)[reply]

So the title of the novel The Faculty of Useless Knowledge contains an oxymoron. --Lambiam 12:56, 29 December 2020 (UTC)[reply]

Also learning this science required pushing the envelope of laser length accuracy and orthogonality and interferometry and the technology invented to find the waves may have practical benefits in other applications that will be invented in the 21st century and might not even be thought of yet. If you already know how to do it when the applications are invented in the future you won't have to waste time learning how to do it cause the envelope has already been pushed. Sagittarian Milky Way (talk) 00:59, 29 December 2020 (UTC)[reply]

It is useful to our modern lives by not having any use at all, thereby diverting resources that we would otherwise use in a destructive way. Count Iblis (talk) 07:47, 29 December 2020 (UTC)[reply]

And it keeps people at work and off the streets who otherwise might become hooligans or street robbers. --Lambiam 14:10, 29 December 2020 (UTC)[reply]

That's it. As I always said to my kids during their formative years, "You've got two choices, boys. Either become hooligans or street robbers, or go and discover gravitational waves. There's not much in the middle, frankly." -- Jack of Oz ^{[pleasantries]} 21:52, 29 December 2020 (UTC)[reply]

When did GPS satellites launched in space?

When did GPS satellites launched in space? I didn't find any information about in this article. Rizosome (talk) 16:03, 28 December 2020 (UTC)[reply]

Actually, the article says "with the first prototype spacecraft launched in 1978 and the full constellation of 24 satellites operational in 1993." Mike Turnbull (talk) 16:25, 28 December 2020 (UTC)[reply]

That's the first generation, there have been replacement launches of new generation satellites pretty much continuously ever since. The last one was last month, see List of GPS satellites.Fgf10 (talk) 16:44, 28 December 2020 (UTC)[reply]

It was definitely usable at some level in 1982, as I did a project with Ferranti on it then. That implies there must have been 4 satellites at least. Greglocock (talk) 20:53, 28 December 2020 (UTC)[reply]

What's the difference between photovoltaic and photoelectric effect?

What's the difference between photovoltaic and photoelectric effect? Wiki says they are closely related. Rizosome (talk) 16:58, 28 December 2020 (UTC)[reply]

From the lead of the Photovoltaic effect article:

The main distinction is that the term photoelectric effect is now usually used when the electron is ejected out of the material (usually into a vacuum) and photovoltaic effect used when the excited charge carrier is still contained within the material. In either case, an electric potential (or voltage) is produced by the separation of charges, and the light has to have a sufficient energy to overcome the potential barrier for excitation. The physical essence of the difference is usually that photoelectric emission separates the charges by ballistic conduction and photovoltaic emission separates them by diffusion, but some "hot carrier" photovoltaic device concepts blur this distinction.

-- ToE 19:09, 28 December 2020 (UTC)[reply]

December 29

UV-C sanitizing machine that works against the covid?

I've been considering getting one of these, so I can disinfect things like my keys, mobile phone, cards, money, masks (if I only wore them briefly), cigarettes, stuff that came in the mail, documents related to my work, etc.

Unfortunately I've heard that there are a lot of scams and products that are just crappy on places like eBay and Amazon.

What do I need to be looking for, to find one that actually kills the covid/China virus/corona/whatever? I know it needs to be a purpose-made UV-C emitter, not just a general ultraviolet tube/blacklight - apparently scammers are selling these at inflated prices and advertising them as working against the virus.

Are there any specific products/manufacturers that are recommended? --Iloveparrots (talk) 10:30, 29 December 2020 (UTC)[reply]

Don't buy the LED models, as they are probably just pale blue lights. UVC LEDs are a very special product, not likely to be sold cheaply. I bought a UVC fluoro tube. It is a clear tube with no fluorescent coating. It produces ozone, which you can smell, when it operates. I got it before the outbreak, so there was no shortage. Graeme Bartlett (talk) 12:20, 29 December 2020 (UTC)[reply]

Is it true that most of those handheld UV wands are useless blue lamps - and if they're not useless, they're actively dangerous, as the intensity of UV-C required to kill the covid would also hurt your eyes and blister your skin? Not something you should be waving around. Saw that claimed. --Iloveparrots (talk) 12:59, 29 December 2020 (UTC)[reply]

Let me quote from ultraviolet germicidal irradiation: "For human beings, skin exposure to germicidal wavelengths of UV light can produce rapid sunburn and skin cancer. Exposure of the eyes to this UV radiation can produce extremely painful inflammation of the cornea and temporary or permanent vision impairment, up to and including blindness in some cases." Draw your own conclusions. Fgf10 (talk) 15:01, 29 December 2020 (UTC)[reply]

As this is the reference desk, let's try a reference: UV Lights and Lamps: Ultraviolet-C Radiation, Disinfection, and Coronavirus. Quick summary: mostly does not work, easily causes more harm than good, but the definitive science is not in yet. Unproven medical interventions are usually not a great idea. 85.76.64.226 (talk) 17:09, 29 December 2020 (UTC)[reply]

Does Rabies virus harmful to dog also?

I know Rabies virus harmful to humans, what about dogs health? Rizosome (talk) 18:07, 29 December 2020 (UTC)[reply]

I googled "does rabies kill dogs" and the answer is definitely YES. Before they die, they can become aggressive (hence the term "mad dog") and bite, which is one way humans can get it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:18, 29 December 2020 (UTC)[reply]

Untreated rabies is almost always fatal in humans, dogs or any other mammal. Cullen³²⁸ Let's discuss it 18:20, 29 December 2020 (UTC)[reply]

See Rabies in animals. Deor (talk) 18:48, 29 December 2020 (UTC)[reply]

vaccination after COVID 19 infection

If somebody is unknowingly infected w/ Covid 19, and then the next day, while stil presymptomatic and still in the incubation period, they receive the first dose of vaccine, would their recite of the vaccine be expected to have any effect on their subsequent course of illness with COVID 19? Please note, I am not seeking medical advice for myself as I am months away from vaccination. I am merely curious because I have heard that for some other viral diseases, ( measles , Hepatitis A) vaccination within a certain amount of time after exposure can sometimes prevent or at least reduce severity of illness. — Preceding unsigned comment added by 63.247.53.11 (talk) 20:55, 29 December 2020 (UTC)[reply]

December 30

Cryogenic freezer at Monterey aquarium

[4] The Aquarium has kindly lent one of its two cryogenic freezers to a nearby hospital for storage of Covid vaccine, and it made a nice news story. Not answered is: why does an aquarium have something like that around anyway? The vaccine apparently must be stored at -94 degrees F, so the freezer has to be even colder than that, and in the photo it looks pretty big (it has to hold 1000s of vaccine vials). I'm sure the aquarium has a perfectly good use for the freezers but I can't help puzzling over what it might be.

Also, are there any serious technical challenges to building lots of such freezers out of parts on hand, as part of Operation Warp Speed? It seems strange that there should be a big shortage. It's just ordinary pumps and compressors at that temperature, right? No special magnetic whatevers like liquid helium temperatures would require. Thanks. 2601:648:8202:96B0:0:0:0:313A (talk) 04:50, 30 December 2020 (UTC)[reply]

As to the second question, see ULT freezer and Refrigerator#Ultra-low temperature refrigerators for the requirements. It does seem like something that could be built largely "out of parts on hand", but if course you'd have to make sure that those parts were usable at the applicable temperatures, and you'd need a suitable low-temperature refrigerant.

The articles also indicate that such freezers are used to preserve biological samples, so if the aquarium is doing zoological research, that'd probably be why they had them. --174.95.161.129 (talk) 05:33, 30 December 2020 (UTC)[reply]

@@ Line 200: / Line 200: @@
 Also, are there any serious technical challenges to building lots of such freezers out of parts on hand, as part of Operation Warp Speed?  It seems strange that there should be a big shortage.  It's just ordinary pumps and compressors at that temperature, right?  No special magnetic whatevers like liquid helium temperatures would require.  Thanks. [[Special:Contributions/2601:648:8202:96B0:0:0:0:313A|2601:648:8202:96B0:0:0:0:313A]] ([[User talk:2601:648:8202:96B0:0:0:0:313A|talk]]) 04:50, 30 December 2020 (UTC)
-:As to the second question, see [[ULT freezer]] and [[Refrigerator#Ultra-low temperature refrigerators]] for the requirements.  It does seem like something that could be built largely "out of parts on hand", but if course you'd have to make sure that those parts were usable at the applicable temperatures.
+:As to the second question, see [[ULT freezer]] and [[Refrigerator#Ultra-low temperature refrigerators]] for the requirements.  It does seem like something that could be built largely "out of parts on hand", but if course you'd have to make sure that those parts were usable at the applicable temperatures, and you'd need a suitable low-temperature refrigerant.
 :The articles also indicate that such freezers are used to preserve biological samples, so if the aquarium is doing zoological research, that'd probably be why they had them. --[[Special:Contributions/174.95.161.129|174.95.161.129]] ([[User talk:174.95.161.129|talk]]) 05:33, 30 December 2020 (UTC)