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August 23

Overview of true flies mimicking wasps and bees

Would you call me a "hoverfly"?

Hoverflies are known for mimicking powerful hymenoptera like wasps and bees. But they are not the only true flies doing so. Other examples include several soldier fly species. Two questions:

1. Can an overview be given which fly families include hymenoptera-mimicking species?
2. Would a layman, not familiar with the specific species, call such a mimicking fly probably a "hoverfly", even if it does not belong to this family?

Beetles, butterflies etc. using this mimicry are not included the question. --KnightMove (talk) 15:29, 23 August 2016 (UTC)

The Bombyliidae fit the bill. Mikenorton (talk) 15:45, 23 August 2016 (UTC)

In my experience, laymen don't often know the word or concept "hoverfly". If they do, then sure, they may well apply it to bee-looking flies outside the Syrphidae. But some people use the common name drone fly, some may use the term bee fly to pseudo-incorrectly refer to a Syrphid, etc.

Acroceridae is another Dipteran family with some bee mimics, as is Asilidae. Together with they Bombyliidae Mike mentions and the Syrphidae you mention, I think that covers all the mimics that I already knew about. Here is an interesting article on behavioral mimicry of honey bees in some Syrphidae spp. [1]. Here [2] is an article that discusses a few different bee mimics, and looks at their relative similarity, frequency, and potential benefits. This paper [3] discusses some of the interplay between bees, their mimics, phenology, and birds. I am unable to find a list of Dipteran families in which presumed hypmenopteran mimics occur. SemanticMantis (talk) 21:36, 23 August 2016 (UTC)

Well, I thought that picture was a hoverfly, until I looked it up, so I suppose that's one instance of someone calling such a mimicking fly probably a "hoverfly". I suppose it would depend on how similar the non-hoverfly mimics were to hoverflies (unlike the one here, the pictures on the soldier fly page don't look much like hoverflies to me). Then there's behaviour - hover flies hover, hence the name. Do soldier files and other mimics also hover? If so, I expect a lot of people would mistake them for hoverflies. If not, well, maybe fewer would. Iapetus (talk) 11:39, 24 August 2016 (UTC)

By now I should clarify the motivation for my question. In my native language German, pretty much all such flies are called hoverflies ("Schwebfliegen" in German, which is both the factual and literal translation), unless there is an established term for a single species (Drone flies are usually called Mistbiene, "dung bee"). Somewhat prematurely, I've assumed this will be the same in English.

I do not know whether all hoverflies always "hover" when flying, and whether this can always be recognized clearly. Once I've seen a bumblebee-mimicking fly in the forests, humming loudly in flight. I do not know for sure whether it was a hoverfly (but quite sure it was, very possibly a Volucella bombylans). However, I would not have regarded its flight as "hovering". Anyway, you might catch a wasp-mimicking fly sitting on a flower or somewhere else; and even in flight, you hardly would regard a non-hovering-but-wasp-mimicking fly as non-hoverfly.

This image of a wasp-mimicking-non-hoverfly was my very motivation for asking, as I had not been aware of the existence of such flies. --KnightMove (talk) 10:51, 25 August 2016 (UTC)

Just to say that the term "hoverfly" is quite well known in the UK as far as I know (our fauna is pretty similar to that found in Germany), and would generally be used for any "mimicking fly" of this sort. I would have called the insect in the photograph "a hoverfly" and am a bit surprised that it isn't. Alansplodge (talk) 09:55, 26 August 2016 (UTC)

Dark clouds

How thick must a rain cloud or thunderhead be in order to completely block sunlight and reduce the ambient illumination from normal daytime levels to nautical twilight levels? (Assume that the sun is 45 degrees above the horizon.) 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 23:21, 23 August 2016 (UTC)

Define "thick"? Do you mean the droplet density inside the cloud, or the vertical dimensions of it? They both would be factors in the ability to block sunlight, and they both could be defined as "thickness". Indeed, the sunlight blocking ability of clouds is likely due to a number of factors, and isolating any one is likely difficult. --Jayron32 01:30, 24 August 2016 (UTC)

The vertical dimensions, given a typical droplet density for these two cloud types. 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 03:02, 24 August 2016 (UTC)

This document discusses the concept in general terms (search for the word "clouds") and references another NASA document called a "Clouds Fact Sheet" that may be promising. --Jayron32 10:40, 24 August 2016 (UTC)

August 24

Does the International Space Station have enough radiation hardening to survive outside LEO?

Does the International Space Station have enough radiation hardening to survive outside LEO?

According to International_Space_Station#Communications_and_computers, there are ~100 regular Thinkpads on board, so those won't survive outside LEO for sure. But I'm unable to find out:

1. Whether those ~100 Thinkpad on the ISS are mission critical or not. Maybe they're just there for the various scientific missions and are not critical to the functioning of the space station.

2. Whether the mission critical computers on the ISS have enough radiation hardening to survive outside LEO. Pizza Margherita (talk) 00:29, 24 August 2016 (UTC)

ISS only orbits at an altitude of ~400km which is within even the ionosphere. Low earth orbit extends out to about 2000km, so I doubt ISS is intentionally "hardened" to survive outside of LEO. It's intentionally hardened to survive precisely where it is. Whether it actually "would" survive outside LEO or not is a different question. Earth's_magnetic_field#Magnetosphere extends out at the "short end" to 65,000km, so even well above LEO I don't think the "radiation" is much worse, AFAIK it only gets really bad once you get outside of the magnetosphere. Discounting CMEs. Vespine (talk) 02:45, 24 August 2016 (UTC)

"Whether it actually 'would' survive outside LEO or not is a different question." Yes, that's the question I'm asking. Pizza Margherita (talk) 03:05, 24 August 2016 (UTC)

Well that's a question of "probabilities". Like I said, I don't think the radiation outside of LEO is dramatically different to the radiation at the normal orbit of the ISS, at least until you start reaching the upper levels of the magnetosphere. So undoubtedly everything would survive for some time, including normal laptops. I'm not sure why you say "those won't survive for sure"? What's your reasoning for that? I don't think anything would necessarily "fry" immediately even if you took it out of the magnetosphere. How long on average would a regular laptop survive in space? Well we didn't take any laptops to the moon so I don't think anyone has done the experiment. Vespine (talk) 04:17, 24 August 2016 (UTC)

This is a bit outside my wheelhouse (and more importantly, not referenced) but my understanding is that ambient solar radiation in the space that Earth's orbit occupies is more than substantial enough to fairly well guarantee that a non-shielded device like a laptop would be rendered non-operational instantly, if moved outside the magnetosphere (indeed, probably well before you cleared what is considered the outermost edge of the magnetosphere). As you say though, LEO is a more nuanced, probabilistic question with quite varied answers depending on the specific circumstances. It's also worth mentioning, in looking at the scenario the OP proposes, that the station itself is shielded, as an essential safeguard of the health of the crew and redundancy on protection of critical hardware--although this protection is variable by module and even at its best allows for significantly higher levels of radiation exposure compared to a typical terrestrial context. Snow ^{let's rap} 08:10, 24 August 2016 (UTC)

You are wrong here. The dangerous ionizing radiation from calm Sun is nil or near so. The really dangerous thing is galactic cosmic rays, which are constantly present and partially deflected by the magnetosphere. There are also solar flares, which can generate beams of accelerated protons and electrons, but they relatively rare and partially predictable. Ruslik_Zero 19:32, 24 August 2016 (UTC)

Yes, I actually do appreciate the prevalence of cosmic rays; I'm not sure why my mind went to focus on stellar emissions so strongly; that said, the sun is a non-trivial source of high-intensity radiation, and not just when there is enough activity to register a geomagnetic storm. Snow ^{let's rap} 07:40, 25 August 2016 (UTC)

Whether the station will survive is a different question from whether the inhabitants of said station will survive. What is your definition of LEO? If you shift up to >1000 km, you're in the inner van Allen belt. Both electronics and inhabitants would be fairly swiftly fried in there (yes radiation is dramatically different there than in LEO). If you leave the Earth's magnetosphere altogether, you'd have both increased background radiation from cosmic rays, and be very much at increased risk from solar events, such as CMEs. The ISS is not designed for these. Have a look at the specialised computer required for BEO work, see Mongoose-V for one. There are significant other issues as well. For instance, the thermal management of the station is designed for LEO, that is regular alternation between orbital day and night. The (near-)constant sunshine in higher orbits would most likely overwhelm the thermal control system. Lastly, it would be a short trip for anyone in the Station, even if all the above wasn't a problem, as no resupply is possible with current craft at above LEO. Fgf10 (talk) 07:15, 24 August 2016 (UTC)

Metabolism

What is the average age that metabolism starts to slow down, ignoring lifestyle etc and only considering the physiological aspects of the human body? 82.132.220.29 (talk) 19:09, 24 August 2016 (UTC)

Here are the google results for "age of peak metabolism". μηδείς (talk) 19:44, 24 August 2016 (UTC)

...These are mostly magazine blurbs, and not very good references. Generally, googling simple phrases is not a good way to get good references. Generally, people who can find our desks are aware that google exists. This is a reference desk, and our goal is to help people find good references. SemanticMantis (talk) 20:12, 24 August 2016 (UTC)

Here [4] is a research article titled Influence of Aerobic Capacity, Body Composition, and Thyroid Hormones on the Age-Related Decline in Resting Metabolic Rate - it discusses how other factors affect the decline, and also gives results for the net decline on average. See Fig.1 for details and trend. SemanticMantis (talk) 20:12, 24 August 2016 (UTC)

Visualizing the Earthlike planet around Proxima

I just asked something similar, but I plead special circumstances: an Earthlike planet found just four light years away, around Proxima Centauri. Now I assume IRL people will keep blundering on like nothing happened, but if any decent author were writing sci-fi, this would be the precise moment when astronomers all over the world *DROP EVERYTHING* and point their telescopes at the planet, time and cost be damned, get the ALMA array pointed at it, improvise whatever kind of VLBI in visible light to analyze the signal is possible, invent anything they can with a few tens of billions of dollars, and come up with an image of what this providential and perilous world might hold for us.

If they do, how much can they see? What kind of data can they get? Proxima is something like 60,000 271,000^[5] [d'oh, forgot to multiply by 4!] AU away, I think, or 12000 50,000 times the distance of Jupiter; in the previous thread we had somebody speculating we could "read a license plate" on Jupiter's moons with the right VLBI around the Earth, so that implies seeing details less than a four thousand feet across, and presumably taking detailed spectra to see which kind of chlorophyll they use. But what can we really do? How far can we go that direction? (Heck, I'd be happy just to see the moon that keeps it from being tidally locked to its star...)

Stoking my interest is that I'm imagining that the polite method of first contact is that you visualize the other planet, you visualize its people, you visualize their telescopes, you see them looking at you, you put out a decoration to show them you see they're looking at you, and they reciprocate... Wnt (talk) 20:03, 24 August 2016 (UTC)

By "ALMA array" I guess you mean the Atacama Large Millimeter Array array. —Tamfang (talk) 02:41, 25 August 2016 (UTC)

• Read Mary Doria Russell's The Sparrow and sequel about intelligent life in Alpha Centauri. It's in my top ten of novel or novel series. Deals with the same star system, and a signal of alien life, although an accidental one. Quite a deep, engaging, and literary read, along the lines of Dune, or Lord of the Rings. μηδείς (talk) 20:42, 24 August 2016 (UTC)
• According to the report in Nature, the next step is to find a transit of the planet across the sun, which might reveal whether it has an atmosphere.[6] Our article on the planet is Proxima Centauri b.-gadfium 23:00, 24 August 2016 (UTC)

One priority for the future will be to get a direct image of the planet.This should be possible with the European Extremely Large Telescope now under construction in Chile. "It is being given a 39m-wide primary mirror and state-of-the-art instrumentation precisely to do this kind of observation.

"A planet around even a wimpy star like Proxima Centauri is going to be more than a billion times fainter than the star itself. So, what you do is block out the light from the star using a special device and that allows you then to go deeper into the star's surroundings," explained Cambridge University's Prof Gerry Gilmore. "This is one of the E-ELT's design goals. There's also a Nasa mission under development called W-First. It will have a high-resolution coronagraphic mode which again is designed for the same purpose."" Count Iblis (talk) 23:25, 24 August 2016 (UTC)

A 100 meter radius screen about 1.4 million km from Earth blocking the starlight would probably do. It would be large enough for diffraction effects to be small enough. The diffracted starlight would still overwhelm the light from the planet in an unprocessed image, but one can subtract the diffracted starlight from the image using the observations of the star and the known shape of the blocking screen. Count Iblis (talk) 23:57, 24 August 2016 (UTC)

See coronagraph for how it's really done. --Wrongfilter (talk) 10:49, 25 August 2016 (UTC)

To clarify, a very large telescope like E-ELT should be able to visually distinguish the planet from its star (E-ELT resolution at that distance ~0.004 AU). This would allow spectroscopic studies of the planet, which could provide us with some interesting observations. Such telescopes would still not be able to resolve any spatial details on the planet itself though, which would still appear as point-like. To resolve spatial details on the planet itself, you'd really need some sort of telescope array whose baseline is comparable to the size of the Earth itself. Maybe some day, some how, but we are very far from being able to do things like that with visible light right now. Also, Proxima Centauri is 260,000 AU away and not 60,000 AU as suggested above. Dragons flight (talk) 07:24, 25 August 2016 (UTC)

Exploding batteries

I have an electric pencil sharpener which can run with either 4 AA batteries or using a 6V AC adapter. The manual is warning me that I should not use the batteries and AC adapter at the same time, because the batteries might explode. Why is that? What would cause the batteries to explode and how likely is it? bamse (talk) 20:51, 24 August 2016 (UTC)

The AC adapter will charge the batteries in some circumstances, and it can be dangerous to charge batteries if they are not designed to be charged. Even rechargeable batteries can explode if incorrectly charged. Dbfirs 21:12, 24 August 2016 (UTC)

Yes, but I am interested in the details (physics) of it. bamse (talk) 21:50, 24 August 2016 (UTC)

• "Explode" is a bit much (for AA at least). It is quite likely that they will be over-pressured and will burst, or at least vent. This dumps corrosive battery contents into your pencil sharpener and so is not a good idea. It's unlikely to be a personal hazard though.

AA batteries will probably be alkaline, could be the older zinc chloride and might well be the rechargeable NiMH. Any of these will "burst" in an operator-safe manner. If it was using Li-ion though (which won't be in AA format, but are becoming much more popular for the next few years - look out for '18650' cells) then mis-charging can and does cause battery explosions sufficient to damage furniture or carpet and sometimes to burn a house down. Those are normally protected by the circuit surrounding them, but still it has (and will) happen. Andy Dingley (talk) 21:58, 24 August 2016 (UTC)

Sorry for being persistent, but I'd really like to know more about the reason for the "explosion". Do they just heat up due to the current running through them? Is some gas produced which causes them to explode? Does the polarity (which way I put the batteries) matter for this? bamse (talk) 22:20, 24 August 2016 (UTC)

Just google "What can happen if Non Rechargeable Batteries are Recharged". There's plenty of articles. Vespine (talk) 22:43, 24 August 2016 (UTC)

This Nature paper, ...materials for safer batteries (January 2016) was described in the Stanford news service a little while ago. That article has a lot of technical information and extensive citations for the electromechanics of the battery overcharge and overheat failure modes.

Nimur (talk) 22:57, 24 August 2016 (UTC)

• Persistence is good - you're going to need it to understand batteries. There are so many different types that you'll not get a single simple answer to this.

Since alkalines replaced zinc-carbon as the general household "torch battery", batteries have been made with steel cases. Before this they leaked because the corrosive contents had etched through the zinc case and the paper wrapper. Now it's usually because internal pressure has caused the end seal (at the negative end for alkaline) to fail. Corrosion as primary cause is now less common, but we've all seen the mess they can make of contacts or a circuit board. An AA is a small battery - small enough that a pressure failure won't make the case fall apart, but larger than a coin cell which can bulge a little and yet still contain the excess.

The mechanism of pressure buildup is complex and depends on the battery technology. It could be simple heating, and thus expansion. This is why fast charging batteries is a problem and why good fast chargers either cool the battery under charge or measure its temperature and limit the current accordingly.

Mis-charging is likely to cause the wrong sort of chemistry to happen. If a battery is charged (when not rechargeable), charged in reverse, for too long or at too high a current, then not only the useful chemical process (which stores energy for recovery later) can happen, but also some other ones. Simple electrolysis is one, especially for excess current - an aqueous electrolyte can be split into hydrogen and oxygen. Gases occupy far more space than liquids, so up the pressure goes...

The classic zinc–carbon cell uses a reaction between zinc and manganese, with an electrolyte of white zinc chloride paste and another black paste of manganese dioxide. The carbon rod is just there as a non-corrodible electrode to give a connection to the manganese paste. As well as being a reactant in the main reaction, the manganese dioxide has a second function to mop up any loose hydrogen produced. It can only do this slowly, so excess current (charge or discharge) can overwhelm it and free gas is released.

Most battery cells are sealed, but with the expectation that they will vent in a controlled manner. A few types have a resealable vent, many stay open once ruptured. Some battery chemistry then goes awry because the contents are exposed to the air. Alkaline batteries are noted for this - they may first vent only a small quantity of potassium hydroxide, which then produces a large mass of soft, spongy white potassium carbonate as it reacts with CO₂ from the air. If this starts to happen inside the battery, it may split right in half.

Li-ion and Li-polymer bring in a further range of issues. See Lithium-ion battery#Safety. They're sensitive to almost every form of abuse, are more sensitive to it, react more violently than other domestic types. Oh, and the components are flammable too, if exposed. A fire in stored batteries awaiting disposal led to the closure of the M6 motorway in England [7]. Modern versions are safer, but there are still real hazards from mis-charging with fake chargers [8] or just impact damage [9]. Andy Dingley (talk) 02:39, 25 August 2016 (UTC)

Thanks a lot. That's what I wanted to know. No more questions ;-) bamse (talk) 10:14, 25 August 2016 (UTC)

Just for completeness I'll mention what people are assuming above: as batteries deplete, the voltage they produce drops. Presuming the AC adaptor is not set at a voltage level where the electronics are at the verge of failing, or even at the point where a "low battery" light would flash, a set of batteries wired in parallel with the adaptor would be charged when it is active, at least if they were sufficiently depleted. Of course, some sort of mechanism might be made to interrupt the connection to the batteries when the AC adaptor is in use, but this costs money and volume and if it doesn't work 100.0000% they'll still advise people not to keep batteries in the device when the AC is active, just in case. Wnt (talk) 15:03, 27 August 2016 (UTC)

Titanic

2 questions about the sinking of the Titanic: (1) Had Captain Smith ordered one engine full astern and the other two full ahead (instead of putting them all full astern and trying to steer with the rudder alone, like he did), could he have avoided hitting the iceberg altogether? (2) Once the ship hit the iceberg, it was doomed to sink (that much practically everyone agrees on), but by deliberately flooding one or more of the aft compartments in order to keep the ship's bows up, could they have stayed afloat long enough for help to arrive? 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 23:25, 24 August 2016 (UTC)

It's been said that if he had hit the berg head-on, the ship would have been disabled but would have stayed afloat. For a practical example, look at the ship that hit the SS Andrea Doria straight on, albeit not on purpose. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:56, 25 August 2016 (UTC)

Captain Smith was not on the bridge at the time. Command had passed to First Officer William Murdoch, who was left with very little time to react. Akld guy (talk) 08:05, 25 August 2016 (UTC)

• If he was equipped with that much hindsight, he could just as well avoided the iceberg altogether.

It's an interesting question in naval architecture - the problem of over-topping the watertight bulkheads - if keeping the ship level, albeit lower, would have kept it afloat, or afloat for longer. Certainly Titanic went down because of the bow-down angle. How well would a lowered but level Titanic still float? As that's accurately calculable (but I haven't) I express no opinion here. It's worth remembering that it's a passenger ship though, not a warship. Decks are connected by staircases, not ladders with sealable hatches. A warship has options for sealing itself into compartments which just aren't practical on a liner. HMS Audacious is an interesting comparison, just a couple of years later - much of the questioning around that sinking was about how well hatches had been closed to control the flooding. Andy Dingley (talk) 10:21, 25 August 2016 (UTC)

It was a moonless night, and they didn't see the berg until they were almost on it. By trying to turn away from it, they hit it with the side of the ship, which popped several plates and doomed the ship. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:42, 25 August 2016 (UTC)

Yes, but the question (which has been debated for decades) was whether it would have been better to 'port around' (Murdock's alleged manouevre - a kind of fish tailing) the iceberg without attempting to slow down by throwing the engines into reverse. Reversing the propellers is known to make a rudder's angle less effective than when at speed. My guess is that in the 37 seconds available, the engines were probably only stopped and there was no time to throw them into reverse, consequently the stationary propellers didn't make any difference in the few seconds remaining. Akld guy (talk) 11:42, 25 August 2016 (UTC)

I recall a television documentary in which a model of Titanic was tested in a water tank. Some of the aft compartments were flooded to test the hypothesis that this would have prevented or sufficiently delayed sinking of the ship. The test suggested flooding aft compartments would not have saved Titanic. I regret I have no details of the documentary. Dolphin (t) 11:54, 25 August 2016 (UTC)

See also Russian Engineers: Did Titanic Have a Chance? for some rather implausible suggestions. Hindsight is a wonderful thing. Alansplodge (talk) 21:51, 25 August 2016 (UTC)

A more sensible article is at Saving the Titanic which supports the proposal of ramming the iceberg bows-on and also suggests fothering. Alansplodge (talk) 22:00, 25 August 2016 (UTC)

If you are piloting the Titanic, it would take some extreme confidence to decide that ramming an iceberg head-on was the preferable course of action. Can you imagine trying to defend that action after-the-fact? How many people could you really convince that the "unsinkable" Titanic would be at risk but only if one tried to dodge? After smashing the bow of the boat, the person in charge would probably never work again and have a high risk of going to jail. Dragons flight (talk) 09:54, 26 August 2016 (UTC)

A minor and tangential point, but to correct a common misconception: the "unsinkable" description was used by some newspapers of the time, but Titanic's operators, the White Star Line, never claimed she was unsinkable. [Disclosure: For over 30 years I have lived near and worked in Southampton, Titanic's home port, where the public are still mindful of the disaster and can even be a little touchy about such inaccuracies.] {The poster formerly known as 87.81.230.195} 2.219.83.36 (talk) 15:06, 26 August 2016 (UTC)

They may not have said it, but they "acted like" they had. They were totally unprepared for an emergency. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:44, 26 August 2016 (UTC)

A few note on preparedness:

1) Obviously travelling at high speed through icebergs was a dangerous thing to do, especially without using a speedboat to speed ahead of the ship and communicate icebergs sooner. A searchlight on the bow would have extended visual range further forward, at least in clear weather.

2) The lack of adequate prep to evacuate the ship (like a lack of boats) was also critical.

3) The rivets may also have been more brittle than they should have been, and thus popped more easily (saw this in a documentary).

4) The compartments that didn't seal at the top and the lack of a double hull also sealed Titanic's fate.

5) As for what actions the command staff could have taken, I agree with "all engines in reverse and hit it head on" approach. Of course, there wasn't time to think all this through when the berg was spotted, so they would have needed to think all this through in drills ahead of time. There also wouldn't be time to look it all up in the manual, so the proper response needed to be committed to memory on anyone who pilots the ship. StuRat (talk) 16:26, 26 August 2016 (UTC)

I'm not sure if reduced dark adaption would've hurt less than increased forward visibility would've helped (statistically, obviously it would be better in this specific case). They accidentally left the binoculars in Southampton, 1,500 people died because some dude forget binoculars.

August 25

Proxima Centauri b

How come that we have discovered thousands of exoplanets located very far away -- and even know some amazing details about them -- and yet had not discovered a planet orbiting the CLOSEST star to the Sun until yesterday (Aug 24, 2016)? --Qnowledge (talk) 12:18, 25 August 2016 (UTC)

Firstly, it wasn't discovered yesterday, our article states first hints were seen in 2013, and targeted observations started in January this year. Exoplanets get discovered though a number of different techniques. The 'simplest' is if a planets orbit puts it between its star and us, periodically dimming the host star (transit method). This is likely not the case of Prox B, and is indeed not the case of most exoplanets. It's only because of the transit finding Keppler mission that we have this larger number of new exoplanets, until that the number was a lot lower (see timeline in Methods of detecting exoplanets, only a 100 or so in 2013).

The way to find an exoplanet regardless of orbital plane is through the radial velocity method, or observing the movement of the star and seeing how the gravity of the planet affects it. This movement is proportional to the relative size of the planet and its distance. This is why a lot of the initial exoplanet findings were massive planets, orbiting very close to their star. Detection of roughly Earth sized worlds is still a fairly new thing. In the case of Proxima Centauri, this is a very dim star (0.1% of Solar luminosity). So although it's nearby, the amount of light we can observe will be lower than a bigger star that is considerably further away. I would imagine this hindered the detection, which as it is took I believe almost two months of near-continuous nightly observation by two massive telescopes. Fgf10 (talk) 12:47, 25 August 2016 (UTC)

How do we place a "date" on the discovery, anyway?

I used to hang out with some of the folks who made their professional careers out of studying Kepler scientific data. They mentioned observations, and surveys, and research. Among our many conversations, we talked about Proxima Centauri, because it's a very interesting target for observation and analysis. Surely they were thinking and hoping to find something noteworthy in our neighboring system.

Maybe the data that has now been published came up in casual conversation - who can remember?

But casual conversation about a few bits of tantalizing data do not meet the bar for good science.

It takes years of controlled, repeated observation before a professional scientist will publish a finding. For people whose professional reputation depends on being reliable and correct, they like to be very very certain before formally announcing a finding to the outside world. This is a different culture than we have here on Wikipedia: scientists do not "boldly publish" in primary-source peer-reviewed journals and hope that someone fixes up any errors later.

This makes it difficult to ascertain "discovery date." Astronomers have studied Proxima Centauri for a very long time. They have collected optical images and other data for years. Legions of researchers have pored over the results. If a planet was present, we've been "seeing" it for a really long time - but the picture, metaphorically, was always too "blurry" to say very much about it with strong certainty.

Finally, we have some certainty. That is why the research was announced now.

As exciting as this kind of discovery is, we have to be responsible scientists: we need to track down the official press release, the (main) peer-reviewed paper published in the journal Nature, read the findings, scour the data, read lots of good books and research on the topic, and maintain healthy skepticism, and let the entire community of expert astronomers and scientists weigh in. Here at the Wikipedia Science Reference Desk, we have lots of friendly people who can help you find excellent reading material to provide context at whatever technical depth you are interested in.

This is big news - and in context, it's a pretty important finding. It will hopefully motivate policy-makers in the United States and elsewhere to continue supporting (with money) the scientists and the equipment that enable these discoveries. It will hopefully inspire a large segment of the population, who are not professionally involved, to keep looking up. But let's not get ahead of ourselves: science moves slow. If you formally study astronomy, a big part of your education will be grokking and re-grokking that in space, things are big. Really big, just immensely vast. When we concern ourselves with cosmic length and time scales, which are inherent to the search for extrasolar planets, everything happens very slowly.

Nimur (talk) 15:51, 25 August 2016 (UTC)

Basically it comes down to the High Accuracy Radial Velocity Planet Searcher. The way this planet was found was by slight changes in the frequency of the light from the star (Doppler effect). This ever so slightly changes what angle the light passes through a prism or bounces off a diffraction grating, such as the HARPS echelle grating. The HARPS instrument is extraordinarily sensitive, kept mechanically isolated, incidentally developed the most accurate spectrum of thorium emission known etc. All this sensitivity, which was improved only recently, gave it the power to find Earth-sized planets around small stars (still not big ones).

So this is a procedure where the color of the light is absolutely critical, yet its intensity (and the distance of the star) is not so much so. Wnt (talk) 18:34, 25 August 2016 (UTC)

You're still going to have to get photons through your grating to measure them. Luminosity and collecting area are still important parameters. One photon isn't going to be enough. Fgf10 (talk) 18:48, 25 August 2016 (UTC)

Of course. But the point is, given existing telescopes, the image can be made bright enough to get that data for stars much further away nearly as easily as for Proxima Centauri. The improvement in this search instrument was the rate limiting factor for getting this result. Wnt (talk) 19:18, 25 August 2016 (UTC)

The Nature paper actually addresses the question: "The Doppler semi-amplitude of Proxima b (approximately 1.4 m/s) is not particularly small compared with other reported planet candidates. The uneven and sparse sampling combined with the longer-term variability of the star seem to be the reasons why the signal could not be unambiguously confirmed with pre-2016 data rather than the total amount of data accumulated." --Wrongfilter (talk) 19:43, 25 August 2016 (UTC)

"Space is big. Really big. You just won't believe how vastly, hugely, mind-bogglingly big it is. I mean, you may think it's a long way down the road to the chemist, but that's just peanuts to space." —The Hitchhiker's Guide to the Galaxy --71.110.8.165 (talk) 03:58, 26 August 2016 (UTC)

Thanks for the answers, really helpful! --Qnowledge (talk) 11:23, 26 August 2016 (UTC)

Why soap foam is white irrespective of the color of the soap?

Sandeep Bhadkamkar (talk) 16:35, 25 August 2016 (UTC)

Your assumption is not entirely true. Soap bubbles can have color. Usually, they don't - if you look down at them. Adding color to bubbles turns out to be a rather difficult thing to do. Kids like to blow soap bubbles. Imagine a product that blows orange, blue, or purple soap bubbles instead of the normal clear bubbles. They exist - now. They didn't until some people put the hard work into identifying ways to color bubbles. What you normally get are clear bubbles with all the color pushed into a tiny dot on the bottom (due to gravity). If you have a lot of tiny bubbles (foam), they look white. That is just because you are seeing a lot of light reflected off a lot of little bubbles. If you were to look at them from the bottom, you'd see the color. I did this as an example. I put green dye in soap bubble solution and used a bubble machine to blow bubbles all over a glass table. From above, they began to look like a whitish foam on the table. From under the table, you could see a little green dot on the bottom of the bubbles. Where did I get the idea? This is a much better story...

I knew a guy named Tim Kehoe who worked for years on making colored bubbles. He got the soap and dye just right and made red, blue, and green bubbles. He got people to back his product. He took it public at a huge presentation. The crowd was huge. He told the public about it. The kids were excited. The parents were ready to buy all he could produce. He turned on the bubble machines. As the bubbles popped, the crowd noticed the red, blue, and green color splotches on everything. They acted like they were being sprayed with mustard gas. Kids were gathered up and the crowd quickly evacuated. He tried and tried to get the people to hear that all you had to do was rub the dye stain and it would go away. That was the trick. The dye that would remain in the bubble happened to be a dye that broke down in very slightly warm temperatures. So, just rubbing it would create enough heat to break down the dye and the stain would go away. It was a failure. Crayola stepped in and branded the product to turn the failure into a mediocre success. You can now purchase Crayola colored bubbles. Just remember to rub the stains to make them go away. 209.149.113.4 (talk) 17:09, 25 August 2016 (UTC)

Here's an RS for the IP editor's claim. μηδείς (talk) 17:39, 25 August 2016 (UTC)

Some foams (using a detergent base) used in firefighting are orange -- but I can't find a source from a cursory search. 2606:A000:4C0C:E200:1821:CD59:E35A:CB68 (talk) 20:03, 25 August 2016 (UTC)

None of you are anywhere near the answer, you can't see the Forrest for the trees. If you have kids and have ever used food coloring at bath time, you will know that "suds" are still white, no matter the color of the water or the soap. The reason is because a tiny bubble acts more like a mirror than a "droplet" of water. In fact most of what you are actually "seeing" when you look at soap foam is actually internal reflection. Therefore when viewing soap foam under white light, the foam will appear white. If you put them under a red light or a blue light, the bubbles will appear red or blue. Vespine (talk) 23:30, 25 August 2016 (UTC)

Sort of--the situation is a little more nuanced still, and sort of between you perspective and one voiced above, imo. There are substances which can produce bubbles that will selectively reflect different wavelengths of light; even the average bubble formed of a saponified material could have some surface irregularities in this regard. But you're explanation I feel is incomplete. The reason the bubbles appear white, even though in reality they are largely transparent, is because the bubbles are so small and numerous and they are all refracting the ambient light from all sources and directions at a multitude of different angles. Your analogy of a mirror isn't quite apt because most of the light actually passes through the bubble, but it's passage is altered as a result, and only a small part is outright reflected so that it passes not at all through the surface of the bubble. Those different colors blend to a white for us because the density of the photoreceptors on our retina (and our ability to process the stimuli they receive and then relay) are limited by biophysical reality. If we had theoretically "perfect" (but physically impossible) resolution to our eyes and visual cognition centers, such that we perfectly perceived and mapped each and every photon which reflected from those bubbles and struck our retinas, then we would see a beautiful cacophony of color. But the reality is that we receive that stimuli as "white light"; that is, light that is roughly distributed across the visible spectrum, with a little bit of tint from the base color of the soap when it is in it's solid state, since some of the soap "froth" is not composed of bubbles. It's always worth remembering that colour does not exist as a physical force; light traveling at different wavelengths exists, but "colour" is purely a matter of perception and qualia, and therefore there are many cases where what we experience does not map 1-to-1 with physical analogues. Snow ^{let's rap} 05:43, 26 August 2016 (UTC)

Question about wire

How many volts and amps can BT telephone wire take safely when uses as a power supply rather than a telephone wire? I read the article but it doesn't seem to mention it in plain English, and I'm too stupid to divine meaning out of the complicated mathematical equations listed there. I've currently got 12v DC at 2 amps going through a 30 meter cable powering a fan from a car battery and it seems okay. Can I ramp it higher?

RomanBirdy (talk) 17:10, 25 August 2016 (UTC)

You need to know the gauge of the wire. Telephone wire tends to be 24 gauge. Then, look at a chart like the one on this page to see what the limits are for that gauge. If your telephone wire is 22 or 18 gauge, it will have different limits. 209.149.113.4 (talk) 17:15, 25 August 2016 (UTC)

See this datasheet (page 4, under "ESP TN/JP") for a typical set of ratings. This particular manufacturer specifies 296 V (as it has to take the voltage for a mechanical bell ringer) at 300 mA, so using it at 2 A is outside the specification. The problem will be the voltage drop rather than any safety-related issues, but using a properly-specified (automotive) cable would be better. Tevildo (talk) 22:48, 25 August 2016 (UTC)

• This isn't a great idea. Firstly you'll see a voltage drop across a long piece of thin wire, so your fan is running under-voltage. Secondly phone wire (unlike alarm wire) is single core, so it's not happy with an impermanent installation or any movement. Expect trouble with cracking and ends falling off. Thirdly, the current question. Cable doesn't have a "current rating" as such, it has a temperature rating and the current flow raises the temperature. The 17th edition of the wiring regs (expensive and unreadable) gives ways to calculate this in a standard manner. More easily, just feel the cable - if you can't feel it getting warm, it's OK.

A car battery needs to be fused at the battery end (seriously!). They have an enormous capacity for firey mayhem otherwisem if anything goes wrong. A car battery _will_ start a fire, given half a chance with thin wire.

If it were me, I'd use "bell wire". This is cheap two-core stranded wire with a single insulation layer. It's cheaper than phone cable too. Andy Dingley (talk) 23:07, 25 August 2016 (UTC)

As long as the wire doesnt heat up, there is no limit to the amount of current that it can carry.--86.187.161.98 (talk) 00:27, 26 August 2016 (UTC)

That is true, but the practical limit is reached when the voltage drop from one end of the wire to the other due to Ohms Law causes the device at the far end to malfunction. That can occur long before the wire shows any sign of distress. Akld guy (talk) 02:55, 26 August 2016 (UTC)

The categorical claim by IP user 86.187.161.98 is not true because a) all wires that are not superconducting have Resistance so any current causes Joule heating, and b) superconducting wires lose their property of no resistance when the current causes a magnetic field exceeding a threshold (here called the second critical field strength H_c2). It is true that very high levels of Joule heating can be tolerated for short high-current pulses. AllBestFaith (talk) 11:21, 26 August 2016 (UTC)

IP 86.187 was not talking about wires in general. He spoke of "the wire", meaning the telephone wire that the OP is using. Therefore, your objection over superconducting wire is irrelevant. Akld guy (talk) 20:47, 26 August 2016 (UTC)

The wire can be cooled externally so that its resistance renains constant whatever the value of current.--86.187.175.218 (talk) 20:20, 26 August 2016 (UTC)

It's much simpler to use a thicker wire than to run a thin wire through liquid nitrogen or some similar cooling agent, and there would still be a limit. Dbfirs 20:25, 26 August 2016 (UTC)

An intriguing question! I feel like there must be "only so many electrons that can fit" into the conduction band in a piece of metal of given size and shape, no matter what the cooling. Yet I have no idea what that limit would be called, if it even exists as a concept. Maybe at some point the voltage differential over a short space ought to become so extreme that pair production becomes possible and the energy disperses uselessly as gamma rays causing V=IR to fail? But below that, is there a hard limit to how much cooling can theoretically be done? I have no idea. Wnt (talk) 20:32, 26 August 2016 (UTC)

Well, for a real wire, the voltage (between the conductors) will eventually reach the dielectric strength of the insulation and arc over, giving us an upper limit to the current even with unlimited cooling. Another issue will be the ability of the cooling system to extract heat from the conductors through the insulation - even if the outside of the insulation is maintained at room temperature (or lower) by removing an arbitrarily large amount of heat from it, the temperature gradient across the insulation will increase with the power produced in the wire, and eventually the inside of the insulation will melt. Tevildo (talk) 16:42, 27 August 2016 (UTC)

Speed of sound and quantum entanglement

For the concept of "substance" you need a local speed of sound, i.e. a traveling pulse of energy. Isn't this an excited state above the ground state of the quantum entangled atoms? If the collection hasn't settled on a ground state then you can't have this collective action of a well defined wave. So is "substance" defined by a quantum entanglement of the atoms comprising the substance? Hcobb (talk) 17:59, 25 August 2016 (UTC)

Substance, stuff, matter, mass. I don't think any of them traditionally and canonically depend on quantum entanglement, but that doesn't mean your idea hasn't been explored. SemanticMantis (talk) 18:21, 25 August 2016 (UTC)

Quantization sound results in the phonon, which is as you say an excited state. Graeme Bartlett (talk) 10:36, 26 August 2016 (UTC)

Distribution of mass estimates from Doppler spectroscopy

The news of Proxima Centauri b brings up a basic question with Doppler spectroscopy - how much more massive is the planet than the minimum value? In theory you can put up a sort of histogram curve with probability on the x-axis and mass on the y-axis, which starts at 1.27 Earth masses on the left and goes up to infinity at the right. Of course, other factors intervene to make some of those possibilities not so possible, but it is a start. But in reality, trying to go from the integral of a sphere by theta as an indication of the distribution of unit vectors to an actual estimate of what proportion of orbits are measurable is... really freaking confusing me right now. And I can't even use it in the article if I get it. Can someone provide a source I can use for what this curve comes out as? Wnt (talk) 18:13, 25 August 2016 (UTC)

It is not Abel transform? Ruslik_Zero 20:06, 25 August 2016 (UTC)

Doppler spectroscopy is sensitive to $M_{obs}=M_{true}\sin(i)$, where $M_{true}$ is the true mass of the planet and $i$ is the inclination of the orbital plane relative to us. The minimum mass occurs if we assume the observed system is edge-on relative to us, $\sin(i)=1$, and in general $M_{true}={M_{obs} \over \sin(i)}$. In principle, every inclination between 0 and $\pi /2$ is equally likely. This would imply that the average true mass is $<{M_{obs} \over \sin(i)}>={2M_{obs} \over \pi }\int _{0}^{\pi /2}{1 \over \sin(i)}di=\infty$. In practice though, if $M_{obs}$ is too small then we will never detect it, and if $M_{true}$ is too large then it couldn't be a planet and would need to be a second star. Astronomers sometimes say things like, there is a 90% chance, $M_{obs}\leq M_{true}\leq {M_{obs} \over \sin(0.1{\pi \over 2})}\approx 6.5M_{obs}$. Dragons flight (talk) 07:45, 26 August 2016 (UTC)

@Dragons flight: I don't think every inclination is equally likely though. There's only one [circular] orbit [of a given size] that has an inclination of 0, but there are many orbits that have an inclination of 90 degrees (their axes could point in any direction perpendicular to us). I think there are an intermediate number with an inclination of 45 degrees (axes around a smaller circle) but I wouldn't bet my life on it. There are a lot of little gotchas like that that have made me resolve firmly not to even kick at WP:OR on this one; if I add anything to Doppler spectroscopy I'm gonna need a decent source. Wnt (talk) 19:40, 26 August 2016 (UTC)

Yes, there is an error in the above calculation. Correct averaging is

$<{M_{true}}>={M_{obs}}\int _{0}^{\pi /2}{\sin(i) \over \sin(i)}di={\frac {\pi }{2}}M_{obs}$,

though the dispersion is infinity. The distribution function is

$F\left(M_{true}\right)={\sqrt {1-\left({\frac {M_{ods}}{M_{true}}}\right)^{2}}}\quad M_{true}\in [M_{obs},\infty ]$,

whereas the corresponding density is

$f\left(M_{true}\right)=\left({\frac {M_{obs}}{M_{true}}}\right)^{2}{\frac {1}{\sqrt {M_{true}^{2}-M_{obs}^{2}}}}$

Ruslik_Zero 21:04, 26 August 2016 (UTC)

If I understand this correctly, the mode is that the real mass is the observed mass; the median is that the real mass is 2/sqrt(3) = 1.1547 times the observed mass, and the average is that the real mass is pi/2 = 1.5708 times the observed mass. Additional limitations placed on the distribution because the star doesn't noticeably orbit the planet would affect the average most, the median less, and the mode not at all. One of the more interesting features here is that it is 50% likely that the mass of Proxima Centauri b does not exceed 1.446 the mass of Earth; if we assume equal density (big assumption) the radius goes up as the cube root of that and the gravity decreases as the 2/3 power, so there is a 50% chance that gravity there is 13.6% or less greater than that of Earth. For some of us that's a whole lot of weight, but still less than we've handled before. It is indeed no word of a lie then that this is an Earthlike planet in mass ... probably.

Presently our article says that there is a 90% chance that the mass is less than 3 Earth masses. To check this, Mobs/Mtrue = sqrt(1 - (0.9)^2) in the F distribution above, or 2.294. Checking the source ... well by golly, it says 2.3 -- which gives 3 Earth masses for the 90% value as said. Chalk one up for Ruslik Zero! Wnt (talk) 14:38, 27 August 2016 (UTC)

Why are there zero calories in water?

Water is something you ingest, but the body's cells can obtain no useful energy from it in the form of ATP. In fact, I would guess that there is not one organism on Earth that can obtain energy from the oxidation of water, not even lithotrophs such as the hydrogen bacteria. It also doesn't seem to be possible to use water as a fuel in a machine, such as a water-fueled car. I know that there are many energy-rich substances from which the body can extract no calories, such as gasoline, but it seems to me that nature would have found a way, given the abundance of water on Earth, if it were really possible to oxidize water and obtain useful energy from it. I know that water is an energy-poor substance that is a byproduct of the oxidation of carbohydrates, fats, and proteins in cells. Its chemical bonds are very stable and difficult to break. We can measure the calorie content of foods in a calorimeter and water doesn't burn because it's fully oxidized hydrogen. However, I have a couple of questions. First, how did we find out that we can't get any calories from water? Was it something that we could tell just by observing that water doesn't burn? Or were there studies, perhaps ones showing that there is no increase in body temperature after a person drinks water? Second, is there any substance on Earth that reacts with water to release energy? I'm talking about an electron acceptor here, not an electron donor. I would appreciate any information you can give about the energy content of water. — Preceding unsigned comment added by 174.131.55.2 (talk) 21:58, 25 August 2016 (UTC)

Oh, I forgot to mention that water passes out of the body in an, ahem, unchanged form. Was that how we knew? I'd love to know the history of calories and how scientists figured this all out.174.131.55.2 (talk) 22:12, 25 August 2016 (UTC)

Hydrogen peroxide is oxidized water. Sagittarian Milky Way (talk) 22:59, 25 August 2016 (UTC)

Water is "burned hydrogen". It would be like trying to start a fire using the ashes from a previous fire. Vespine (talk) 23:05, 25 August 2016 (UTC)

So should I never say oxidized x to mean "x but extra oxygen"? Well if it can be made from x, oxygen, and less energy than is released I'm sure you still can. Sagittarian Milky Way (talk) 00:02, 26 August 2016 (UTC)

Not if you want to use the term correctly. oxidation has a specific chemical meaning which doesn't actually rely specifically on adding "oxygen" atoms, but the change in oxidation state, which is specifically related to electrons, not oxygen molecules. Water has a higher oxidation state than hydrogen peroxide (+1 vs -1) so I believe it is incorrect to say hydrogen peroxide is "oxidized water". Vespine (talk) 00:32, 26 August 2016 (UTC)

This is a somewhat pointless question, unless one gives the context. Liquid water on Titan certainly hasn't zero calories on the Moon Titan. 00:14, 26 August 2016 (UTC)

We're talking about chemical Food energy, a completely different question to how much energy it would take to keep water liquid on Titan. Vespine (talk) 00:35, 26 August 2016 (UTC)

Here's the short short explanation as to why you cannot extract energy from water by digesting it. When you digest food, what you're doing is a series of chemical reactions during which chemical bonds are broken and reformed in new ways. Roughly speaking, you can only extract energy from the food if those chemical reactions are exothermic, that is if the products of the reaction contain less chemical potential energy than the reactants. Your body basically takes food and turns it into waste products, extracting energy so long as the waste products have less potential energy than what you started with. For carbohydrates, the reaction is roughly

(CH₂O)_x + xO₂--> xCO₂ + xH₂O

Now, as long as the products (water and carbon dioxide) have less chemical potential energy than the reactants (the carbohydrate and oxygen) your body can extract energy from the reactions. Why can't we extract energy from water? Because water has very low chemical potential energy. There isn't any product you could make from the water that would have less chemical potential energy, so there's no way to extract excess energy from any reaction with water as a starting material. Thus, you cannot get food energy from it. --Jayron32 13:19, 26 August 2016 (UTC)

Great answer. Thanks!174.131.35.50 (talk) 13:37, 26 August 2016 (UTC)

It's not strictly impossible to get energy from water... but close enough. From the first source I saw I'm getting that you get 94.64 kJ/mol out of breaking down hydrogen peroxide into water with catalase, which is a lot. But formally, the Gibbs free energy depends on entropy, and Le Chatelier's principle applies. Which is to say, if someone hands you a bottle of absolutely positively impossibly pure water, and you put it under an oxygen atmosphere, then some small fraction of the molecules (calculated via this relationship) will get converted to H2O2. In theory, you could even have some variant of catalase that produces ATP when you convert water and oxygen to H2O2, and you could use it to extract a couple of ATP molecules out of pure water, thereby proving "there is free energy to be extracted from pure water". But this is only in theory given perfectly pure water that may not be possible even to obtain, and certainly would be impossible to preserve, since otherwise, even lacking an enzyme, over time the water has probably found a way to do that to itself already. For example, at some rate it splits to H* + OH* and those OH*s find each other. But they do the same in reverse, and so there's only the appropriate miniscule amount of peroxide in normal water. Of course, all of this is really minor as an energy source compared to something like getting pure water and seawater and using osmotic pressure produced by allowing them to come into contact across a semipermeable membrane, etc. ... and that isn't a practical energy source either. Wnt (talk) 19:22, 26 August 2016 (UTC)

But not a single one of those is "getting energy from water". Every one of those is "do a chemical reaction to water to make it not-water, and then get energy from that". --Jayron32 01:53, 27 August 2016 (UTC)

Yes and no. The trick here is what is "water"? Is water defined as a collection of pure H2O molecules and nothing else, or as the collection plus such reactive oxygen species as are found at equilibrium under a certain set of circumstances such as temperature and exposure to the air? Yes, this is basically a mind game - nothing here is going to really turn an engine - but it's just funny to think about. The thing about philosophy is that you can look at something like water and realize that you're not sure what you really mean when you talk about it. Wnt (talk) 14:45, 27 August 2016 (UTC)

August 26

A liquid other than water that is safe to put on your skin

Suppose that it's 50 C outside and the relative humidity is 95%. It would then be difficult to keep your body cool by sweating. But if you take a bottle with a liquid other than water with you with a sufficiently high latent heat and a sufficiently high rate of evaporation, you could spray that on your skin where it would evaporate quire rapidly and keep you cool. There are a few problems with this solution. One problem is that most compounds that are liquid at room temperature tend to be poisonous when put on the skin in large quantities, but perhaps some here know of some compound that is not going to kill you. Another problem is that water vapor from the atmosphere could condense on the liquid, so the Gibbs free energy for water-liquid mixture needs to be sufficiently high for this method to work. Count Iblis (talk) 02:26, 26 August 2016 (UTC)

Isopropanol? It's very drying if you keep doing it and hurts like Satan if it gets on mucous membranes though so you might want to dilute it with um, water. Or maybe not – it's very hot. I have no idea how hot that feels and it must depend on exposure time but 50C/95%RH doesn't actually occur on Earth. Maybe in a sauna. This will use up liquid fast! Sagittarian Milky Way (talk) 02:52, 26 August 2016 (UTC)

That article doesn't say it doesn't occur, just that if it did it would be extremely dangerous. And the other word to insert here is --- YET. We'll see where we are five years from now... Wnt (talk) 19:25, 26 August 2016 (UTC)

SMW is correct -- this value is far outside the observed range. 50C with 95% relative humidity corresponds to a dew point temperature of 49C. The global record high observed dew point is 35C. Shock Brigade Harvester Boris (talk) 04:24, 27 August 2016 (UTC)

Perfluorocarbons could do what you want. They may not be good for global warming, but you should be able to select one. Perhaps Perfluoroheptane or Perfluorohexane which is biologically inert. Graeme Bartlett (talk) 10:24, 26 August 2016 (UTC)

There isn't much that matches water for heat capacity, and I doubt that it takes nearly as much energy to boil perfluorocarbons either. Though then again, lacking these properties, Liquid nitrogen seems like a fair solution here since it starts off cold, if you can just arrange to atomize it a bit better with some kind of sprayer, and invent some kind of surfactant so it wets skin better (once you have it in small enough drops that you're not burning yourself if it does). What the hell can you use for a surfactant for liquid nitrogen? I definitely stumped Google with that phrase. :) Wnt (talk) 19:30, 26 August 2016 (UTC)

In this case the relevant property is not heat capacity, but latent heat of vaporization. Shock Brigade Harvester Boris (talk) 04:24, 27 August 2016 (UTC)

Hyperthermia#Treatment may or may not help you. --Jayron32 12:26, 26 August 2016 (UTC)

August 27

magnesium

Is magnesium citrate and magnesium sulphate basically the same thing but in a different form? Like water an ice are both h2o? Do they both dilate the epididymis ducts? — Preceding unsigned comment added by 168.9.40.11 (talk) 00:08, 27 August 2016 (UTC)

No, they are not the same thing, any more than water and hydrogen peroxide are the same thing. We don't give medical advice. It should go without saying that "administering" anything into your epididymis is a phenomenally bad idea that could kill you. --47.138.165.200 (talk) 00:16, 27 August 2016 (UTC)

I think you need to actually read the article you linked rather than just blindly posting it. Specifically the section titled Distinguishing between what is and what is not acceptable. From that it is very clear that my question is NOT a request for medical advice. 168.9.40.11 (talk) 00:25, 27 August 2016 (UTC)

You might forgive me for wondering why you are interested in things that dilate the epididymis. It's not exactly a common question. If you are having a possible issue with your epididymis, see a medical professional. --47.138.165.200 (talk) 00:48, 27 August 2016 (UTC)

Well, as I said before this is not a request for medical advice. The article states; "Magnesium citrate, as a supplement in pill form, is useful for the prevention of kidney stones.[4]" This is apparently because it dilates the kidney ducts and allows calcium deposits to pass easily. I was just curious if the same principle applied to the epididymis where calcium deposits also collect. There doesn't seem to be an article on epididymis stones. 168.9.40.11 (talk) 01:12, 27 August 2016 (UTC)

Are epididymis stones are a thing? I did a little looking and I don't think they are. I did stumble upon testicular microlithiasis but that's not quite the same thing. Epididymitis exists, but as the article states it's not generally caused by stones. I believe you are incorrect about the mechanism of action of magnesium citrate on kidney stones. As our article on kidney stones states, magnesium citrate and similar things reduce the risk of kidney stones by altering the composition of the urine. Kidney stones are formed when minerals in the kidney filtrate precipitate into a solid form. Altering the filtrate's composition can prevent this. --47.138.165.200 (talk) 01:36, 27 August 2016 (UTC)

I removed this policy nonsense. We're talking about chemicals here. Wnt (talk) 01:57, 27 August 2016 (UTC)

... and re-removed it. If edit warring is the golden ticket here to get your version of policy to be the rule, we all need to do our part this time. Asking about a chemical's effect on the body, not your body, is routine biology, and I'll not see biology banned from the Science Refdesk. Wnt (talk) 02:37, 27 August 2016 (UTC)

Now as for the question, it's worth noting that ionic compounds are generally the sum of two components, anion and cation. So potassium citrate has some of the same medical applications for kidney stones, but lacks some others, like obviously it isn't a good magnesium supplement. It is worth looking up the two components independently. Wnt (talk) 02:37, 27 August 2016 (UTC)

The top web hit for epididymus and magnesium is this thing (obviously not a quality medical source), which describes some people taking a maximum dose of Epsom salt by mouth. They are not injecting this stuff into anybody's ducts with a needle. The maximum dose recommended on a package of magnesium citrate may be different. I didn't find anything obvious matching this description on PubMed, and there's no guarantee there's any valid theory there or that they're trying to do anything but sell a specific kind of epsom salt pills (I mean, they make a point of linking some kind of epsom salt pills even though I eat (much smaller amounts of) epsom salt on occasion and it's not anything terrible - sometimes bitter tasting, sometimes even sweet tasting, it varies) Wnt (talk) 03:04, 27 August 2016 (UTC)

Time limit for data storage devices

See HD-Rosetta data storage device. It says "Technologies have made HD-Rosetta extremely durable compared to most archival data devices. It has an estimated longevity of 10000 years, and it can withstand a minimum of 1000 years". What does this mean? I didn't know data storage devices had a time limit. Why can't you just store data on a USB stick for 10000 years, or indefinitely? Is there something that prevents storing data indefinitely? 49.199.45.88 (talk) 04:18, 27 August 2016 (UTC)

Sure, materials decay over time. Everything breaks down, and media is only as good as the material it is made out of. Here is a pretty good article about the lifespan of various storage media. Your USB stick (according to that article) is only rated to last about 10 years, not 10,000. This article from 2002 (so a bit dated) rates USB storage devices at about 50 years, which is optimistic, as the media was very new back then; I'd trust the more recent estimates. Wikipedia has an article titled Media preservation which also has some figures for you. It should be noted that these estimates are based on expected averages and reliability; you will find outliers always, but not reliably so. --Jayron32 04:28, 27 August 2016 (UTC)

Thanks for that. That's interesting. It appears that every data storage device has its own unique reason for expiring (photos fade, magnetic tapes lose their magnetism,...). I guess I'm just curious to know if there's some fundamental law that means that *any* data storage device will lose its data eventually. There may not be, but if even HD-Rosetta won't keep its data forever, what will? 49.199.45.88 (talk) 05:30, 27 August 2016 (UTC)

The fundamental law is impermanence. You might be interested to read our article on the Digital dark age and the links therefrom.--Shantavira|^{feed me} 06:54, 27 August 2016 (UTC)

One way valve as an alternative to refrigeration?

Does anything exist that can act as a one way valve for products that have been sterilized ( think salad dressings, etc) that must be refrigerated after opening so that instead of it needing to be put in the fridge, it could stay out in the pantry and still have a similar shelf life? I'm thinking that the only reason it needs to be cold is to inhibit bacteria growth, but if you stop the bacteria from getting into the product in the first place it will still act as though it is sterilized, correct? Seems like it could be a way to lengthen shelf lives after being opened?

2601:406:4C01:5480:CCF8:4DA:F064:50E1 (talk) 05:55, 27 August 2016 (UTC)

If you have it in a squeeze out tube, like toothpaste the inside will stay away from the environment, and only the bit coming out will be exposed. Graeme Bartlett (talk) 08:55, 27 August 2016 (UTC)

Lichen 4th component

Hey All, I was listening to this scientific American podcast the other day 60 second science when I came across this episode. It is about how scientists in this study found lichen do not just consist of fungus and algae, but also yeast in some cases. It finishes with the scientist speculating that there could be other things that lichen consist of. What would be a likely candidate for this? JoshMuirWikipedia (talk) 06:46, 27 August 2016 (UTC)

Yeast is fungus. —Tamfang (talk) 08:23, 27 August 2016 (UTC)

Some lichens can contain more than one species of multicellular fungus. Some can also vary their algae with differing results. You could also expect that there are bacteria and virus that may live with a lichen, but they may be a parasites rather than useful. And don't forget the mineral kingdom additions, or air, water, stone and dust. Different fungi also partner with other plants by growing on their roots. Graeme Bartlett (talk) 08:51, 27 August 2016 (UTC)

Does an isolated system definitely approach (arbitrarily closely) thermodynamic equilibrium?

The thing about the second law of thermodynamics is that it says the entropy of an isolated system is nondecreasing, not that it is increasing. Strictly speaking, this means that the second law alone does not guarantee that an isolated system will reach its maximum entropy state, or even approach it. Are there additional laws that assure this? 203.45.134.227 (talk) 08:18, 27 August 2016 (UTC)

Sodium vs potassium: electrical conductivity

Why is sodium a better conductor of electricity than potassium? (Electrical resistivities of the elements (data page) gives Na a lower resistivity than K.) The obvious way to predict a trend down the alkali metals is that conductivity would increase down the group (Li < Na < K < Rb < Cs), since the outermost electron is less and less tightly held, but instead the trend is Cs < Rb < Li < K < Na; why? Double sharp (talk) 11:08, 27 August 2016 (UTC)

Orange

If I have two identical oranges. One I eat whole, the other I put into a juicer and then drink the juice, pulp and all. Which is healthier? My mom says that eating the orange is healthier than drinking orange juice, and that the orange juice does not count as one of my "five a day". Is she correct? Also how does juicing an orange increase its sugar content and "make kids hyperactive" compared to eating the same orange? — Preceding unsigned comment added by 202.20.99.196 (talk) 12:01, 27 August 2016 (UTC)

I'll take a punt and say the whole orange is healthier, as your body has to work harder to get it inside your tummy. You'll get some exercise from the chewing. I can't see how juicing an orange will increase the sugar content, assuming that you don't add any sugar. --TrogWoolley (talk) 12:13, 27 August 2016 (UTC)

Fruit juice has had a bad press recently, see this for example, but as far as I can tell applies to juice made from concentrate. The problem with squeezing it yourself is that you tend to leave the dietary fibre behind, but as you say that you're using "pulp and all", I'm not sure that is an issue here. Alansplodge (talk) 13:11, 27 August 2016 (UTC)

• Define "heathier". And while Alansplodge makes a reasonable point, the "Life and style" column of the Guardian (or of any other mainstream press outlet) is certainly not the place to find scientifically validated information. Tigraan^{Click here to contact me} 13:23, 27 August 2016 (UTC)

The whole fruit contains fibers, and most people don't get enough of it. Orange juice often has sugar added to it, and most people get too much of it. Llaanngg (talk) 13:38, 27 August 2016 (UTC)

When the orange is juiced, the sugars are released from the cells, and therefore have a more significant effect on teeth. If you eat the fruit, most of the sugar will be released further down the digestive system - so healthier for the teeth, even if there is no difference in the total amount. Wymspen (talk) 14:39, 27 August 2016 (UTC)

The main difference is what's tossed in the trash beside the juicer, which is to say insoluble fiber. The 5 a day site for the UK's NHS makes particular comments about fruit juice. [10] Prioritizing which effects of fiber and fruit are most important to you is medical advice we can't give - some people might think more about cavities or constipation than others when making personal decisions. Wnt (talk) 14:54, 27 August 2016 (UTC)

What triggers a regular childbirth?

Oxytocin? Other hormone? But what triggers these? How does the body "know" that the baby is ready? Or, does the baby trigger the whole process? Llaanngg (talk) 13:39, 27 August 2016 (UTC)

Our Oxytocin article explains: oxytocin causes contractions during the second and third stages of labor -- so it doesn't seem to play a role in the onset of labor. Childbirth § Onset of labour mentions oxytocin as having a possible "synergism" with melatonin relating to reports of labor more commonly occurring during late night and early morning hours. This doesn't answer your question, however; but I hope it helps clarify a bit. 2606:A000:4C0C:E200:1821:CD59:E35A:CB68 (talk) 18:03, 27 August 2016 (UTC)

The first clear sign of childbirth is the appearance of regular uterine contractions. The mechanisms that cause contractions to start are complex and not completely understood -- for a rather thorough recent review you could look at http://humupd.oxfordjournals.org/content/16/6/725.long -- it's not easy reading though. Two factors that clearly play a role are oxytocin and prostaglandins. Looie496 (talk) 18:14, 27 August 2016 (UTC)

(Courtesy link added: 2606:A000:4C0C:E200:1821:CD59:E35A:CB68 (talk) 18:25, 27 August 2016 (UTC))

Order of substituents in the IUPAC nomenclature for organic chemistry

Hello.

In the nomenclature of organic chemistry, whenever there are several substituent prefixes of different lengths where each prefix begins exactly the same as the next shorter one, how are they sorted to generate preferred IUPAC names?.

Example: What prefix goes first, "methyl" or "methylphenyl"?. So is it "1-methyl-2-(methylphenyl)-propan-1-ol" OR "2-(methylphenyl)-1-methyl-propan-1-ol"?.

I checked P-14.5 of the IUPAC Blue Book 2013 but it is not clear if this provides a decision rule. It provides rules for the case when "all Roman letters are identical". I would say that here they are not identical.

What is the official decision rule here for preferred IUPAC names according to the Blue Book 2013?.

I am interested exclusively in what the official standard has to say on the matter. I searched but I did not find anything conclusive.

Regards and thanks. Mario Castelán Castro (talk) 17:35, 27 August 2016 (UTC).