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October 25

Is it possible to see Philadelphia from New York City?

The highest point in Philly city limits is 1,548 feet above sea level (1255 above ground plus site altitude, both rounded up to at least next foot). New World Trade Center is 1,806 feet above sea level. They're 79.42 miles apart. These are high enough to be seen up to 113 miles apart with the help of average atmospheric refraction but there's 80 miles of trees and hills in the way. Also the tops are only a few feet wide and it would take ridiculously steady air to see antennae that thin with a telescope so the seeing might be theoretical. And one side of the Princeton area is in the way and near the midpoint so there will be buildings. Air below the standard temperature (15°C?) refracts more though and occasionally freak looming occurs with some kind of weird temperature inversion light duct (I think the world record is between Greenland and Iceland). As an alternative tower if this route is blocked, Philadelphia's tallest building is near or at final height now (1,121 feet) and about the same depth into Philadelphia but the Trenton area's in the way. Sagittarian Milky Way (talk) 08:52, 25 October 2017 (UTC)[reply]

It might be easier to spot buildings that are lit up, at night. ←Baseball Bugs ^{What's up, Doc?} carrots→ 10:18, 25 October 2017 (UTC)[reply]

They would if there were an ocean between them. There isn't an ocean between them. There's a place called New Jersey which is not sea-level flat on the line of sight between New York and Philadelphia. There are several lines of low hills that could block such views. If you look at a relief map of New Jersey, you'll also see several lines of hills, for example one near Princeton known as Princeton Ridge or Rocky Hill, it lies in a park known as Woodfield Reserve. Looking here the ridge is at least 260 feet above sea level for the entire line of it, and the peak of the ridge is about 320 feet above sea level. Coupled with the curvature of the earth, this MAY be high enough to cover the view of the tops of the highest buildings of each city from the other. Not entirely positive, but if something did block the view, it would be hills like that. --Jayron 32 12:16, 25 October 2017 (UTC)[reply]

Just to add some evidence possible the other way This thread shows pictures of Philadelphia from Allentown, PA and from Apple Pie Hill, NJ. The Allentown one is from a Helicopter some undetermined height above ground, so it may be cheating, but the NJ one is from a ground level observation from the top of a hill in the Pine Barrens. It's only 30 miles away, though. The 80ish miles to NYC is a different story entirely. --Jayron 32 12:22, 25 October 2017 (UTC)[reply]

www.skyscraper city.com/showthread.php?t=848608 (remove space, blacklist issues) notes that one cannot see any of Milwaukee from Chicago's Sears Tower, and the line-of-sight between Chicago and Milwaukee is better, there's no significant changes in elevation between the cities; its all fairly flat Lake Michigan coastline, and the distance between the cities is about the same as NYC-Philly. --Jayron 32 12:27, 25 October 2017 (UTC)[reply]

There are webcams now at WTC1 in NYC and at Comcast Tower, Philadelphia. Equipping them with long lenses and pointing them at each other could answer the OP's question. Since a 193-km path microwave link is achievable a 129 km (80 mile) Philly-NY link should also be feasible if there is indeed a free LOS. Blooteuth (talk) 12:53, 25 October 2017 (UTC)[reply]

This utility is VERY useful. It does a line-of-sight topographic cross section between any two points on the earth's surface. Plugging in the heights of the buildings in meters (i used the listed observation for Freedom Tower and the top of the Comcast Technology Center) shows that the topography shouldn't be a problem. There's an easily open line-of-sight assuming that curvature-of-the-Earth issues also aren't a problem. --Jayron 32 15:51, 25 October 2017 (UTC)[reply]

Here [1] is the elevation transect as depicted by the tool Jayron linked. Pretty much everything over 40m elevation should be mutually visible between the the Comcast center and 1WTC, assuming good enough optics, given a flat Earth. However, here [2] is a tool that shows you how much the Earth's curvature gets in the way, and if I'm reading it right, it says that if you're in NYC and your eye is 382 m up (the height of obs. deck at 1WTC), then the horizon will occlude everything in Philly (130 km away) under 284m. Since the Comcast center is 297m tall, you may be just barely able to see it with a good scope on a clear day. SemanticMantis (talk) 17:21, 25 October 2017 (UTC)[reply]

Question about gravity assists and space probes

How come space probes that are only intending to fly by the planets of the outer Solar System (i.e. the Pioneer and Voyager probes, as well as Ulysses and New Horizons), such probes tend to go there directly from Earth, but probes intended to orbit around those planets (i.e. Galileo, Cassini, Juno) tend to first make one or more flybys of either Earth, Venus, or both? Narutolovehinata5 ^tccsdnew 13:30, 25 October 2017 (UTC)[reply]

Voyager and Pioneer made extensive use of gravity assist in their trips. For one example, see the graph at right. Every one of those spikes is a gravity assist event in the travels of Voyager 2. Your question is based on a false premise, so is unanswerable. We cannot answer "why didn't they" when the answer is CLEARLY that "they did". --Jayron 32 13:42, 25 October 2017 (UTC)[reply]

@Jayron32: You misunderstood my question: my question is why the other probes made gravity assists of Earth and/or Venus before going to Jupiter, as opposed to the Voyager and Pioneer probes that went from Earth directly to Jupiter without flying by Earth or Venus first. Narutolovehinata5 ^tccsdnew 13:46, 25 October 2017 (UTC)[reply]

In that case the answer is apophenia, which means that your mind is creating false patterns where none exists. Every individual mission is unique, and the decision to choose, or not choose, to use a particular trajectory, and thus a specific set of "gravity assist" events is based not on any pattern based whether or not the probe is going to stop at Jupiter or not, but rather because the specific orientation of the planets at the specific time when the probe was launched and the specific location of the target trajectory either does or does not owe itself to a specific set of gravity assist events. There is no grand scheme on when or when not to use Venus other than "It happens to be in the right place at the right time for our purposes". --Jayron 32 15:32, 25 October 2017 (UTC)[reply]

(ec):Its all about conserving fuel and getting free speed boosts from tagging planets. Sometimes they even go in the opposite direction from their target. New Horizons got a boost from Jupiter, Ulysses went by Jupiter to study the Sun. Rmhermen (talk) 13:50, 25 October 2017 (UTC)[reply]

Here [3] is NASA's HORIZONS system, which can tell you where many thousands of objects are in the solar system, and where they will be in the future, so far as we can tell at present. Here [4] [5] are a few research papers that describe methods for how to plan out gravity assists and flight plans. As you can see, it's pretty heavy stuff, and I'm not sure if there is any "easy" way to understand how they do it. There may be heuristics available (e.g. "It's often good to hit planets in orbital order", or "big backtracks are seldom useful*), but I think the only people qualified to discuss those would be people who have personally worked on planning these things.

* N.B. These are completely made up by me, and I am not saying they are good or accurate, merely that such rules of thumb may exist. SemanticMantis (talk) 16:53, 25 October 2017 (UTC)[reply]

Just as a point of order, if only because it sometimes confuses people (not that it necessarily confused you), it may be perfectly logical to use an assist from Venus to get to Jupiter because, for large parts of the year, Venus would be on the way to Jupiter. If we assume a stationary solar system (just to simplify an otherwise messy problem), any time we have Earth on the opposite side of the sun from Jupiter, Venus would almost always be between them. If Jupiter and Earth were on the same side of the sun, Venus is never useful, and Mars is only useful on the rare instances where it is actually between Earth and Jupiter. People think "Venus is closer to the sun than Earth, and Jupiter is farther, so why use Venus to get to Jupiter" forgetting that these are orbits, and one can easily draw a picture (actually MANY such pictures) where Venus is on the way to Jupiter. --Jayron 32 17:43, 25 October 2017 (UTC)[reply]

For a specific example in relatively easy to understand terms, here [6] several features of the Juno trajectory are discussed, including info on why those choices were made. SemanticMantis (talk) 16:57, 25 October 2017 (UTC)[reply]

Gravity assist#Purpose explains this well. Going to an orbit around Venus or Mercury, a spaceship is accelerated too much by the sun to be able to enter orbit, so a ~~flyby~~ gravity assist is used to decelerate. Going to orbit around Jupiter or beyond, the sun slows it down too much, so again it needs a gravity assist, this time to speed up to enter orbit. Flybys don’t need to change their speed, although Voyager 2 used gravity assists to speed up so it wouldn’t take so long to get to Uranus. Loraof (talk) 17:45, 25 October 2017 (UTC)[reply]
Loraof gave the best answer here. I've stricken my earlier non-answers because I clearly am confusing the problem with my extemporaneous answers. He's right, I'm wrong here. Forget what I said. That completely answers the OP's question. Mea culpa. --Jayron 32 18:05, 25 October 2017 (UTC)[reply]
The reason why some probes went directly to Jupiter while others did not is that orbiters were much more massive than first flyby probes. It was just impossible to send them directly to Jupiter - no launch vehicle heavy enough was available at those times. And even if such vehicle had been available, it would have been much more expansive to use it than going by gravity assists. Ruslik_Zero 20:30, 25 October 2017 (UTC)[reply]

Hellenistic astrology

This section speaks of the "rising of decans". However, if I got it right, decans as such are basically just distances. So, it cannot really be the decans that "rise", but only the constellations forming them, am I right? Sorry, if this might seem a silly question for any of you.--Cleph (talk) 15:20, 25 October 2017 (UTC)[reply]

Decans are not distances, Decans are units of time equal to 10 days. As noted at Decans, "Because a new decan also appears heliacally every ten days (that is, every ten days, a new decanic star group reappears in the eastern sky at dawn right before the Sun rises, after a period of being obscured by the Sun's light), the ancient Greeks called them dekanoi (δεκανοί; pl. of δεκανός dekanos) or "tenths" (and when the concept of decans reached northern India, they were called drekkana in Sanskrit.)" I hope that helps explain the name! --Jayron 32 15:28, 25 October 2017 (UTC)[reply]

@Jayron32: Thanks a lot. But still, when you say "Decans are units of time", why should one speak of their "rising" or – in case of the article reffered to by you – "appearance"? Aren't it constellations that rise / appear? After all, something that "rises" or "appears" must be physically observable (visible), and units of time do not meet that requirement, do they? So, that wording simply doesn't seem reasonable to me, and probably also wouldn't to the most other laymen reading these articles. But please excuse me if I'm getting something wrong here. Best wishes--Cleph (talk) 17:05, 25 October 2017 (UTC)[reply]

No, the word decan comes from a unit of time. The usage of that word means, in the context of astrology, 1/3rd of a constellation. In formalized astrology, a decan just means "1/3rd of a sign". Since each sign lasts about a month, a decan lasts 10 days. To say a "decan is rising" just means "this portion of the constellation is rising". It means the exact same thing in the context of astrology as a certain constellation or planet is "rising". See Ascendant for a discussion of what "rising" means in this context (if that is the source of the confusion). However, to use the term "rising of a decan" is no different than "rising of a constellation". --Jayron 32 17:24, 25 October 2017 (UTC)[reply]

Ah, okay. I guess it's become clearer to me now. So thanks a lot for that explanation!--Cleph (talk) 18:08, 25 October 2017 (UTC)[reply]

@Cleph: Note that there is a much better article at decans that is not decan (astrology). Our article gives the impression that some decans had more of an individual recognizability. The bottom line is that if you have a good view of sunrise and know the stars well enough, you can spot which day it is by which stars are visible just before the sun comes up - and each day they will move up by one degree relative to where they were. (One degree in the sense of one-thirtieth of a month = zodiac constellation or one-tenth of a decan) Wnt (talk) 13:26, 26 October 2017 (UTC)[reply]

@Wnt: Thank you very much, too! Dealing with the article linked by you would probably confuse me even more though. At this point, I must admit that I am really an absolute amateur in this field! However, I tried to get to the bottom of the astrological (!) concept explained at decan (astrology). But what I really don't get is the following statement in the introductory section: "These divisions are known as the "decans" or "decantes" and cover modifications of individual traits What does that exactly refer to?, attributed to minor planetary influences, which temper or blend Same question with the ruling influence of the period And once more…." Can one of you translate that for a six-year-old? PS: I'd say at least that sentence should be rewritten by someone who knows what's what if we still want non-professionals to understand our articles. Don't you think?--Cleph (talk) 18:24, 26 October 2017 (UTC)[reply]

Well, this is more editorial than answer now... "Astrology" in the ancient sense was in considerable part the respectable science of measuring the true date, with the reasonable extensions of providing useful prognostications of whether it would be a good or a bad idea to plant wheat or start the spring march to war. But the things you mention sound more like the bad sort of "astrology" we think of today, and frankly, I would not be optimistic that they mean anything at all. At the very least, this being the Science desk, I don't have to worry about figuring it out here. ;) Wnt (talk) 23:59, 26 October 2017 (UTC)[reply]

You can get some idea of what they're talking about here: [7]. 92.8.218.38 (talk) 14:29, 27 October 2017 (UTC)[reply]

Both of these fields should've been called astronology till about the 1600s. Kepler invented the quintile, when things are near 0.2 circumferences apart in ecliptic longitude. When the part of astronology that would've been astronomers if they were born later stopped believing astrology the community kept giving readings for awhile to pay for their livings and telescopes. By now of course professional readers are generally really woo people of the kind who would've been one of the last to believe in vampires and the ghost-blocking properties of iron and drowning a pretty virgin to appease the hurricane god threatening villagers' lives. Especially since the computer revolution of 1995 meant that professional astrologers don't even need to know how to use any of the math and tools needed to make a chart anymore. Like a book of house and planet positions or even a book of zillions of birthplace coordinates and historical time zones. Software can give birth charts and progressions and things without adjusting the house positions for latitude and longitude and calculating the missing ones from the ones given and drawing the thing with a compass and protractor and a few other maths. The computer shows a chart with just a time and town name so the astrologer can focus on what's really important: unconscious or conscious warm, cold and hot reading and cherry picking! And predicting! And making these unnecessarily vague and seem less vague than they are! Which isn't hard cause people who believe astrology are some of the right-brainedest people on Earth. Sagittarian Milky Way (talk) 18:38, 27 October 2017 (UTC)[reply]

Vertebrate intelligence

Around noon this morning during my lunch break home I watched the Nat Geo channel of Direct TV in the United States. The title was "South Africa" and when I began watching the camera was looking at a small water pool full of what turned out of be hundreds of tadpoles. The pool was literally packed with them and first I was not sure if those were small fish or something else. The realization that they were what I said came up later.

It was clear the little critters had hard time breathing in the pool. They all were in perpetual motion. Then all of a sudden a massive frog or a toad appeared in the view. The toad moved resolutely from dry land of the bank of the little pool across it stumping the tadpoles along the way. The toad then moved across the pool which was perhaps 10 feet in diameter and stopped at the opposite bank. It then began to move her hind legs methodically sideways. The toad was sitting on a pool bank that was a patch of wet dirt, nothing more. I stared at the motion but could not figure out what the critter was doing. In a couple of minutes it became clear. The toad was making a water passage for the tadpoles to escape and once it dug a channel deep enough that the water began escaping from the pool, the toad melancholically moved away. The little tadpoles then began swimming to a larger water pool which was behind that bank that was in fact a barrier. I wonder if the whole spectacle was smartly staged but nonetheless, how would you explained the toad's behavior? It is incredible. --AboutFace 22 (talk) 23:04, 25 October 2017 (UTC)[reply]

It could all be instinctual. That is, the frog lays eggs in an isolated spot where they will be protected from predators, then, once they've all hatched, she breaks open the connection with a larger pool. If it's all instinct, there's no intelligence involved, just hard-wired behavior. StuRat (talk) 23:58, 25 October 2017 (UTC)[reply]

@StuRat, you disappointed me again :-) Thanks, --AboutFace 22 (talk) 00:34, 26 October 2017 (UTC)[reply]

Probably not a mother toad, but an African bullfrog dad. Is this your video? In short, he doesn't want his children to die (unless it's to feed him). Filial cannibalism tries to explain this. InedibleHulk (talk) 05:16, October 26, 2017 (UTC)

The word "want" is problematic when dealing with such lowly animals. I think of them more like computer programs, doing what they were programmed to do. Would you say a computer program "wants" to process data ? StuRat (talk) 16:37, 26 October 2017 (UTC)[reply]

In high school, I carefully dissected a frog and smashed a computer with a rock (in some order or another). The stuff inside the frog looked far more like the stuff inside me than the stuff in the computer. It was a 386, though; mother and daughterboards have come a long way, while frogs are still slow enough to be caught by the nice people who programmed early '90s models like myself. InedibleHulk (talk) 09:07, October 27, 2017 (UTC)

In elementary school, I built a bird, tested a robot and portaged goods cross-country, all using a critter without any memory or processor at all. Nothing but a link to the queen. The queen was evil, sadly, so the entire colony was wiped out by the government. Some say her core spirit survived, though, and still commands legions of cars to this day. InedibleHulk (talk) 09:44, October 27, 2017 (UTC)

Father explains how, why and when some dads are alright, and the "Non-human fatherhood" section has critter examples, including the ridiculous Darwin's frog. InedibleHulk (talk) 06:40, October 26, 2017 (UTC)

@InedibleHulk, thank you for the video. It is certainly the same episode but the one I saw on Nat Geo Wild was much better edited in comparison with this one, although here there are more details. Yes, the nature can easily encode complicated patterns of behavior in simple brains. --AboutFace 22 (talk) 21:26, 26 October 2017 (UTC)[reply]

Some relevant info at Frog#Parental_care. I don't think this was staged at all, I think this is the common method of care. Here [8] is a PBS video specifically about African Bullfrogs(Pyxicephalus adspersus), and describes exactly the same behavior you describe. (P.S. Parental care is a good general search term and article, but I found the PBS video link by searching /frog brood pond/, where it was the top hit.) Parental care and its evolution is a large field of ongoing research. See here [9] for an overview, or if you have more specific questions, I can try to help if you ping me. SemanticMantis (talk) 21:50, 26 October 2017 (UTC)[reply]

@SemanticMantis, thank you but @InedibleHulk has already posted that PBS video before. Come to think of it. Somewhere in the Frog's DNA there is a gene, perhaps a few that control this behavior. How is it done? --AboutFace 22 (talk) 00:27, 27 October 2017 (UTC)[reply]

I'm not sure if we know that yet. It's complicated to even find where the instinct is in the brain, much less to figure out which genes build that area and how. StuRat (talk) 02:44, 27 October 2017 (UTC)[reply]

@AboutFace 22:, ah, sorry, @InedibleHulk:'s link is to a different place, and while I think he does good work here, I think his links would be improved if they were less cryptic :)

As for the rest, yes, this is very complicated, complex, and in addition hard to study. But that doesn't mean we don't know a lot about it! Here are a selection of research papers that discuss genetics and evolution of parental care behavior in frogs. There are more papers out there, and some of them better, but I will limit to a few that are freely accessible. I will start with the least relevant and move towards the most.

Here [10] is a paper about mate choice and genetic basis of color variation in a frog species. This is relevant be cause sexual selection can be a key driver of evolution of traits and behaviors, and even more so when species exhibit parental care. Near the end, they mention that the importance of parental care in that species, making it a candidate for imprinting and further self-reinforcing selection.

Here [11] is the paper Phenotypic and Genetic Divergence in Three Species of Dart-Poison Frogs With Contrasting Parental Behavior (NB I think my URL link will expire, put the full title in to google scholar to find the pdf if you have problems). As it says, it describes how different types of poison dart frogs have genetic differences, and it suggests that they are responsible for differences in parental care. This one is highly relevant, but the story is complicated, because it also has a lot to say about extremes of color polymorphism.

Here [12] is The evolution of female parental care in poison frogs of the genus Dendrobates; evidence from mitochondrial DNA sequences. This one uses direct genetic evidence to create a [phylogenetic tree]], showing that parental care evolved exactly once in this clade.

Now, TL:DR: all that research gives very strong for the genetic basis of parental care behavior in frogs, and the last paper is getting very close to identifying which genes are responsible.

I have interpreted your question as being specifically about genetic control of parental behavior in frogs. However, that is a very narrow question, and so there's less known about this particular thing, compared to the general concepts at play. If your interest is more about parental care in general, then we know lots more about that, including genetic basis, evolution, etc., but it is put together from a wide range of taxa (e.g. lots from birds and bugs). If your interest is more about genetic control of behavior in general, then again, we can get in to far more detail on that: we know remarkable things about what genes cause what behavior, and sometimes in great detail, e.g. in Drosophila. So, if you want to know more about these general issues, we can address that, but it might make sense to ask a new question in that vein. Hope this helps, SemanticMantis (talk) 15:53, 27 October 2017 (UTC)[reply]

@SemanticMantis thank you. It is very kind of you. I'm an MD but I'm involved in a different kind of research although connected to genetics. This is my only point of contact with the subject. This is my puzzle actually. Let's say this behavior is coded in the frog's DNA and it certainly is. Let's say the frog moves to the pool to release the tadpoles. How does it know that it has to move its hind legs at a certain place where the pass for them to escape is reasonably short? Is it also coded in the DNA? Then how? How does it know that it had finished the job and there is no need to dig further? Is it also coded? How? I am sure some hormones are involved in this behavior, it easy to imagine that perhaps a surge of Cortisol could start the behavior, to force the frog to move to the pool but how about the rest? --AboutFace 22 (talk) 18:01, 27 October 2017 (UTC)[reply]

David Attenborough has taken an interest in this [13]. 92.8.218.38 (talk) 18:40, 27 October 2017 (UTC)[reply]

I must confess this is a bit beyond my ken. We know that this behavior has a genetic basis, and we can fairly easily imagine how genes control simple behaviors. But this business with the frog nest is much more complex. My instinct is that to learn more about precisely how it is that genetics control complex behavior, you'll do better to look at organisms other than frogs. Mice are one model species of interest, since they are far more amenable to lab experiments, we have zillions of lines of knockout mice, and also a much longer history of studying mice. Stuff like this [14] is at least drilling down to documenting specific behaviors related to a specific locus, and in principle a detailed analysis of that gene and its expression could reveal how it is that it really "work" in situ.

The absolute best, most hard-core and iron-clad research on genetic control of behavior I know of is on honeybees, specifically the work of Gene_E._Robinson. Here [15] is only of his earlier key papers on the topic, but it is not freely accessible.

This really is a fascinating field, and I do think others might be able to provide better refs and explanations. That's all the time I have for today, but do consider asking a more general question on genetic control of complex behavior, maybe we can get more input, and next time I'll try to find some of the relevant stuff I've read about nest construction in birds. Cheers, SemanticMantis (talk) 19:57, 27 October 2017 (UTC)[reply]

@SemanticMantis, thank you. It is a lot of information --AboutFace 22 (talk) 19:54, 28 October 2017 (UTC)[reply]

October 26

Lead leaching out of metal

We sometimes fry things on a big slab of what seems to be carbon steel. Someone gave it to us from some plate steel place where they make stuff out of it, but not cookware. There are giant, thick sheets laying all over the place. It looks like steel or carbon steel or something. It rusts quickly but is nicely seasoned now and so is very non-stick. Do you think it's loaded with lead? Would lead leech out into the oil. Is there a way to test this? Anna Frodesiak (talk) 05:48, 26 October 2017 (UTC)[reply]

Your piece of steel plate is highly, highly unlikely to contain any lead. The only steel to contain lead is free-machining steel. This is a very specialised application for steel and there is no reason for free-machining steel to be rolled into flat plate. Alloying elements in steel, such as carbon and manganese, are tightly bound within the atomic lattice and they do not leach out of the steel. Dolphin (t) 06:28, 26 October 2017 (UTC)[reply]

Thank you very much, Dolphin51. :) Anna Frodesiak (talk) 08:43, 26 October 2017 (UTC)[reply]

Also, with a properly seasoned iron surface, the food never touches the actual metal. --Guy Macon (talk) 15:57, 26 October 2017 (UTC)[reply]

Yes, but that doesn't mean the two don't chemically interact. Iron can dissolve in the oil, and some of that gets in the food. This is actually considered a benefit of a cast iron pan, that they increase the iron content in your food. StuRat (talk) 16:33, 26 October 2017 (UTC)[reply]

Note carbon steel is the (current) most common material for making woks, Wok#Carbon_steel. May have been part of why the locals knew it was good for cooking. SemanticMantis (talk) 21:39, 26 October 2017 (UTC)[reply]

Thank you, all. Your helpful information led me to create Media related to Carbon steel at Wikimedia Commons and populate it and add the commonscat to the main article.

Now, I see Media related to Crystal structures of steel at Wikimedia Commons and wonder if any or all of those should have the carbon steel parent category added. Thoughts?

Oh, and they want to get rid of the refdesk because it doesn't help other parts of the project. Phooey to that. You folks are wonderful and so helpful. Anna Frodesiak (talk) 01:31, 27 October 2017 (UTC)[reply]

The articles listed under “Crystal structures of steel” are all eligible to be included under “Carbon steel”. Incidentally, I notice the heading “Perlite (Steel)”. This spelling is definitely incorrect because perlite is something of interest in geology. In the context of carbon steel the spelling should be “pearlite” and is so named because of its resemblance to mother-of-pearl when viewed under a microscope. Can you tweak the spelling? Dolphin (t) 07:10, 27 October 2017 (UTC)[reply]

Hi Dolphin51. Thank you! I've made the new cat, added the items to it, and speedy tagged the old one. I also fixed the article's commonscat.

Now, should I simply add carbon steel as a parent cat to Crystal structures of steel, or individually add carbon steel parent cat to Austenite, Bainite, Cementite, Ferrite (Steel), Ledeburite, Martensite, Pearlite‎? Best, Anna Frodesiak (talk) 00:33, 28 October 2017 (UTC)[reply]

I think it will be sufficient to add Carbon steel as a parent cat to Crystal structures. Dolphin (t) 11:11, 28 October 2017 (UTC)[reply]

Done! Thank you, my friend! Anna Frodesiak (talk) 13:30, 28 October 2017 (UTC)[reply]

Small linguistic remark: You mean leaching. "Leech" with the double-e is another thing entirely. --Trovatore (talk) 08:29, 27 October 2017 (UTC) [reply]

Ah, leaching, yes, of course. Thank you Trovatore. :) Anna Frodesiak (talk) 00:33, 28 October 2017 (UTC)[reply]

Mass to the Moon

I understand the moon is moving away from the earth by 4 centimetres every year, how much mass would have to be added or lost for it to stay in perfect orbit? JoshMuirWikipedia (talk) 12:59, 26 October 2017 (UTC)[reply]

Well, momentum is potentially unlimited, so if a well-placed alien has a sufficiently decent particle accelerator, and we wrap the Moon carefully in some sci-fi quality electrical tape to keep it from exploding, we ought to be able to knock it back where you want it with just a few protons. Of course, with current technology ... any method is impossible.

Also note this doesn't change the tidal acceleration; it would only be modifying the present orbit. The same should be true of any one-time mass impact. Wnt (talk) 13:31, 26 October 2017 (UTC)[reply]

Changing the mass wouldn't have any effect.

Sadly WP doesn't have a clear introductory article to this. Circular orbit is about the closest. Also Kepler's third law "The square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit." was determined by observation, before Newton had worked out the gravitational theory behind it.

For a simplified circular orbit, the period of that orbit

T=2\pi {\sqrt {\frac {a^{3}}{GM}}}

where:

$T$ is the orbital period
$a$ is the orbit's semi-major axis in metres (altitude from the centre of the Earth, in our simplified view)
$G$ is the gravitational constant,
$M$ is the mass of the Earth

So the Moon is moving away because it's slowing down. To bring it back, you'd have to speed it up. Andy Dingley (talk) 13:43, 26 October 2017 (UTC)[reply]

And the moon is slowing down because of gravitational drag due to tidal effects. Basically, some energy in the moon's motion is lost because it goes into distorting the earth's shape a bit. That lost energy causes the moon to slow down ever so slightly which causes its orbit to drift outward ever so slightly. This will not last forever, because other factors will lead to the moon-earth system becoming tidally locked so that there is no more drag on the moon. --Jayron 32 15:14, 26 October 2017 (UTC)[reply]

Wait, slowing down? No that's backwards. The moon is speeding up. (Higher orbits are faster orbits.)

It's speeding up because earth's spin (one rev/day. Fast) and the Moon's orbit (one orbit/month. Slow) are slowly converging. So the Earth is slowing its spin, while the Moon is speeding up its orbit.

ApLundell (talk) 15:56, 26 October 2017 (UTC)[reply]

Yes, of course. Damn sign conventions get me every time. My bad. --Jayron 32 17:33, 26 October 2017 (UTC)[reply]

I don’t think “higher orbits are faster orbits” is right. In the formula given above by Andy, the time period T is proportional to $2\pi a^{3/2}.$ Speed S = distance per unit time, so T = const × distance/ S where distance travelled is the circumference $2\pi a.$ Equating the two expressions for T gives $ka^{3/2}=a/S.$ So higher radius a is associated with lower speed S. Loraof (talk) 17:39, 26 October 2017 (UTC)[reply]

No, he's right. It's simple orbital dynamics. I've seen Buzz Aldrin (who did his PHD thesis on the matter) discussing it in layman's terms before; but the basic principle is faster = further out. When you are in orbit, and you increase your forward velocity, you move out in orbit. More kinetic energy = further from barycenter. This is true in any rotational system (that's why electrons with more energy are at further distances from the nucleus of an atom, for much the same reason) Thus if the moon is moving outwards, it must be doing so because it is moving faster. If you slow down, you move into lower and lower orbits; if you go too slow your orbit intersects the larger object and you crash into it. --Jayron 32 17:45, 26 October 2017 (UTC)[reply]

You’re describing speed between orbits. For objects in orbit with no externally imposed acceleration (other than gravity maintaining a given orbit), my math looks correct to me. Examples of orbital speed around the Sun: Earth 29.78 km/s; Mars 24.07 km/s; Jupiter 13.07 km/s. I was objecting to the statement “higher orbits are faster orbits”. Since the Moon is continually changing orbit, so to speak, part of its speed is not speed of orbit. Loraof (talk) 18:05, 26 October 2017 (UTC)[reply]

You know what, forget me again. I really shouldn't get involved in these problems. I'm such an asshole. --Jayron 32 18:17, 26 October 2017 (UTC)[reply]

No, you’re not – you’re far and away the most helpful person on these ref desks. And your last comment was valuable in clarifying the difference. Thanks for all your work here! Loraof (talk) 18:24, 26 October 2017 (UTC)[reply]

If you add mass to Earth instead of the Moon and do it gradually then it might work. PrimeHunter (talk) 15:47, 26 October 2017 (UTC)[reply]

The moon is actually gaining energy from the rotation of the earth via the leverage of the tidal bulges (the earth's rotation drags these around so that they are ahead of the moon). Perversely (but in accordance with the virial theorem), for every one unit of energy transferred from the earth to the moon, the moon spends two units of energy in climbing higher: the one it got from the earth plus one from its own store of kinetic energy - so it ends up going slower. --catslash (talk) 16:47, 26 October 2017 (UTC)[reply]

As is always the case with questions like "what would happen to [gravitational phenomenon] if we added mass to [celestial body]", the answer is: it depends on how the mass is added. The above answer (in particular AD's) give the answer with the assumption that mass is instantaneously added with no change in any of the velocities at that instant. Tigraan^{Click here to contact me} 18:43, 26 October 2017 (UTC)[reply]

Given

Moon's radius 1757.1 km

Moon's mass 7.342E22 kg

the Moon's center of gravity can be moved about 4 cm closer to Earth by adding a mass (7.342E22 x 0.04)/1732.1E3 = 1.70E15 kg on the side facing Earth, taking care to match velocities before contact. Continual deliveries of 2E11 kg every hour (the US annual waste production) might be a nice way to keep the Moon's orbit constant. Blooteuth (talk) 19:12, 26 October 2017 (UTC)[reply]

People think the moon is speeding up because the lunar month is getting shorter. What is actually happening is that the moon is slowing down but our clocks are also slowing down because of the tidal drag (as measured by successive transits of the meridian by the sun, mean solar time). The clocks are slowing faster than the moon, so it appears to be going faster. 92.8.218.38 (talk) 14:15, 27 October 2017 (UTC)[reply]

Kepler's third law requires that "the square of the orbital period of a planet is directly proportional to the cube of the semi-major axis of its orbit." Hence we have

{\frac {T^{2}}{a^{3}}}={\frac {4\pi ^{2}}{G(M+m)}}\approx {\frac {4\pi ^{2}}{GM}}=\mathrm {constant}

where M is the mass of the Sun, m is the mass of the planet, and G is the gravitational constant. When this law is applied to any two masses, the constant of proportionality has, in turn, a value that changes with the system's total mass M + m. Thus changing the Earth-moon system's total mass in any way has to change either the system's orbital period, the distance of their semi-major axis or both in order for Kepler's law to remain valid. With the problem at hand, if the angular momentum of the original Earth and moon masses are conserved then we also require that

{\frac {a^{2}}{T}}=k

where k is a constant. In other words, as their orbit about their common barycenter becomes more distant their orbital period is longer (as noted by others above). Consequently, solving these two equations shows that increasing the system's total mass will arrest their separation and shorten the lunar months (such that Kepler's third law holds). It's not a difficult calculation, but I haven't a lot of patience to punch in the numbers to determine how much mass would need to be added from afar each year, but you can have a go with it by first calculating the conservation constant for the current Earth-moon system as it now stands and plugging away into the following:

\Delta M={\frac {(2\pi *k)^{2}}{G\left(a+\Delta a\right)}}-(M_{1}+M_{2})

-Modocc (talk) 04:59, 28 October 2017 (UTC)[reply]

Hydraulic motors

Why are hydraulic motors not more popular for vehicles? Hydraulic pump and motor pairs seems to be a very efficient way to transmit motive force from an engine to wheels. It eliminates friction losses from multiple gears, shafts and other moving parts in conventional transmission systems, and also weighs much less. I get the idea I'm missing information about one or more major disadvantages that explain why it's so rare. Roger (Dodger67) (talk) 19:01, 26 October 2017 (UTC)[reply]

Hydraulic linkages are indeed efficient and are employed in automatic transmissions. But your vehicle will need a prime mover i.e. a motor that converts energy from a source energy into mechanical energy. What source energy would you like to pay for? Blooteuth (talk) 19:25, 26 October 2017 (UTC)[reply]

Blooteuth I'd imagine an internal combustion engine driving a hydraulic pump would be the most obvious prime mover. The hydraulic linkage within a conventional transmission just one small component, I'm wondering why hydraulics are/were not used far more to basically eliminate almost the entire mechanical gear-and-shaft based drivetrain between engine and wheels? In recent years of course eletric drive has become far more efficient with hybrid IC/battery or even pure battery driven vehicles becomming more common. Hydraulics just seems to have never been considered a viable replacement for the conventional drivetrain. Roger (Dodger67) (talk) 19:43, 26 October 2017 (UTC)[reply]

Don't confuse hydrostatic transmission with hydrodynamic. Hydrostatic transmissions (pump and motor) are limited in power, speed and efficiency. They're mostly used when controllability is important, or high force vs. speed. They can also make accurate positioning mechanisms, as well as continuous rotation.

Hydrodynamic transmissions are those involving fluid couplings, torque converters and the transmissions of diesel-hydraulic locomotives are quite different. They can transmit high powers (multi-thousand horsepower) at high speeds, and are lighter, simpler and more compact than comparable diesel-electric transmissions. Andy Dingley (talk) 20:11, 26 October 2017 (UTC)[reply]

One problem with hydraulics is that they behave differently at different temperatures. Fluid viscosity changes, volume changes, etc. Thus, a cold vehicle would drive very differently than a hot one. There are ways to compensate for this, within limits. StuRat (talk) 03:08, 27 October 2017 (UTC)[reply]

Hydraulic fluids in power transmission systems operate at a fairly constant temperature, set by their cooling systems and thermostats. They are heated by use plenty to rise above ambient. If they're in a cold climate, they may be pre-circulated beforehand, just to warm them. Andy Dingley (talk) 13:58, 27 October 2017 (UTC)[reply]

Yes, and preheating is fine for, say, a crane, but car owners neither want to wait to preheat the hydraulics nor pay to keep them heated at all times. So, one point against hydraulic cars. StuRat (talk) 22:45, 27 October 2017 (UTC)[reply]

There are no hydrostatic cars. Nor are there going to be. Andy Dingley (talk) 22:56, 27 October 2017 (UTC)[reply]

Agreed. Of course, if we are looking at this from a historic perspective, then hydraulics might have worked better with steam engine cars, since they also require preheating. StuRat (talk) 23:03, 27 October 2017 (UTC)[reply]

What possible benefit would a hydrostatic transmission convey to a steam-powered vehicle? They already have the advantages of a hydrostatic drive (the ability to generate considerable torque from zero speed, without needing any transmission) as they are. If you can cite all these "hydrostatic transmission steam cars", then please do so. Andy Dingley (talk) 10:01, 28 October 2017 (UTC)[reply]

I found Human Friendly Transmission, used by Honda in a few motorcycles. Roger (Dodger67) (talk) 06:16, 27 October 2017 (UTC)[reply]

That is a continuously variable transmission (i.e. a continuous-ratio gearbox), which makes up only a small part of the drivetrain. An important part of OP's question is why isn't most / all of the drivetrain made by hydro links, which presumably have less friction (hence power losses) than mechanical drivetrains. (I do not have a clue.) Tigraan^{Click here to contact me} 11:26, 27 October 2017 (UTC)[reply]

In case there's some confusion, Roger is the OP. Nil Einne (talk) 11:37, 27 October 2017 (UTC)[reply]

October 27

Zero living diet

Are there any foods that have never lived? Meaning, no animals, plants bacteria etc. Would it be possible to live on such diet?

Water... most people might last a few weeks. Roger (Dodger67) (talk) 06:18, 27 October 2017 (UTC)[reply]

Only prokaryotes can do that, they have the enzymes to take in abiotic chemical compounds and make all the stuff they need. Eukaryotes are dependent on other organisms for their survival, e.g. they can't make vitamin B12, they don't have the enzymes for nitrogen fixation either, so they are dependent on prokaryotes for their amino-acids. Count Iblis (talk) 06:32, 27 October 2017 (UTC)[reply]

It is possible to make synthetic fatty acids [16] - mercifully, it doesn't seem to have caught on; I guess the odd-numbered ones did not even meet up to the standards of the trans fat era. Synthetic sugars are harder. [17] Vitamin supplements are an issue, yet some are produced synthetically. There is no theoretical reason why such a diet cannot be produced (though you might need to go off-planet to find carbon you are somewhat confident 'never lived'), but it would be exceedingly difficult, so I would not expect the first test subjects to live long. Also note that ethane, present on Titan, is metabolized by the rat [18] so at least some "foods" presently exist that match this criterion, though it would be poorly nutritious and a bit over-chilled on the palate. Wnt (talk) 11:03, 27 October 2017 (UTC)[reply]

There are many kinds of extremophiles that live on, for example, organic chemicals that seep into the oceans from mid-oceanic hydrothermal vents. Chemosynthesis would be the term. As to the main question, no, it is not possible for you as a person to live on food which has never lived. Excepting certain dietary minerals, which do not provide energy to your body, food entails life. All food must have been living at some time previous, for any reasonable definition of "previous". Some foods are currently living. Indeed, many raw plant foods we eat are alive while we consume them. --Jayron 32 11:06, 27 October 2017 (UTC)[reply]

Can we say that plants have a diet of non-living food? I mean they just need water and minerals from the ground, CO2 in the atmosphere, and sunlight for energy. I guess the question is more about whether you accept that plants "eat" at all.— Preceding unsigned comment added by Lgriot (talk • contribs)

Well, that's it. We need to define "eating". I mean, I would define that as ingesting a substance for the purpose of obtaining energy and building materials. There are other forms of ingesting we do (drinking, smoking, taking medicine or vitamins) which we don't call eating. Wikipedia's article on eating specifically excludes most plants, since plants are autotrophs. If you change the definition of eating, then sure, you can define plants as eating. But really, if you can just change the definitions of words to fit your needs, you can "prove" anything with those words. --Jayron 32 14:42, 27 October 2017 (UTC)[reply]

Note that plants depend on bacteria to do the nitrogen fixation necessary to make amino acids. Count Iblis (talk) 18:00, 27 October 2017 (UTC)[reply]

The answers to a similar question from 2014, Wikipedia:Reference_desk/Archives/Humanities/2014_August_14#Non-living_food, may be of interest.--Wikimedes (talk) 18:39, 27 October 2017 (UTC)[reply]

There aren't any foods currently consumed that have never lived, but it would be possible in principle in make some. Probably the easiest, as far as I can tell, is ethanol -- which in spite of its use as an intoxicant is actually a high-calorie food source. Other edible foods can be made by artificial photosynthesis or chemical synthesis, for example simple sugars such as glucose, but the process is very expensive. Looie496 (talk) 21:14, 27 October 2017 (UTC)[reply]

There are many minerals which, by definition, are produced by inorganic processes. Sodium, iron, calcium, potassium, etc. These are essential parts of the diet, but obviously not sufficient alone. Of course, just like with carbon, they may have been part of a living organism at some point in the past. StuRat (talk) 22:50, 27 October 2017 (UTC)[reply]

October 28

How many N-receptors are there (2 or 3?)

I was reading different sources about the number of the N-receptors (nicutinic receptors) among the cholinergic receptors. The most of the sources say that there are 2 nicutinic receptors (N1 and N2) but other source says there are 3 nicutinc receptors: "Nicotinic receptors are found in the CNS, in autonomic ganglia, and in striated muscle. They are divided into N1, N2, N3-cholinoreceptors. N1 - and N2 -cholinoreceptors are localized in the CNS, N1 -cholinoreceptors – in ganglia, N2 -cholinoreceptors – in muscular synapses, N3-cholinoreceptors – in the adrenal glands. The mechanism of nicotinic action has been clearly defined." Is that correct?--212.90.60.81 (talk) 04:08, 28 October 2017 (UTC)[reply]

We have a detailed article about Nicotinic receptors (note spelling). It categorizes them into two major groups based on location—muscular vs neuronal—and then further into ganglion-type and CNS-type of neuronal. It not mention a type specific to adrenal-gland location and does not use N1/N2/N3 terminology at all. Could you cite the source you are quoting so we can see context and if it cites other refs for us to read? DMacks (talk) 04:25, 28 October 2017 (UTC)[reply]

If you want other sources than our article, see "Mammalian Nicotinic Acetylcholine Receptors: From Structure to Function", most recent review I could find in two minutes on PubMed. Look at tables 1 and 2. Fgf10 (talk) 10:30, 28 October 2017 (UTC)[reply]

Physical exertion causing rheumatism

This comes from the 19th-century book that I referenced in the toothache question of Wikipedia:Reference desk/Archives/Science/2017 October 8. I've got someone born in 1811 who moved to Iowa in 1851 and lived there until his 1880 death, and about him it's said:

The exposure which he was required to endure in a new country and among scattered societies, caused inflammatory rheumatism, which completely wrecked his physical frame, and the last ten years of his life were spent in intense bodily suffering.

Can the environment or physical exertion cause rheumatism of any sort? Apparently it can't cause rheumatoid arthritis, since Rheumatoid arthritis#Risk factors for this autoimmune disease are all irrelevant for a preacher in 19th-century Iowa who rejected drinking and smoking as sinful. I'm guessing that our Iowa friend got some sort of illness along the way (per the first sentences of Rheumatism#Types), or that he had an autoimmune disease that simply started after he moved. Is this a reasonable conclusion? Nyttend (talk) 13:16, 28 October 2017 (UTC)[reply]

I think the article rheumatism is pretty clear -- it's a generic term for pain. Serious physical exertion might cause osteoarthritis, either directly or as the result of physical injury to the joints. Damage to the sacroiliac joint or to the spine itself might cause sciatica or related conditions. There are a lot of options and I certainly can't diagnose a sentence (and am not qualified to diagnose a patient either). But going from rheumatism to rheumatoid arthritis specifically seems like a vulgar error. Wnt (talk) 15:19, 28 October 2017 (UTC)[reply]

Without knowing where this unfortunate person was and the nature of the terrain, it's impossible to even guess. It's possible it might have been what we now know as Lyme disease. When I received the diagnosis of RA, I was told that there are hundreds of conditions that all get lumped together as "rheumatoid arthritis" for ease of discussion. What might shed light on whether it was rheumatoid arthritis is a trace of his descendants and looking at their medical history, to see if any of them had rheumatoid arthritis or not. (OR here, well it's not my research but... I am currently taking part in a clinical trial to establish the degree of hereditability of RA, and as part of that, I have found this horrible disease seems to have affected at least 4 out of the past 6 generations of my family, up to and including myself.) --TammyMoet (talk) 10:42, 29 October 2017 (UTC)[reply]

Time for Wow signal to reach Earth

Assuming it was genuine, approximately how many years it took for Wow signal to reach the Earth? If there's an RS, one might want to add it to the article. Thanks--212.180.235.46 (talk) 17:44, 28 October 2017 (UTC)[reply]

Depends on which star it (might have) come from. The article on Wow says that the closest easily visible star in the direction of Wow is Tau Sagittarii. The article on that star says that it is 122 light years away. But that is just a possible answer to your question,!of course. Attic Salt (talk) 17:54, 28 October 2017 (UTC)[reply]

And, in case it's not obvious, it would take a signal 122 light years away 122 years to reach us, at the speed of light. StuRat (talk) 16:02, 29 October 2017 (UTC)[reply]

October 29

E-Z notation: why not just use "cis" and "trans" as infixes?

(Z)-1-Bromo-1,2-dichloroethene could just be bromotransdichloroethene.

Are there any cases in which cis-trans notation would still be ambiguous if -cis- and -trans- were used as infixes before pairs of substituents? For example, (Z)-1-Bromo-1,2-dichloroethene could just be called bromotransdichloroethene. (Note the advantage of also being able to eliminate the numeric infixes in that case, since 1,1-dichloro wouldn't be transdichloro.) Likewise, the haloalkene with SMILES C(/Cl)(\Br)=C/F would be 1-chloro-cis-1-bromo-2-fluoroethene. Neon Merlin 11:59, 29 October 2017 (UTC)[reply]

I think it is hard to answer this sort of "why didn't they do it like that?" question. The rules used have some arbitrary components. At this point though, practically, suppose someone introduces your rule. What does it mean? Well, sometimes you can use it, sometimes you might use it, often you would encounter things labelled with E/Z notation. So it means we have to learn your scheme and how to apply it to compounds like [19] with four different kinds of atoms attached to the double-bonded carbons (which is actually not recommended according to our cis-trans article) and whether the "cis" applies to the thing directly after it or the two things in the "di" or ... whatever. And then we also have to be ready to understand E-Z notation. Which amounts to more trouble to learn, more entries in the tables of synonyms in a PubChem entry (exponentially more, since this permutes with every other arbitrary decision we make between naming systems), more errors. I think many people would not be pleased to encounter this kind of creativity in their chemical closets. Wnt (talk) 15:52, 29 October 2017 (UTC)[reply]

@@ Line 243: / Line 243: @@
 Assuming it was genuine, approximately how many years it took for [[Wow signal]] to reach the Earth? If there's an RS, one might want to add it to the article. Thanks--[[Special:Contributions/212.180.235.46|212.180.235.46]] ([[User talk:212.180.235.46|talk]]) 17:44, 28 October 2017 (UTC)
 :Depends on which star it (might have) come from. The article on Wow says that the closest easily visible star in the direction of Wow is Tau Sagittarii. The article on that star says that it is 122 light years away. But that is just a possible answer to your question,!of course. [[User:Attic Salt|Attic Salt]] ([[User talk:Attic Salt|talk]]) 17:54, 28 October 2017 (UTC)
+:And, in case it's not obvious, it would take a signal 122 [[light year]]s away 122 years to reach us, at the [[speed of light]]. [[User:StuRat|StuRat]] ([[User talk:StuRat|talk]]) 16:02, 29 October 2017 (UTC)
 = October 29 =