Wikipedia:Reference desk/Archives/Science/2017 October 25

= 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)
 * 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)


 * Here 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  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)

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)
 * 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)
 * 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)
 * 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)
 * (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)


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


 * Gravity assist 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)
 * 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)
 * 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)

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)
 * 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 <b style="color:#090">32</b> 15:28, 25 October 2017 (UTC)
 * 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)
 * 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 <b style="color:#090">32</b> 17:24, 25 October 2017 (UTC)
 * 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)


 * 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)


 * 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)
 * 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)
 * You can get some idea of what they're talking about here: . 92.8.218.38 (talk) 14:29, 27 October 2017 (UTC)
 * 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)
 * Thank you very much! In accordance with your comments, I have commented out the relevant statement at least. As I do not have enough sound knowledge of this topic, I am afraid that I cannot do much more to improve the said article. Best wishes--Cleph (talk) 17:32, 29 October 2017 (UTC)

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)


 * 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)

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


 * 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, 26 October 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)
 * 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, 27 October 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, 27 October 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, 26 October 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)


 * Some relevant info at Frog. I don't think this was staged at all, I think this is the common method of care. Here 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  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)

@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)


 * 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)


 * , ah, sorry, '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 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 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 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)

@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)


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


 * 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 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  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)

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