Wikipedia:Reference desk/Archives/Science/2012 August 30

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August 30

Star positions in the past

Is there a website or a software that's capable of telling me where were certain stairs on the sky in a given year (e.g. in 1400)? 193.224.66.230 (talk) 13:11, 30 August 2012 (UTC)

This page will do it, but it's a bit tricky to navigate. Page down to the "virtual telescope" and select the "controls" link to set the date and time you wish to look at the sky for. The Earth's view of the stars has changed over time, but I think that a difference of 600 years isn't going to have changed it much; excepting the locations of the planets and comets and things like that. The star map would only look noticibly different on scales of 1000s of years or 10,000s of years. --Jayron32 13:18, 30 August 2012 (UTC)

Celestia. If you haven't used it before, and you're at all interested in space, you're missing out. I agree that 600 years isn't enough to see the stars move noticeably. To get a sense of how slowly they move, Barnard's star, the star with the highest proper motion, moves 3 degrees in 1000 years. Almost every other star moves many times slower than that. You can use Ptolemy's star charts today and they wouldn't seem wrong. --99.227.95.108 (talk) 15:40, 30 August 2012 (UTC)

As far as I can tell, Celestia doesn't model proper motion. TenOfAllTrades(talk) 21:23, 30 August 2012 (UTC)

I'd go with Stellarium as it's probably the easiest program to get the hang of. (There are download links on the article page.) But as said above, there wouldn't be a noticeable difference in the positions of stars over a 600 year period. FlowerpotmaN·(t) 19:04, 30 August 2012 (UTC)

Attractiveness

Is attractiveness subjective? From my understanding, attractiveness is based on certain dimensions an proportions of the face and body of a person. However is this subjective? And if so, are there certain faces, which people universally find attractive or unattractive? Clover345 (talk) 15:16, 30 August 2012 (UTC)

Physical attractiveness has both objective and subjective components. That is, there are some trends and nearly universal principles, but there are also many factors that are determined by individual taste, and will vary culturally or even person to person. --Jayron32 15:54, 30 August 2012 (UTC)

You may be interested in research on facial attractiveness [1]. You can also participate in real research at that site, making your preferences part of the process. Recently, many different studies have demonstrated that averaged faces are rated as more attractive than the average of many facial attractiveness ratings. This starts to get at "universally attractive" faces, but as Jayron points out, there will always be a large degree of subjectivity in attractiveness. Google /average face attractive/ for many news and pop-sci accounts. SemanticMantis (talk) 18:09, 30 August 2012 (UTC)

Physical attraction is an objective quantity.

F = G m₁ m₂ / r².

However the Greater Internet Uncertainty Principle states that you can know either m₁ or m₂ but not both. Good luck, as escape velocity is a known issue with internet dating. ;) 217.251.154.242 (talk) 07:02, 31 August 2012 (UTC)

Forget it, I will NOT add a link to "Spherical Cow Approximation."

You shouldn't ever call a girl that, you know... --Jayron32 14:15, 31 August 2012 (UTC)

A friend of mine once described fellatio from a spherical cow as like sodomizing a bowl of room temperature oatmeal. That seemed rather objective to me. μηδείς (talk) 21:59, 31 August 2012 (UTC)

Star Gazing Hobby

I want to start this hobby but with the meager savings I have. I will like to purchase a used telescope on eBay however I don't know where to begin to look or what to look for. Please give me any suggestions on how to start my hobby the right way Reticuli88 (talk) 16:25, 30 August 2012 (UTC)

One option is to see if a local astronomy club exists. Near where I live, the Morehead Planetarium and astronomy department at the University of North Carolina sponsors a monthly stargazing night at Jordan Lake, far enough away from light sources but close enough to see some cool stuff. They bring some really powerful telescopes and set them up on the beach, and it doesn't cost anything to come by and use their telescopes. This google search turns up a wealth of other similar arangements. --Jayron32 16:49, 30 August 2012 (UTC)

I strongly second Jayron's suggestion. Speaking as someone who read Astronomy at University and helped to run a local Astronomy Club myself, I'd say it would be near-impossible for someone new to the activity to choose with confidence an appropriate instrument from eBay or similar sites. You may be able to track down a local club from the back pages of Sky and Telescope or a similar magazine. Alternatively, if you can get to a specialist Astronomical Telescope vendor, they're likely to give you reliable advice because they'll be hoping to get repeat business from you when, as is likely, you trade up to better/more expensive equipment. {The poster formerly known as 87.81.230.195} 84.21.143.150 (talk) 17:16, 30 August 2012 (UTC)

The beauty of astronomy is that it can be done purely with the eyes alone. Learn the patterns of the constellations: learn the planets, what they look like in the skies: try and see how many of the Seven Sisters you can see with the naked eye (northern hemisphere only). If you get a cheap pair of binoculars from Ebay second hand, you can see details in some of the globular clusters. Be warned, however: you will never see the range or depth of colours you see in the professionally produced deep sky photos. I have known some enthusiastic amateurs give up when they realise that. --TammyMoet (talk) 18:38, 30 August 2012 (UTC)

Other people have written much more about this exact subject than we possibly can. See, for example, this Sky&Telescope article. --99.227.95.108 (talk) 03:48, 31 August 2012 (UTC)

I can tell you from childhood experience that a small refracting telescope will probably be worth far less than you would pay for it. You might as well get a good pair of binoculars. A friend's father had a six inch reflecting telescope. Due to its mass it was much more stable, and you could see the disks of planets which were mere dots with my "telescope". μηδείς (talk) 05:28, 31 August 2012 (UTC)

Check out Ice In Space, it's a huge website full of amateur astronomers and astro photographers. They have lots of "beginners" articles and a massive forum for support ranging from the very basics all the way to people who have had pictures published on NASA's APOD. I now own a 12" dob, but I started with a pair of 8x56 binoculars which I still use every time I go observing. That's the thing with a pair of binoculars, getting a telescope later won't make them obsolete, you'll still use them regularly to spot things or get a wider field of view, so they really are a good way to start rather then a cheap telescope which at best will become obsolete if you decide to buy a better one and at worst will be crap and will put you off entirely. Vespine (talk) 23:17, 2 September 2012 (UTC)

Raptor factoid

Concerning fish-eating raptors, such as Ospreys and Sea eagles that hunt by swooping down and grabbing fish from the water with their talons... any truth to the oft-quoted fact(oid?) that because the bird is allegedly physically unable to unclench its feet whilst they're embedded in the prey's flesh and let go, unless it returns to dry land, that if the bird happens to 'attach' itself to a fish that's too large to carry, that it will probably either drown on the surface due to becoming waterlogged - still attached to a dead fish, or be dragged under by the fish as it tries to escape - and drown that way?

I'm aware that these birds can only swim a little and do sometimes drown after miscalculating/missing their prey, getting too wet to fly and being trapped on the water's surface but that would seem to be a different scenario. --Kurt Shaped Box (talk) 20:06, 30 August 2012 (UTC)

I call shenanigans. What's so different about being on land? Does the bird have to eat the fish away from its claws before it can use them again? I think not. I think the claim is based upon a nugget of truth: the way raptor talons work. But the claim takes it to a silly extreme, and is also influenced by your observation that yes, these birds do sometimes drown.

The key principle is that raptor talons are similar to ice hooks, like this one [2], in the sense that they convert downward force (supplied by gravity and the ice/fish) into a compressive force of the hooks on the load. This means they can carry heavy things without using any more energy to grip than they would for lighter things (of course it still takes more energy to lift). This does mean that it's difficult to release under load, but it doesn't mean it's impossible. And if the fish is still in the water, it's not putting much load on the talons yet anyway. You may also be interested in this nice (freely accessible) paper "Predatory Functional Morphology in Raptors: Interdigital Variation in Talon Size Is Related to Prey Restraint and Immobilisation Technique" here [3]. SemanticMantis (talk) 17:24, 31 August 2012 (UTC)

Why did people in the late 1800s think an aether was necessary for the propagation of light, when Maxwell's equations show that this is unnecessary?

Maxwell described light as an electromagnetic disturbance of self-propagating E and H fields. Surely people in the late 1800s knew that magnetic and electric fields could exist in vacuum. So why did they think an aether was necessary to "carry" light waves? 71.207.151.227 (talk) 20:11, 30 August 2012 (UTC)

It is not self-evident that electric and magnetic fields can exist in a vacuum, even if you have Maxwell's equations in front of you. This requires careful, meticulous understanding of the equations, and of course the equations require a lot of experimental effort to validate. Among the relevant work that helped establish this fact: the Michelson-Morley experiment, which you've undoubtedly read about; and the experiments that established Vacuum permittivity and Vacuum permeability constants. Maxwell's original work, A Dynamical Theory of the Electromagnetic Field, which you can read online, was a study of the relationships between electric fields and magnetic fields and charges. It is not immediately obvious, just from that work, that his work implies propagation of energy in a vacuum. The science developed; the theories became more perfect, and the experiments continued to validate assertions; and eventually the majority of scientifically-minded people accepted as fact that there need not be any transmission medium to hold the fields. We can say that Faraday and Coulomb discovered these facts; but that's almost irrelevant: at what point did the consequences of these facts become well-known? There's hardly a single instant when we can say "this was the moment that people understood that electromagnetic waves propagate in vacuum." Nimur (talk) 20:34, 30 August 2012 (UTC)

The fact that waves propagate in a vacuum feels intuitively wrong when you consider what a wave is: it is a rhythmic motion that propagates through something. When light displayed wave-like properties, people began to ask "what is it propagating in". The Maxwell equations don't require a medium, but people's expectations did. --Jayron32 21:32, 30 August 2012 (UTC)

"It is not self-evident that electric and magnetic fields can exist in a vacuum.." What decade of the 19th century were the experiments done, with vacuum pumps and bell jars, to prove that magnets worked just fine in vacuum, and that electric fields in a vacuum affected charged objects? I suppose one could cavil that the bell jar vacuum is imperfect compared to the vacuum of outer space. Faraday found magnetic effects in a Torricellian vacuum (like the inside of a mercury barometer above the mercury) (p 194) in his research published as a collection in 1855, but much of the research was done and published earlier. Didn't anyone experiment in the mid or early 1800's with electrified objects in a high vacuum jar to [rove the functioning of electric fields? The writings of Brewster suggest so, though he wrote mostly about discharge and glow effects in vacua. rather than basic attraction and repulsion experiments as done in air. They knew by the 1830's that a charged object would discharge and that charge could be transferred in a Torricelian vacuum. Anyone calling himself a physicist or "natural philosopher" by 1860 would likely have been familiar with this. Edison (talk) 00:40, 31 August 2012 (UTC)

Lots of people experimented with discharges and vacuums, but it was harder than you let on to get a good vacuum in the 19th century. If your vacuum was poor, you got very messy results — the gas inside the tube would ionize, for example, insulating the discharge stream, and give you completely the opposite conclusion. The fundamental work done that established that indeed, cathode rays were affected magnetically was done only in 1896, by J.J. Thomson, and was part of the discovery of the electron. The real breakthrough experimentally was creating an unambiguously good vacuum, something that evaded even the great German experimentalists like Hertz and Lenard. All of which to say is — the point at which it became unambiguous was really quite late into the game, just a few years prior to Einstein and all that. The limitations were for the large part technical. --Mr.98 (talk) 00:56, 31 August 2012 (UTC)

I think two different meanings of vacuum are used here; "It is not self-evident that electric and magnetic fields can exist in a vacuum.." refers to an "absolute" vacuum (without aether). But in those days it was assumed that aether was still present in a vacuum, only air (gasses) was removed. As Newton wrote: "a much subtiler Medium than Air, which after the Air was drawn out remained in the Vacuum" Ssscienccce (talk) 15:12, 31 August 2012 (UTC)

Because it was known that according to Maxwell's equations, EM waves travel at a specific, finite speed c. The question immediately asks itself: relative to what? Usually, if you have a speed, you must have some definition of a stationary point with v=0. Defining stationarity at every point in space gives you a sort of aether. Of course, we know now that the speed of light is invariant and comes out the same for all observers. However, this requires us to give up any notion of absolute time, stationarity, and a lot of other notions in order to formulate special relativity. It seemed far more parsimonious to keep Newtonian physics and to suppose that light travels through an aether, than to eliminate the aether and also throw out all the known laws of mechanics. Given what was known at the time, I think this was a reasonable application of Occam's razor. --Amble (talk) 00:47, 31 August 2012 (UTC)

Just a point: the constancy of c was not in fact known until the late 19th, early 20th century. This was part of the point of Michelson-Morley. --Mr.98 (talk) 00:56, 31 August 2012 (UTC)

The constancy of c (or $1/{\sqrt {\epsilon _{0}\mu _{0}}}$ or however you want to write it) is a property of Maxwell's equations. To someone ignorant of later developments (such as Maxwell himself) the theory looked mathematically like a description of transverse sound waves in a solid, and it was natural to wonder about the properties of that solid, including its state of motion. -- BenRG (talk) 02:54, 31 August 2012 (UTC)

As I said, the invariance of c was not known until later. The fact that it's a constant comes out of the equations, and it was natural to take it as a constant velocity relative to some medium, as with other waves. Hence, the aether. --Amble (talk) 07:04, 31 August 2012 (UTC)

Sorry, what I meant was, this wasn't experimentally confirmed until much later than Maxwell. There were plenty of folks at the time who still thought this might be an open question until the measurements had come in. It was a hard thing to measure, obviously. --Mr.98 (talk) 14:46, 31 August 2012 (UTC)

That's why I said "according to Maxwell's equations." --Amble (talk) 15:26, 31 August 2012 (UTC)

Maxwell himself used the idea of the aether as a way to think through how the world worked. It was a visual metaphor to use as a means of interrogating nature. (Maxwell's own visualizations of the aether are amazing — pulleys and gears and whatnot. See figure 2 here. Very industrial age U.K.) Maxwell derived all of his original equations from these sorts of models, and had tremendous success with them. (The version of Maxwell's equations you are now familiar with are not Maxwell's own; they were re-written by Heaviside and others some time later.) When you get success out of a model, you don't turn around and throw out the major components of it immediately afterwards.

For the physicists of the day, the aether was actually considered a brilliant theoretical innovation. It was more than just the medium through which light moved — it was the interface between the world of electromagnetism and the world of matter. The theorists of the day came up with beautiful, elegant, and totally physically sensible models about how all matter arose out of whorls and knots in the aether; how this sublime otherworldly realm of pure energy lent itself towards the manifestation of all that we are and can observe. They saw it not as an appendage onto Maxwell's equations, or as an extremity on to the physical universe, but as a supremely elegant concept that also made good intuitive sense (light is a wave in something, right? Who's heard of a wave in nothing?). Beautiful physics came out of it. The problem was, well, it didn't exist, it wasn't necessary, and in fact they were going about it all the wrong way. We know that now, and it's hard to put yourself in the head of someone then, but look at the aether as the original theory of everything, the one-stop theoretical shop for All of the Rest of Physics. --Mr.98 (talk) 01:08, 31 August 2012 (UTC)

Honestly, not much has changed. The modern quantum vacuum has a lot of structure, and any particle physicist will tell you that particles are oscillations of the vacuum, not objects in the vacuum. The vacuum is similar enough to a solid that many phenomena of fundamental quantum field theory appear also in solid-state physics. The vacuum undergoes phase transitions, like the Higgs field condensation that breaks electroweak symmetry. Mechanical analogies haven't died. Quantum Field Theory in a Nutshell by Anthony Zee introduces the field as a "mattress" of weights connected by springs. It seems unlikely that the world really is a mattress simply because Lorentz invariance unifies space with time, and it would be strange if at a deep level space and time are aspects of the same thing but at an even deeper level they're not. There are hints (from gravitational holography and AdS/CFT) of a radically different underlying structure for the world. But the best modern theories of fundamental physics (general relativity and the standard model) are still mattress-based. In fact the next thing Zee does after introducing the mattress analogy is complain about the lack of anything better. -- BenRG (talk) 02:54, 31 August 2012 (UTC)

would maxwells aether be able to penetrate a black hole or its event horizon?GeeBIGS (talk) 04:04, 31 August 2012 (UTC)

Read Luminiferous aether and it should clear up any questions. The problem with the idea was that it had to be infinitely dense and infinitely malleable, which kinda doesn't work. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:27, 31 August 2012 (UTC)

Again, anyone who replies, "obviously it doesn't work" doesn't really understand it. Henri Poincaré and Hendrik Lorentz thought it worked and made sense; they were much smarter, and much deeper, than you or I. It is unilluminating to dismiss in a flip way ideas that were highly persuasive to luminaries in the not-even-that-far-back past. (Additionally, that article does not clear up the question about black holes. I have no idea how you'd make an aether world view compatible with a black hole. The former worldview was abandoned before General Relativity and my guess is that it is probably not easily compatible with it.) --Mr.98 (talk) 14:51, 31 August 2012 (UTC)

I do. The black hole is so dense that it forces the aether out of that space entirely.165.212.189.187 (talk) 15:04, 31 August 2012 (UTC)

I'm pretty ignorant about this, so take with a grain of salt, but my impression/recollection is that...

• versions of the aether that "work" with changing perspective are based on Fresnel's 1818 Aether drag hypothesis, which postulates that there is more "aether" inside glass than inside air.
• Some people, somewhere, I know not who, have tried to describe electromagnetic forces as curvature of space in some other dimension, just as gravity is described, so that objects subject to such forces actually follow straight paths (geodesics) just like objects subject to gravity.
• I would assume ...... that just as gravitational waves are transmitted as waves within the underlying spacetime (note that that is definitely a speed-of-light, inverse square transmission which by all contemporary formulations does occur in a sort of medium, i.e. spacetime!), that so electromagnetic forces are transmitted as fluctuations in this postulated electromagnetic dimension...
• And as such, the notion of the aether remains current.

Feel free to poke holes. :) Wnt (talk) 16:07, 2 September 2012 (UTC)

What are the differences between male and female human faces? In words...

This may be easy for lots of editors but not for me. Forgetting facial hair, which not all men have, how can we describe the general differences between men's and women's faces? Tom Haythornthwaite 22:41, 30 August 2012 (UTC) — Preceding unsigned comment added by Hayttom (talk • contribs)

Look at Eric Roberts and Julia Roberts and tell where you see differences - if any. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:49, 30 August 2012 (UTC)

Thank you, I think, but either you didn't understand my question or I didn't understand your answer or we have different senses of humour. It is easy to describe the general differences between male and female bodies because men are generally taller and have penises and women generally have breasts, and so on. But I cannot think of words to generally differentiate between their faces. hayttom 23:11, 30 August 2012 (UTC)

What I'm saying is that you can't, necessarily. To my mind, forgetting any facial hair, Eric and Julia look a lot alike. If you were to somehow remove all the hair anywhere on their heads and put their faces side by side, it would be hard to tell the difference. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:57, 30 August 2012 (UTC)

See this article on the role of testosterone in the development of male facial features. Alansplodge (talk) 23:34, 30 August 2012 (UTC)

My impression is that women are more likely to have the so-called "heart-shaped face", where the sides of the face slope inward as you go from the temples towards the mouth, whereas men are more likely to have straight-sided faces. Not sure I'm right; would be interested to hear about any real studies. --Trovatore (talk) 23:37, 30 August 2012 (UTC)

Leaving out individual variations, the basic difference is that female faces are more round, and male faces are more rectangular. Looie496 (talk) 00:07, 31 August 2012 (UTC)

That would be the reason rectangular, straight-side faced women, Ann Coulter for example, are sometimes referred to as "horsey" looking. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:11, 31 August 2012 (UTC)

Males tend to have more prominent brow ridges - the easiest way to tell from just a skull, as I learned in the palaeoanthropology lab at uni - though even that can be misleading sometimes. As for the heart-shaped vs straight-sided face, that is mostly due to males having more developed jaw musculature, I'd assume - and that will be rather variable. Combined, these two traits tend to make a male face look 'squarer', though I think that if you remove the cultural clues, it is often difficult to be sure just from the face. With children, it is even harder, and I suspect pre-puberty next to impossible from a casual inspection. AndyTheGrump (talk) 00:12, 31 August 2012 (UTC)

How would you characterize the brow ridge of Roy Blunt? 20.137.18.53 (talk) 13:58, 31 August 2012 (UTC)

Just to add in, those are the two things they told us in my forensic anthropology as well. The square jaw is not from musculature; it is skeletal. Women on the whole have large jaw angles than men do. Again, as you note, none of these skeletal features — even the non-facial ones, like hip bone shape — are a sure-thing, because there's a lot of variation in the species. --Mr.98 (talk) 00:47, 31 August 2012 (UTC)

How would you characterize the jaw structure of this Savannah they have on the Today show now? There's something odd-looking about her - like a squirrel with its cheeks stuffed, or something. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:30, 31 August 2012 (UTC)

The Adam's apple is one differenece. Not 100% of the time, but on the balance, men tend to have a more prominent Adam's apple than females. --Jayron32 04:11, 31 August 2012 (UTC)

Yes, always check the neck before necking. And, if going further, check for other lumps, too. :-) StuRat (talk) 09:02, 31 August 2012 (UTC)