Science desk
< July 7	<< Jun \| July \| Aug >>	July 9 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

July 8

Climate in Kuwait

I have a friend living in Kuwait City, which is currently experiencing temperatures bordering on 50 degrees celsius. Where does this place rank globally in terms of summertime maximum and average temperatures? I've never heard of a place this hot. Thanks. 49.185.136.107 (talk) 03:04, 8 July 2011 (UTC)[reply]

It ranks pretty high, but there are many spots in that region that frequently reach similar temperatures in midsummer. The average temperatures are actually a lot lower, because the dryness and lack of vegetation produce a lot of cooling during the night. For what it's worth, the hottest place on Earth, in terms of average temperature, is said to be the Afar Depression in Ethiopa -- not all that far away from Kuwait. Looie496 (talk) 03:29, 8 July 2011 (UTC)[reply]

See Climate of Kuwait. The hottest recorded temperature in Kuwait was 52.6°C in Abdaly, on June 15, 2010[1]. ~AH1 ^(discuss!) 15:44, 8 July 2011 (UTC)[reply]

Nuclear reticulum

Is nuclear reticulum same as Nuclear lamina? --111Engo (talk) 04:07, 8 July 2011 (UTC)[reply]

No, the nuclear lamina is the meshwork of proteins adjacent the phospholipd nuclear membrane. The nuclear reticulum is a term used to refer to a network like pattern seen in the nucleus. Depending on the context it may be the

the pattern of chromatin when it is stained
the distribution of ribonucleoproteins seen by immunostaining .
the tubules and vesicles formed by the nuclear membrane protruding into the centre of the nucleus.(think of this as an endoplasmic reticulum) in the nucleus.

(maybe the nuclear architecture article needs updating?)Staticd (talk) 07:57, 8 July 2011 (UTC)[reply]

Hello, a question about the article "Wilson's disease"

it says (in the part; "nutrition"); "In general, a diet low in copper-containing foods is recommended, with the avoidance of mushrooms, nuts, chocolate, dried fruit, liver, and shellfish".[1]

my Q;

Nuts, what kind of nuts?, and also, organic for example also contain copper?.

and mushrooms, what kind?.

BTW, is it true that some plants organically contain copper? — Preceding unsigned comment added by 79.182.28.217 (talk) 07:31, 8 July 2011 (UTC)[reply]

All plants contain copper as it is part of many essential enzymes. However the levels vary depending on the species, the part and how it was grown. Regarding what foods to avoid, that would be medical advice, you would have to ask a doctor. It's taboo to offer it here. :). Staticd (talk) 08:01, 8 July 2011 (UTC)[reply]

It's a little bit late telling the OP we can't help with dietary recommendations, when those he listed above came straight from Wikipedia anyway. Even the title of this section says the question is about the Wilson's disease article just as much as the disease itself. And that list of foods to avoid IS questionable, including, as it does, nuts. That's such a catch-all category of foods in English. It includes things as diverse as peanuts, pistachios, walnuts and macadamias. To assign a common characteristic to them all is not very scientific. Given what the OP has already garnered from Wikipedia, I think anyone who can is almost obliged to help clarify further. HiLo48 (talk) 09:07, 8 July 2011 (UTC)[reply]

The book Wilson's disease: a clinician's guide to recognition, diagnosis, and management, (from 2001 though) suggests that diet isn't important apart from liver and shellfish which can be significantly high in copper. See page 73. Sean.hoyland - talk 10:25, 8 July 2011 (UTC)[reply]

Electric Power

IN DIRECT CURRENT,flow of electron is continues i.e.,from negative terminal to positive terminal.but in ALTERNATING CURRENT, electron moves forward and again backward but does not move from negative terminal to the positive terminal so that only current wave travel like when we throw a stone in a river then wave only travels not the water particle. is it true or not. PLEASE GIVE ME BRIEF DETAIL ABOUT ELECTRON FLOW IN A.Cvsnkumar (talk) 12:20, 8 July 2011 (UTC)[reply]

Have a look at Alternating current and Wave. Dolphin (t) 12:44, 8 July 2011 (UTC)[reply]

You seem to have the right idea. For both AC and DC, it is the movement of the charges ("current") that matters, not where they end up. In AC, electrons move into the terminals and out of them again. The electrons do work on the load both when they move in and when they move out. --Srleffler (talk) 17:31, 8 July 2011 (UTC)[reply]

Electric power2

I put a Electric tester in a socket's neutral,it shows zero voltage.we know that Alternating current is a sinusoidal.i.e.,for positive cycle it travels in one direction and for negative half cycle it travel in opposite direction.according to this,is phase and neutral reverses for every cycle in a socket or not? if not how electrons flow in a conductor for A.C. Also in d.c, please give me brief detail about electron flow in a.c according to my questionvsnkumar (talk) 12:23, 8 July 2011 (UTC)[reply]

Have a look at Alternating current. Dolphin (t) 12:46, 8 July 2011 (UTC)[reply]

The electrons flow into and out of both the live and neutral sockets, however this flow is driven by the live socket. The electric field in the live socket pushes electrons into the wire and pulls them out of it. The flow of electrons into and out of the wire pushes and pulls electrons along the whole length of the wire, through the connected device, and back up the wire to the neutral socket. This pushes electrons into the neutral socket and pulls them out of it, on alternating halves of the cycle.--Srleffler (talk) 17:35, 8 July 2011 (UTC)[reply]

Inertial mass, again

This is based on a question I asked earlier.

E=mc² means that the potential energy between particles will manifest as mass. But if the potential energy function is defined up to a constant, then shouldn't the mass of this potential energy likewise be not uniquely determined? What would the actual mass be? — Preceding unsigned comment added by 74.15.136.219 (talk) 15:25, 8 July 2011 (UTC)[reply]

In relativity, unlike in classical mechanics, energy isn't defined up to a constant. (just like classically, temperature was only defined up to a constant (calcius, farenheit) but now we know better and have an absolute scale (kelvin) ). 213.49.89.68 (talk) 15:32, 8 July 2011 (UTC)[reply]

Could you clarify this a bit? Why won't potential energy in SR be defined up to a constant? Where does the constant go, mathematically? 74.15.136.219 (talk) 05:10, 9 July 2011 (UTC)[reply]

The constant is absorbed into the definition of the rest mass. Dauto (talk) 14:10, 9 July 2011 (UTC)[reply]

Why? 74.15.136.219 (talk) 21:22, 9 July 2011 (UTC)[reply]

Because that constant, unlike in non-relativistic mechanics, has real measurable effects such as inertia and gravity. Dauto (talk) 14:28, 10 July 2011 (UTC)[reply]

Okay, thanks. 74.15.136.219 (talk) 14:56, 10 July 2011 (UTC)[reply]

The flagpole experiment

Hi. Imagine about two dozen people gathered arms stretched out, holding hands in a circle centred on a flagpole. Simultaneously, all the participants run toward the centre of the flagpole, keeping their arms streched out. What would occur in this instance? Would the people start rotating in a circle? If this is the case, in what direction would the rotation most likely be psychologically? Would the same occur of all the people were running outwards or facing inwards and running backwards? What would be the average speed of the revolution? Thanks. ~AH1 ^(discuss!) 15:34, 8 July 2011 (UTC)[reply]

Well if they must keep their arms stretched out and if they are not allowed to change the angle of their arms, then the circle will somehow be broken. I don't see how motion towards the center of a circle will translate into a rotation in this scenario. Googlemeister (talk) 15:44, 8 July 2011 (UTC)[reply]

Same response: arms outstretched equals an impossibility as zeroing in on the flagpole progresses beyond a certain degree. But I don't think rotation of the group around the flagpole has to take place. Bus stop (talk) 15:47, 8 July 2011 (UTC)[reply]

I see people falling over but no general rotation. The circle ceases to be a circle as the stronger push aside the weaker. One person reaches the flagpole, though the center of the flagpole is out of reach. In the case of running away from the flagpole the pair of hands with the weakest hold break first. If every runner follows exactly a radial from the flagpole, all the handholds have to break. In any practical experiment some handholds will last longer than others as runners veer off course. Cuddlyable3 (talk) 17:29, 8 July 2011 (UTC)[reply]

If all 12 are of identical strength, I would think they would end up simply running in place. I don't know why they would run in a circle. Now, if they've just been pinged with pixie dust or something, perhaps they'll shrink as they get closer to the flagpole, proportional to their distance from it. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:34, 9 July 2011 (UTC)[reply]

In the inscrutable way of Wikipedia, Pixie dust links to an article about Tinker Bell who is featured in the opening of all Disney films flying over the Magic Castle (in a counter-clockwise direction, right to left). Such an overflight could create a vortex that sweeps the runners in a circle. Cuddlyable3 (talk) 16:15, 9 July 2011 (UTC)[reply]

Suppose that all the runners start by running in place, before a few of them gain momentum in a certain direction around the flagpole rather than any straight-line velocity relative to it, thus pulling all the other runners around in that particular direction. Iff this were to be the case, in which direction is the rotational movement more likely (50%+) to occur? I was imagining it as a movement that had forces similar to orbital mechanics, in which the "pull" toward the "centre" (i.e. "gravity") and the resulting inward centripetal acceleration (caused both by the running toward the centre and the linking of arms) exactly balances out the outward tangential acceleration (imparted by the vector momentum, which is the force I am asking for whether it would result from this theoretical set-up).

Another way to imagine the situation would be to suppose the runners are all holding onto a single rope instead of holding hands, arms outstreched. Of course, in this scenario the rope would quickly lose its tension and a messy situation would occur. Instead of a rope, however imagine that the circular shape is maintained by compression, which may or may not require a tremendous amount of effort to keep the arms outstreched. (If it helps, suppose that everyone runs in a 30° angle relative to the centre) Now, say there is enough momentum early on in the running, so that less overall compressional force is required to maintain the circular shape. Could this work? ~AH1 ^(discuss!) 18:03, 9 July 2011 (UTC)[reply]

Somehow I missed the radial comment. Would the circle break only owing to the irregularities between the strengths of the runners? ~AH1 ^(discuss!) 18:07, 9 July 2011 (UTC)[reply]

Plant identification

While out chopping down burdocks from the roadside (they get in the dog's fur when on walks), I saw a bunch of these. Can anyone identify them? The pic was taken in Vermont and just a few minutes ago. Dismas|^(talk) 16:06, 8 July 2011 (UTC)[reply]

I think it's wild grape. We had some in my back yard as a kid in Connecticut. -RunningOnBrains^(talk) 17:16, 8 July 2011 (UTC)[reply]

I don't think it is a grape, wild or tame, because the leaf stalks appear to come from a central point which is not a characteristic of a grape which grows leaves along a rambling stem. It looks like it might be petasites, more commonly known as butterbur, specifically the white butterbur (petasites albus). The temperate geographical zone is right. Certain identification is always difficult until one can see the flower and/or the whole mature plant. Richard Avery (talk) 17:53, 8 July 2011 (UTC)[reply]

Let it be known that I am by no means a plant expert, so I default to Richard Avery's assessment. The leaves just looked very similar to what I remembered (and the website I saw). -RunningOnBrains^(talk) 18:27, 8 July 2011 (UTC)[reply]

I don't remember ever seeing them bloom (they do a decent job of cutting down the weeds on the roadsides around here) but I think Richard has it. These don't have any tendrils like the grapes do. So, White Butterbur it is then! Thanks, Dismas|^(talk) 21:40, 8 July 2011 (UTC)[reply]

It's a vine, though, right? In which case, it would be something else (could be a few things). Juliancolton (talk) 21:05, 12 July 2011 (UTC)[reply]

is using a whiteboard and markers a health hazard?

Is using a whiteboard and whiteboard markers a health hazard? (cancerous, small particles into lungs, etc etc). Not asking for medical advice. 188.29.193.67 (talk) 16:19, 8 July 2011 (UTC)[reply]

I'm not sure about small particles. The pigment solvent you are asking about is mostly harmless. I hope it was tested on laboratory animals. Are white board users acting strange? Remind them not to concentrate or inhale the solvent. If the concentration is such as to cause a headache or euphoria, move to a well-ventilated area. This is not medical advice. 99.24.223.58 (talk) 18:24, 8 July 2011 (UTC)[reply]

I noticed that some brands make me light-headed, while others do not. StuRat (talk) 04:46, 9 July 2011 (UTC)[reply]

The brands that don't make you light-headed are the water-based ones. They're the ones I'd recommend. --TammyMoet (talk) 07:47, 9 July 2011 (UTC)[reply]

So, when, as a teacher, I'm having a bad day with the little darlings, they're the ones to avoid, right? ;-) HiLo48 (talk) 07:53, 9 July 2011 (UTC) [reply]

An Interactive whiteboard is a chemical-free gimmicky alternative. Cuddlyable3 (talk) 08:13, 9 July 2011 (UTC)[reply]

Radio waves

Do radio waves have angular momentum? This is unclear. Cuddlyable3 (talk) 16:57, 8 July 2011 (UTC)[reply]

Yes. Not that I have any idea what that means: Photon_polarization#Angular_momentum_density_of_classical_electromagnetic_waves. -RunningOnBrains^(talk) 17:12, 8 July 2011 (UTC)[reply]

Every photon carries a momentum equal to Planck's constant. So radio waves actually carry much more angular momentum than an equivalent mass-energy of visible light. Wnt (talk) 19:16, 8 July 2011 (UTC)[reply]

Does the angular momentum of light from the Sun cause a Solar sail to rotate?
I assume an electromagnetic wave gets angular momentum from its source. Can a transmitter rotating at a certain speed emit a radio wave with zero angular momentum?
The Sun is a rotating omnidirectional radiator. Does that mean that a solar sailor could navigate by measuring his angular acceleration relative to the fixed stars?

Cuddlyable3 (talk) 07:38, 9 July 2011 (UTC)[reply]

Only circular polarized waves will carry a bulk angular momentum. Light from the sun is not very polarized on average. Graeme Bartlett (talk) 09:15, 9 July 2011 (UTC)[reply]

So far as I know, each photon must carry an identical Planck constant angular momentum - the only question is whether it is one way or the other (and whether quantum weirdness means we don't yet know which). So any overall transfer of momentum is a statistical effect based on the degree of overall circular polarization of the light. I don't know the relationship between rotation of the emitter and rotation of the emitted light - but note that the rotation of any given atom in the Sun at a given moment is really very slow. Wnt (talk) 15:48, 9 July 2011 (UTC)[reply]

In addition to the spin angular momentum that other replies are referring to, a photon obviously carries angular momentum due to its linear momentum, ${\vec {L}}={\vec {r}}\times {\vec {p}}$ , with ${\vec {r}}$ being the position of the photon (relative to the origin of your choice), and ${\vec {p}}$ being the linear momentum.

Regarding spin angular momentum, its directly measurable projection (see spin (physics) for details) is $\pm \hbar =\pm {\frac {h}{2\pi }}$ , where $h$ is Planck's constant (and the $\hbar$ or "h-bar" is called the reduced Planck's constant). The absolute value of the spin angular momentum is $\hbar {\sqrt {2}}$ .

Regarding the solar sail, the reflected light wouldn't transfer its spin angular momentum onto the sail, only the absorbed light. If you would have a highly polarized light source (unlike the Sun), you might be able to see a rotation from the absorption of a large amount of the light. I don't quite understand how you want to navigate around the Sun by measuring the angular acceleration - the Sun is not a source of polarized light, but you might have heard of the Sun's magnetic field and the Zeeman effect, which produces a bit of polarized light, but only at certain frequencies at certain spots on the surface of the Sun (sunspots occur due to strong magnetic fields). Icek (talk) 18:15, 9 July 2011 (UTC)[reply]

Current plan for NASA

What is the current (perhaps read yet-to-be-cancelled) plan for NASA that isn't cancelled? I know there used to be Constellation, but that is no longer. 20.137.18.50 (talk) 17:57, 8 July 2011 (UTC)[reply]

For human space flight, robots to clear the dangerous Low earth orbit#Space debris. Those can probably be similar to the robots which weld asteroids together for shielding from cosmic radiation on extended trips outside the LEO's Van Allen belts. The most cost effective James Webb Space Telescope replacement is a far side lunar cryostat cooled infrared VLBI array capable of detecting exoplanet ozone and the first two infrared spectral lines of hydrogen. 99.24.223.58 (talk) 18:11, 8 July 2011 (UTC)[reply]

The Space Launch System is the current project filling the role of the now-cancelled Ares rocket. Note that, like Ares, it is a Shuttle-Derived Launch Vehicle. Similarly, Constellation's Orion capsule has morphed into the Multi-Purpose Crew Vehicle program. — Lomn 18:20, 8 July 2011 (UTC)[reply]

Last I heard, the MPCV reentry testing was scheduled for 2013. Is that still on? 99.24.223.58 (talk) 18:26, 8 July 2011 (UTC)[reply]

Also, is NASA going to do a synthetic fuel demonstration? I'd love to see that. 99.24.223.58 (talk) 20:14, 8 July 2011 (UTC)[reply]

There's sometimes a very easy way to answer questions like the OP's. Just yesterday I went to nasa.gov, and on the very first screen was a button labelled What's next? Suggest you look there. HiLo48 (talk) 23:14, 8 July 2011 (UTC)[reply]

Another good question is what is NASA's track record for programs accomplishing the goals they set out to accomplish before the projects get canceled. 76.27.175.80 (talk) 00:50, 9 July 2011 (UTC)[reply]

That depends on what you think the goals are, and I suspect the goals might be far more advanced than what most people think they are. 99.24.223.58 (talk) 01:49, 9 July 2011 (UTC)[reply]

You mean programs don't by habit have specific, measurable, objective goals stated outright with time tables such as "we will put a man on the moon by the end of this decade" (though of course not always as big)? How many times has NASA themselves said "we will do X within Y years" and made it? That's what I'd like to know.76.27.175.80 (talk) 02:08, 9 July 2011 (UTC)[reply]

They do that all the time, but nobody notices when they achieve something early or cancel it because it's no longer necessary. 99.24.223.58 (talk) 10:06, 9 July 2011 (UTC)[reply]

"They do that all the time" great! Then I'd just be pleased to see the cold hard numbers out of curiosity. What baseball fan would be satisfied with "Babe Ruth hits home runs all the time!"?76.27.175.80 (talk) 12:06, 9 July 2011 (UTC)[reply]

Budget cuts, budget cuts, budget cuts. ~AH1 ^(discuss!) 02:21, 9 July 2011 (UTC)[reply]

Meanwhile, other nations move on and leave us behind, with our visionless bean counters. The only thing bean counters ever invented was double-entry bookkeeping. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:30, 9 July 2011 (UTC)[reply]

Haven't the actual decisions to cut budgets and cancel major projects been ultimately made largely by politicians, rather than the bean counters? HiLo48 (talk) 18:23, 9 July 2011 (UTC)[reply]

Seeing how often they get the rug pulled out from them or how often they can chew what they bite off--it's all valuable information in seeing how functional or dysfunctional the complete system is at being able to do what it says it wants to do. 76.27.175.80 (talk) 18:29, 9 July 2011 (UTC)[reply]

There's a factor that may make your assessment somewhat difficult. Much of what they have wanted to do at any given time has never been done before, by anybody, anywhere. It's a lot harder to predict than if one is building say roads or houses. From experience, not with NASA but in a couple of other bleeding edge endeavours, that factor really confounds the bean counters. HiLo48 (talk) 02:29, 10 July 2011 (UTC)[reply]

Does special relativistic length contraction "hide" matter?

I get that if something is travelling at the speed of light (relative to you), it has zero length in the direction of travel. But does that mean that there could be complex, large objects that are "collapsed" out of sight because they are travelling too quickly for you to see? I guess I don't understand whether photons are the only things that travel at the speed of light, and how it is that we can "see" photons if they have zero length. johnpseudo 18:47, 8 July 2011 (UTC)[reply]

We don't see photons! We see other things, by way of the photons they emit or reflect. Photons themselves are invisible, because (barring extremely minor quibbles) they neither scatter nor emit photons. --Trovatore (talk) 22:57, 8 July 2011 (UTC)[reply]

Nonsense. Photons are all that we do see. Everything else is inferred. Photons that don't hit your retina are invisible, of course, but you wouldn't say "we don't taste salt" just because most salt never enters your mouth. -- BenRG (talk) 00:44, 9 July 2011 (UTC)[reply]

The claim that "photons are all we do see" is incorrect. Right now I see, for example, my keyboard. My keyboard is not made of photons.

CCDs are one technology that captures and records data collections of photons. ~AH1 ^(discuss!) 02:25, 9 July 2011 (UTC)[reply]

So what? I wasn't talking about recording the incidence of photons. I was talking about seeing. Seeing is something that people and animals do, and what they do it to is not so much photons, as the cause of the disturbance of the photons. The seen thing might even be indicated by an absence of photons, rather than their presence (you see a shadow, for example).

As I say, it's a linguistic point. This is what the word see standardly means in English, and what it has meant for various centuries, long before anyone knew anything about photons. I won't disagree that people also generally understand what you mean if you say you see a photon, but this is a secondary and subordinate usage; the principal usage is the one I'm explaining. --Trovatore (talk) 02:47, 9 July 2011 (UTC)[reply]

This is a linguistic point, of course, not a physical one. Nevertheless I think I have a very good argument here. When a photon hits your retina, you do not see the photon (if you did, what shape was it?) You see what caused the photon to enter your eye. --Trovatore (talk) 00:51, 9 July 2011 (UTC)[reply]

The thing is, when talking about relativity and cosmology it's really important to understand that we don't have a sense that directly perceives a 3D external world, that what the eye actually detects is light that is local to us. Everybody knows that in a Socratic sense, but they often don't think about it unless you point it out, and this is a cause of a lot of misunderstanding and confusion about relativity. Even the fact that for fifty-five years no physicist realized that length contraction can't be seen is probably attributable to this unconscious prejudice.

I said below that a moving observer will see the face of the cube as a trapezoidal shape with curved edges. The cube itself isn't physically distorted in that way; the only thing distorted in that way is the observer's field of view, which is an abstraction of the image formed on the retina. (Or CCD.) I think that's a reasonable and natural use of the word "see". -- BenRG (talk) 20:07, 9 July 2011 (UTC)[reply]

Quite so. You see the distorted cube that isn't really there in any sense of the word. What you do not see, however, is the photons. You se the abstract, not-quite-existent object that you infer from the photons. --Trovatore (talk) 21:20, 9 July 2011 (UTC)[reply]

Well, the classical approximation is either that a photon is a point particle with zero length, width, and breadth; or else that it is a wave that diffuses out for some distance in all directions. Quantum mechanics combines this in particle-wave duality. But the point is, the probability distribution or waveform of the photon isn't compressed down to nothing, because there's an uncertainty in the time when it was emitted, not just a physical length. Though the difference between these might be interesting to consider... for example, I suppose a particle of slow light, crawling through a medium at some few km/h, must be much more compressed from front to back than it is in free space. Odd... Wnt (talk) 19:15, 8 July 2011 (UTC)[reply]

Also, to answer your other question, nothing with mass can ever reach the speed of light, where it would theoretically have zero length in a "stationary" rest frame, since it would take an infinite amount of energy to do so. If you managed to somehow accelerate a macroscopic object to near the speed of light (impossible with today's technology), it would appear massively distorted (shrunk) in the direction of travel, but all scales would be affected; even down to the atoms themselves. No matter is "hidden". You might be interested in the ladder paradox.-RunningOnBrains^(talk) 19:37, 8 July 2011 (UTC)[reply]

Don't confuse the Lorentz contraction with the actual visual appearance of the object. That (to the extent that you'd have time to see it) is different, because light reaching you from different parts of the object was reflected at different times (in your inertial coordinate system).

An approximation is to say that the object appears rotated, rather than shrunk. I am not sure how well "rotated" really captures the exact distortions involved. We should probably have an article on this, if we don't. Here is the classic paper on the subject. --Trovatore (talk) 22:02, 8 July 2011 (UTC)[reply]

Although that is the classic paper, in the sense that it's the one that everyone cites, I think it does a poor job of explaining the situation. It uses two objects at the same location but moving at different speeds, and a single stationary observer. It's much easier if you use a single stationary object and two observers. Then it's easy to see that the two observers will see the same view of the object, because their eyes receive the same light. If the object is a cube, then there is a region of space which is only reached by light from one face, and if they are in that region of space then they will both see only that face. They won't both see it as square, because of the aberration of light. But relativistic aberration is conformal (preserves angles), so they will both see 90° angles at the four corners of the shape they do see. Conformal transformations also preserve circles, so if you draw a circle on the face that touches the four edges, both observers will see it as a circle touching all four edges. This gives you an idea of the limits of the distortion introduced by aberration. There's no way it can "length contract" the square, for example, because you can't draw a circle inside a narrow rectangle that touches all four edges. In fact what you get is a trapezoid-like shape, with curved edges that meet at 90° angles. All of this is true even if the object is close by, contrary to Weisskopf's analysis which only works when it's far away.

So why does Weisskopf say that the object is rotated? Because he's treating the two objects as coincident when the emit the light, while I'm treating the observers as coincident when they receive the light, and these aren't the same thing. If you split Weisskopf's observer into two separate observers in two separate experiments, each with one object, and boost so that both objects are at rest in the same place, the observers aren't in the same place when they receive the light, so they really are seeing the object from different angles (in addition to the distortion introduced by aberration).

The behavior in the speed-of-light limit depends on how you take the limit. If you do it Weisskopf-style, with the object suddenly accelerating to high speed, you see a highly redshifted and slightly distorted square of pretty much the same size as before. It may be redshifted out of detectability, though. It doesn't shrink away, but does fade away. If you take the limit my style, with the observer accelerating to high speed, the object shrinks to a point (the headlight effect), blueshifts, and actually gets brighter overall. It shrinks away, but doesn't fade away. So this question has no easy answer; it depends on how you set it up. -- BenRG (talk) 00:44, 9 July 2011 (UTC)[reply]

Picture quality in digital cameras

Which factors are the most important to choose? I know that the MBs are only secondary, and that the lens is probably the most important, but what else should I choose? Wikiweek (talk) 21:53, 8 July 2011 (UTC)[reply]

That depends almost entirely on what you intend to use it for. --Tango (talk) 22:43, 8 July 2011 (UTC)[reply]

Are you asking, perchance, that you should obtain a camera which is not also a cell phone? I can not say. 99.24.223.58 (talk) 23:46, 8 July 2011 (UTC)[reply]

I know that cell-phone cameras are horrible. I intend to use the camera for making pictures, I don't know what are other options. Wikiweek (talk) 00:24, 9 July 2011 (UTC)[reply]

For sensors of a given generation, the single biggest impact on image quality is pixel density: a big sensor with a small megapixel count will produce a better image than a small sensor with a high count. Larger sensors in general do better than smaller ones because of this. --Carnildo (talk) 00:32, 9 July 2011 (UTC)[reply]

See Image sensor format. As mentioned, bigger is generally better (though also gives a bigger camera, and costs more). Buddy431 (talk) 04:59, 9 July 2011 (UTC)[reply]

Wikiweek, Tango was asking you what type of pictures you intend to take and what type of quality you require. Landscape, portrait, action, low light snap shot, macro? Do you plan on using a tripod? This makes a fairly big difference in what factors to consider. I'm sure many people here could recommend a particular camera or camera type if you were specific about your plans for use or tell you which stats are more important. When people who don't know much about photography ask me what camera to buy, I tend to just recommend the Canon S95, it is a decent all around camera although it isn't all that cheap. --Daniel 05:10, 9 July 2011 (UTC)[reply]

Do you intend to go out for the specific purpose of making photographs? In that case consider an SLR; with a few objectives this can get pretty expensive though. If you don't know if photography will be an active hobby for you, a point-and-shoot camera that you always have with you gets better photographs than a bulky SLR you left at home. For a first camera I'd suggest a point-and-shoot; even if you get an SLR later you can have a camera in your pocket whenever you go out the door. I bought my point-and-shoot by looking at photography magazines' "editor's choice" lists - google will be your friend there. 88.112.59.31 (talk) 10:37, 9 July 2011 (UTC)[reply]

To clarify (the last poster geolocates to Finnland): The Finnish term "objektiiv" translates as "lens".

OR only: A year ago, when I considered the option of taking up photography after a break of 25 years (in the last millennium we had analogue cameras:) I invested into a bridge camera, a pre-loved Lumix costing EUR 250. My prime purpose was to find out if a) I could still "see" a scene and b) to "learn" the required new tricks which are available with digital cameras. This is a step up from the above mentioned P&S boxes, but it was important to me to be able to control aperture / shutter speed and ISO manually. I still use this camera (having purchased in the mean time a DX camera and a few lenses at an initial outlay of approximately EUR 2 000) as a "note pad".

As has been stated above, photography is a vast field and it depends on what are your interests. Architecture / landscape / animals / insects / humans / stage work / sports / photography as a basis for graphic work / etc ad infinitum. The required equipment will vary accordingly.

Amongst many other sites, you may be interested in this website, which has numerous reviews on cameras and lenses.

As you state correctly, an excellent lens (which costs a whack, if you want a measly three) is desirable for IQ / image quality. However, kit lenses may be adequate for learning and - if you want to work with manual control - "old" lenses of high optical performance can be obtained at surprisingly good prices.

If you want to go the whole hog and invest in full-frame digital SLR cameras, you will require a better nourished piggy bank. Good luck! --Cookatoo.ergo.ZooM (talk) 18:30, 9 July 2011 (UTC)[reply]

It should be mentioned that some modern point-and-shoot cameras (generally at the middle or high end of the market) offer many of the same manual controls (aperture, shutter speed, ISO speed, and even focus) that once were exclusively found on (d)SLRs. A friend of mine owns a Canon PowerShot SX210 IS (review), for instance, which includes all of those features coupled with an extremely wide zoom range (14x, corresponding to 28mm-392mm focal lengths on a regular 35mm full-frame camera), which takes a lot of the sting out of not being able to swap lenses. Plus, it's all in a compact P&S form factor, which means that it comfortably fits in any reasonably-sized pocket. The SX210 running about $300 on Amazon right now, which puts it at less than half the price of pretty much any new dSLR.

That said, going P&S does entail some tradeoffs. Smaller pixels have inherently worse low-light performance, a problem exacerbated by the smaller sensors of P&S cameras and the drive to cram more megapixels onto each sensor; this can make taking high-quality indoor and night shots a challenge. The built-in flash will be located physically close to the lens, which maximizes the opportunity for glare and redeye; the built-in flash will generally be smaller and less powerful than even the built-in on a dSLR (and the dSLR will have a hot shoe where you can attach all manner of additional lighting accessories). Where manual control modes and settings are available on a P&S, they may be more difficult to access and adjust—you may have to 'drill down' through menus and whatnot, because there just isn't room on the camera body (or in the design and construction budget) for the dedicated buttons, toggles, and wheels one can fit on the exterior of a full-sized dSLR. Unlike an SLR, the viewfinder of a P&S does not display exactly the same frame as the lens and sensor see; many P&S cameras these days are also dispensing with the viewfinder altogether. The LCD-only preview has pros and cons, but be aware that it can be difficult or uncomfortable to view the display when outdoors in bright sunlight. Generally P&S cameras don't give access to RAW image files, though there exist firmware hacks for some P&S cameras now. Residents of larger cities with well-stocked camera stores may enjoy being able to rent premium and specialty lenses for their dSLRs. TenOfAllTrades(talk) 15:57, 10 July 2011 (UTC)[reply]

What looks like peas? We may soon know

I asked the question here and here and was referred here in the second section. The conclusion was that it was Crape myrtle, and what I believe to be Crape myrtles are now blooming. The trees near my house are not blooming yet and I won't be going to Myrtle Beach, South Carolina until the blooms are gone and what looks like peas are back. I'll update this as the trees bloom.Vchimpanzee · talk · contributions · 21:54, 8 July 2011 (UTC)[reply]

Peas are pulses which would be fruits if they had not been defined to be vegetables. Long story. 99.24.223.58 (talk) 22:45, 8 July 2011 (UTC)[reply]

What's your point, exactly? --Mr.98 (talk) 23:28, 8 July 2011 (UTC)[reply]

Well, that is a difficult question having to do with the fact that vegetables and fruits were named before biology was understood. 99.24.223.58 (talk) 00:04, 9 July 2011 (UTC)[reply]

What in the world does that have to do with it? The culinary uses of fruit and vegetable don't have much to do with botany, and there's no real reason they should. Culinarily, "fruits" have a lot of sugar, and usually some dibasic acids like citric acid and malic acid. Vegetables don't have that much of either one. Who cares what they do for the plant? When I'm eating it, that's the last thing on my mind. --Trovatore (talk) 08:27, 9 July 2011 (UTC)[reply]

Oops — I guess citric acid is actually tribasic. Polybasic acids, I guess.

Anyway, there apear to be small white blooms on some of the trees, with tiny yellow blooms in the middle. They sort of look like daisies. Thie other Crape myrtles, if that's what they are, have poink or purple blooms.Vchimpanzee · talk · contributions · 15:23, 9 July 2011 (UTC)[reply]

After scrolling down in the Lagerstroemia article, I see blooms (on the actual trees) that look very much like the ones I saw in the second photo from the left, and the "peas" in the third photo from the right, after they are no longer green.Vchimpanzee · talk · contributions · 15:26, 9 July 2011 (UTC)[reply]

Thank you for the update Vchimpanzee, I'm looking forward to getting this finally and definately resolved. 2.101.8.57 (talk) 19:46, 9 July 2011 (UTC)[reply]

Based on what I've seen now, I think we know for sure.Vchimpanzee · talk · contributions · 17:08, 11 July 2011 (UTC)[reply]