Wikipedia:Reference desk/Archives/Science/2011 June 18

= June 18 =

Text readable only at low zoom


How do you explain something like this? The text seems almost completely unreadable at high zoom - yet in the fine print, which seems clearly legible to me, the exact same picture is present (use the Zoom on your browser if you don't believe me). Is there a scientific description of this phenomenon? Wnt (talk) 23:17, 17 June 2011 (UTC)


 * Seems to me like pixelation effects of a low-resolution text image. In other words, the letters are made of tiny pixels, which get magnified along with the image at higher zoom levels and act like a sort of pattern-disruptive camouflage for the letters.  I know this from personal experience -- I've had much the same problem with the cover I created for my book, which had to be completely reworked as a result. 67.169.177.176 (talk) 23:40, 17 June 2011 (UTC)


 * The rendering in squares of homogenous hues is dependent for clarity on failing visual resolution which occurs more at the smaller scale than at the larger scale. Bus stop (talk) 23:44, 17 June 2011 (UTC)


 * It's a "can't see the forest for the trees" issue. If you can make out individual pixels, your brain focuses on those, not the overall image.  This is why zooming in on something only helps you make out detail to a point, then things start to get worse. StuRat (talk) 23:54, 17 June 2011 (UTC)

This is the phenomenon that Leon Harmon and Bela Julesz described in their 1973 Science paper, Masking in Visual Recognition: Effects of Two-Dimensional Filtered Noise -- exemplified by their famous pixelized image of Abraham Lincoln. Looie496 (talk) 00:10, 18 June 2011 (UTC)
 * Thank you for that link, Looie496. This paper is amazing.  Nimur (talk) 00:53, 18 June 2011 (UTC)
 * The Abraham Lincoln picture is really cool. I just printed it A4 size, and when you hold it close in your hand it looks totally meaningless. If you then prop it up and walk away from it across the room, it gradually becomes clearer and clearer what it portrays. 86.160.209.60 (talk) 03:03, 18 June 2011 (UTC)


 * Just curious, the OP says that the small text "seems clearly legible". For me, it is far from being "clearly legible" (though I am probably about 80% sure I can guess what it says). Is it "clearly legible" to everyone else? Btw, I can read the large version better if I almost close my eyes so that everything is very blurry and I can no longer see the sharp pixel outlines. 86.160.209.60 (talk) 00:37, 18 June 2011 (UTC)
 * It depends on the resolution, display clarity/sharpness and viewing distance. It's illegible (can't even guess what it says) on my CRT at my default zoom. It's fairly legible on my LCD at default zoom. It's legible on my CRT at greater zoom although still not as clear IMHO. At in between zooms it becomes somewhat legible like for you. (Although I saw it on my LCD before this.) Past that it starts to become illegible again. If you want to do more experiments I suggest an image viewer with high quality zooming interpolation but fine zooming control. Nil Einne (talk) 00:57, 18 June 2011 (UTC)
 * Oh yes, of course. When I zoom to 200% it is easy to read. 86.160.209.60 (talk) 01:05, 18 June 2011 (UTC)
 * Note that the rendered text uses subpixel rendering, which makes an assumption about the layout of pixels in your monitor. Many modern monitors do not use the conventional "RGB" side-by-side rectilinear pixel.  For example, an iPad display looks like this under a microscope.  If text is rendered for sub-pixel antialiasing, assuming an RGB-horizontal array pixel geometry, it will look very different on an unconventional display.  Nimur (talk) 01:14, 18 June 2011 (UTC)
 * Really? That blue text over there? Are you sure? It doesn't have the rainbow artifacts on the edges that I would normally associate with sub-pixel rendering. APL (talk) 02:11, 18 June 2011 (UTC)


 * I think it says "PREZOOM", whatever that means. Plasmic Physics (talk) 05:27, 18 June 2011 (UTC)
 * It does? I thought it said "FREEDOM".  -- Jayron  32  05:30, 18 June 2011 (UTC)
 * Yes, it says "freedom". It's amazing that such a heavily pixilated image still contains enough information for our eyes to decode it. Dauto (talk) 07:49, 18 June 2011 (UTC)
 * If you think about it a bit, it's actually not particularly amazing. (Sorry to be a wet blanket.)  The regular English alphabet contains 26 letters, represented by 52 symbols (upper and lower case).  That's a bit less than 26 unique symbols.  In the image shown, there's an array of something like sixteen pixels for each letter.  If we limit ourselves to turning each of those pixels (bits) on or off, we have 216 possible unique 'characters'; roughly speaking, that's space for a thousand different alphabets.  In practice, of course, it doesn't work quite like that.  On the up side, we actually are allowed several different values possible values for each pixel&mdash;if we conservatively estimate each pixel might have one of four readily-distinguishable colors then there's room for a billion unique characters.
 * On the side of reality (the 'down side') human alphabets are generally not designed for efficient use of low-resolution pixels&mdash;though when we put our minds to it, we can certainly design such representations; consider Braille. Written characters are generally composed of strokes rather than arrays of stippled dots; this means that lines of adjacent pixels in their graphical representation will all have the same value, and will tend to be surrounded by buffers of wasted white space.  As well, some characters have shapes that are similar to one another: o, c, e, for instance.  Even then, though, we're partially rescued from ambiguity by our human pattern-matching abilities.  If I see a the partially obscured W_k_p_d_a or __kipedia or Wikipe___, I've got a pretty good shot at correctly assigning the missing letters.  TenOfAllTrades(talk) 13:36, 18 June 2011 (UTC)
 * Sorry but that's nonsense. Dauto (talk) 19:45, 18 June 2011 (UTC)
 * Sorry, I may have been too concise, or slipped in some oversimplifications in places. Which part did you not understand? TenOfAllTrades(talk) 21:01, 18 June 2011 (UTC)
 * Your demonstration is incomplete. Most of the pixel combinations do not represent anything. You have not assessed what fraction of these combinations can be used to represent letters. More to the point, the pixilated picture contains the same amount of info when you zoom in but becomes illegible. That means that some heavy information processing is being performed by the eyes and that's what makes it amazing. Dauto (talk) 03:03, 19 June 2011 (UTC)
 * Actually, it doesn't say anything - it's just a pattern of pixels that resembles what we think it ought to. It is simply a mind trick played by our brain, as it tries to make sense of the visual world. Plasmic Physics (talk) 08:44, 18 June 2011 (UTC)
 * Sorry but that is also nonsense. Dauto (talk) 19:45, 18 June 2011 (UTC)
 * - Running On Brains (talk) 04:26, 19 June 2011 (UTC)
 * See CAPTCHA. Cuddlyable3 (talk) 13:19, 18 June 2011 (UTC)
 * Appealing to Plato's cave rarely contributes anything to a discussion. APL (talk) 20:40, 18 June 2011 (UTC)
 * What is Plato's cave? 67.169.177.176 (talk) 21:53, 18 June 2011 (UTC)
 * See Plato's Cave. Tevildo (talk) 22:02, 18 June 2011 (UTC)
 * Now why is that article not in the category Pseudoscience? 67.169.177.176 (talk) 00:20, 20 June 2011 (UTC)


 * I was not refering to Plato's cave, I highlighted the fact that the letters you supposedly see doesn't actually exist. This is proven by the enlarged image. Plasmic Physics (talk) 08:03, 19 June 2011 (UTC)
 * Does Abraham Lincoln with hat actually exist? Cuddlyable3 (talk) 15:45, 19 June 2011 (UTC)
 * I would say that the letters we actually see do indeed exist. This is proven by the smaller image. Dauto (talk) 16:09, 19 June 2011 (UTC)
 * Cuddlyable3: yes he does exist, but that is not an image of him; yes, the letters do exist, but that is not an image of them.


 * Dauto: the enlarged image is carries the same amount of information as the smaller image, ergo the enlarged image clearly does not contain letters. And circular reasoning does not work. Plasmic Physics (talk) 07:07, 20 June 2011 (UTC)
 * This is kind of silly reasoning. It invites the question, "at what level of information do they cease to exist?" which I think points out how silly it is. The question is not whether they exist in an ontological sense. The question is about human perception and pattern matching, which is what everyone else has been gesturing towards. --Mr.98 (talk) 14:15, 20 June 2011 (UTC)


 * The letters clearly exist. At larger sizes we're distracted by the more obvious pattern of the pixels. Like the Lincoln image. For some reason we're only capable of seeing one of the patterns at a time.
 * The secondary pattern doesn't have to be pixels. That's just a side-effect of the technology used. Hybrid Images can be made with all sorts of images.  The most famous is a picture that contains both Marilyn Monroe and Einstein, super imposed in such a way that the Einstein image is obvious from up close, but the Monroe image is obvious from far away.
 * Lots of other optical illusions exploit tricks where our brain latches onto one or the other interpretation of an image but not both simultaneously. (The dancer can't twirl both ways at the same time, the rabbit and the duck can't coexist, etc.)
 * In short, yes, both images contain the same data, but we can't see the text in the larger image because of a limitation in the way our visual cortex functions. APL (talk) 22:59, 20 June 2011 (UTC)


 * The method of presentation requires the use of squares of varying hues, although the hues within each square are required to be the same throughout. We only see the letter as a result of our failure to visually resolve the image at a certain scale of presentation. Bus stop (talk) 14:31, 20 June 2011 (UTC)


 * Does the smallest image contain information indicating it represents a word? Plasmic Physics (talk) 08:21, 21 June 2011 (UTC)
 * Not in any way that I know to decode it.
 * What does that prove?
 * That it's possible to reduce an image of letters to the point where the original letters can no longer be decoded? No one is arguing that.
 * The point is that when it is possible to decode the pixels into letters it's because the information is still there, even if the information isn't obvious to humans in every possible way you want to look at it.
 * Many people have trouble reading things that are upside-down, but surely you wouldn't argue that the meaning of a sign is lost if it's hung upside down? It simply means that our brains are not perfect computers and sometimes how data is presented makes a big difference as to whether or not we can decode it. APL (talk) 20:51, 21 June 2011 (UTC)


 * My point is that the amount of information contained in small script like this, is exajurated in an illusional construct of our brain, see apophenia. Plasmic Physics (talk) 06:32, 22 June 2011 (UTC)

Spotting Jupiter with the naked eye during daytime
This article mentions successful observations close to Sunset. But Jupiter now rises before the Sun does, and then you get a better opportunity to try to spot it when the Sun is in the sky, you just follow it starting at dawn for as long as possible.

I was wondering if people have done this and what the record (in terms of how high the Sun is in the sky when jupiter can no longer be seen) is. Count Iblis (talk) 03:26, 18 June 2011 (UTC)


 * It probably depends a lot on where you are, and what the atmospheric conditions are like when you are looking. Even if it is a nominally "clear" day with no clouds, there are a lot of factors which can affect if stars and planets are visible during the day.  I have personally seen both Venus and Sirius during the day time, and the article on Sirius notes that it has a lower apparent magnitude than Jupiter, meaning that under ideal conditions, Jupiter should be visible when the sun is out.  -- Jayron  32  06:06, 18 June 2011 (UTC)


 * There is a risk in doing this with a telescope, however: leaving the telescope statically pointed at any planet visible before sunrise means that the Sun could eventually enter the field of view–exploding the telescope. ~ AH1 (discuss!) 15:12, 18 June 2011 (UTC)


 * Or permanently blinding you if you happen to be looking through it at the moment. 67.169.177.176 (talk) 20:25, 18 June 2011 (UTC)

If we(humankind) build 1 000 000 000 starships, Project Daedalus mass, that is around 50 000 tons each
If we(humankind) build 1 000 000 000 starships, around Project Daedalus mass, that is around 50 000 tons each.

We would use only resources found and mined on Moon. How big percent of Moon mass such advancement consume? Will humans who would still live on Earth notice any change to the ocean tides, how Moon shrink in size at nighttime?

Most of that 50 000 tons of every ship would consist of hydrogen, and to some degree of carbon/aluminum/lithium. Other elements would have trace mass compared to ship total mass.

I'm not talking about how industrialization would change texture of visible side of the Moon, only asking about visible perception of the size of the Moon and how huge would be consequences of building 1 billion of such massive ships on Earth ecology("tides" might not be the perfect choice of words, but Moon affect see level due to gravitational influence, please excuse my English).

76.64.30.242 (talk) 03:47, 18 June 2011 (UTC)


 * The Moon's mass is 7 kg. Your ships mass only 5 kg, and hence they would have essentially no impact on tides or Earth ecology.   Dragons flight (talk) 04:40, 18 June 2011 (UTC)


 * Even if we would build 100 billions of such ships (lower estimate of number of starts in Milky Way), we would still get 5 kg vs 7. Am I correct? So that mean building 100 billion of starships each 50 000 tons would still barely affect Moon(in terms of size and diameter), in fact it would consume only less then one thousands of Moon mass? Do I understand yr calculations correctly? 76.64.30.242 (talk) 04:58, 18 June 2011 (UTC)


 * The moon has that much hydrogen? Plasmic Physics (talk) 05:24, 18 June 2011 (UTC)


 * I think it should have to have that much. If building those ships consume only 0.1% of Moon mass... But not sure. 76.64.30.242 (talk) 16:00, 18 June 2011 (UTC)


 * You might be interested in Advanced_Automation_for_Space_Missions. ( I faintly remember there was once even a wikipedia article on that, but if so it has probably been deleted for political correctness or something like that. ) 5BYv8cUJ (talk) 10:58, 18 June 2011 (UTC)


 * Question: How would that article be politically incorrect?
 * Question: Since when does wikipedia delete articles for being politically incorrect?
 * Dauto (talk) 19:36, 18 June 2011 (UTC)
 * You might be interested in Mogis. 5BYv8cUJ (talk) 20:47, 18 June 2011 (UTC)


 * The article you are linking to was only deleted on the German wikipedia which is well known for it's strict and controversy inclusion policy which as is most important in this context, rather different from the English wikipedia one. You appeared to be referring to the deletion of an article on the English wikipedia earlier so the policy of the German wikipedia is irrelevent to this discussion.
 * Your confusing and unsourced claims not withstanding, I find zero evidence we ever had an article on Advanced Automation for Space Missions. There is however extensive discussion at Self-replicating machine and Clanking replicator. There is brief mention in Asteroid mining. And evidentally the public domain I presume NASA study report from wikisource was used as the original source while writing parts? of Powder metallurgy and Cold welding and is used as WP:RS in Self-replication. Rather a lot of usage and mention for something we supposedly 'deleted for political correctness' which as 5BYv8cUJ pointed out doesn't even make sense (what's politically incorrect about it?).
 * Nil Einne (talk) 06:21, 19 June 2011 (UTC)


 * Answer to your second question: Since when does Wikipedia editorially trash formerly well-written articles for purposes of censorship and ban users such as myself for attempting to revert the damage caused in this manner? I tell you from personal experience, the commie WikiMafia (what the hell, no article?) has been doing this for a year or more! 67.169.177.176 (talk) 20:31, 18 June 2011 (UTC)


 * User:Paul Siebert has only ever been blocked once, for violating a 1rr on Mass killings under Communist regimes (not the article you linked to). If an article is under 1rr by arbcom restrictions (including discretionary) or by comunity consensus, it is a hardline rule with few exemptions. Nothing to do with censorship. If you add stuff to an article multiple times against multiple people removing it you will also break the 1rr. If you are unfamiliar with this, I suggest you read up on policy. The reason of course is to encourage discussion on a collaborative encylopaedia rather then blind edit warring which usually benefits no one. In fact, from my experience a lot of the time those who will accuse others of censorship when they remove something they want in the article and so are willing to break 1rr (or 3rr) will themselves be quite willing to do the same when it comes to adding content they do want. Or in other words a lot of the time the problem arises because of users inability to put aside their strong POV and to colloborate which will mean they are both willing to 'censor' content as well as add 'unwanted' content.
 * Incidentally, the 1 and only block for User:Paul Siebert was less than a year ago. Also 5BYv8cUJ and Dauto was referring to the deletion of articles which is a different thing from the removal of content from an article which is not delete. If you didn't even understand that, perhaps it explains any problems you may have had in collaborrating.
 * P.S. From further research the 1rr at Mass killings under Communist regimes arises from the well known Eastern European area. Anyone who has ever dealt with that area or looked at the infamous mailing lists knows it is a hell hole. Also I'm even less surprised User:Paul Siebert has had problems before. He? seems to think that 1rr means whoever has the most users 'wins' because they have greater numbers but while that may make mathematical sense, it makes no sense for anyone who has any understanding of the nature of wikipedia particular trouble articles under arbcom restrictions and high scrutiny. In reality if it ever comes down to that the article will quickly be locked and the participants in such a mass edit war will probably all be banned since 1rr is not and never a right and people who think it is or that it will be treated like one clearly don't understand how things work. Ironically though, User:Paul Siebert himself was clearly aware at the time that 1rr doesn't actually function to allow censorship since he's clearly aware people from either 'side' can be blocked.
 * Nil Einne (talk) 06:21, 19 June 2011 (UTC)
 * Just to clarify: User:Paul Siebert is not my wiki-profile (is there such a word?), but actually the one who had trashed the article Extermination through labor and then got me blocked when I tried to revert his vandalistic edits (that was a few days, maybe a couple weeks before that other flap with the article Mass killings under Communist regimes). Anyway, here's what happened: the article Extermination through labor used to have two main sections, one discussing the Nazi concentration camps (which still exists substantially unchanged), and the second one discussing the Soviet gulags (which used to be titled "In Communism" -- analogously to the first section title "In Nazism" -- but has been changed to "Controversial cases").  What Paul Siebert did was, he changed that second section by deleting information (even direct quotes from WP:RS) that substantiated the assertion that extermination through labor was taking place in the gulags, and instead added a bunch of sources that questioned and/or denied that assertion.  Naturally, when I saw this I totally blew up (after all, several people from my own family had been repressed by the Soviets in various ways) and tried to revert it (unsuccessfully).  I still hold a grudge against Siebert -- not because he unjustly got me blocked, but because he did so in the process of advancing an ideology that has caused untold pain and suffering in many countries around the world -- and in fact, if I ever get around to starting an alternative wikipedia of my own (for which I have tentative plans) and he joins it, I will consider preemptively putting a topic ban on him editing any article that has to do with Marxism.
 * As for the difference between deleting articles and removing content from articles without deletion, of course I understand this full well. The reason why I brought up the matter with Extermination through labor is not to try to somehow conflate the two, but to illustrate my point that Wikipedia does in fact carry out censorship for political reasons. 67.169.177.176 (talk) 21:00, 20 June 2011 (UTC)
 * This isn't the right place to talk about this (meet me at the talk page); in brief, I think there was a rationale for focusing the article, but it is important not to abandon the goal of making an article to cover all such abuses including workhouses and Jim Crow. Wnt (talk) 01:15, 21 June 2011 (UTC)
 * Workhouses and Jim Crow did not involve any attempts to exterminate people, unlike the gulag. Don't you understand the difference between just plain forced labor (which is still wrong) and extermination through labor? 67.169.177.176 (talk) 05:03, 21 June 2011 (UTC)
 * Certainly the workhouses had that overall intent; if the English had figured out a way to make sausage out of the Irish and the poor there wouldn't be one left today. Admittedly Jim Crow was the brainchild of people who knew how to keep slavery going for extended periods, but the system had considerable tolerance for casualties, and calling that "accidental" is beneath us. Wnt (talk) 17:10, 22 June 2011 (UTC)
 * Haven't you even READ the articles you linked to, dammit?! I have, and in the article Workhouse it DOES NOT say anything not just about "extermination", but even about any kind of excessive mortality!  On the contrary -- it CLEARLY SAYS that the food was usually "nutritionally adequate" -- NOT something that would be the case if you set about to work people to death!  And the ONLY THING that Jim Crow had in common with slavery is that both were designed to keep blacks in a degraded position -- Jim Crow wasn't even a system of forced labor, but rather a system of racial discrimination, and if anything it would in some cases prevent blacks from gaining employment, rather than forcing them to work!  Quit making up stuff out of your head and passing it off as historical facts, will you?!?! 67.169.177.176 (talk) 21:24, 22 June 2011 (UTC)


 * Thank you! Looks interesting. 76.64.30.242 (talk) 16:01, 18 June 2011 (UTC)

Why would we want to do that? Cuddlyable3 (talk) 12:57, 18 June 2011 (UTC)


 * Maybe if we have to evacuate all of mankind from Earth for some unforeseen reason (nuclear war, alien invasion, etc...) 67.169.177.176 (talk) 20:33, 18 June 2011 (UTC)


 * Maybe the hydrogen could come from hydrogen-alpha from the Sun. ~ AH1 (discuss!) 15:10, 18 June 2011 (UTC)
 * ?? I'm assuming that's meant as some sort of joke...? H&alpha; (hydrogen-alpha) is a particular type of red light emitted by excited-state hydrogen atoms; it isn't a type of hydrogen. TenOfAllTrades(talk) 15:51, 18 June 2011 (UTC)


 * The fusion proposed for Project Daedalus can't do with Hydrogen (H1) but needs Deuterium. 5BYv8cUJ (talk) 15:57, 18 June 2011 (UTC)


 * I know, but by the time we would seriously talking about mass production of star ships, fusion technology should be perfectly possible with ordinary hydrogen. Reaction is harder to archive, but fully possible. 76.64.30.242 (talk) 16:11, 18 June 2011 (UTC)


 * p+p-reactions depend on the weak force and therefore are very slow. I guess there are many "cheaper" alternatives. You might be interested in Astrochicken (as an idea, not to take it literally). 5BYv8cUJ (talk) 22:09, 18 June 2011 (UTC)


 * Astrochicken idea do outshined by what is known in my language as Von Neumann probes. Closest article here - Von Neumann probes. It is much easier to imagine them, but IMHO synergy/composite idea, when self replicating starships used for first couple generations, or even first few dozen generations, and then model switch to simple "build a single starship" for every star system out there would be more efficient, both in terms of complexity and in terms of speed of exploration. My current understanding (we talking about very distant future, like 70 years from now), there would be more economical to build not a Von Neumann probe per se ("just" a single one!), but instead robotic based industry on Moon or Eris, and use that body as a base to build a billion, or 5 hundreds billions probes to target every star system in Milky Way. If for any reason that would not be possible, then create similar base on nearby Alpha Centauri or any other nearby planetary system. And use it for mass production. But it looks like potential damage to Moon would be so negligible, thus Eris or close-by star systems do not have to be targeted. Not to mention trillions of bodies in Oort cloud... My original question was - how damaging would be such activity to the Moon? Hopefully no one cares about Eris. Seems that Moon still be pretty much intact after massproduction of billions of starships. Anyhow, here is science paper that was exploring different strategies of Milky Way exploration: http://www.rfreitas.com/Astro/ComparisonReproNov1980.htm  Hope you find it interesting. 76.64.30.242 (talk) 01:51, 19 June 2011 (UTC)


 * Plenty of reasons possible, including but not limited to exploration of our Galaxy. Imagine NASA thousand years from now wanting to send probes to each star in Milky Way. Was wondering how big loss of mass Moon would suffer if matter would be taken solely from it. 76.64.30.242 (talk) 16:07, 18 June 2011 (UTC)

Seven people per ship? μηδείς (talk) 02:15, 20 June 2011 (UTC)
 * You migth be interested in Golgafrincham. 5BYv8cUJ (talk) 18:28, 20 June 2011 (UTC)
 * 50,000 tons is about 1/2 that of a US aircraft carrier, so these must be ultra-luxury yachts. Googlemeister (talk) 13:59, 20 June 2011 (UTC)

Space telescopes
--58.174.69.136 (talk) 06:39, 18 June 2011 (UTC)How can people using Space Telescopes work out details like the atmospheric composition of a planet 30 light years away? How do they achieve such amazing resolution and sensitivity?58.174.69.136 (talk)
 * I think that feat has not been completed yet. read spectral lines to understand how that can be done. Dauto (talk) 07:19, 18 June 2011 (UTC)
 * Here's an example of detecting Oxygen on an exoplanet approximately 150 light years away. http://www.spacetelescope.org/news/heic0403/ Pretty good resolution and sensitivity I believe. — Preceding unsigned comment added by 101.169.7.177 (talk) 09:55, 18 June 2011 (UTC)

Accuracy of Altitude measurements
When the "height above sealevel" of somewhere like Mt Everest is given, what exactly is the reference system used to compare sealevel and altitude? Could it be "distance from the centre of the earth"? In that case sealevel must have a pretty wide range of "distances from the centre of the earth" with the earth being the shape it is? (ie bulged out at the equator etc). Is the centre of the earth an easy thing to define? I assume earth-orbiting satellites travel around the "centre of mass" of the earth, so radar altimeter measurements would use that as their reference point? Is it possible to tell if Pacific islands like Kiribati are "sinking" (as in getting closer to the centre of the earth) or suffering from local increase in sealevel? I know this is a lot of questions, but any answers or links to appropriate reading would be much appreciated — Preceding unsigned comment added by 58.174.69.136 (talk) 07:08, 18 June 2011 (UTC)


 * These days points of altitude are referenced from the World Geodetic System 86. Satellite interferometry can even measure continental drift of a few centimetres per year. --Aspro (talk) 07:17, 18 June 2011 (UTC)


 * What you ask is a major surveying challenge on which whole books have been written. The idea is to work out where the sea level would be close to the mountain and then work out the elevation from that.  Graeme Bartlett (talk) 11:03, 18 June 2011 (UTC)


 * The world's tallest mountain in terms of the greatest distance between the Earth's centre and the mountain's peak is Mount Chimborazo. As for Pacific nations such as Kiribati and Tuvalu, they are being innundated because of current sea level rise. When land actually drops and sea level stays the same, this is subsidence but the result is the same: saltwater intrusion. ~ AH1 (discuss!) 15:07, 18 June 2011 (UTC)


 * See the article geoid, which I believe describes what Graeme Bartlett is referring to. The geoid is a mathematical description of a surface which would coincide exactly with the mean ocean surface of the Earth. The height above sealevel is calculated relative to the geoid. --NorwegianBluetalk 16:26, 18 June 2011 (UTC)
 * In the last few decades mountaineers and geographers have been able to use the Global Positioning System to determine the geometric height of mountains and other landmarks of interest. Prior to the advent of the GPS, measurements were made using pressure altimeters.  The datum was an assumed air pressure of 1013.25 hectopascals, as specified in the International Standard Atmosphere.  This arrangement was sufficiently accurate for the time, but is nowhere near as accurate as the modern GPS.  Dolphin  ( t ) 12:20, 19 June 2011 (UTC)

Lunar eclipse
Ok, so I imagine this will be one of those "stupid questions", but nonetheless: Recently there was a lunar eclipse with a lot of media attention. As I understand it, a lunar eclipse happens when the alignment of Earth's shadow in front of the Sun obscures, or partially obscures, the visible moon. So what is the difference between a lunar eclipse, and the phases of the moon? Don't we often see the shadow of the Earth affecting visibility of the moon; i.e a crescent moon, half moon, etc.? Quinn &#10048; BEAUTIFUL DAY 07:10, 18 June 2011 (UTC)


 * The phases of the moon have nothing to do with the earth's shadow. They are simply the result of where the moon is in relation to the sun and the observers, us. Think about looking at a ball which is lit only by a single light off to one side. The lit up part you see is equivalent to a phase of the moon. The article Lunar phase may help, but it looks a bit heavy to me. HiLo48 (talk) 07:16, 18 June 2011 (UTC)
 * Shit. My first instinct was correct:  It was a stupid question.  Phases of the Moon specifically states that the lunar phases are not a result of Earth's shadow.  Good grief!  But in my defense, Lunar eclipse really offers no help with this question. Quinn &#10048; BEAUTIFUL DAY  07:19, 18 June 2011 (UTC)
 * An eclipse of the Moon is always the Earth's shadow passing across a full Moon. Cuddlyable3 (talk) 12:49, 18 June 2011 (UTC)
 * The phases of the Moon are caused by the Moon's shadow, so to speak, just like nighttime on Earth is caused by the other half of Earth blocking the Sun's light. During a total lunar eclipse, the Earth's umbra obscures the entire Moon. What usually happens during a full Moon instead is that the Moon's tilt above or below the Earth's ecliptic is too far away from any part of Earth's shadow during the greatest point of Full Moon that the Moon completely misses the shadow and you get no eclipse; conversely, during a solar eclipse, the shadow cast by the Moon lands on the Earth when it would usually miss the Earth completely. ~ AH1 (discuss!) 15:04, 18 June 2011 (UTC)


 * And, as far as observations go, a lunar eclipse varies from a change in phase in two ways:


 * 1) It's much quicker, lasting only minutes instead of about 28 days.


 * 2) Since the radius of the Earth is larger, the radius of the shadow cast on the Moon is larger during a lunar eclipse. StuRat (talk) 23:03, 18 June 2011 (UTC)


 * Lunar eclipses can last a few hours. Dauto (talk) 16:06, 19 June 2011 (UTC)


 * Another way of thinking about the difference is this: Lunar phases involve only 2 celestial bodies, the Moon and the Sun.  We here on Earth are simply observers, and we could just as well be observing from Mars (assuming we had a telescope that could let us observe from that distance).  But a lunar eclipse involves 3 bodies: the Moon, the Sun and the Earth.  The Earth's shadow on the Moon is a fundamental part of this scenario.  --   Jack of Oz   [your turn]  23:10, 18 June 2011 (UTC)

Kill or capture a household fly
How can I kill or capture an irritating fly in my living room? Whacking it with a rolled-up newspaper would damage things, and I always miss. Going to buy some fly paper would take too long. In the past I captured a fly alive by covering it with a very large plastic bag, but I havnt got a large enough bag, the fly is very agile, and the clutter in the room makes it more difficult. Thanks. 92.29.126.21 (talk) 11:59, 18 June 2011 (UTC)
 * You must disable it. You can buy a charged racket and wave to those fly. When the fly pass though those grid, its nervous system will temporary disabled.Nilman (talk) 12:31, 18 June 2011 (UTC)


 * Take a fairly large, preferably see-through container which has, or in which you can create, a small entrance aperture: an empty 2-litre soft drinks plastic bottle might work, or an old mesh meat cover.
 * It helps if you can make the entrance convex to the inside of the container, perhaps by making and fitting an open ended paper tube in it. In the case of the plastic bottle, you could cut off the top just below the shoulders, reverse it to sit in the top of the main body, and tape it in place.
 * Put something smelly and attractive to the fly into it.
 * Wait until the fly enters the container, then close the aperture. Because the entrance/exit is small, difficult to find and (depending on the created configuration) difficult to negotiate from the inside, the fly will not have time to escape even if it sees you coming.
 * This is an adaption of the old method, common in freshwater angling, of knocking a hole in the recessed conical bottom of a wine bottle, baiting the closed neck, submerging the apparatus in a stream, and using it to catch small fish for use as bait for larger fish. {The poster formerly known as 87.81.230.195} 90.201.110.145 (talk) 12:33, 18 June 2011 (UTC)
 * Butterfly net. Cuddlyable3 (talk) 12:43, 18 June 2011 (UTC)
 * I can think of two ways. One is to create a cone-shaped container with some meat or other aromatic food in the middle, and a small hole at the bottom through which the fly can fly in, and hang it up in the room. The fly is unlikely to fly underneath in order to get out. Also, if you have a see-through curtain in any room, try to wait until the fly gets close to the window there. Trap the fly between the curtain and the window, and do whatever you need to do next. ~ AH1 (discuss!) 15:00, 18 June 2011 (UTC)

What I do is wait until the fly sits on a wall, get a drinking glass and a piece of paper large enough to cover the glass. Then put the glass slowly over the fly. You then gently move the paper betweeen the wall and the glass, this pushes the fly into the glass. You then take the covered glass outside and release the fly. Usually this takes me one or two minutes per fly. If the fly is flying around a lot, then this won't work well, but then you can move the fly by making the room dark, open a door to another room and put a light on in that room. The fly will then fly toward the light and thus leave the room. Count Iblis (talk) 15:32, 18 June 2011 (UTC)
 * Flyswatter. 75.41.110.200 (talk) 15:45, 18 June 2011 (UTC)
 * Eventually a fly goes to the light in the window. Given drapes, shades, etc., it is difficult for it to get back, and easy for misfortune to befall it.  But when I was younger my pleasure was to do battle with the fly using a can of Lysol (essentially spray alcohol) and a lighter.  It only harms the wings, and then the rest of the fly is yours to experiment with at your leisure.  I think I blame Dragonriders of Pern for that. ;) Wnt (talk) 18:35, 18 June 2011 (UTC)

No-one's mentioned just squirting it with bug spray yet? Flies are very, very quick - but even they struggle to dodge an aerosol spray (most of the time anyway). --Kurt Shaped Box (talk) 18:46, 18 June 2011 (UTC)


 * Once upon a time some brilliant person cogitated very deeply on this very problem, and came up with a brilliant and creative solution. It is known as a "flyswatter". Looie496 (talk) 18:55, 18 June 2011 (UTC)


 * Incidentally, the reason a flyswatter works better than a newspaper is that it has holes to let the air pass through. Thus the flyswatter moves faster, due to the lack of air resistance, and there's no whoosh of air in front to blow the fly out of the way.


 * Another approach I've had luck with is to open a window (yet leave the screen in). The fly will go to the screen, then I close the window behind it and leave it closed until the fly dies (a few days, typically).  I usually "mark" the window in some way as a reminder not to open it too soon.  I have one trapped right now, as a matter of fact, and a toilet paper roll tied to the pull string for the blinds is my reminder.


 * I suggest you close doors to restrict the fly's movements, and then open all the windows it can reach, to maximize the chances of catching it quickly. Also, a warning on fly paper, it's very messy, getting brown glue all over anything it touches.  StuRat (talk) 19:28, 18 June 2011 (UTC)


 * That sounds like a lot of trouble to kill the fly rather than just letting it fly away outside. Are fly corpses useful? Rckrone (talk) 19:57, 18 June 2011 (UTC)


 * "Letting it fly outside" involves leaving a door or window open (without a screen) until it decides to leave on it's own, by which time several more insects are likely to have flown in. StuRat (talk) 22:29, 18 June 2011 (UTC)


 * Depending on the species of fly, a flyswatter may not be effective unless the fly is at rest on a surface. I'm not entirely sure what species of fly this is (it's smaller than a bluebottle, medium-sized-ish) - but there's one in the UK that's very good at evading attempts to swat it in mid-air. FWIW, a vacuum cleaner hose can be good against flying insects - I once sucked up 30+ wasps from my living room (nest was in an air vent) with the Dyson... I don't see why it wouldn't work on flies. --Kurt Shaped Box (talk) 20:36, 18 June 2011 (UTC)


 * I've also used a vacuum cleaner on stinging insects. The big advantage is that they don't see it as an attack, so don't get angry and try to sting you, unlike trying to swat them.  However, this doesn't apply to flies, and flies are also often faster with a more chaotic flight, so catching them this way may not work. StuRat (talk) 22:39, 18 June 2011 (UTC)

Why don't you just try an exploit, doing something useful with it? No, no, thanks, don't feel worthy enough for that myself, thank you all the same. 5BYv8cUJ (talk) 19:47, 18 June 2011 (UTC)

There are self-replicating robots available that catch flies and use them to make copies of themselves. Unlike sprays, fly swatters, etc. they are free of charge.Count Iblis (talk) 02:51, 19 June 2011 (UTC)
 * True. AndyTheGrump (talk) 03:01, 19 June 2011 (UTC)


 * You might want to make sure it's not The Fly. "Be afraid. Be very afraid." HiLo48 (talk) 03:00, 19 June 2011 (UTC)
 * Or better yet, the 1950s version with David Hedison while he was still known as Al. "HELP ME! HELP ME!" We also need a companion to the flyswatter pic: The Far Side cartoon called "the last thing a fly ever sees." ←Baseball Bugs What's up, Doc? carrots→ 06:46, 19 June 2011 (UTC)


 * As a practical matter, one trick is to position your hands apart and a few inches above the fly. As soon as it moves, clap your hands together, and there's a reasonable chance you'll get it. Then, of course, wash up. You don't know where they've been (although you can guess). ←Baseball Bugs What's up, Doc? carrots→ 06:55, 19 June 2011 (UTC)


 * Here's a technique my father taught me. Take a long thin pole (bamboo garden poles for keeping plants upright work well) and a length of elastic cord. Fix the end of the elastic to the end of the pole, stretch the elastic back along the length of the pole and hold it against the pole with one hand. Stand back from the fly and aim the pole at it (you can get quite close if you go slowly). Once you are lined up just let go of the end of the elastic. It's the flyswatting equivalent of a sniper rifle. Equisetum (talk &#124; email &#124; contributions) 07:51, 19 June 2011 (UTC)


 * We've just got rid of a fly in our living room by opening the window and waiting for it to head towards it. Is that not an option in this case? --TammyMoet (talk) 10:12, 19 June 2011 (UTC)

Or you can try to do brain surgery on a fly to turn it into a remotely controlled spying machine. You can e.g. let it fly into the CIA headquarters without anyone noticing it... Count Iblis (talk) 14:59, 19 June 2011 (UTC)
 * Gotcha! It was you who sent that spy fly that Obama swated! (This is a totally new aspect of a no-fly zone.) 5BYv8cUJ (talk) 15:08, 19 June 2011 (UTC)
 * Back in the early 90s, when they were talking about a no-fly zone in Iraq, Jay Leno said, "What we really need is a no-fly zone around Denny's!" ←Baseball Bugs What's up, Doc? carrots→ 18:12, 19 June 2011 (UTC)


 * Bit of a long shot on having the right materials around, but this method always worked when I was a kid: Spray Starch. Hit the fly with a short burst; it will drop out of orbit within two seconds when the starch dries. Advantages: the product, if you have it, is cheap; you can expel the fly with no harm to either party, if that's a concern; and unlike many other products, the overspray does not stain and wipes up if needed with a damp cloth.
 * DaHorsesMouth (talk) 01:19, 20 June 2011 (UTC)
 * Plus, it's nontoxic (unlike bug spray). 67.169.177.176 (talk) 04:11, 20 June 2011 (UTC)

Does Gamma Ray travels slower than Light Speed?
Those are from Wikipedia:Gamma ray burst: "gamma-ray bursts are thought to be highly focused explosions, with most of the explosion energy collimated into a narrow jet traveling at speeds exceeding 99.995% of the speed of light." But ALL electromagnetic wave travels as a constant speed in vacuum. Gamma ray is a kind of electromagnetic wave. Gamma-ray travels at 99.995% of the speed of light. So there's a contradiction, Why?Nilman (talk) 12:16, 18 June 2011 (UTC)


 * I don't really know but if you think of the "gamma-ray burst" not as the gamma rays but as the explosion that accompanies and/or generates them, this would resolve the paradox. 5BYv8cUJ (talk) 12:40, 18 June 2011 (UTC)


 * As 5BYv8cUJ says, the explosion itself is of matter: just how this is partially converted into gamma rays is not yet properly understood, and is the subject of ongoing research. See the Emission mechanisms section further down in the article from the quote, and the longer and more detailed article Gamma-ray burst emission mechanisms to which it links for current theories. {The poster formerly known as 87.81.230.105} 90.201.110.145 (talk) 12:46, 18 June 2011 (UTC)


 * That's the speed of the jets. The gamma rays move at the speed of light. Dauto (talk) 19:29, 18 June 2011 (UTC)

Thank you.Nilman (talk) 09:51, 19 June 2011 (UTC)

Did the military have mobile phones?
In an episode of the 1960s series I Dream of Jeannie, Don Rickles played a senior military officer who was putting the astronauts through rigorous military training on a remote area of what I believe was a military base. He stayed in touch with the people in charge using a telephone in a bag of some kind. It looked like regular phones looked back then, and it had a wire connected to something. The mobile phone article doesn't seem helpful. Vchimpanzee ·  talk  ·  contributions  · 16:19, 18 June 2011 (UTC)
 * Our article on field telephones describes these devices. Looie496 (talk) 18:06, 18 June 2011 (UTC)
 * When I think of field phones I always imagine some pioneers laying wires. I guess by the sixties these would have been replaced by wireless walkie-talkies. But still without any possibility to play pac-man. 5BYv8cUJ (talk) 18:42, 18 June 2011 (UTC)


 * Actually, two-way radios first appeared during World War 2, but they were big and heavy (typically taking up a whole standard-issue Army backpack). 67.169.177.176 (talk) 20:38, 18 June 2011 (UTC)


 * Yes, so only a few soldiers were assigned to carry them, meaning anyone isolated from those soldiers was out of communication with everyone else. Also, since there weren't many, they could all be destroyed in battle, cutting off communications with the entire group. StuRat (talk) 22:35, 18 June 2011 (UTC)
 * The Motorola SCR-300 was used during WWII - it weighed 32 lb or 38 lb depending on the battery and had a range of 3 miles with the long aerial. BTW the website olive-drab seems good for this sort of info, it's where Google led me. CS Miller (talk) 09:58, 19 June 2011 (UTC)
 * Coming back to the OP's question, the 1968 AN/PRC-77 Portable Transceiver is about the size of an ammo box, its externally identical predecessor AN/PRC-25 Portable Transceiver was produced in 1962. However, the TV series may have shown Korean-War era equipment not Vietnam-War era, which would be the AN/PRC-10 -- CS Miller (talk) 10:08, 19 June 2011 (UTC)
 * Wireless telephones were first invented about a century ago, but the evolution of their practical usage was rather slow until the last 20 years or so. ←Baseball Bugs What's up, Doc? carrots→ 06:40, 19 June 2011 (UTC)
 * Thanks. I'll look at the other sites tomorrow. I'm sure field telephone is what I was looking for, though I think the Mobile phone and History of mobile phones articles (I forgot to list that second one above) should be updated with this informtion. I'm not sure just how to insert it since ther couldbe some overlap with radiophony. I don't want to just have two separate paragraphs on two topics that could be related. Vchimpanzee ·  talk  ·  contributions  · 18:23, 19 June 2011 (UTC)

Hitting cows on their noses
If you hit an imposing cow on the nose with a stick or a fist, will it likely turn more aggressive or turn and leave? --2.216.135.118 (talk) 19:25, 18 June 2011 (UTC)
 * Depending on the circumstances and the cow, it might do either. However, since "more agressive" may include seriously injuring or killing you, which a cow can do quite easily, you ought to avoid getting into such close contact with cows in the first place until you know what you're doing. In the UK, one or two farmers - who do know what they're doing - are nevertheless killed by cows every year, as sometimes are country walkers who venture into fields of cows and somehow annoy one or more of them (usually by having a dog with them). {The poster formerly known as 87.81.230.195} 90.201.110.209 (talk) 19:47, 18 June 2011 (UTC)
 * Cows become very aggressive when they have their young calves with them. They stampede and/or trample people to death. So stay away from cows with calves. 92.29.112.181 (talk) 19:54, 18 June 2011 (UTC)
 * Cows are inquisitive, and don't normally attack humans (though a bull might), but there are three situations when they might be dangerous:
 * 1. When a person is holding a dog (which the cow sees as a threat), so it is always wise to allow a dog to look after itself in an emergency.
 * 2. When they panic and "stampede", trampling anything that gets in the way, so move slowly to avoid frightening them.
 * 3. When anything gets between a cow and its offspring (in common with most mammals, including humans).
 * A stick might help if a cow is becoming over-inquisitive, but will not make any difference to a panicking cow and probably not to one protecting its calf.   D b f i r s   06:45, 19 June 2011 (UTC)
 * You forgot (4): When someone purposely annoys them by persistently waving a piece of cloth in their face. 67.169.177.176 (talk) 00:30, 20 June 2011 (UTC)


 * What's an "imposing" cow? One that always shows up right at suppertime? ←Baseball Bugs What's up, Doc? carrots→ 06:38, 19 June 2011 (UTC)


 * My wife has been in the "dog irritates cows that have calves nearby" while walking in one of those preserves in the East Bay, California. It's times like that that city slickers like us realize exactly how large a cow is. Fortunately they managed to talk their way out of it. --Mr.98 (talk) 18:36, 19 June 2011 (UTC)
 * I'm glad to hear that those cows were intelligent enough to respond to a reasoned argument from your wife and dog. I never seem to be able to get cows to understand what I am saying, but they do seem to respond to a calm tone of voice.    D b f i r s   21:21, 19 June 2011 (UTC)
 * Bovines have horns, and they know how to use 'em. ←Baseball Bugs What's up, Doc? carrots→ 18:41, 19 June 2011 (UTC)
 * One tip i learned from a farmer once when I was helping him feed his cows once was whenever you are near cows, never get between a cow and anything solid: like a barn, fence, trees, the truck, another cow. Cows don't really know their size and don't take time to consider what they might be squishing when they move around. Vespine (talk) 01:22, 20 June 2011 (UTC)
 * I've heard they could even smash up a small plane (like Amelia Earhart's Lockheed Vega) just by leaning on it. 67.169.177.176 (talk) 04:15, 20 June 2011 (UTC)


 * Here we have "Dangerous Cows" for your reading pleasure. Bus stop (talk) 12:19, 20 June 2011 (UTC)

Woman killed by cow: http://www.desmoinesregister.com/article/20110619/NEWS/110619007/Update-Family-says-woman-died-protecting-toddler-from-cow?odyssey=tab|topnews|text|Frontpage μηδείς (talk) 16:32, 20 June 2011 (UTC)
 * With all due sympathy to the family, I love the description of the incident - "The cow hit her with its head and her heart stopped." That, folks, is how to write English sentences. Tevildo (talk) 18:35, 20 June 2011 (UTC)

Relative pulling power of one horse
I remember being told at school (decades ago) that there was an experiment or comparison of horse pulling powers done about 200 - 300 years ago, which showed relative powers (if I recall correctly) of: - horse can carry a few hundred pounds on its back (this was pre-metric) - pull about a ton in a cart on decent road - pull 8 tons on a metal rail - pull 70 tons in a canal boat

Is this correct? Is there a specific experiment or something that proved this, or did the knowledge just accumulate over time? — Preceding unsigned comment added by J987 (talk • contribs) 20:44, 18 June 2011 (UTC)
 * See Horsepower. James Watt is _reputed_ to have carried out the experiment (in 1782) to determine a suitable unit of power for his steam engines, but whether his results (as opposed to the magnitude of the unit) are reliable is a matter of debate. Tevildo (talk) 21:56, 18 June 2011 (UTC)


 * In the first case, the horse is actually carrying the weight, while in the rest, assuming level ground and no air or water flow, all that must be overcome is friction. In the cart and rail cases, there is a static friction to overcome to get things started (they must assume this to be worse for the cart).  In the boat case there is none of that, and only the fluid resistance of the air and water (which grows with speed).  Thus, to move the boat very slowly should require almost no effort, assuming no winds or water current.  In reality, I'd expect how much a horse can haul to vary dramatically depending on the horse, lubrication of the cart and train, condition of the road and track, and the winds and water currents. StuRat (talk) 22:47, 18 June 2011 (UTC)


 * You don't have to do any work to carry a weight unless you are lifting it. As long as the horse's back doesn't rise and fall too much as it moves, the energy required probably isn't much greater than overcoming friction in the other scenarios. (There may be some energy required to maintain the muscle tension required to hold up the weight, but that's biology not physics, so I don't know anything about it!) --Tango (talk) 22:55, 18 June 2011 (UTC)
 * Only in the simplifications of physics that are applied for students. In reality, you go and carry 50 lbs around on your back all day and tell me that isn't work.  Googlemeister (talk) 13:24, 20 June 2011 (UTC)
 * It gets complicated. Since horses don't have wheels on them, they need to to lift their legs to move.  The more weight distributed on each leg (in addition to their own weight), the more work this requires.  And they don't get all this energy back when they put the leg back down again, so energy is lost.  Depending on how the weight on their back is positioned, they may be able to reposition it a bit by their movements, and thus have less on each leg as they lift it.  This also would be affected by the type of walking or running done by the horse, as each has different legs off the ground at once.  Converting all this to physics formulae would be quite an effort. StuRat (talk) 23:09, 18 June 2011 (UTC)
 * They are only lifting the leg, so only the weight of the leg matters. The weight of the load will inevitably shift to the other legs, but that doesn't take energy. The weight of the load is only important if you actually increase the height of the load (which may happen slightly due to way the horse moves and will obviously happen if the horse goes up hill). --Tango (talk) 00:42, 19 June 2011 (UTC)
 * Why would the weight not matter on a level field? Certainly to support a weight, the horse must meet this weight with opposite and equal (and constant) force, otherwise the load would just fall to the ground?  Anecdotally, I can fairly easily hold a hundred pounds on my shoulders.  I can also easily walk 15 miles.  It would be extraordinarily difficult for me to walk 15 miles carrying a hundred pounds on my shoulders, but fifteen miles with fifteen pounds would be much more doable.  Why would a horse be different in that regard, other than the obvious fact that a horse can carry much more than I can? Falconus p  t   c 05:04, 20 June 2011 (UTC)
 * Edit: Part of that is that it would be extremely difficult, indeed I rather doubt that it's something I could to to hold a 100 pounds for three or four hours, regardless of distance walked. Falconus p t   c 05:10, 20 June 2011 (UTC)
 * Yes, the load makes a big difference in practice, much more than would be expected from the simplified physics of moving a load horizontally. As mentioned above, some of the work goes into raising and lowering the load an inch or two with each step, but probably more of it goes into the chemical energy expended in the muscles that have to deal with much higher tensions than normal.    D b f i r s   18:45, 20 June 2011 (UTC)