Wikipedia:Reference desk/Archives/Science/2012 January 11

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January 11

Mercator projection of Earth for a different rotation axis position

I put a climatology experiment on the shelf a while back because I searched all over and could not find a way to convert my globe or any map of the Earth to the new Lat./Long. alignment I created. As it is globes and maps of the Earth converted into the Merctor projection spread out what are the current 90° North/South axis points, the North Pole and the South Pole. I repunched my globe so that it rotates from the point on the current system at 30 degrees North by 173 degrees East, The new South Pole rotation axis at 30 degrees South by 7 degrees West.
This has nothing to do with any predictions of any future Earth, the reason I chose the middle of the North Pacific was because if frees up the most amount of land from being covered by snow and ice, obversely making the largest amount of land available as naturally habitable.
My curiosity is about the climates that would exist with such things as the Himalayas nearer the Equator, all of North America below the Arctic Circle (Alert, Nunavut like Miami, Florida), the Equator passing below Australia instead of above it with Antarctica instead like Australia, the change of orthographic rain patterns, new ocean currents, etc.
So I am asking if anyone can create a Mercator Projection for a globe that has the North pole at 30°N/173°E and the South pole at 30°S/7°W, or if anyone knows of a program, or anyway other way I can visualize and work with it other than actually painting my globe because I would like to have it all figured out before I take the step of painting my globe. 24.79.40.48 (talk) 02:14, 11 January 2012 (UTC)

Searching on "Oblique Mercator projection" might be useful. We also have an article on Transverse Mercator projection, which is the version that goes through the poles. As far as programs, you could try some Geographic information system software. It sounds like you just need some program that can make oblique Mercator map projections with user-defined parameters. Pfly (talk) 02:24, 11 January 2012 (UTC)

Oh and by the way, it's not clear to me why you need a Mercator projection. There are many map projections, and if you are mostly interested in visualizing an alternate axis there are probably better choices than Mercator. Pfly (talk) 02:29, 11 January 2012 (UTC)

If someone here can't help, you might try asking at Wikipedia:WikiProject Maps or Wikipedia:Graphic Lab/Map workshop. --Jayron32 02:30, 11 January 2012 (UTC)

The reason I chose Mercator is that I can roughly transfer ocean temperatures from other Mercator projections of the current poles that have been made to show the ocean temperatures at the current latitudes, and that in turn will affect the land temperatures. http://aquarius.nasa.gov/images/global_sst_map.jpg
Also it is the most common projection of the Earth, as far as I know, and I want to make the comparison. I'm an algebra person, trig is the worst for me, imagining the mathematical coversions seems like a nightmare to me. 24.79.40.48 (talk) 02:48, 11 January 2012 (UTC)

I can write a program to do it. Can you give me a reference map to transform? Ideally it shouldn't have any labels, because they'll obviously get severely distorted. --140.180.15.97 (talk) 02:56, 11 January 2012 (UTC)

If I had a "map" I wouldn't need a conversion (transform), I literally drilled new holes in my globe at 30°N/173°E and the South pole at 30°S/7°W,
I don't know what else I can give you. Any basic mercator projection would do if that's what you mean, even ones like these
http://danwbailey.com/wp-content/uploads/2012/03/earth.jpg
https://commons.wikimedia.org/wiki/File:Normal_Mercator_map_85deg.jpg

http://en.wikipedia.org/wiki/File:Peirce_quincuncial_projection_SW.jpg
http://en.wikipedia.org/wiki/File:Mercator_projection_SW.jpg
There was one like that last one that looked like a photograph there before.
http://upload.wikimedia.org/wikipedia/commons/7/74/Mercator-projection.jpg
It would also be helpful to be able to have a completely blank copy
http://www.freeusandworldmaps.com/images/WorldPrintable/WorldMercator6LinesPrint.jpg
If you could swap in various maps, and it would draw the new longitudinal and latitudinal lines after that it would be awesome!
24.79.40.48 (talk) 03:42, 11 January 2012 (UTC)

I couldn't access the first map, but here are transformed versions of the other three:

• http://i1234.photobucket.com/albums/ff408/ideasrule/mercator.png
• http://i1234.photobucket.com/albums/ff408/ideasrule/photolike.png
• http://i1234.photobucket.com/albums/ff408/ideasrule/blank.png

I also dumped the code as a comment, at the end of this section. --140.180.15.97 (talk) 22:42, 11 January 2012 (UTC)

Generic Mapping Tools can do stuff like this.

 ( GMT pscoast -K -R-180/180/-67/67 -Jo-7/60/173/-60/1:256000000 \
                                             -G200 -N1/0.25p -Dc ;
   GMT psbasemap -O -B30g10/30g10 -R-180/180/-67/67 -Jo0/0/180/0/1:256000000
 ) > tiltedmap.ps

The above command produces one very weird-looking map. 68.60.252.82 (talk) 05:59, 11 January 2012 (UTC)

The first two photobucket pics are great but the original lat/long lines are there and I'll have to do a lot of editing to remove them and add the new ones, The third photobucket pic looks like it is missing something since it is different from the other two in that Africa is much more warped. Thank you very much, that saves me a lot of work as it is. I'm now going to check out the software, and may have other comments. I just noticed the code that is surpressed as a hidden comment. Although I'm not sure why, it's not active code either way is it? 24.79.40.48 (talk) 07:15, 12 January 2012 (UTC)
I was wrong, because I chose a simple number like 30°N/S, the old lat/long lines make it ridiculously obvious where the new lines should go. 24.79.40.48 (talk) 08:04, 12 January 2012 (UTC)
♦ Pic of work in progress ♦ - 24.79.40.48 (talk)

Incremental cost per nuclear bomb

What is the rough incremental cost of building a nuclear bomb given that you are a nation state with the capability to refine the material and already have designs and tools to manufacture the bomb? I assume it varies considerably by bomb type, but I'm only looking for rough estimates, so I don't care too much about the details. I'm sure the research and development is very expensive, but if you ignore that part is it still very expensive? Dragons flight (talk) 02:38, 11 January 2012 (UTC)

The Brookings Institution's U.S Nuclear Weapons Cost Study Project has all kinds of interesting stuff. Their book "Atomic audit" (from page 93 onward) considers the question, "What do nuclear bombs cost?" (Google Books preview.)

The answer, in the U.S., has always been basically a secret, but there is some data out there. In 1973, in a congressional hearing, it was stated that the (later cancelled) W74 and W75 nuclear artillery shells would cost about $400,000 each, or a couple of million in today's dollars. In 1981, it was revealed that the W84 warhead was projected to cost $1.1 million apiece, or about $3 million today. And in 1990, the U.S. GAO accidentally let slip that the W80 had a unit cost of $720,000, or about $1.2 million today.

The book also notes that unit costs have been going up because of increasing complexity, and the later designs have often significantly overrun their budgets.

So the answer would seem to be from about a million dollars up.--Rallette (talk) 07:27, 11 January 2012 (UTC)

Also, the correct term is "marginal cost", so the google search string <marginal cost nuclear weapons> gives some results confirming the above answer, although they seem to be about fission bombs eg. [1] . IBE (talk) 09:48, 11 January 2012 (UTC)

Note that this makes it expensive from an average consumer point of view but on par with other big weapons. Each nuke is about 2X the price of a Tomahawk, 1/6th the price of an M1 Abrams, 1/20th of an F16, 1/1000th of a B-2. But you can't ignore the fact that the total prices are high. You're including R&D as the expensive part, and it's certainly expensive, but the biggest costs, by far, are from developing delivery vehicles (rockets and planes and etc.) and maintaining them in alert status and all that. The Brookings Institution page (and book) makes that pretty clear. The price doesn't stop once you have the nuke in hand, it only goes up. --Mr.98 (talk) 12:22, 11 January 2012 (UTC)

Research and development would be cheap because you don't need to reinvent the wheel. A basic nuclear pile (using uranium-238 with graphite moderator) can be used to produce plutonium cheaply. A plutonium processing plant can be built cheaply to produce plutonium. Hydorgen bombs using plutonium-239 can be built from the plutonium cheaply (as long as plutonium-240 is less than 7% of the plutonium). However, plutonium can be detected from space with satellites. If you don't want your nuclear bombs to be detected from space, then you need to build hydrogen bombs from uranium-235. U-235 processing from U-238 is prohibitively expensive even if you import the processing equipment. You need a lot of spare electricity either from a nuclear power plant or a hydro-electric power station. Also, U-235 processing takes a long time so you will have very few hydrogen bombs.
Sleigh (talk) 12:32, 11 January 2012 (UTC)

Detected from space? Yeah, let's see some evidence of that before we blindly claim it to be true. An engineer working 10 m from a plutonium warhead is receiving ~2 billion times the radiation that a satellite 500 km overhead receives. Either the engineer can't work there for more than about 30 seconds or the satellite can't actually detect anything above background noise. Now, granted, there are other ways that space-based reconnaissance can detect nuclear warheads, but none of them are particular to plutonium vs uranium designs. — Lomn 14:24, 11 January 2012 (UTC)

Alright, I'll bite. I've long suspected that plutonium could be detected from space (ever since they caught some fellow driving across then still East Germany with a pound of it rolling around in the back of his car) but can you point us to a source saying they definitely do it, and more importantly how? Plutonium doesn't say anything about satellites or spacecraft, at least, and we ought to add it. ;) Wnt (talk) 14:19, 11 January 2012 (UTC)

You can't detect quantities of plutonium from space. If it is unshielded there are ways to detect it terrestrially (looking for specific radiation) but it's not hard to shield. The odds are your specific East German incident is either related to regular old radiation detectors, or from human (not technical) intelligence. Plutonium-producing reactors give off characteristic emissions that can be detected by plane (maybe by satellite, I don't know). Plutonium facilities are generally pretty large and look pretty distinctive, so plain old satellite photography is used in many instances. If you could detect raw plutonium metal from space, it would vastly simplify the problem of keeping all of it under control... I wish we could! --Mr.98 (talk) 16:21, 11 January 2012 (UTC)

You're confused on a few points here. R&D is still not cheap — you don't have to reinvent the wheel, but if you don't already have means of making nuclear reactors, extracting plutonium from spent waste, and fabricating the explosives and etc. in the right shapes, that still costs. If you don't already have a nuclear complex, then it's not cheap. (And if you already have one, then you've already spent the cash on R&D.) This isn't to say you have to make a Manhattan Project's worth of effort, but it's still not cheap. Probably a billion or so USD at the minimum.

Nuclear reactors of sufficient size to produce sufficient amounts of plutonium for weapons purposes are not cheap to produce. If you already have lots of civilian power reactors, then you just need reprocessing facilities. Still not straightforward.

You can't "detect plutonium from space." You can detect the signatures of various nuclear facilities from space. But not plutonium itself. Production reactors and reprocessing facilities are fairly detectable, though. But so are uranium enrichment facilities, on the whole.

Why you would jump from U-235 to hydrogen bombs, I don't know. You can have perfectly good U-235 bombs without trying to make hydrogen bombs. Hydrogen bombs are much harder to manufacture than fission bombs, and the general consensus is that you won't be able to produce them without doing nuclear testing first. Which probably excludes the possibility of making them covertly. You seem confused about what hydrogen bombs are. --Mr.98 (talk) 16:16, 11 January 2012 (UTC)

Molecular form of carbon gas

If pure carbon is heated above the sublimation temperature in a closed vessel, what molecular form will the gas be? C1 (monatomic), C2 (diatomic), or C3 (tricarbon), or a mixture? I would have thought that it would be a mixture with a temperature-dependent proportions as with other gasses like dissociated oxygen or hydrogen, but references indicate that C2 and C3 are rare transient forms. I cannot find any arrhenius data for C3 + x > product reactions, not any relative enthalpy data, which would allow calculation of the proportions. Does such data exist? Does anyone know a good reference? 121.221.232.241 (talk) 02:53, 11 January 2012 (UTC)

Buckminsterfullerene C₆₀ sublimes as C₆₀ gas and is interesting in that there is no liquid phase, whatever the pressure or temperature. (triple point above critical point). Wikipedia articles are at dicarbon and tricarbon but they do not answer your question. Graeme Bartlett (talk) 03:12, 11 January 2012 (UTC)

[2] talks about creation of carbon gas using a laser pulse, and all three of your carbon forms are produced. C₂ must be pretty stable as it is detected in carbon stars. [3] has some data for C2 if you can understand it. Graeme Bartlett (talk) 04:24, 11 January 2012 (UTC)

Thanks Graeme. I can understand it with difficulty. More help from somebody would be nice. AKH121.215.152.114 (talk) 05:32, 11 January 2012 (UTC)

Suicide bombing

Do suicide bombers feel pain at the time of explosion? If yes, how long? --Amoeba159 (talk) 07:18, 11 January 2012 (UTC)

Yes, for the rest of their lives.--Shantavira|^{feed me} 08:35, 11 January 2012 (UTC)

Have any of them ever survived long enough to describe the pain of having their legs and arms ripped off in a split second, or their entire stomach blown up, or to express any remorse for what they did to innocent others? -- Jack of Oz ^{[your turn]} 08:51, 11 January 2012 (UTC)

Plenty. These guys tend not to be the brightest buttons in the box and a lot of them mess up.--Shantavira|^{feed me} 08:57, 11 January 2012 (UTC)

Jeff Dunham#Achmed the Dead Terrorist. No, they do not. Plasmic Physics (talk) 09:36, 11 January 2012 (UTC)

A simple search finds [4], I'm sure there are others. Note that in this case it doesn't appear he had planned to be a suicide bomber, rather he was (probably intentionally) caught in the blast of a remotely trigerred device. Nil Einne (talk) 13:59, 11 January 2012 (UTC)

There are various stories of people being caught in explosions (e.g. IEDs and mines), and looking down to see body parts missing without having felt anything. Also similar stories about people being shot without realising. So it's possible they wouldn't feel it. But some have survived explosions so there should be accounts somewhere (albeit surviving would be far more painful). --Colapeninsula (talk) 10:11, 11 January 2012 (UTC)

In such an explosion, you are ripped apart faster than what your central nervous system can communicate a sense of pain. Shock isn't even an issue. Plasmic Physics (talk) 10:23, 11 January 2012 (UTC)

I recall a figure of 120 m/s for nerve communication. A simple test is to let a friend squeeze your to and measure the time from squeeze to detection ;) Electron9 (talk) 13:57, 11 January 2012 (UTC)

I do not see a value for nerve conduction velocity in either the Nerve conduction velocity stub nor the Nerve conduction study or Action potential articles. Someone please help out with a referenced value! DMacks (talk) 06:34, 12 January 2012 (UTC)

Yo, self, read more carefully! Action potential#Myelin and saltatory conduction gives several values for the speed and discusses what affects it. DMacks (talk) 07:21, 12 January 2012 (UTC)

As they say: the proof of the pudding is in the eating. Many a great scientist experimented upon themselves. So, if the OP would like to offer themselves up to science, I'm sure we can test this out. Then, with the aid of a Ouijaboard or two, we can elicit the answer as to whether it hurt or not and for how long. We might even create an Wikipedia article in s/his honour, for s/his quest to resolves this often pondered about question. Should s/he feel a little ambivalent or harbour any reservation about this suggestion, then do please let s/him voice them, so that we can reassure s/him with a suitable Wiki-vote. As you know, we treasure verifiability and will do almost anything to secure a good source. --Aspro (talk) 19:58, 12 January 2012 (UTC)

Black lung

Are there any plans of research for future treatment options of black lung disease, or plans of research for a cure to completely rid the disease in a person? 71.146.10.10 (talk) 11:32, 11 January 2012 (UTC)

The only things I can find as a possible treatment for Coalworker's pneumoconiosis are lung transplants: [5] and [6], breathing exercises and lung lavage: [7] SmartSE (talk) 13:02, 11 January 2012 (UTC)

Interesting lead. See also PMID 8794962, which says lavage gets out about a gram of dust in a treatment. What I find interesting about this treatment is that macrophages should be able to be directed to move. In concept, I would think that the right migration factors added to the lavage fluid or inhaled beforehand ought to increase the yield of dust-laden macrophages considerably, whether the dust is coal or silica. Wnt (talk) 14:56, 11 January 2012 (UTC)

Oh, thanks. 71.146.10.10 (talk) 06:25, 12 January 2012 (UTC)

"Black lung" isn't a disease in the conventional sense. It's the damage & scarring of the lungs due to inhaling coal dust. Either the dust itself damages the tissue, or macrophages surround the dust but can't remove it from the body. The aveoli are very sensitive, so you can't just scrape the dust or macrophage clusters out without causing more damage to the tissue. — The Hand That Feeds You:^Bite 18:59, 11 January 2012 (UTC)

A possibility might be cell cultivation to build new lungs. But there are problems with cancer and structural support and associated nutrition support system ie blood supply. When these problems will be solved is any ones guess. Another option might be some kind of fluid or gas that would react with foreign objects in such way that they can be removed or dissolved. But both options requires plenty of research to be of any use! Electron9 (talk) 20:37, 11 January 2012 (UTC)

Okay, thanks. What exactly are the possible long-term effects of this disease? 71.146.10.10 (talk) 06:48, 12 January 2012 (UTC)

Electron in a magnetic field

Recently in a physics test, a question was this: "An electron with a constant speed enters a uniform magnetic field in a direction perpendicular to the magnetic field. What is the shape of the path that the electron would follow?

• Parabolic
• Circular
• Elliptical
• A line parallel to the magnetic field"

The answer is circular, but however I try to think about it, I do not understand why it is not parabolic. Can anyone please explain? Chaosandwalls (talk) 16:42, 11 January 2012 (UTC)

is it not Helical? Basically, the force is always(?)(F = v x B) perpendicular to the velocity. circularity is probably provable from this rule. The centripetal force in uniform circular motion is also perpendicular to the velocity if you recall. Cplusplusboy (talk) 17:10, 11 January 2012 (UTC)

It would be helical, if not for the stipulation about the direction being perpendicular to the field. --Trovatore (talk) 18:53, 11 January 2012 (UTC)

It can be viewed as a matter of symmetry.

There are no changes in potential energy involved here, so the electron can't change speed, because a change in speed would change the electron's kinetic energy, which would mean that the total energy was violating the conservation of energy. There's nothing preventing the electron from changing velocity, but only the direction of the velocity can change, not the magnitude.

Furthermore, the electron starts off with a zero component of velocity parallel to the magnetic field, and a zero component of force parallel to the magnetic field, which means that there's a zero component of acceleration parallel to the magnetic field, so the electron remains with a zero component of velocity parallel to the magnetic field.

If you put the above two together, at any time t₁, the electron's properties and environment must be the same as at the initial time t₀, in that the electron is still travelling at its initial speed, perpendicular to a uniform magnetic field of the same magnitude. If the electron's properties and environment are the same at the two times, except for a change in coordinates used to measure those properties consisting of at most a translation and a rotation, then the shape of the electron's path at the two times must be the same. A circular path has the property that the shape of the path (specifically, the curvature) is the same at all points along the path. A parabolic or elliptical path would not have that property. So the right answer must be the circular path. Red Act (talk) 18:44, 11 January 2012 (UTC)

I have a hunch as to why you thought the path would be parabolic. The path would indeed be parabolic, if the force on the electron were constant. But although the magnitude of the force is indeed constant, the direction of the force changes as the direction of the electron's velocity changes. Red Act (talk) 20:59, 11 January 2012 (UTC)

I think I understand in now. Thank you very much. Chaosandwalls (talk) 23:01, 11 January 2012 (UTC)

As always, elementary physics courses teach electron gyro motion in the form of a spherical cow. The problem specifies a dramatically simplifying assumption: a perfect and uniform magnetic field that is encountered instantaneously and with no edge effects or fringing or transient field intensity rise. In reality, no magnetic field behaves like this; but in reality, the motion of charged particles in magnetic fields is very hard to analyze. So, the physics student should work within the parameters of the canonical problem definition and solve the equations of motion, using the Lorentz force. The solution to this equation is circular motion with a specific angular frequency that only depends on the intensity of the magnetic field, the charge, and mass, of the electron. Note that the electron's kinetic energy (... ergo, its velocity) does not affect the resonant frequency. This result is important and empirically useful, because it still applies fairly well even when the other simplifying assumptions do not. In more advanced studies, you may encounter other invariant plasma parameters - derived observables that are independent of other variables in the system. Nimur (talk) 22:08, 11 January 2012 (UTC)

Buying a Telescope : list of celestial objects versus magnification required

My friend is planning to buy a telescope. Is there a site/page which lists as a table the magnification (and aperture or other parameters) versus the objects (planets, nebulae, saturn's rings, jupiter's red spot, its satellites, pluto ;) asteroids, comets) that can be seen. This to decide what magnification(and diameter) to buy assuming he already has a list of bare minimum celestial objects he wants to see. (Budget is also limited). I suggested that he visit a planetarium, but he wants to make it a regular hobby. Cplusplusboy (talk) 16:56, 11 January 2012 (UTC)

As a rule, you should completely ignore any mention of magnification when shopping for a telescope. Further, any telescope that puts the 'magnification' in the biggest type or in the most prominent place on the packaging gets a major red flag, and is apt to be toy store junk. (High magnification factors also make the telescope harder to aim, will need to be re-aimed more often as objects will move faster across the tiny field of view (unless you have a properly-set-up motor drive), make faint objects fainter by spreading out their light over a larger area, and accentuate any optical defects in the telescope or eyepiece.)

Our article on Apparent magnitude has a table with the brightnesses of a number of solar system objects (planets, asteroids, moons) as well as some important stars, galaxies, and nebulae.

The following web sites offer advice on buying a telescope:

• Astronomy Today] has an excellent, multi-part FAQ
• Heretic's Guide - offers quick recommendations for a given price range, though you really should get to the more-detailed (but still brief) FAQ.
• Scope Reviews has advice for the beginning amateur astronomer—it's worth it to scroll to the bottom of the page to see the 'reality check' comparisons between what you'll be able to see at the eyepiece and professional astrophotos.

A big consideration is how and where your friend plans to use his telescope. Some scopes will fit in a lunch box or a large purse, some need a van and three people to move. A lot fit between those two extremes. TenOfAllTrades(talk) 17:33, 11 January 2012 (UTC)

Just to explain a little further, far more significant than the magnification is the amount of light the telescope can collect, which means the size of either the mirror (reflecting telescope) or the objective lens (refracting telescope). A good telescope will come with a range of magnification options.--Shantavira|^{feed me} 17:50, 11 January 2012 (UTC)

Light is much much more important than magnification. Department stores usually display telescopes claiming to get something like 500x magnification, but that's just nonsense; while you may get the 500x magnification, all you'll see is extremely blurred images. Go to a proper store and get a decent light collecting scope. With patience and experience, you'll be able to see almost all the planets and many nebulae. Just don't expect too much out of a small telescope; you won't be able to see any features on Venus and Mars (Jupiter and Saturn look great though), and the nebulae take a lot of practice. You'll also be doing your friend a favor by gifting him a good, steady mount. Lynch7 18:19, 11 January 2012 (UTC)

To spend a fat wad of cash on a really nice telescope if you live in and will use it in an area with lots of light pollution would also be a waste. 69.243.220.115 (talk) 19:31, 11 January 2012 (UTC)

Partly true; where I live, the light pollution is so high that I've never been able to see Polaris in my life (not kidding there). But the Moon and objects near the zenith look great. Lynch7 19:38, 11 January 2012 (UTC)

I agree with previous speakers. Any good telescope will come with a set of exchangeable eyepieces and, using the right eyepiece, you can get any magnification you want. Whether you can see anything at that magnification, that really depends on the diameter of the lens/mirror.

You did not specify your budget, but, based on the description above, a 6-inch or a cheap used 8-inch reflector should do the job, a basic one of these could be had for about US$250 (if you opt for a manually aimed model, that is, without an electric motor and a computerized aiming system.) --Itinerant1 (talk) 20:44, 11 January 2012 (UTC)

I know nothing about telescopes, but I was suprised that "As a rule, you should completely ignore any mention of magnification when shopping for a telescope." Say you want to see lunar craters in close-up detail, or Jupiter's spots, or something, does it not help to have a high magnification? Is it not even essential? 86.179.113.11 (talk) 02:05, 12 January 2012 (UTC)

One of many essential factors. But magnification alone is meaningless, as mentioned above. StuRat (talk) 02:12, 12 January 2012 (UTC)

Read this.--Itinerant1 (talk) 02:23, 12 January 2012 (UTC)

Magnification is equal to the objective's focal length divided by the eyepiece's focal length. If you want a higher magnification, you can just go out and buy an eyepiece with lower focal length. Alternatively, you could buy a Barlow lens, which are often higher-quality and less expensive than low-focal-length eyepieces. --140.180.15.97 (talk) 06:29, 12 January 2012 (UTC)

As an added note, short focal length (higher apparent magnification) eyepieces tend to have a shorter eye relief. Eye relief is just the maximum distance allowed between final surface of the eyepiece and the front of your eye that still allows you to see the entire image. Short eye relief (less than about 15 mm) means that viewers must remove their glasses in order to get close enough to see the entire field of view; lenses with very short eye relief can be uncomfortable to use for extended periods of time. Eyepieces with a short focal length and a long eye relief do exist, but they are more complex, cost more money, and in some cases can be heavy enough to tip a smaller telescope. A 2x Barlow lets you use the same eyepiece (with the same eye relief) but get twice the magnification. TenOfAllTrades(talk) 14:14, 12 January 2012 (UTC)

The reason that magnification is irrelevant is because you can construct a projective optic, (or use a digital system) to magnify anything to any magnification. It is a fact of optical physics: arbitrary values of magnification can be obtained (at the expense of clarity and brightness, e.g. photon-resolution and photon-count).

The important parameter in an optical system (at least, one that's being set up as a telescope) is primarily its angular resolution. The second-most-important parameter is the amount of light it collects. Both of these parameters directly correspond to the size of the primary (usually, the objective mirror or the primary lens, unless you have a "weird" telescope - I guarantee that you will not find one of those in a telescope store).

Of course, don't discount other usability parameters: are the optics high-quality? Is the scope sturdy? Can the optics be calibrated? (Do you want to have calibrated optics? If you don't know what you're doing, it's easy to miscalibrate the mirrors on a higher-end scope; but if you buy a cheap scope that can't be calibrated, and the mirror bangs out of alignment, you'll never be able to repair it!) Is the scope convenient to use? My major tube is 203mm, and it's really heavy. I basically can't take it anywhere that I can't get my SUV to. This works alright, because I have an SUV, but a scope this size is not an option for everyone. A lighter scope would probably be useful for a lot of the things I image, but I have a really good telephoto-lens, so the trade-off for me is a little different. On the other hand, despite already being clunky, I sometimes wish I had a larger scope when I'm shooting Jupiter moons. It's really about usability: my scope is already large enough that it can't be taken out casually; so for me, the opportunity cost of having a bigger and clunkier scope is not really very huge. My next upgrade will be a bit larger.

One of the things that a first-time scope-buyer may be surprised about is the tripod. Spend almost as much on tripod and mount (combined) as you spend on optics. If you've got a good scope and nothing to mount it on, you're wasting your time!

Finally, if you plan to view, almost any scope will work. If you plan to photograph, you should be a little more particular: make sure your scope is well-matched to your camera. Can you buy a mount that fits your SLR? (Almost all scopes fit T-rings to the eyepiece, so you'll need a converter for your camera). Will your be able to project through your barlows and your eyepieces or are you going to have to shoot straight to the sensor? Are you shooting through a point-and-shoot? Can you buy an afocal mount that lets you affix your point-and-shoot for afocal imaging? Are you planning to buy an astrocamera (e.g., a direct imager, without any other optics)? Does your scope fit that? Will your mount and tripod support the weight of all this extra gear? (My mount has configurable weights, so when I add on 10 or 15 pounds of Nikon gear, I usually have to recalibrate that).

As a last note: my 200mm primary is right on the edge where it can take a useful photo of Jupiter (direct, focal imaging). It can do some pretty fancy afocal imaging of the Galilean moons, too, when I'm patient enough. If I were to attempt to shoot Earth's moon, I have to be very careful not to burn my camera sensor. You may want to invest in filters, if you like Earth's moon, which can be very bright. At 200 mm, my biggest problems are not my scope: they are, in order of importance: (1) compensating Earth's rotation (and/or scope wobble as a result of compensation); (2) Earth's atmosphere, when I shoot locally; (3) the rotation of Jupiter, and the motion of its moons around the planet; (4) the temperature gradient between my primary and my camera inside my optical tube; and (5) electronics imperfections in my Nikon. If you feel like tackling these challenges, this is a good size scope. Nimur (talk) 20:46, 12 January 2012 (UTC)

Thank You. I will look at the scope diameter, and ability to change eye-piece. As far as I'm concerned, watching big white spots is not really interesting. It would not be worthwhile if I could not see the rings of Saturn and Jupiter's red spot. In you opinion what else are interesting features to look at? O.P 203.200.153.7 (talk) 11:47, 13 January 2012 (UTC)

Clouds on Jupiter are pretty fascinating; they are easy to view and moderately easy to photograph. Personally, I'm more interested in planetary imaging than deep-sky objects or stars; in my opinion, most of the interesting observations of those other astronomical objects are not done in visible light nor with ground-based telescopes, so they're really not well-suited for the beginner amateur astronomer; after you have a lot more experience, and a lot more money sunk into equipment, they may be a worthwhile pursuit.

When Jupiter is up, it is my favorite target; I have also shot Saturn, Mars, and Venus. My greatest efforts so far have been focused on obtaining photographs with better resolution than 1 pixel per Galilean moon. It can be a little emotionally taxing to spend so much effort and still obtain such fuzzy photos; but we've all really been spoiled by the space program, with its flyby missions to faraway worlds. Trying to photograph these objects from Earth's surface helps put in perspective the magnitude of the accomplishment of space flight - especially crafts that can produce such incredible Jupiter Moon photos. Bear in mind that the distance from Voyager II to IO was some 10-million-times closer than the distance from me to San Francisco; and Voyager had a slightly larger camera-budget.

I have also used my scope for some fascinating landscape photography. Shooting Jupiter is only slightly more difficult than photographing San Francisco from the open spaces at the south end of Skyline Boulevard. With Jupiter, the target is moving pretty fast (and is on a different planet), but on the other hand, there's a lot more air between myself and San Francisco

I would just close this by reminding you why anyone looks through a telescope in the first place. You have to be interested in seeing things. If you aren't interested in seeing things, then chances are, spending a lot of money on glass and metal won't make you interested. But, you might find other benefits by adopting unique perspective of looking at things in space. It becomes difficult to look at Earth in the same way - or to say another way, you begin to realize that Earth is just another fuzzy dot that's barely visible, even with a lot of effort. Nimur (talk) 17:46, 13 January 2012 (UTC)

The rings of Saturn can be seen with a quality 4 inch aperture, or certainly a 6 inch aperture. For observing Jupiter's cloud features, a 6 inch is probably a good minimum. Here's an interesting guide about looking at Jupiter, and what sort of equipment you might want. Buddy431 (talk) 22:21, 13 January 2012 (UTC)

Pure energy

Hi, in popular science settings I sometimes hear the phrase "pure energy". From what I can gather, this actually means electromagnetic radiation. Is that correct? Is there any other form in which so-called "pure energy" could exist? Furthermore, given the equivalence between matter and energy, how is electromagnetic radiation any more "pure energy" than, say, a lump of rock? 86.179.113.11 (talk) 18:40, 11 January 2012 (UTC)

I think you're right to be skeptical of the term "pure energy". Energy is a property of a system or an object, not an object or substance in and of itself. Everything which is known to exist always has additional properties besides energy. For example, photons have a nonzero spin. If you want to describe a particle with a zero rest mass, then the way to say that is that the particle has a zero rest mass. The phrase "pure energy" is meaningful as a disco group and as an album, but it's not a good physics term. Red Act (talk) 19:04, 11 January 2012 (UTC)

Interestingly, the Turkish word for "lip synching" is pronounced "positive energy". --Trovatore (talk) 19:07, 11 January 2012 (UTC)

Electromagnetic radiation isn't even pure energy, like everything else it has energy. For that matter, what is impure energy? Plasmic Physics (talk) 23:13, 11 January 2012 (UTC)

You also have gravitational radiation which must also accompany any electromagnetic radiation in a minuscule amount, so even electromagnetic radiation in a vacuum is not pure.[8] Potential energy is another form, and once you go to derived forms you can have thermal energy. Graeme Bartlett (talk) 02:12, 12 January 2012 (UTC)

Maybe impure energy is energy which has been contaminated with un-energy. Plasmic Physics (talk) 03:02, 12 January 2012 (UTC)

Are you getting pure energy mixed up with zero-point energy?
Sleigh (talk) 03:34, 15 January 2012 (UTC)

Me or the IP? Plasmic Physics (talk) 22:52, 15 January 2012 (UTC)

"wrought iron" vs "forged iron"

What is the difference between "wrought iron" and "forged iron"? Is there any? --82.113.98.208 (talk) 18:56, 11 January 2012 (UTC)

Wrought iron is an iron alloy with a very low carbon content, and fibrous inclusions known as slag. Forged iron is iron which has been forged. One term refers to the metal's composition, the other term refers to how the metal was shaped into the desired shape. Some wrought iron is forged, but not all wrought iron is forged, and not all forged iron is wrought iron. Red Act (talk) 19:17, 11 January 2012 (UTC)

It depends on the sense in which you mean wrought iron. According to our article, the term can refer to the composition of iron, or to the methods used to make a certain piece. The two are conflated, because iron products made by bending required the iron to be malleable enough not to crack. In particular, in modern usage, it seems to mostly apply to the method, not the source material:

"Wrought iron is no longer produced on a commercial scale. Many products described as wrought iron, such as guard rails, garden furniture and gates, are made of mild steel. They retain that description because they are wrought (worked) by hand."

For modern products, "wrought iron" usually means "mild steel worked by hand". SemanticMantis (talk) 19:28, 11 January 2012 (UTC)

Thanks. --89.204.130.47 (talk) 19:10, 12 January 2012 (UTC)

So is the wording at Bronze (history) correct then or could it be improved? --92.202.74.103 (talk) 06:15, 14 January 2012 (UTC)

steroids before steroids

Basically, I'd like to know whether there were other methods of chemically enhancing performance of athletes back before steroids were invented? How far back? What were these substances called? How effective were they?

An argument came up recenly in an online debate that I participate in that http://www.sandowplus.co.uk/Competition/Pandour/pandour.htm this guy, Bobby Pandour, could not have juiced because he died before 1927. Would he have access to drugs or whatever they called it in those days that improved performance (made his muscles bigger, etc.)?

Thank you, Agtren. — Preceding unsigned comment added by 68.8.168.251 (talk) 23:20, 11 January 2012 (UTC)

Ergogenic_use_of_anabolic_steroids has a bit of brief information about historic performance enhancing substances. The references (e.g. http://web.archive.org/web/20071008174029/http://www.dopingjouren.se/page.asp?page=history) also include further information on the subject. I personally no nothing about any of this so may be getting wrong end of stick - hopefully the above helps anyhow ny156uk (talk) 23:32, 11 January 2012 (UTC)

Just yesterday I visited the (Australian) National Sports Museum in Melbourne. A display on drugs in sport had a little poster saying that ancient Greek athletes ate the testicles of sheep in order to boost their testosterone levels. Obviously I have no better source at this stage, but it's a quality museum. HiLo48 (talk) 01:21, 12 January 2012 (UTC)

There are lots of places you can find this story. Google "sheep testicles doping" or "sheep testicles steroids". They also tried bulls. A quick history lesson: in 1889 Brown-Sequard published his famous paper on self-injection with testicular extracts and claimed self-rejuvenation. In 1929 Koch and associates treated a human enuch with "testicular substance" and proved its effectiveness." In 1935 David and co-workers isolated crystalline "male sex hormone" from bull testicles. Von Restorff (talk) 13:16, 12 January 2012 (UTC)

I got all that just from reading the article. However, it also says eating testicles to boost testosterone doesn't work. Was there another way to boost testosterone levels before invention of steroids? I need something more solid as evidence. Anybody? Agtren — Preceding unsigned comment added by 68.8.168.251 (talk) 17:30, 12 January 2012 (UTC)

I think you may get some mileage from examining Chinese medicine. Ephedrine, which is a stimulant, comes from Ephedra which is a Chinese plant, for example. It may take some digging to find which plants act as artificial steroids though. Wang Junxia's coach, Ma Junren, claimed that the success of the athletes he coached was due to drinking teas made from particular plants/animals, for example. What exactly these particular substances were, or what they contain, has (from what I can see) never been fully ascertained.--TammyMoet (talk) 18:07, 12 January 2012 (UTC)

Chemical performance enhancement in general is quite a broad topic. The myth of Jason and the Argonauts includes an account that Medea gave him an unguent which one source asserts to be Rhodiola rosea.^[9] While of course it is a fanciful tale, the story gives a pretty precise description of a flower whose sap is used, warning that its effect lasts only a day (on the other hand, it does include a direction for him to sprinkle his shield with it...). I do have a problem believing the source I cited though, as the flower I see in the Wikipedia article is yellow and the flower of saffron is purple... (though maybe they just mean saffron as traded?). Still, I can't shake the feeling that some real plant is being described in the story. Wnt (talk) 19:40, 12 January 2012 (UTC)

As for testosterone, there must naturally be some in Rocky Mountain oysters; I'd think it should be somewhere near the right order of magnitude to be effective. Note that oral testosterone works but it is partly degraded by the liver, some suggest partly degrading the liver in the process. I didn't find a precise figure for the testosterone per "oyster" as generally traded, though, and without the number I can't suggest the magnitude of the effect. Wnt (talk) 19:42, 12 January 2012 (UTC)

There's widespread documentation of baseball players using amphetamines as performance-enhancers well before the current steroid era. See e.g. here. Meelar (talk) 22:02, 12 January 2012 (UTC)

Some of the many substances that were used in the old days that are now being re-discovered because of the crackdown on doping: Vitamin D, Acetyl L-Carnetine, Alpha-Lipoic acid, Creatine and Sodium bicarbonate. Count Iblis (talk) 01:23, 13 January 2012 (UTC)

Are identical twins common in any non-mammalian species?

I understand that identical twins are common in mammals such as cats, sheep, ferrets, and deer. Are identical twins common in any non-mammalian species?82.31.133.165 (talk) 23:29, 11 January 2012 (UTC)

I would assume all New Mexico whiptails born from one mother are practically identical to each other, since whiptails reproduce by parthenogenesis, though, as the whiptail article states, the children are not perfect clones of the mother. 69.243.220.115 (talk) 00:16, 12 January 2012 (UTC)

This book: [10] has a whole chapter on sexual clonality in nature. It says that, in some parasitoid wasp species, hundreds of clone-mate 'twins' can emerge from a single zygote. My understanding is that, in species which this occurs, it would be very common. Further references to the academic literature are given in the google books link above. SemanticMantis (talk) 00:39, 12 January 2012 (UTC)

And to add to the list of mammals with twins, don't forget the curious case of the armadillo (most members of the genus Dasypus typically have identical quadruplets). StuRat (talk) 02:17, 12 January 2012 (UTC)

Thanks for your answers, everyone. I especially look forward to learning more about parthenogenesis and the work of Avise on the division of the parasitoid wasp zygote. 82.31.133.165 (talk) 14:46, 12 January 2012 (UTC)