Wikipedia:Reference desk/Archives/Science/2009 July 13

= July 13 =

Tornado Hypothesis
Hi all,

I would like to open a discussion about a thunderstorm and tornado hypothesis I have developed. Where in Wiki would be the best place to present the theory and data I have compiled as it is to long to be placed here? Thanks
 * Original research doesn't belong anywhere on Wikipedia. There are lots of places where you can start a blog; that's what you need. Looie496 (talk) 05:53, 13 July 2009 (UTC)
 * Yeah, see Wikipedia's no original research policy. Blogger is one very popular place to start a blog.   It’s what my girlfriend uses for her dog agility blog.  The blog article would be a good place to start to find other possible places to host a blog.  Red Act (talk) 06:20, 13 July 2009 (UTC)
 * http://weather.wikia.com might be suitable (I don't know their policies, you'd have to ask there), or you could search for a meteorology discussion board. AlmostReadytoFly (talk) 08:55, 13 July 2009 (UTC)
 * I'm thinking that looks like an OK forum and on  there's even a discussion on tornadoes. These are good places to discuss your hypothesis. As other stated, wikipedia would have been the wrong place :-) EverGreg (talk) 09:30, 13 July 2009 (UTC)


 * Once your hypothesis is published in reputable, peer-reviewed journals (Nature (Journal) or The Journal of the American Meteorological Society - for example) - and has perhaps been received favorably at some prestigious meteorological conferences - then Wikipedia should probably have an article about it. But until then, it's just some idea some guy had...and if we had articles about every idea any random person had - we wouldn't be an encyclopedia anymore!  Our job is to collect facts - and your hypothesis isn't yet a fact - other than "It is a fact that you thought about it"...and that's not a particularly notable fact.  Good luck with turning your hypothesis into a theory!


 * Remember: A good hypothesis explains phenomena for which we currently have no good explanation - and it makes predictions that can be tested experimentally. SteveBaker (talk) 11:42, 13 July 2009 (UTC)

INMARSAT segment
Does anyone know what are network coordination stations (NCS)and Network operations center(NOC)in the ground segment of INMARSAT satellite system? or any other info about segments of INMARSAT..ThanksShraktu (talk) 11:58, 13 July 2009 (UTC)

What do mango pleco's eat?
What do mango pleco's eat?Mangopleco (talk) 14:23, 13 July 2009 (UTC)
 * This site says it's an aufwuchs eater: "Feeding off the bottom of the aquarium, it gets most of its nutrition from left over food and algae. If there is no algae or left over food present, supplement with high quality flake food, sinking carnivore pellets, freeze-dried bloodworms, and tubifex". --Sean 15:54, 13 July 2009 (UTC)
 * Possibly avoid too much meat and give veg. —Preceding unsigned comment added by 83.100.250.79 (talk) 16:32, 13 July 2009 (UTC)
 * Baryancistrus by the way - possibly L47
 * Wood - ie Bogwood or driftwood is a very good idea - for juveniles it can be essential - not only does the wood provide roughage - but aufwuchs can grow and colonise the driftwood far better than glass/other things in the aquarium.
 * They might like soft leaved plants like cabomba (they will totally eat it if they do)
 * Also in the aquarium catfish wafers (ie plec wafers are good)
 * Also any vegetable - cucumber, spinach etc.
 * Also algae.
 * 
 * or just search for "mango plec feeding"83.100.250.79 (talk) 16:31, 13 July 2009 (UTC)

Was this a question about a pet fish? What they eat in the wild is different.83.100.250.79 (talk) 17:44, 13 July 2009 (UTC)

As above, almost all plecs eat aufwuchs (also see periphyton which is pretty much the same thing)
 * http://www.scielo.br/scielo.php?pid=S1679-62252005000400011&script=sci_arttext Here someone cut open a dead baryancistrus (not the same species) and found - guess what - aufwuchs.
 * Also see this http://www.planetcatfish.com/shanesworld/shanesworld.php?article_id=382 - it's about plecs in general - some dead ones that people are going to eat (if you are very squeemish) - there are some interesting images
 * Image 11 - Aufwuchs - if you are wondering what aufwuchs are - they are the tiny things that live on slimy rocks that you find in a river - image 11 is of slimy rocks - they eat the slime, the things that live in the slime, and the green algae that is part of the slime.
 * In fact they are alot like sheep or cows - that eat grass - constantly grazing (obviously they are smaller)
 * Last image - very long stomach.
 * Also in the wild they will eat dead stuff - eg dead fish, or dead animals that have fallen in the water - ie carrion. But most of the time they just graze - they're not fussy eaters.83.100.250.79 (talk) 17:58, 13 July 2009 (UTC)
 * Note that aufuchs/periphyton contains a lot of small insects and larvae - so there is 'meat' in it - a bit like meat and vegetable stew.83.100.250.79 (talk) 18:00, 13 July 2009 (UTC)

Alcohol and Exertion
Not medical advise. I get exceptionally winded when working out hard for more than 20 minutes. After that, it feels like I can't go on and my lungs are gonna burst. However, one day I went to a bar before hand and had a vodka shot with a friend. 15 minutes later, I went to work out and for some odd reason, I was able to work out beyond 20 minutes and not feel like my lungs were gonna burst. I was sweating, my heartright was up and I did the same exact thing I did everytime I went to the gym. So to test this again, I repeated this the next week. Monday, no vodka shot, same situation, winded after 20 mins. Tuesday, one vodka shot, was not winded. What medically could be happening? I am not looking for medical advise. I am asking those medically inclined how the alcohol could somehow affect the lungs in such a way that it allows for more oxygen, I dunno. --Reticuli88 (talk) 15:17, 13 July 2009 (UTC)


 * (Wild speculation) could it be that the alcohol relaxes your muscles a little? I'm just guessing, but without my inhaler any amount of sport is liable to make me gasping for a deep breath, yet with my inhaler (a wonder of modern medicine I might add) I can compete with almost all my friends in terms of longevity of energy. Perhaps the alcohol is having a similar impact as my inhaler does (which I think is that it relaxes the ventricles/something in my lungs to make breathing easier). ny156uk (talk) 15:43, 13 July 2009 (UTC)


 * Alcohol is known to dilate blood vessels (see here and here), increasing blood flow. I'm unaware of any information on the effects of alcohol on the lungs.  Disclaimers notwithstanding, you should direct any serious inquiries to a medical professional. &mdash; Lomn 15:52, 13 July 2009 (UTC)


 * Use of performance-enhancing drugs in the Olympic Games, Doping at the Tour de France, and List of doping cases in sport all list alcohol as a performance-enhancing drug (mostly from the lower-tech past). --Sean 16:04, 13 July 2009 (UTC)
 * While you might be correct, there may be some bias built into your experiment. The scientific controls would seem to be lacking, the exact amount of time you spend lifting vs resting, the quality of how you do the exercises, other things you've done that day, what classifies as "winded" and so on.  Just the belief you have formed that alcohol has improved your performance may affect your results.  Perhaps while you're trying things, however, you might have a go with caffeine - I've heard it's one of the most effective legal performance enhancing drugs and that many competitive athletes use it before events (I read specifically on runners).  TastyCakes (talk) 16:33, 13 July 2009 (UTC)


 * I agree with this. Scientific studies say that alcohol reduces the ability of muscle cells to use glycogen, their primary fuel.  Since alcohol also impairs judgement, it is likely that you're not really working as hard after the drink as without it.  I have to say that for me personally, the sedative effect of alcohol is so strong that I would never think of taking a shot before working out, it would make me too lethargic. Looie496 (talk) 17:05, 13 July 2009 (UTC)

Einstein equations for scalar field plus gravitation
My question is: Is it true that static solutions to the Einstein equations for a real scalar field coupled to gravity always have a singularity? I found this statement in several research papers, but without any reference to a paper or book where this is proved (I know that there exist some explicit examples of such solutions with singularities, but I am interested in a more general statement).XYZsquared (talk) 16:19, 13 July 2009 (UTC)

Amount of life on Earth
Is this quantity fairly constant? I guess you can interpret this question in terms of the number of living cells. Whenever any living organism dies it provides food and nutrients to some other organism which then can reproduce. So, barring a global catastrophe, is the amount of life on Earth constant? —Preceding unsigned comment added by 75.52.253.33 (talk) 16:47, 13 July 2009 (UTC)


 * Probably not. Atmospheric carbon dioxide and oxygen levels have varied quite substantially for the last billion years, and amount of sunlight available for photosynthesis was not exactly constant, either. Besides, different species comprised the bulk of the biomass at different times. So I do not see any solid basis for your hypothesis. Sorry. --Dr Dima (talk) 17:05, 13 July 2009 (UTC)
 * I'm not aware of any rigorous data on this, but I would say it's surely not constant across all time scales. On a yearly time scale, the amount of land life is quite a bit higher during the northern hemisphere summer than during the northern hemisphere winter.  On geological time scales, the total amount of life seems very likely to decrease during heavily glaciated periods, and also following catastrophes that lead to mass extinctions. Looie496 (talk) 17:11, 13 July 2009 (UTC)
 * Organic matter doesn't always get consumed by another organism. It sometimes gets turned into oil, for example. Limestone contains large amounts of animal produced calcite. There are various other examples of ways organisms get removed from the cycle. --Tango (talk) 17:40, 13 July 2009 (UTC)
 * The number of living cells on Earth may be constant over a decade, a century or a millennium. That is possible. I don't think there is any reason to believe that the number of living cells in one decade in time is likely to be any different from the number of cells alive in an adjoining decade. The questioner should specify what time frame is intended to be considered. Bus stop (talk) 17:53, 13 July 2009 (UTC)

white paint to fight golabal warming plan?
I read on CNN today the the US secretary of Energy wants to fight global warming by painting roads and the roofs of buildings white. My question is, will the amount of global warming fighting from the reflected sunlight be more then the penalty of producing millions of gallons of white paint? Googlemeister (talk) 18:25, 13 July 2009 (UTC)
 * I'm not going to calculate this. Where is that sunlight going to be reflected to? the heat will just be hanging around 4 feet above the roadways instead of 4 inches above. Overall I can't see it making any difference. The making of the paint and the labour to apply it would involve substantial costs, not to mention additional accidents from driving on glary and slippery roads. A white roof may reduce INTERNAL temperatures slightly in a building (but not as much as good insulation would). But the air above the roof is much hotter than over a dark roof which absorbs more heat (tho' this will radiate back more heat once the sun is off it). This is fine for keeping the interior of a building cool. Otherwise, this type of scheme just rearranges the deck chairs by a few feet; it won't reduce the total heat in the atmosphere....which is where global warming is happening, not under our wheels. - KoolerStill (talk) 19:01, 13 July 2009 (UTC)


 * Not quite true. White reflects a lot in the optical wavelengths. The atmosphere is quite transparent in the optical - that's how most of the heat came down from the sun in the first place. So a lot of the reflected light goes back into space. On a global scale this is a very small contribution. However, it reduces heat in cities and buildings, and hence reduces the need for air conditioning - which a) uses energy and hence (with the currently prevalent technology) causes CO2 production and b) adds to the urban heat island effect (there ain't no free lunch from the second law of thermodynamics...), causing cities to heat up, requiring more air conditioning... I don't know how quickly this pays of, but (some) roofs need regular painting anyways, so painting them in a highly reflective color the next time seems like a no-brainer. --Stephan Schulz (talk) 19:12, 13 July 2009 (UTC)
 * Painting roads a reflective white sounds like a horrible idea for a sunny day. Not to mention it would make it difficult to stay on them or anticipate curves when they are covered in snow. Livewireo (talk) 20:52, 13 July 2009 (UTC)


 * It sounds like another bullshit solution for a real problem; instead of addressing the problem head on, lets propose an ultimately worthless and probably even harmful solution (see Ethanol fuel, especially Corn ethanol ). The better solution is to instead work on accelerating non-combustion technologies (like solar and wind) or to get the hydrogen economy up and running.  The problem with those solutions is not that they are substantially harder to implement, its that there are monied interests on maintaining the old infrastructure, or in coming up with solutions like ethanol fuel which was merely an excuse to make Archer Daniels Midland a shitload of cash.  These are all distractions from the real solutions, and the sooner we get on implementing the final solutions, the better we all will be. --Jayron32. talk . say no to drama  21:17, 13 July 2009 (UTC)
 * Not to mention an irresistible canvas for graffiti artists. Clarityfiend (talk) 22:07, 13 July 2009 (UTC)


 * Does anyone know whether their "back of the napkin" calculations included the green-house gases emitted in producing that much paint? Also what type of paint were they talking?  Whitewash won't stay put, so they'd have to consider something polymer like. They'd have to apply a pretty thick layer because otherwise it's just going to rub off in a hurry.  With a thick layer your road will get as slippery as ice or you'll have to add grit.  (OR around the corner from where I used to live in Germany a company managed to coat a bike-path in bright red polymer.  They had to redo it after the first couple of cyclist's accidents.)  Adding grit in turn will erode the rubber of tires like shoe-marks on no-wax floor, again leading to dark tracks.  Unless they come up with a formula for white asphalt this sounds like a half-baked idea.  Passing a law to have homeowners use white shingles when redoing their roof won't look pretty, will take a while to take effect (average roof life=10-15 years) but is doable. 71.236.26.74 (talk) 22:16, 13 July 2009 (UTC)


 * Putting the paint on roofs is not a silly idea - there are paints that aren't too harmful to the atmosphere - and it really doesn't matter if the stuff cracks and breaks up because 90% of the surface will probably still be reflective decades later. However, this isn't the thing that's going to save the planet - if it made a 1% improvement - I'd be very surprised indeed.  Picking lighter materials for the roof makes more sense - pale grey roof-tile rather than dark brown or black.  Waterproofed concrete roofs rather than tar-covered roofs - light-colored stone chips embedded in tar roofs where they can be retro-fitted.  Rooftop gardens are probably a yet better idea.  But there are two effects going on here.  One is that the total albedo of the planet is improved - but that's likely to be a tiny effect.  The other is that the interior of the building will be kept cooler - which in hot climates has the potential to dramatically reduce the amount of air-conditioning required.   I think that's actually the main reason for doing it - and you don't have to go so far as to have a totally white painted roof to do that.  Simply choosing lighter colored materials gets you most of the benefits.   Painting roads does seems like a bad idea - but building concrete roads instead of tarmac is probably a reasonable alternative.   The only snag is that concrete production uses a hell of a lot of energy and produces a TON of CO2.  Of course when we finally realise that we have to stop oil production, there won't be any tarmac around anyway - it's basically just a waste-product of oil refining...so no more oil refining means no more tar.  Currently, concrete is the only alternative...which is not so great. SteveBaker (talk) 23:06, 13 July 2009 (UTC)


 * Our so-called ecological footprint is largely a result of the technology we use and the energyconsumption - a person can do about 100 W of work, yet your average person's energy consumption is around 3000 W  (on average, not just working hours). That's our real impact. However, our literal footprint (the amount of surface we occupy on the planet) is not all that great. And most of that is agricultural land. The actual built-up area is just a fraction of the Earth's surface. I can't find any figures, but let's assume that's on average 20 m² per person (eg 200 m² for someone living in a 10 storey building). Let's take a world population of 5 billion. That makes for a total of 100 billion m², which is 100.000 km². Earth's surface is 500 million km². So our houses occupy about 0.2 % of Earth's surface. That's a tiny amount, and even that would require a major effort. There are much better ways to invest our time and money, to put it extremely mildly.
 * Also, not all roofs are fit for this. In Europe, most roofs have tiles. Not that that would not be doable, but it would be butt-ugly. Especially since white buildings have a tendency not to stay white, so you'd have to do a lot of cleaning. And, as anon points out, this is especially true for roads, where you get the extra disadvantage of drivers being blinded by the light, increasing the already catastrophic deathtoll on roads (about 30 million dead and counting).
 * Now I don't mind if people think of alternative solutions - that's a good thing. The problem is that silly solutions like these, that can be debunked with a bit of secondary school knowledge, draw attention away from the real solutions like the development of solar cells, because it reduces them to 'just another one of the solutions'. If some politician without a clue has a silly plan that's good. At least he's thinking. What's bad is that he doesn't consult (or ignores) people who do have the brains to implement secondary school knowledge. That a news agency reports this idea makes perfect sense. But they also should have someone with some intelligence on their staff who can at the least ask the right questions, thus effectively debunking the idea.
 * Now I hope I haven't made any mistakes in my reasoning or calculation, because else I'll get this little rant flying back in my face. :)
 * Btw, Jayron is right about biofuels. Solar cells are at present already 10 times more efficient than plants can ever be (20% vs 2%). And you can put them wherever you like - on rooftops or in deserts, where they don't compete with food-production. And you don't have to harvest of process anything (which costs energy) - just install them and sit back (well, almost, but certainly in comparison). That said, it might make sense to use the parts of food-crops that are not the food-bit. That won't have a very high energy content, but if you already produce this 'waste', you might as well throw it in the oven of an power plant. The gain may be small, but the same goes for the required effort if you just use what you already have more efficiently. At least, that's just a thought of mine - please debunk where needed. DirkvdM (talk) 11:22, 14 July 2009 (UTC)


 * Have you ever considered that solutions being offered by a Nobel Laurette and the US government might not actually be debunked by secondary school knowledge? Either because you don't really understand the proposal, or because the implications are different than you imagine?  Dragons flight (talk) 11:47, 14 July 2009 (UTC)


 * A Nobel Laurette perhaps, but you appear to have far more faith in the US government in scientific areas then I do. After all, the lawyers are the ones who are in charge, not the scientists, and the job of a senator is 1 part helping the country and 6 parts looking good to the voters.  Googlemeister (talk) 19:08, 14 July 2009 (UTC)


 * The problem is that DirkvdM is only seeing one side of the benefits here. Whilst he's 100% correct that the amount of light we'd reflect back out into space would be negligable - he's neglecting the important part.  A dark-roofed building is going to be hotter inside than a light-roofed one.  If it's a LOT hotter - and in a place with a warm climate - that means that you're going to need airconditioning...and the amount of energy consumed by air conditioners is FAR from negligable!  Worse still, the airconditioner puts out yet more heat into the outside environment - causing something of a feedback effect.  Painting the roof white cuts out a significant chunk of heat - which saves on the airconditioning - which cuts yet out more heat and CO2.   So the simplistic 'percentage of the earth's surface' calculation - while true and interesting - doesn't explain why the US government thinks it's a good idea.  The true calculation would have to estimate the amount of additional energy expended by airconditioners in black-roofed buildings - and compare that to the total energy consumption of humanity.  As I said - I doubt it's as much as 1% - but since it's a fairly cheap fix (and every little helps), new buildings really OUGHT to have lighter colored roofs (not bright white paint...but maybe lighter tiles and white gravel pressed into black tarmac roofs) - and I'd like to see the government moving towards mandating that by law. SteveBaker (talk) 20:35, 14 July 2009 (UTC)
 * You don't need to mandate any particular building material. Just tax energy enough while subsidizing remedies. Dirk, you seem to believe in the silver bullet. I don't. It will be extremely hard to find one technique that will cut carbon emissions by 50%. But we only need to find 50 that each reduce it by 1% (of the original, otherwise around 70, says the mathematician in me) to have the same gain. --Stephan Schulz (talk) 21:13, 14 July 2009 (UTC)


 * Dragon's Flight, read the question. I can't comment on the original proposal, because there is no link. But the question is about "painting roads and the roofs of buildings white". If that was in the orignal proposal, then obviously they weren't thinking about airconditioning, because else they would have left the roads out. (A bit of a late reaction, sorry.) DirkvdM (talk) 17:55, 19 July 2009 (UTC)

Steven Chu is not an idiot, so such notions arise from a misinterpretation of what he's proposing. He's an expert in cooling atoms with laser light, so I'm pretty sure he understands the physics of heating and cooling. His colleagues think so. Anyone who's paid any attention knows that a white T-shirt is cooler in the afternoon sun than a black T-shirt. This fact applies to buildings that are air-conditioned: using white siding, or white exterior paint, or light-colored shingles will reduce the amount of heat that's absorbed by the building. The questioner doesn't need a bunch of half-baked opinions: s/he needs references to Chu's proposal and expert reactions to it. Chu was not talking about 'painting roads white', he was talking about using lighter-colored materials to make roads. (Compare the heating of asphalt to that of concrete.) He's not talking about applying millions of gallons of white paint to existing surfaces; he's talking about changing the color of materials that are going to be produced anyways so that they reflect light back into space (as the clouds and the ice at the poles do.) If you really want to understand energy use and options well enough to understand what's being said, I highly recommend this book (it's a free download). Those who prefer to engage in pointless and non-productive bickering won't be interested. Twang (talk) 22:24, 19 July 2009 (UTC)

Optical Contact Bonding
What is optical contact bonding? How does it work? --72.197.202.36 (talk) 20:07, 13 July 2009 (UTC)
 * Google it, the google books results are particularily useful if you are looking for an explanation.
 * We do seem to lack an article, if no-one voluteers, of finds one, I might write it.83.100.250.79 (talk) 20:28, 13 July 2009 (UTC)
 * Optical contact bonding —Preceding unsigned comment added by HappyUR (talk • contribs) 20:44, 13 July 2009 (UTC)
 * ok stub article exists - Haven't got much time so it's not very good.
 * Please categorise, expand, and correct. Thanks.HappyUR (talk) 21:20, 13 July 2009 (UTC)

Thanks! --72.197.202.36 (talk) 04:52, 14 July 2009 (UTC)

amateur astronomy questions.
Lets say I buy a 8 inch telescope....

1) Are the images of moon, planets and nebulae impressive?

2) Is imaging the sun impressive?

3) Are we talking laptops and software for best effects?

I suppose the most important question....

4) Even if I get a good telescope and laptop [and a few years of observations] are we really still talking about "fuzzy dots" rather than good solid images? —Preceding unsigned comment added by 89.242.135.49 (talk) 22:21, 13 July 2009 (UTC)
 * I hope you realize that looking at the sun requires a special sun filter - otherwise, you could blind yourself.-- SPhilbrick  T  22:25, 13 July 2009 (UTC)


 * 1) yes
 * 2) Sure
 * 3) why not?
 * 4) you can get best images in the world, selling them for $$$$$ and giving names to new comets in case you got good telescope and patience to do the observations. Vitall (talk) 22:40, 13 July 2009 (UTC)

yes...ANY sun imaging would be done with a laptop..NO DIRECT OBSERVATION ... —Preceding unsigned comment added by 89.242.135.49 (talk) 22:34, 13 July 2009 (UTC)


 * WARNING!!! EXTREME DANGER!!! Do not EVER look at the sun through your telescope. You will quite literally burn out your retina before your eyelid has time to close.  There are ways to use a telescope to project an image of the sun - but even then, you have to be really careful because you are not only concentrating the light - but also the heat.  If you accidentally leave your telescope with the main lens cap off - and it happens to be pointing to a place where the sun will be in a few hours time - you could come home to a burned out house!  You have to be super-careful when using a telescope in daylight.


 * That said:
 * The moon looks very impressive - it seems somehow more "real" than the naked eye view. Planets - less so.  You'll be able to see the rings of Saturn - but it's not going to be a huge, sharp image.  Most of the other planets are relatively featureless.  Nebulae are soft smudges...this isn't the Hubble we're dealing with!
 * The sun...well, WARNING!!! EXTREME DANGER!!! ...remember?! Let's not go there!  You can safely get a good image of the sun with a home-made pinhole camera (a sheet of cardboard with a pinhole in it taped across a window works well) to produce a magnification of say 2x to maybe 8x in a darkened room.  That lets you see prominances and sunspots - it costs $1 to make and it's SAFE.  So just forget all about using an actual telescope to observe the sun...bad, bad, BAD idea!   There are ways to do it - but you have to be really careful and do it exactly right...not the sort of thing I'd advise an amateur to attempt when the pinhole camera approach works so amazingly well.
 * The single greatest thing about computer-driven telescopes (those with TWO axis motorized mounts) is that when they are properly set up - you can tell the thing "Find me Jupiter" and it'll obediently take you there. That's a lot easier than messing around with star charts and ephemerus to find the darned thing - and as a beginner, one fuzzy off-white blob looks much like another - if you're trying to get the thing focussed in on Jupiter and you're actually pointing at a star five degrees away...you're in for a frustrating experience.  The other thing a motorized mount does for you is to automatically counteract the slow rotation of the earth - which can be really annoying when you're trying to set things up because the star or planet you're looking at keeps moving!  The computer can fix that for you - which is especially nice if you want to take long-exposure photographs.
 * A lot of what you see will indeed be dots...or (in the case of most of the planets) slightly enlarged dots. The moon and Saturn are very cool - but if that's all you're going to use it for, you're better off borrowing one for a few nights.  When there is a comet just below naked eye visibility, the telescope will bring it into amazing clarity...probably the best thing I ever saw in my 8" reflector was comets.   You can also pick up things like the space station...but without a fairly fast computerized mount, it's hard to keep it in view!
 * One other HUGE thing to think about is how good the "seeing" is where you live. If there is a significant city anywhere within the range of the horizon - or a small town somewhere within a mile or two - or even a street lamp 100 yards from the end of your back yard - then you may have a hard time seeing ANYTHING other than the moon and the brighter comets clearly.  This cannot be over-emphasised.  If you don't have REALLY dark nights - forget it - don't buy a telescope.  I have an 8" reflector - which isn't a great telescope - but it was good enough when I lived out in the wilds of nowhere with a gigantic hill between me and the nearest main road.   When we moved to the USA and bought a house just 20 miles from Dallas - there was simply nothing in the sky worth seeing other than the moon.  Everywhere else, you just see a dim glow of the city lights reflecting off of the sky...no astronomy is possible under those circumstances.
 * Another consideration is the weather. You obviously need a lot of clear-sky nights (People from Seattle need not apply!) - but remember that you can't do astronomy indoors.  You'll be outside - late at night - for hours (potentially).  In cold climates - this is no fun!  Serious amateur astronomers soon realise that they need a mini-dome system so they can be at least sheltered from the worst of the weather.
 * SteveBaker (talk) 22:47, 13 July 2009 (UTC)


 * Uh, Steve? There are safe full-aperture solar filters for telescopes that are made from materials that block enough of the Sun's light to make it safe for direct observing. That being said, an 8" telescope, even with a filter, might deliver an image bright enough to hurt while looking at it. Large-aperture telescopes are generally not good for observing the moon, either, one reason being that the light will be very bright, and another is that the magnification required to resonably work with such an aperture might make the moon appear too large. How much an 8" telescope costs depends on the type: expect to pay roughly $450 US for a Dobsonian of that size, $1300 for a Newtonian reflector, and $2500 for a Schmidt-Cassegrain. That's without any special equipment such as CCD cameras and the like. An 8" telescope may also be good for imaging deep sky objects. ~ A H  1 (TCU) 00:27, 14 July 2009 (UTC)


 * Yes, it IS possible to observe the sun - with care - with the RIGHT equipment and knowledge (and I said that) - but it's really dangerous - and we really shouldn't be recommending it...especially when a pinhole camera and a darkened room works every bit as well. I've heard of people who assumed that the "moon filter" that comes with many larger aperture scopes was a "sun filter" - and lost an eye in the process.  On an 8" telescope - even the moon is bright enough to hurt your eyes (that's why most scopes come with a "moon filter").  Most scopes that come with a sun filter are much less than 8" aperture.  Remember - the sun filter that works for a cheap 4" scope is letting through four times too much light if mounted on an 8" scope!  This is totally not a thing for a novice telescope user to be messing with...losing an eye is just FAR too serious. SteveBaker (talk) 01:30, 14 July 2009 (UTC)


 * Extra warning: I had a telescope that came with a filter for solar observation at the ocular end (eyepiece). Someone at my astronomy club told me that that is also dangerous because, as Steven pointed out, you are not only concentrating the light, but also the heat. That heat still reaches the ocular, which may burst, as a result of which splinters may come off. If you've got your eye at the ocular, those splinters may end up in your eye. Sun also mentions this. The way to obsserve the Sun is by projection, as Steven mentioned. I believe that's how Galilei also did it - he held a piece of paper behind the telescope, on which he then copied the image. A modern alternative to Galilei's method is to mount a digital camera behind the telescope, connect that to a computer and view the image on your computer screen. And of course take photos. I'm not sure if this will work with a standard camera, but there are setups for this. Of course you still need a filter to avoid damaging the ocular or the camera's ccd (its retina, so to say). But even if that goes wrong, you'll still have your eyesight intact.
 * To get an idea of how beautiful the images are, you might contact an astronomy club to meet up with them on an observation night. They'll probably let you have a look through their equipment. And then you'll be able to compare and decide what kind of equipment you like best.
 * Btw, the most beautiful thing I ever saw was the Moon - with the naked eye. That was a few days after new moon, just after sunset, with just a narrow strip lit up by the Sun (waxing crescent). The rest of the Moon was quite visible, and suddenly I saw the Moon for what it is - a huge rock at a huge distance. Until then, I knew that, but that was the first time I saw it. Then it sunk in that that strip of light was a mere reflection of the Sun, which gave me a feel for the immense amount of light it emits. And that's just our little corner of our galaxy, which is just one of billions of galaxies. I never felt so tiny. Mind you, this was not so much what I actually saw, but the realisation of what it was that I saw. The same holds true for the zoomed in versions of whatever you see in the sky with your telescope. For example, Hubble images can be very beautiful in an abstract sense, but when you realise what they really are, they're mindboggling. A lot of beauty comes from knowing what it is that you're seeing. DirkvdM (talk) 09:11, 14 July 2009 (UTC)
 * The first time I had the opportunity to look at Jupiter through a relatively small refractor (perhaps 3 inches) it was literally breathtaking to see the moons of that planet standing out in clear detail. Years later, with my own similar telescope, and some care, it was possible to see the weather bands around Jupiter as well as its moons, and to see the rings of Saturn. A larger telescope such as the OP discusses, especially with a computer controlled drive, would make it much easier to find and observe planets. A CCD camera should make it possible to create some amazing photos. Edison (talk) 14:23, 14 July 2009 (UTC)

A spring in space
If you had a setup so a ball was put onto a spring and tied back with some force to compress the spring (as in space the ball would be weightless, no?), and then the ball was released would it oscillate forever? What would cause damped motion--no air in space, no friction due to it oscillating up and down without touching anything.

xxx(ball) (compressed)

xxxxxxxx(ball)

xxxxxx (ball)|[plate|

2) If the setup involved placing a plate a distance x from the compressed spring so that x was less then the amplitude of the springs oscillation would it strike the plate and come back (3rd law force of plate on ball), compress the spring and then repeat infintly? I think energy would be transferred to the plate though no?

3) Finally what happens if the plate in question to is replaced with a piezoelectric crystal. Could that serve as a battery? (obviously this is just a hypothetical question)

24.171.145.63 (talk) 23:16, 13 July 2009 (UTC)


 * 1. There is friction within the spring.
 * 2. Energy would be lost when the boll bounces against the plate. It would be transferred to both in the form of heat.
 * 3. Energy would be lost to the piezoelectric crystal in the form of electricity.
 * Also, tiny amounts of energy will always be lost in the form of gravitational waves, so a perpetual motion machine is totally impossible. — DanielLC 00:07, 14 July 2009 (UTC)


 * If we're talking about a physical spring, there will be some friction inside the spring itself, so it will lose energy over time. With an ideal spring, or eg. a gravitational field working as one, it's possible for your ball to oscillate forever, at least in an isloated system. For example, a planet orbiting a star can actually be seen as oscillating along two perpeticular axes.
 * Regarding 2) and 3), as you've already said, when you make the ball strike the plate you transfer the energy, so you'll at best be able to recover the energy you already put in the system by compressing the spring, most of it however would be lost heating the ball and the plate.  You're right that this could be used for energy storage, but the efficiency would probably not be very impressive.

85.222.93.28 (talk) —Preceding undated comment added 00:35, 14 July 2009 (UTC).
 * It won't work forever. As I already said, energy will be lost in the form of gravitational waves. This will be unimaginably slow, but it will happen. 67.182.169.172 (talk) 00:17, 15 July 2009 (UTC)

Sky colors on remoter stars
So If the star is white, then what will be the color of planet's sky, if Terra-like. Would white sun make white or purple sky? I know a blue star make a golden sky, what about a blue-white star will make deep yellow or pale yellow sky. A orange star is said on one site to make turquoise sky while pink star gives green sky.--69.226.33.240 (talk) 23:47, 13 July 2009 (UTC)


 * I believe the Sun is white. It just looks yellow because the blue light is scattered by the sky, hence the sky looking blue. — DanielLC 00:02, 14 July 2009 (UTC)


 * Some stars is technically white. Like is Vega was the su, will our sky still look blue, if sun was A STAR?--69.226.33.240 (talk) 00:15, 14 July 2009 (UTC)


 * Our sun IS white - but when the light enters the atmosphere, the blue light is scattered (that's why the sky is blue). Because our eyes basically see only mixtures of red, green and blue light - when you subtract some blue, you have more red and green than blue.  Red and green makes yellow - so from down here at the bottom of the atmosphere, the sun looks a little yellowish.


 * Sorry, but this is not entirely accurate: white stars are classified as A-class on the spectral scale, while the Sun is G-class (i.e. a yellow star).

76.21.37.87 (talk) 08:15, 14 July 2009 (UTC)


 * 76.22.37.87, I don't think you see the true science world. I've been told, human eyes do a terrible perception shift. Language scientifically, ur sun looks yellow in cmputer screen, white when seen in our blue sky, who knows what you'll see in space. 76 IP, you don't see strange human shifts on earth, when you go to Mars or Moon, then all your color vision cell will go hay tangle.--69.231.5.71 (talk) 21:24, 14 July 2009 (UTC)


 * 76 IP, the source I past past discussion is found on this.--69.231.5.71 (talk) 21:28, 14 July 2009 (UTC)
 * Sorry i need to fix 76 IP's answers. He just don't know enough. For a gentle reminder, is just to clarify the rules the goal of desk is the answers to be "done right". If answers is not answer right then this destroys purpose of desk. Questioners won't want to go back and try to see what the answers is wrong. Questioners usually wants answers answer right at the "first time". And also we people won't want to bite newcomers. Since 76 IP answer is too simple and to general, it's good ot just fix comments and leave it ther. --69.231.5.71 (talk) 21:42, 14 July 2009 (UTC)

Perhaps I should have put in a disclaimer that astrophysics is not my area of expertise. 76.21.37.87 (talk) 01:10, 15 July 2009 (UTC)
 * The color of the sky is determined by the nature of raleigh scattering - and the color it scatters depends on the size of the particles in the atmosphere - not the color of the star. So if the earth was orbiting a different star, then there are two possibilities:
 * If there is a reasonable amount of blue light being emitted by the star - then the sky will be blue.
 * If there is little or no blue light from the star - then the sky will be black and you'll be able to see stars in the daytime sky.
 * The star itself might look a completely different color however. SteveBaker (talk) 01:23, 14 July 2009 (UTC)


 * Just to clarify: You can only ever see stars in the daytime if you shield your eyes from the sun or anything lit by the sun. This applies on the hypothetical planet Steve describes in the same way it does on the Moon. --Tango (talk) 02:11, 14 July 2009 (UTC)


 * I think the OP is referring to white as in the spectral class: OB A FGKM. -- penubag  (talk) 07:48, 14 July 2009 (UTC)

I believe the Sun is considered yellow because that is the area of the spectrum where it radiates the most intensely. However, it could easily be considered white, as it emits strongly throughout the visible spectrum. - Running On Brains (talk page) 21:53, 14 July 2009 (UTC)


 * The sun actually radiates most intensely in the green which makes it "techinically" a green star. Dauto (talk) 05:03, 16 July 2009 (UTC)


 * Is just plot of spectrum Sun counts as yellow. When you actually go in space, you look as a totally different things. Your human eyes is very sensitive. Same situation as Mars. you won't even notice the coral color at all if you actually going to it personally. That's enough.--69.231.5.71 (talk) 22:01, 14 July 2009 (UTC)