Wikipedia:Reference desk/Archives/Science/2013 September 6

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September 6

relation between speed and pressure of the fluid

I could not understand the concept of "relation between speed and pressure of the fluid". I read that where the speed is high, pressure will be low. I could not understand this statement. please elaborate and explain in simple language so that I may have a better understanding to this concept. thanks--39.55.149.184 (talk) 07:13, 6 September 2013 (UTC)

The intro to our Bernoulli's principle article is a pretty nice mix of technical details and lay-language summary if you know a few key ideas. That article defines the principle as "an increase in the speed of the fluid occurs simultaneously with a decrease in pressure". To quote the relevant parts from a few paragraphs later: "Bernoulli's principle can be derived from the principle of conservation of energy. This states that, in a steady flow, the sum of all forms of mechanical energy in a fluid along a streamline is the same at all points on that streamline. This requires that the sum of kinetic energy and potential energy remain constant. Thus an increase in the speed of the fluid occurs proportionately with an increase in both its dynamic pressure and kinetic energy, and a decrease in its static pressure and potential energy." Conservation of energy is a pretty basic idea in science: the total amount of energy must remain constant. The total amount of energy is composed of two parts: Kinetic energy is the energy of motion and potential energy is the energy that is stored (capacity to become/cause motion). Dynamic pressure is the pressure in the direction of motion (like the force of a water jet directed at your hand), and is related to the idea of kinetic energy. Static pressure is the general force pushing outward (causes a garden hose to swell), which is related to potential energy (because the liquid is just pushing not actually moving). So if the flow increases, the kinetic energy increases (more motion), which means the potential energy decreases (to keep same total energy) and therefore less static pressure. DMacks (talk) 08:11, 6 September 2013 (UTC)

Another way to see that is that if the air is moving from the high pressure to the low pressure, the net pressure force will point along the direction of the motion and the air will accelerate aquiring larger speed at the low pressure location. Dauto (talk) 11:54, 6 September 2013 (UTC)

Laminated beams

Can someone explain to me please, whether a beam made of 4 strips of 1/4 inch by 1 inch mild steel bolted and clamped together (flat sides together, thus forming a 1 inch square laminated beam), would be any stronger (more resistant to bending) than a solid 1 inch square bar of the same material? If it is stronger, where does it get this extra strength from? I can't find any information on this by googling. Thanks in advance 122.108.189.192 (talk) 08:27, 6 September 2013 (UTC)

Our Engineered wood article has quite a bit of information and relevant links. I gather that part of the gain in stiffness is due to cross-orienting the stiff axis of alternate layers; bonding of layers also prevents sliding as one mechanism for flexing. -- Scray (talk) 12:24, 6 September 2013 (UTC)

It's been a long time since I took engineering, but I will take a stab at it. The failure actually occurs because compressive forces make the top of the beam want to spread sideways. The bolts and clamps add to the strength by preventing this sideways deformation. Presumably, if you put the exact same bolts and clamps on the solid piece, it would be just as strong. Take this with a grain of salt, because I am using very old neurons. Tdjewell (talk) 12:25, 6 September 2013 (UTC)

Yes - but wood isn't a homogeneous material - our OP wants to know about mild steel. Certainly plywood is much stronger than a solid piece of wood of the same thickness...but that's because of the way the grain of the wood flexes and breaks. Also, I don't think we're being asked about failure modes - only about resistance to bending. I'm not sure what the answer is - but I don't think using wood as an analogy delivers the correct answer. SteveBaker (talk) 12:46, 6 September 2013 (UTC)

It is certainly dubious looking at what happens with wood. For mild steel, first, we need to make a couple of assumptions: We'll assume the volume of steel in the bolts is very small compared to the volume in the mild steel strips. On the limitted information the OP has supplied, this may not necessaily be a good assumption. We'll also assume the bolts are perfect clamps that allow no slip but do not compress the strips anywhere near their their elastic limit. We'll also note that the OP has defined "strength" as resistance to bending. There are of course other forms of strength, eg resistance to breakage or permanent deformation. With all these assumptions, there are two cases.

First case, the bending load is small: Since the elastic strength of steel is the same in both compression and tension (unlike say concrete), a light bending load causes equal stretching on the top of the curve as compression on the inside of the curve. In this case we can see that it makes no difference whether we have clamped strips or just one thick bar - the strength is the same.

Second case, the bending load is high: In this case, the strip(s) on the inside of the curve can buckle inwards, away from the outer strips. Buckling converts the stress in the buckled strips from pure compression into a mix of local compresion and tension. This allows the whole multistrip assembly to bend more. For large loads, the strength of the strip sassemble is thus lower than the single thick bar. Note that the amount of bucking may be imperceptable to the eye but still significantly lower the resistance to bending. In theory, if each strip is made very very thin, in the limit a multistrip assembly will have no resistance to bending at all. However, if the spacing betwene bolts is reduced, the strength is progressively brought back to that of a solid bar. Visualise bending a 100-page A4 book (say 9 mm thick) with your hands. Easy isn't it? Now visualise bending a piece of cardboard the thickness of 100 pages - can you do it? Only if you are a gorilla.

As you increase bending load on a multistrip steel strip assembly from zero, the bending increases linearly up to the point of buckling, the same as for a single thick bar, then it suddenly "lets go" to a certain extent.

Now we can look at bending loads beyond the elastic limit. As the strips on the inside of the bending curve can buckle, the point at which the assembly goes beyond its elastic limit fails is delayed. While a multistrip assembly is easier to bend, it can take higher loads before actually failing. As the strips are increased in number and made thinner, the assembly becomes more and more indestructable.

In a practical assembly, some slippage may occur between strips at each bolt. This obviously lowers the assembly elastic limit, but increases the load at which it will fail.

In a practical case, the bolts will elastically compress the strips - "pre-loading" them. The elastic limit to bending stress is thus reduced, and the assembly will fail at a lower bending load. However this effect should be quite small with properly selected and installed bolting or clamping, and can be neglected.

The non-linear response to bending loads combined with a higher resistance to failure is one reason why leaf springs were used for car suspension until the development of variable rate coil strings and hydraulic shock absorbers (which are actually vibration dampers), and are still used on heavy trucks. In such cases clamps where used instead of bolts to allow slippage and thus make the response even more non linear, and to introduce frictional damping, so that large shock absorbers are not needed.

120.145.46.27 (talk) 15:38, 6 September 2013 (UTC)

It would be weaker in bending, and substantially so. The bolted laminate beam would experience substantial shear forces at the boundaries between the layers, which would be concentrated around the bolts. The solid beam would have similar overall forces, but they would be distributed (relatively) uniformly throughout the beam. --Carnildo (talk) 23:51, 6 September 2013 (UTC)

(OP)Thank you all for your comments, I hadn't thought about the idea that the laminated beam would allow more deformation before actually "letting go". the laminated beam that prompted my question is actually stainless steel and used on a powerboat supporting the base of the rudder, so is subject to a lot of vibration. Maybe it was tried as an experiment to allow slightly more flexing without causing "work hardening" (something stainless steel is notorious for). 122.108.189.192 (talk) 07:44, 7 September 2013 (UTC)

Right - when you WANT more bending - use a laminated beam (hence [[leaf spring]s in some vehicles). When you want stiffness (at least with a homogeneous material like steel) - then a solid beam will be better. If you want resistance to fracturing, then a tube or a cylinder may be better - if you want tolerance to breaking to be a feature - then laminates have advantages. "Strength" is a complicated and rather vague term when it comes to material sciences. SteveBaker (talk) 14:26, 7 September 2013 (UTC)

Is there a list of human organs weight?

I'm looking for a list of human organs weight from the heavy to light, or vise verse. In example what is the heavy organ in the body? (skin & liver) and what is the light organ of the body? (I don't the answer). In sum up, I would like to get proportion about the body organs (weight & size). 95.35.210.39 (talk) 08:54, 6 September 2013 (UTC)

for a partial list, see [1]. Most such lists of normal weights cover only the organs weighed at autopsy, and so exclude the skin. -Nunh-huh 09:39, 6 September 2013 (UTC)

Why did not remain nothing nothing?

Why did not remain nothing nothing — Preceding unsigned comment added by 37.238.108.105 (talk) 11:55, 6 September 2013 (UTC)

Because something happened. --Jayron32 12:06, 6 September 2013 (UTC)

(ec) I'm assuming you're talking about the beginning of the universe, or "before" the big bang. Why would you expect nothing to remain nothing? What rules would have prevented it from becoming something? You also probably shouldn't assume that there was ever nothing. I don't have a name (talk) 12:11, 6 September 2013 (UTC)

Sometimes, there are questions that science can't yet answer - and this is definitely one of them.

The short answer is "we don't know" - or possibly "we don't know yet" - or possibly even "we can never know". Personally, I believe the last option is the most likely. To the best of our present day knowledge, the universe started with a "singularity" - a dot of zero size and possibly infinite mass - in which time was literally stopped and space itself was distorted to a point of zero size. No information can come from "before" that because without time flowing, there cannot be a "before". So in that view, there never was a time when there was nothing. The whole concept of "before" is meaningless when relativity says that infinite mass in zero space stops time. I recognize that this is not the only view of how the big bang started - but it's an answer that works and doesn't violate principles that we broadly understand.

There are many other possibilities, that the universe ends with a "big crunch" when all of time, space, matter and energy is sucked into a gigantic black hole - which then explodes in a big bang to recreate the universe. With that scenario, there could have been an infinite number of bang/crunch cycles, each starting and ending with a singularity that prevents any knowledge of the previous universe from leaking into ours. It's even possible that time loops around so that the universe repeats itself over and over forever, exact in every detail.

But all of those kinds of hypothesis require that the universe started in a singularity - then no information from "before" can possibly pass through the singularity into the present universe - so it seems likely that we can never know what there was before. Without that knowledge, your question doesn't have an answer.

You might find the "Weak Anthropic principle" (WAP) useful in thinking about this. It basically says that in any universe where the conditions would not be enough for intelligent life to eventually form, nobody would have been around to comment on it. It follows that the universe had to have the right characteristics for us to be here.

There are any number of other ideas - things like the Simulation hypothesis that says that the universe is just a software program running in a gigantic computer in "the real world"...I work in computer games and simulation - and when I look at the universe as we know it, there are many aspects of the laws of physics that seem like they were perfectly tailored to being a part of a simulation.

But the bottom line is that (for sure) we don't yet know...and (perhaps) we'll never be able to know, not even in theory.

SteveBaker (talk) 12:40, 6 September 2013 (UTC)

This problem may be an artifact of making the assumption that something exists at all. Similar to assuming that God exists who created the universe and then asking who created God. An obvious possibility to explore here is that God may not exist in the first place, but this is not so obvious to people who are indoctrinated with religion. Similarly, we all assume without any shred of evidence that there exist such a thing as "physical existence" which is supposed to be fundamentally different from merely "mathematical existence". An obvious possibility is to start exploring if in fact "physical existence" = "mathematical existence" as e.g. Max Tegmark has proposed. This hypothesis has yet to be falsified. Count Iblis (talk) 14:23, 6 September 2013 (UTC)

Does it matter? Suppose we dig down deep into string theory (or whatever) and find that at the root of all things, it truly is all just math - does that change anything at all? We'd still want to know more about these "physics" that emerge from the abstract mathematical substrate underlying all things. There are plenty of other ideas of that nature out there: That all of time already exists and we only feel the way we do because the nature of our organic memories is that they only contain representations of things to the left of wherever they are in time and not to the right...or that only this precise instant exists or has ever existed and that all of this memory is just a frozen artifact of the way things are. Or that we merely represent a point in Configuration space (Neil Stephenson's fiction "Anathem" is a great way to 'grok' this concept), or that the universe that we know is just a computer game being played by some uber-geek kid on an uber-computer in his bedroom out there in the uber-universe...and that his universe is also just a simulation...and that we are just now beginning to make our own tiny universes inside our own computers.

Sure, there are a million unfalsifiable prospects out there (including a god or gods, the simulation hypothesis and string theory) - but how do you choose between unfalsifiable hypotheses? The only approach we have is to resort to things like Occam's razor and Russel's teapot that fail us when common-sense and appeals to "simplicity" cannot help. SteveBaker (talk) 14:46, 6 September 2013 (UTC)

That applies only when the opposite of the hypothesis is falsifiable. Saying that there is no god or the universe is not a simulation is only falsifiable assuming specific definitions of god and simulation which allow for deliberate and chaotic intrusion into the normal workings of physics; but the most dignified presentation of either idea allows no chance of such falsification. With an interesting middle ground where people suppose that maybe just and so it can be falsified, which is just the point at which you have to either put up or shut up based on evidence obtained in such a manner. Wnt (talk) 19:51, 6 September 2013 (UTC)

"Why did not remain nothing nothing?" Because there was nothing to prevent it from turning into something. Dauto (talk) 21:02, 6 September 2013 (UTC)

You should provide references, Dauto: because there was nothing to prevent it. μηδείς (talk) 00:43, 7 September 2013 (UTC)

Read the first few lines of the book of Genesis, and that's the best information we have at present. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:49, 7 September 2013 (UTC)

Hmmm...let's see:

"In the beginning when God created the heavens and the earth, the earth was a formless void and darkness covered the face of the deep, while a wind from God swept over the face of the waters. Then God said, "Let there be light"; and there was light. And God saw that the light was good; and God separated the light from the darkness."

That doesn't really work - it says that the Earth existed before light, which is clearly false - we know that the sun was producing light from nuclear fusion while the earth was still forming. It also says that there was water on the surface of the earth before the sun existed. As for the Earth being "a formless void" yet having water on it how does that work? Formless voids don't have enough gravity to hold water in place...and as for "separating the light from the darkness" - what the heck is that supposed to mean? God is also supposed to be an omniscient being - why didn't he figure out that light was "good" before he went to all the trouble of creating it?SteveBaker (talk) 00:31, 8 September 2013 (UTC)

I'm kinda starting to believe that there may be a few plot holes in this book! SteveBaker (talk) 00:31, 8 September 2013 (UTC)

Only if you take it literally. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:08, 8 September 2013 (UTC)

"Blessed are the cheesemakers" --220 of ^Borg 05:56, 8 September 2013 (UTC)

"...for they shall be called the Children of Gouda." ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:37, 8 September 2013 (UTC)

Religion evolved to keep our intellect from being used too productively, it prevents us from being able to give a proper answer to the OP's question. Had our brains evolved to be more immune to religion, then that would have led to our civilization developing faster. We would have reached the point where machines would replace us a lot sooner, in a lot less generations. The probability to exist in such a more rational civilization is thus a lot less than the probability to exist in a more backward religious civilization. So, while we cannot explain yet why we exist, we can explain why God "exists". Count Iblis (talk) 01:53, 8 September 2013 (UTC)

Religion evolved because we wanted it to. It has value in society - a fact that vexes atheists no end (atheism being its own religion). As to God creating heaven and earth - well, that's just stating the obvious. God in that case equates to the creative force that triggered the Big Bang. Created from what, if anything, we can't know until or if we can find some evidence. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:17, 8 September 2013 (UTC)

Atheism is a religion like "not collecting stamps" is a hobby. A global 2012 poll reports that 59% of the world's population is religious, and 36% are not religious, including 13% who are atheists. Religion is an organized collection of beliefs, cultural systems, and world views that relate humanity to the supernatural, and to spirituality . Religion and atheism are mutually exclusive. The only people who ever claim atheism is a religion are religious people trying to demean atheism. Vespine (talk) 00:23, 9 September 2013 (UTC)

Back to the OP's question: there is a recent, well-reviewed, book by Jim Holt that surveys philosophers' and physicists' views on the subject: Why Does the World Exist?: An Existential Detective Story. Physicist Lawrence M. Krauss published his ideas on the question in A Universe from Nothing: Why There is Something Rather than Nothing last year, which sparked a lot of critical discussion among fellow scientists and science writers (links here). Both these works are written for a general audience, so should be readable by the OP and others. Abecedare (talk) 07:00, 8 September 2013 (UTC)

can anyone help with references?

The ref desks are for asking questions, not for proposing theories. SteveBaker (talk) 12:19, 6 September 2013 (UTC)

Has anyone seen things that might support the idea that because microbes live in hydrocarbon reserves and seepage, the reserves might be ecologically important??? I can't find direct references to the idea, although I can find information bits that seem to be relevant to the topic. I post/pasted my argument yesterday, but didn't ask for references, which is my search goal. The concept is currently apparently undecided. I'll post my argument again, and at the end are some links. these links show how microbes are responsible for all the functions that would mean they are important, and they are capable because seepage and reserves allow them to be in that place. it's a little long, but not bad.... argument:: we are wrong about certain important aspects of ecology, both historically and presently. we are not crediting fossil fuels with their worth while underground. currently we state that it is un-important to the bio-sphere if we harvest fossil fuels, although pollution is damaging. I argue that indeed it is important to life both on the surface and underground that fossil fuels remain in place. claim: the recent discovery of microbial populations in deep hydrocarbon reserves should support the claim that there were microbial populations in shallow reserves. claim: The density and quality of hydrocarbons within a reserve affects the type and volume of microbial activity (although it is something I've considered that after getting what we can from a reserve, there might be a short term bloom given the newly found relaxed environment. hydrocarbons of high complexity can be broken again and again for energy) claim: Harvesting fossil fuels dramatically alters the subterranean environment, and therefore the biologic activity. claim: This affect in turn affects the surface. Hydrocarbon seepage is reduced with reduced reserve pressure. discussion: WE farmed and deforested nearly everything. We did a lot of replanting. the vegetation as it is today in nearly every location has changed 100% . Lots of things died on their own or were replaced by invasive species. actually, we can't ever know about invasive species of the time. If it's going on now, I would think it's ok to assume it happened already. discussion: Due to the nature of oil science (get money), it is likely that the kind of data one would use to support these claims isn't available. Not until biological sciences really started producing wild food genetics and such would we have had available data. some independent environmentalist data collector from long ago (or even a bunch of them) would not have been able to collect data that anyone would have found useful. Data collection is huge. discussion: There are so many things happening to the surface due to human activities, many of the effects that may have been from changes in hydrocarbon seepage were likely attributed to something else, such as pollution or infrastructure development. Link list: Link list: http://www.cartage.org.lb/en/themes/sciences/earthscience/geology/oilandgas/HydrocarbonMigration/Hydrocarbon/Hydrocarbon.html http://link.springer.com/chapter/10.1007%2F978-3-642-05297-2_61#page-1 http://ipec.utulsa.edu/28.d/28_Abs.html http://microbiology.okstate.edu/faculty/mostafa/publications/PetMicrorev.pdf http://www.livescience.com/23126-bacteria-sucked-up-200-000-tons-of-oil-after-bp-spill.html http://microbiology.okstate.edu/faculty/mostafa/publications/PetMicrorev.pdf http://levin.ucsd.edu/publications/Levin%20OMBAR%2005.pdf — Preceding unsigned comment added by 67.155.62.160 (talk) 12:01, 6 September 2013 (UTC) Uhh. the encyclopedia is for finding information. you read the topic, and give information as a reference person. in order to ask the question, I have to tell you what I'm finding info about. Please take this to the Talk page. SteveBaker (talk) 12:41, 6 September 2013 (UTC) the talk page looks different. I don't want to talk to an individual I want to walk away with references to relevant information to support of refute my argument. HOwever, whatever. I can post again. I can paste for days. what I'm looking for doesn't really get clearer because I say "does it" before everything. to all: click the show button on the green field to gander at answering. — Preceding unsigned comment added by 69.24.176.113 (talk) 13:08, 6 September 2013 (UTC)

Somehow your links literally have three dots in them and can't be followed. You have an interesting idea which is indeed interpretable as a question (what is the ecological role of biota in oil reservoirs?) Apparently it helps greatly to have both oil and water for microbe growth [2] and the natural microbes can assist in oil extraction [3]. According to this book microbes over many millions of years convert debris to petroleum, mobilize the petroleum, and also assist in its recovery. Since many oilfields have turned naturally into oil seeps, liberating carbon and methane to the carbon cycle, I imagine the effect of these microbes on the environment has been substantial. --WHOOOPS!! I fixed the links. Hilarious! .. I want to make a comment on the liberated carbon. a hydrocarbon is an energy source for organisms, they need not get energy from other sources. metabolism is combustion. cool!! (I've heard the theory that deep life might contribute to earths heat, meaning life can increase the cooling time for earth by storing solar power in photosynthesis and then combusting it in subterranean biomes. off topic.) So these organisms in seepage can add to the surface life without taking away. Wnt (talk) 17:25, 6 September 2013 (UTC)

Feeding live mice to a cat

Edit: I should probably say that some of you might find this video upsetting.

Something I just saw in a YouTube vid here. I know what carnivory and predation entails and that animals eat other animals all the time, but is it really healthier for the cat to feed it the mice whole - and still alive? I'm just wondering if this is really considered nescessary or not - or is it yet another person doing something stupid with animals on YouTube? --46.208.75.245 (talk) 14:37, 6 September 2013 (UTC)

This is a serval, a wild cat, and I assume it has similar things in the wild. Domesticated dogs have specifically evolved to eat more starches [4] - I would suppose the same is true of other domesticated animals, including cats and humans. But mammalian carnivores double as scavengers - I know snake owners feed live mice for a reason, but even lions will eat dead meat. Interesting to compare Luka Magnotta, who put the shoe on the other foot and was vilified and hounded until he snapped; many believe animals are equal to humans but not apparently not so many find them equal to one another. Wnt (talk) 17:15, 6 September 2013 (UTC)

Sorry, I thought that "serval" was a (large) breed of domestic cat. I think that it's generally advised that you don't feed your snake live food, because a mouse/rat/rabbit/etc. can do a lot of damage with teeth to a snake while it's being subdued. They will definitely eat pre-killed stuff. As far as I know, it's snappers that will only eat live prey. --46.208.75.245 (talk) 18:44, 6 September 2013 (UTC)

I stand corrected! The moment I typed the "know" I should have realized I was swallowing something I'd heard once, rather than thinking about it. Wnt (talk) 19:34, 6 September 2013 (UTC)

• Talk about vagina dentata. μηδείς (talk) 01:37, 8 September 2013 (UTC)

ATOMIC MASS AND MOLECULAR MASS

i need 5 differences between molecular mass and atomic mass ... can anyone help me ... i want a proper difference ... plz rep me soon .. hope u will be able to give my answer ... (139.190.134.121 (talk) 15:17, 6 September 2013 (UTC))

See molecular mass and atomic mass - we aren't going to do your homework for you. AndyTheGrump (talk) 15:29, 6 September 2013 (UTC)

Please do your own homework.

Welcome to Wikipedia. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. SteveBaker (talk) 14:20, 7 September 2013 (UTC)

You asked a few days ago and were already given as much information as we have. DMacks (talk) 18:09, 7 September 2013 (UTC)

clonning

what is clonning ??? (139.190.134.121 (talk) 15:21, 6 September 2013 (UTC))

I've no idea what 'clonning' is. We do however have an article on cloning. AndyTheGrump (talk) 15:26, 6 September 2013 (UTC)

Having a clone is like having a twin. If a copy of the genetic code of a life form is used to create a new life form, that new life form is a clone of the first. Dauto (talk) 18:55, 6 September 2013 (UTC)

(Specifically: An identical twin - but different in age, obviously!) SteveBaker (talk) 14:13, 7 September 2013 (UTC)

Why aren't galaxies really bright?

If you take a star and move it farther away from the Earth, our eyes will detect a smaller rate of photons from the star. But its angular area will decrease by the same factor, so the star's angular intensity will remain constant. It seems to follow from this that the stars of distant galaxies should be as bright as the stars closer to home. So why can't the naked eye see them? 65.92.4.247 (talk) 19:22, 6 September 2013 (UTC)

You have a finite number of rods and cones in your retina, and to get one to fire takes a certain number of photons (I think under some conditions a rod can fire because of a single photon, but in any case it takes at least one). So a constant brightness in terms of flux per steradian doesn't help much if you have, I don't know, a quadrillionth of a steradian or something. You just don't get enough photons for your visual system to say "ahah, there's a star". --Trovatore (talk) 19:29, 6 September 2013 (UTC)

Also the total integrated apparent brightness of the nearby galaxies isn't that big anyway. E.g. the Andromeda galaxy has an apparent magnitude +3.44, but it is quite a bit harder to spot than a star of apparent magnitude +3.44 because of what Trovatore says above. See also this account of how hard it is to spot M81with the naked eye which has apparent magnitude of +6.94 compared to stars that have larger apparent magnitudes. Count Iblis (talk) 19:53, 6 September 2013 (UTC)

Agree with Trovotore. In theory, the Andromeda galaxy is far brighter in spots because it has bright blue stars in it. But in practice, seeing full brightness requires an entire receptor to be covered, which is just at the lower limit of the distance at which multiple receptors can be covered, i.e. the region in space where a visible disc can be discerned. Apart from a few of the biggest, nearest stars like Betelgeuse these discs aren't actually seen. Wnt (talk) 19:57, 6 September 2013 (UTC)

Also, the human eye has limited resolution because of spherical aberration which smears the image of distant stars into smudges of very little surface brightness Dauto (talk) 20:42, 6 September 2013 (UTC)

An interesting read relevant to the question is Olbers' paradox. Dauto (talk) 20:48, 6 September 2013 (UTC)

Homemade space suit.

Let's say I discovered a portal in my basement that led to the surface of the moon.

I can't get out and explore unless I have a space suit. I know that space suits are very complex pieces of technology, but how difficult would it be to make one from scratch with hardware store and household materials?

Please hurry. I'm really itching to do my first lunar EVA. ;)

209.182.120.18 (talk) 21:49, 6 September 2013 (UTC)

Hypothetically, if you have such a portal, what's keeping the air in your house once you expose that portal? ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:03, 6 September 2013 (UTC)

An air-lock... --89.241.237.164 (talk) 19:18, 9 September 2013 (UTC)

Space suit is (naturally) our relevant article. There are two major issues that need to be addressed - air and heat. I'm sure it wouldn't be too tricky to adapt a standard diving suit to work in a vacuum rather than underwater, although I'm not sure that would count as a "hardware store" item. However, cooling the suit would be a bit more difficult. See Liquid Cooling and Ventilation Garment for some details of what you'd have to construct. The main problem would be making the sublimator to transfer the heat from the suit to the lunar vacuum, unless you could run a hose back to your basement and cool the water there. Tevildo (talk) 22:21, 6 September 2013 (UTC)

Another big problem is flexibility. A diving suit would blow up like a balloon and the arm and leg tubes would be too stiff to allow you to bend them. A huge question here is how long you expect to be out of the basement. For a short trip, you could dispense with heating and cooling. SteveBaker (talk) 03:09, 7 September 2013 (UTC)

To begin with, what you're looking for is probably a space activity suit. For purposes of fiction it would be tempting to postulate making one from one of those ridiculous latex suits you see on the internet, plus custom padding, but whatever used would need to be exceptionally strong, I think. Given a good helmet seal I suppose a person could probably survive some trial and error for purposes of fiction, but I don't think I'd want to try it! Wnt (talk) 06:30, 7 September 2013 (UTC)

Why not buy on old russian one on ebay? 20000$ might buy you one.--Stone (talk) 21:05, 8 September 2013 (UTC)

Copenhagen Suborbitals are working on a DIY spacesuit, however that's meant to be an IVA suit. An EVA suit would be a magnitude more difficult to build, and much more expensive. WegianWarrior (talk) 08:56, 7 September 2013 (UTC)

Dear OP.

I have a better plan for you.

1. Invest $10 to buy a cheap but sturdy garden rake with a nice long handle.
2. Push one end out of the portal while firmly holding onto the other.
3. You'll probably be able to reach about 10 kg of lunar material and rake it back into your basement.
4. If not, buy one of these - it'll probably work for a while on the moon.
5. Sell your moon rock for $500,000,000 (Current price estimates for moon rock is around $50,000 per gram).
6. (Do it quickly to avoid flooding the market and driving the prices down!)
7. Give $1,000,000 to a really good private detective to quietly track down as many ex-NASA Apollo-era space suit designers and constructors as possible.
8. Bring them into your basement, show them the portal and say "I'll give you guys 250 million dollars to make me a space suit - and when you're done, another 249 million to keep quiet about my portal!" (That's quite a bit more than the moon suits originally cost to develop and build - and they've done it before - so it should be easier this time around).
9. (Don't forget to tell them whether you want the red commander stripe or not - and how to spell your name for stitching onto the pocket. Ask one of them nicely if they'd please come back and help you to put it on - it's not easy to do by yourself and without training.)
10. Wait impatiently for your shiney new spacesuit to arrive via FedEx.
11. EVA party!
12. SteveBaker (talk) 14:10, 7 September 2013 (UTC)

Spectacular plan! Regarding the red "publicity" stripes fashion statement: your first missions should forgo stripes, and you should add them later. Nimur (talk) 22:40, 7 September 2013 (UTC)

protein loosing - sperm

How much protein we loose when we take out a sperm (semen)? and what is the important matter (like minerals etc.) we loose when we do that. thank you. 95.35.210.39 (talk) 22:14, 6 September 2013 (UTC)

See Semen#Composition of human semen. To answer your specific question, on average, 171 mg of protein per orgasm. Tevildo (talk) 22:23, 6 September 2013 (UTC)

"To ejaculate" is the proper verb. Sperm is relatively very high in phosphorus, found in the energy providing chemical ATP and its relatives. This is why police can detect its glow with a black light. μηδείς (talk) 00:37, 7 September 2013 (UTC)

Why am I suddenly reminded of General Jack Ripper? ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:31, 7 September 2013 (UTC)

Another proper verb: "lose" not "loose". (Though I suppose one could be said to 'loose' semen.) AndrewWTaylor (talk) 11:31, 7 September 2013 (UTC)

Picture a very small, very fast German sub commander (in fathers, he wears the Iron Cross): torpedo 23,597,151 - Los! Wnt (talk) 17:27, 7 September 2013 (UTC)