Wikipedia:Reference desk/Archives/Science/2012 June 3

Science desk
< June 2	<< May | June | Jul >>	June 4 >

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

June 3

Can birds see (bright) stars and planets during daytime?

With some effort it is possible to see Venus during broad daylight conditions (even at Noon time), but other planets and stars can only be seen during daytime close to Sunrise/Sunset or else with optical aid, see e.g. here I've been able to see Jupiter last year just after Sunrise, and just a few days ago I could see Arcturus just after Sunrise.

So, I was wondering if birds that have far better eyesight than we have, can see Jupiter and bright stars like Sirius, Arcturus or even some of the dimmer stars all day long. Count Iblis (talk) 03:20, 3 June 2012 (UTC)

It's not really a matter of having "good eyesight" that makes us able or unable to see stars during the day; it's a matter of the sky being brighter than the object you are trying to view. Any given point of the sky during a typical day is 5 times brighter than Sirius is at night, so while I wouldn't say it's physically impossible, trying to resolve an infinitesimal point that is fractionally brighter than the surrounding sky is about as close as you could get to impossible for any animal. -RunningOnBrains^(talk) 05:31, 3 June 2012 (UTC)

Yes, but this depends on angular resolution. If you increase the angular resolution, the amount of scattered sunlight coming from the unresolved area in the sky will become less, as you're integrating over a smaller solid angle. This makes it possible to see even the not so bright stars during broad daylingt with a telescope (up to magnitude +4 during Noon time is doable with a decent amateur telescope, I think). I've read somewhere that some birds have a far better angular resolution than we do.... Count Iblis (talk) 15:11, 3 June 2012 (UTC)

You prompted me to read a lot about this, and it turns out I read the previous source incorrectly; the estimate was that the minimum brightness star a human could see during the day was 5 times the brightness of Sirius. I wasn't aware that you could see some stars during the day with a relatively low power telescope. this site suggests that the animal with the best visual acuity has about 5 times as many receptors per area as the human retina. That would suggest (if I'm reading this right) that their visual accuity is approximately 2.25 times greater than humans'; I don't think that would be enough to see any stars (Sirius is the brightest at magnitude -1.4), but definitely Venus (magnitude -4.3, and as you said, already at the edge of human visibility) and maybe Jupiter (magnitude -2.2). I'll admit though, all the different logarithmic scales working against each other really have me confused. -RunningOnBrains^(talk) 18:01, 3 June 2012 (UTC)

Interesting question, though. — kwami (talk) 03:48, 4 June 2012 (UTC)

Ah, look what I managed to dig out of the browser history. ;) I don't know about the birds, though... Wnt (talk) 20:41, 6 June 2012 (UTC)

Bird vision states that they can see the Sun and stars move in real time and use that as a compass. Sagittarian Milky Way (talk) 18:29, 7 June 2012 (UTC)

Can inchworms walk backwards?

I read that caterpillars can, but wtf about inchworms? I can't even picture them moving laterally so it's like they're doomed to walk forward in a straight line. Jasonberger (talk) 04:23, 3 June 2012 (UTC)

"Inchworms" are caterpillars, it's merely a colloquial name that we give to certain kinds of caterpillars that (usually) walk in a certain way. I'd think that they, like other caterpillars, are physically capable of walking backwards, but they may not have the appropriate instincts or automatic reflexes to be able to (I'd say "mental capacity" but I doubt the term is appropriate for insects). It would be an interesting exercise to take a variety of (common, unthreatened) caterpillar species and introduce then to confined spaces where walking backwards would be immediately advantageous, and seeing if they do it or not. {The poster formerly known as 87.81.230.195} 90.197.66.109 (talk) 11:31, 3 June 2012 (UTC)

Question about the Shenzhou program

Is there any particular reason why a manned Shenzhou mission only occurs every two or so years? I know that the program is relatively young and has only had three manned flights so far, but why is the frequency between flights so long? Even early manned flights of the Soviet and American space programs were more regular - about one manned flight every few weeks or months, not two or more years. And a related question - is there also any particular reason why no Chinese national went to space prior to the Shenzhou program? I would assume that they would have allowed at least one taikonaut to ride a Soyuz to gain valuable information, since the Soyuz and Shenzhou spacecraft are quite similar. Narutolovehinata5 ^tccsdnew 05:38, 3 June 2012 (UTC)

Why would the Chinese want their first taikonaut to fly on someone else's spacecraft when they know (edit:how to/are capable of) and plan to build their own? I'm not quite sure what valuable information they would gain that they didn't either already know or could gain in some other way. In the same vein, while national pride etc are obviously still important when it comes to these things, there isn't the level of competition between China and anyone else that there was between the Soviets and the US, so there's no need to rush their programme that much. Nil Einne (talk) 09:11, 3 June 2012 (UTC)

Well, the obvious way for a Chinese astronaut to get into space would have been through the Soviets as you say, but that of course didn't really work out after the Sino-Soviet split. The West was of course right out, so who were they going to hitch a ride with? As for Shenzhou, there's no need to rush, I guess. The Americans and Soviets were of course in the space race, hence the rather frantic pace of the 60s. — Preceding unsigned comment added by Fgf10 (talk • contribs) 12:31, 3 June 2012 (UTC)

I don't think the 1960s Space Race programs of the USA and USSR should be taken as the "normal" case here. Their rapidity was as more about propaganda than it was about running a sane and safe scientific program. I don't see what a hyper-accelerated program would be getting the Chinese — they are not in a "race" with anyone. --Mr.98 (talk) 16:57, 3 June 2012 (UTC)

As a practical matter, two years between space shots should allow enough time to redesign rockets to fix any bugs, while 2 weeks only allows time for a patch, at best. StuRat (talk) 17:49, 3 June 2012 (UTC)

How did a blue whale evolved?

If all mammals was evolved from Therapsids,how mammals like blue whale and other aquatic mammals evolved.How can a mammal lived in terrestrial habitat evolved back into a aquatic habitat?And what about Echidna,Platypus and Spiny anteater?Are they evolved from a single organism,or are they evolved lately from other organisms like reptiles,rodent like creatures and birds.Can you please tell everything in detail. — Preceding unsigned comment added by Ganesh Mohan T (talk • contribs) 07:19, 3 June 2012 (UTC)

With regard to evolution of whales: in essence, by leaving the terrestrial environment, structures once needed for other uses are freed to evolve to become more useful structures. Thus, the flippers that the whale uses for steering are made of flattened and shortened arm bones. The structure of the skull is altered, with what once were nasal openings becoming a blowhole or two. What once were legs become vestigial. WIth regard to the monotremes you mention, the Spiny anteater and Echidna are different names for the same animal. They are all monotremes, but of different families: the platypus being of the Ornithorhynchidae, while the echidna is of the Tachyglossidae family. There is a chart in our platypus article. Reptiles and birds are different classes of the phylum Chordata; rodents are an order of the class of mammalia. Our article on biological classification should be of interest to you. - Nunh-huh 09:43, 3 June 2012 (UTC)

The details are much too extensive to cover here. Whales are thought to be most closely related to animals like the hippopotamus -- that should help to see how they evolved. The echidna and platypus are thought to have split from other animals as much as 200 million years ago. The split between mammal ancestors and reptile-bird ancestors happened a very long time ago, around 350 million years. Mammals are synapsids; reptiles and birds are diapsids. Looie496 (talk) 17:17, 3 June 2012 (UTC)

To me, the most interesting question about whales is how species that adapted to live on land can go back to the sea and apparently find niches where they are better adapted to that environment than those animals whose ancestors lived there all along. There must be some mammalian adaptations which are actually better suited to the sea than those of fish, reptiles, and amphibians. The improved thermoregulation (temperature control) of mammals may be important, as may the increased intelligence of mammals (some whales use complex group hunting strategies). Feeding the young milk may have some advantage too. Body hair is iffy, since whales lost theirs, but other semi-aquatic mammals, like otters, kept theirs.

Then the meta-question is, if mammalian features are advantageous in the sea, why didn't they evolve directly in the sea ? I would guess that they are even more advantageous on land, and/or there was more evolutionary pressure there, so they evolved more quickly on land. StuRat (talk) 17:44, 3 June 2012 (UTC)

Well, the answer to that is actually very well known: the critical thing is the ability to breathe air. Gills are an extremely inefficient way of getting oxygen compared to lungs, so air-breathers can have a much higher rate of metabolism. Looie496 (talk) 20:17, 3 June 2012 (UTC)

But air breathing long pre-dates mammals. Why isn't the niche filled by whales filled by some kind of lungfish? --Tango (talk) 20:32, 3 June 2012 (UTC)

Creatures that are sea-bound lack the option that a land mammal has to return to the sea at any time for a transitory purpose, which may become a dependence. Examples are seals, whales, dolphins, walruses and humans who go fishing. At some point in evolutions of whales and dolphins, an ancestor found itself surviving better in the sea all of the time instead of part of the time, and the rest is history. See the article Marine mammal. Seals and fisherman however still like to do their breeding on land. DriveByWire (talk) 21:10, 3 June 2012 (UTC)

I'm sorry, but that doesn't make any sense. What creatures that are sea-bound lack is the option to go on land, not the option to go into the sea... --Tango (talk) 22:57, 3 June 2012 (UTC)

Yes, I take it they mixed up the words "land" and "sea". StuRat (talk) 23:48, 3 June 2012 (UTC)

Could animals evolve lungs today, or does that require higher atmospheric oxygen concentrations like existed during the Carboniferous era? Count Iblis (talk) 23:42, 3 June 2012 (UTC)

Even at our current oxygen level, there's still far more accessible oxygen in a given mass of air than water (assuming the oxygen in H₂O stays where it is). The only place the higher oxygen content is important is with large, fast moving animals, like some dinosaurs. Whales, while larger, tend to move slowly and more efficiently, most of the time. StuRat (talk) 23:48, 3 June 2012 (UTC)

Higher oxygen content is also important for animals without complex respiratory and circulatory systems, that rely on diffusion to get oxygen to their cells. That's why insects could be much larger during that era than they can be now. I agree, though, that even primitive, inefficient lungs would be able to extract useful amounts of oxygen from the current atmosphere. -Tango (talk) 23:57, 3 June 2012 (UTC)

Keep in mind that the environment isn't stable. The ancestors of whales could have exploited niches that had opened up relatively recently. thx1138 (talk) 18:46, 5 June 2012 (UTC)

Iminosugars

Is it possible for an iminopyranose to form when the amine group is of the secondary nature in the open chain form? Plasmic Physics (talk) 07:44, 3 June 2012 (UTC)

It appears to work for N-BOC (see doi:10.1021/jo982448c), so it seems likely that it would work for simple secondary alkyl amines at least as well (a carbamate N is generally less reactive than an amine). DMacks (talk) 08:36, 4 June 2012 (UTC)

What is the SMILES for N-BOC, what is its structure? Are you saying that carbamates are generally precluded? Plasmic Physics (talk) 09:00, 4 June 2012 (UTC)

BOC is a common protecting group for amines, deriving the nitrogen as NC(=O)OC(C)(C)(C) and I am saying that in general, carbamates and amides and other such groups would be less nucleophilic than a non-resonance-stabilized N (with respect to your question specifically asking about amines). One of the primary (sorry:) uses for tBOC is to prevent N from acting as a nucleophile (for example, to prevent peptide coupling. DMacks (talk) 09:21, 4 June 2012 (UTC)

So, what is the chance of c converting into CCCCCCCCCCCCCCCCCC(=O)N1CCNC1(O)CCCCCCCCCCCCCCCCC? Plasmic Physics (talk) 13:26, 4 June 2012 (UTC)

Approximately zero, since now you're probably destroying two amide stabilizations to accomplish it (high energy barrier) as well as still having one destroyed in the product (unfavorable equilibrium). On the other hand, you could keep going and do an acyl transfer to get to CCCCCCCCCCCCCCCCCC(=O)N(CCN)C(=O)CCCCCCCCCCCCCCCCC (stable imide). But ethylenediamine bis-amides appear in general to be easily prepared and reasonably stable. DMacks (talk) 17:41, 4 June 2012 (UTC)

So the rule of thumb is: any geminal electron withdrawing group will prevent a cyclic morph from forming, usually a doubly bonded group such as oxygen? What if that group is a halide - does it have the same effect? Plasmic Physics (talk) 23:10, 4 June 2012 (UTC)

A halide is not a double-bonded group or a resonance-acceptor, so it would not behave the same way. Whether it would have the same result in this type of reaction (reduced nucleophilicity of the N due to electronegativity) is a good question. Haloamines are generally X⁺ (or sometimes X• radical) donors or N electrophiles, not N nucleophiles. Even Chloramine-T isn't primarily an N nucleophile. SciFinder isn't finding me any examples of NH₂Cl or RNHCl acting as an N nucleophile except for a single example of a case of R being specially activated. DMacks (talk) 16:11, 5 June 2012 (UTC)

It seems that after so many years, I still haven't mastered the correct use of terminology. I intended to refer to the result, rather than the behaviour with respect to a geminal halide. Plasmic Physics (talk) 22:18, 5 June 2012 (UTC)

I should also mention that by 'geminal', I meant attached to the same carbon. I see that you understood the geminal centre to be the nitrogen. That appears to be muut though, if it has a poor effect even when the halide is connected directly to the nitrogen. Plasmic Physics (talk) 22:25, 5 June 2012 (UTC)

It is strange that we don't have an article on Iminosugar, it's only mentioned once in passing in Glycomimetic. Plasmic Physics (talk) 22:10, 5 June 2012 (UTC)

Body weight reduction and Einstein

It is possible to reduce your body weight by 1 kilogram by exercise in a span of 10 days. This 1 kilogram goes out as energy during exercise. Now applying E=m*c*c, it comes out to be 2.142 billion kilocalories per day !! So, I am leaving out something very important in my calculation. ( Is sweat that comes out unaccounted ?) — Preceding unsigned comment added by 117.193.154.179 (talk) 17:52, 3 June 2012 (UTC)

Lost body weight has nothing at all to do with mass-energy equivalence. When you lose weight through exercise and dieting, it leaves your body as carbon dioxide and urine mostly. That is, you lose mass via the chemical reactions that turn organic matter in your body into carbon dioxide, water, and nitrogenous wastes (Urea), along with trace other stuff. You breathe, sweat, and piss out your weight, basically. Einstein has nothing to do with it. --Jayron32 18:00, 3 June 2012 (UTC)

The OP's calculation is essentially correct - there is a weight loss due to mass-energy equivalence. It is just so tiny as to be unmeasurable. The real loss it, as you say, from breathing out carbon dioxide (and a bit from urine and sweat, although that's mostly just water going in and coming out again). --Tango (talk) 18:42, 3 June 2012 (UTC)

Indeed. The mass you lose from mass-energy equivalence would really exist, but would be immeasurable on any scale ever made. It would basically be all of the energy lost in the chemical reactions which convert your fat, sugars, and proteins into carbon dioxide and water; since this is an exothermic process, there is a tiny amount of mass lost there. There is also a tiny amount of mass lost in just losing the actual mass. 1 kilogram of matter at body temperature has some inherent mass due to the temperature itself (thermal energy), and a really tiny amount of mass is accounted for in this way. Even if you add all of this up, however, the mass is so small as to be negligible. It can be ignored in any calculation and not make any measurable difference. The mass is basically the loss of carbon, hydrogen, oxygen, and nitrogen atoms via the normal way that your body loses those atoms. You're always losing those atoms, but if your body accumlates less of them over time than it loses, you lose weight. That is, if catabolism exceeds anabolism, you lose weight. --Jayron32 18:57, 3 June 2012 (UTC)

Any backing to the thesis that chemical reactions in the body would convert any mass at all into energy as in E=m*c² ? Electron9 (talk) 01:18, 4 June 2012 (UTC)

Sure, chemical bonds contain bond energy which is released or accumulated in bonds via chemical reactions. If a chemical reaction absorbs more energy than it releases in the process of breaking and making bonds, the reaction is endothermic. If the chemical reaction absorbs less energy than it releases in those processes, the reaction is exothermic. Conversion of organic material to carbon dioxide and water is always exothermic. When it happens outside of the context of metabolism, this is called burning, a self-evidently exothermic processes. That it happens slower in your body doesn't make it release less energy, thermodynamic functions are state functions, and the amount of energy released is a simple matter that the energy in the bonds of the products is less than the energy in the bonds prior to the metabolism. Basically, if you want to make it simple, your body causes chemical reactions to turn fat into carbon dioxide and water; since there is less energy in the bonds of the carbon dioxide and water than in the bonds of the fat, a small amount of bonding energy is released as heat. This loss of energy is a negligible, but non-zero, mass. --Jayron32 05:27, 4 June 2012 (UTC)

The above answers correctly stated how you lose weight after exercise, but you might also be interested in why. If we look at one type of molecule, like a fat, it's broken down into other molecules and a very slight amount of energy is released in this process. The actual breakdown of the molecule doesn't measurably lower your weight. However, once it's been broken down, it no longer serves any purpose in your body, so your body excretes some of the products as waste and reuses others. It's the waste removal process where you actually lose significant weight. StuRat (talk) 20:09, 3 June 2012 (UTC)

Previous answers are correct in what they say, but what they haven't made crystal clear for the OP is just what the energy loss is and why the mass loss implied in that via E = mc² is so tiny. Here's how it works: As you exercise, you body is not 100% efficient in converting the chemical energy in the food you consumed and the energy stored in fat etc to mechanical energy to move your body around. The energy not converted into mechanical energy ends up as heat, which you mainly shed as as infrared radiation from your skin, and as latent heat of vaporisation in your sweat. For a hard working human, this is of the order of 300 joules per second max. Re-aranging E = mc² as m = E / c², you get 300 / c² = 3.33 x 10^-15 kg. In other words, sweat your guts out for 24 hours (24 x 60 x 60 seconds), and you lose 0.000 000 288 grammes due to Mr Einstein. Wickwack121.221.74.25 (talk) 01:45, 4 June 2012 (UTC)

I think that's a misconception, the energy is stored and released from chemical bonds. Not from the mass itself. Electron9 (talk) 01:53, 4 June 2012 (UTC)

But the chemical bonds are part of the mass. In the end, there's no fundamental difference. — kwami (talk) 03:44, 4 June 2012 (UTC)

There's still an error though - for some weird reason I wrote it up as only the energy lost as heat (due to inefficient conversion of chemical to mechanical energy) get to subtract mass due to m = E/c², actually it should include the mech energy as well. However, I've made it clearer for the OP just where E = mc² gets involved, and why any mass lost is so small it cannot be measured. Wickwack121.221.74.25 (talk) 04:08, 4 June 2012 (UTC)

Good responses. Let me make it bit more clear. whatever we eat, only glucose can be oxidized to release energy. Carbohydrates are readily convertible to glucose after digestion. This glucose enters the blood stream and releases energy. Now, how does it do that? The glucose diffuses into the the mitochondria of the cell, the oxygen also diffuses. After a complex cycle of reactions, one molecule of glucose releases 38 ATP of energy, water,carbon-dioxide and heat. When we exercise, we need more energy. When the amount of carbohydrate we intake is less than that required by the body, fats get broken down and become glucose after a series of reaction. ( There is a very interesting relation that relates fat with number of glucose molecules). Hence, weight reduction occurs. Now, coming to the einstein part - In any exothermic reaction, mass of reactants > mass of products. Only then heat can be released. This difference in mass is generally in nanogram in normal lab reactions. So this weight reduction is very very less. So, to summarize weight reduction occurs primarily due to Fat ----> Glucose -----> ATP(used by body in exercise) + carbondioxide(eliminated from body) + water (eliminated from body)

True, but the fact that fat passes through glucose on the way to making carbon dioxide and water doesn't matter for the overall thermodynamic calculations. Because thermodynamics depends on state functions, only the intial and final states of a series of reactions actually matter when calculating the net gain or loss of energy. Of course, the path taken in the reaction series does matter, but that is the realm of chemical kinetics. In the end, however, it doesn't matter whether or not you cut a chunk of fat off of your body and set it fire with a blow torch, or whether there are 50 different and complex chemical reactions which convert it to carbon dioxide and water. In the end, the net energy for both processes will be identical. That's the idea behind Hess's law. Thermodynamics is independent of mechanism. --Jayron32 14:07, 4 June 2012 (UTC)

Jayron32, I agree with you. The reason, I mentioned that it is a multi-step process, was to bring out the complexity of the mechanism. I am sure atleast few people would have googled up and reached upto kreb's cycle and the likes in this process. — Preceding unsigned comment added by 117.193.137.186 (talk) 16:33, 4 June 2012 (UTC)