Wikipedia:Reference desk/Archives/Science/2015 January 17

= January 17 =

Tail of comet Lovejoy
Is the tail of C/2014 Q2 (Lovejoy) currently pointing roughly toward the Pliedies? I could see a fuzzy spot and perhaps some tail. Bubba73 You talkin' to me? 00:49, 17 January 2015 (UTC)


 * I just found the setting while looking for which way the post-1997 Great Comets pointed. You can answer questions like this by going to, setting the table to 27 and reading the numbers. The numbers are the direction the gas and dust tails are pointing (0 points to the NCP (use Polaris), 270 to the direction it's setting or rising), 90 away and 180 to the celestial south pole. If you're 45°N say, then 180 points towards the point that happens to be halfway between down and south. At 30°N it points only 30° down. Sagittarian Milky Way (talk) 01:44, 17 January 2015 (UTC)


 * I don't see anything there about setting the table to 27. I'm not wondering about the numerical direction - I'm asking if the tail is pointing roughly towards the Pleiades at the present.  Bubba73 You talkin' to me? 02:17, 17 January 2015 (UTC)


 * Ah, you'll have to fill in the time, place, object and table settings links on that page. And leave only "Table Setting" checkbox number 27 active. I'm not too interested in this comet (invisibly dim here) but I'll fill out the forms for you and translate to English if you want. Sagittarian Milky Way (talk) 02:41, 17 January 2015 (UTC)


 * That seems like an unnecessary amount of work. Someone should know whether or not the tail is pointing roughly toward the Pleiades right now.  If it is, then I think I saw some tail.  If not, I didn't.  Bubba73 You talkin' to me? 03:21, 17 January 2015 (UTC)


 * I filled in the forms and the gas tail indeed was pointing just like you said. It is close to the Pleiades and moving in space so it won't quite point there tomorrow.
 * The dust tail though was pointing sideways from the Pleiades direction (down if it's dusk). If you want to try to see it's best when it's highest around 7:30 pm. Sagittarian Milky Way (talk) 03:57, 17 January 2015 (UTC)


 * Wow, thanks, then I believe I did see some of the tail. My daughter and I saw it tonight about 8PM with 7x50 binoculars.  This was the first clear night in several nights and it is going to cloud over again tomorrow.  The last time it was clear, the Moon was too close and bright.  Bubba73 You talkin' to me? 04:01, 17 January 2015 (UTC)


 * I guess you could try the day after. And I somehow made a mistake out of laziness so it in fact points the most accurately this weekend and not yesterday. Sagittarian Milky Way (talk) 04:25, 17 January 2015 (UTC)


 * The forecast is for mostly sunny Monday and clear Wednesday - otherwise cloudy. Bubba73 You talkin' to me? 04:29, 17 January 2015 (UTC)


 * The gas tail will point 10 and 30 degrees off then. (how far you'd need to rotate it to line up, not how far a line continuing the tail will miss by — that can hardly be 10 degrees when it's only 12 degrees away) Try to look with slight peripheral vision after 30 minutes in the dark (or red light). Make the comet move instead of staring at a fixed spot (as that's what peripheral/night vision is good at detecting). And don't use the temple side blind spot, that makes above and below the only option with binoculars. Let me know if you see the dust tail. Sagittarian Milky Way (talk) 06:20, 17 January 2015 (UTC)


 * My eyes are 60 years old so they don't adapt to the dark as well as they used to. Also, in '99 I had an eye problem that left me with a lot of blind spots.  It is hard for me to recognize constellations that I used to know because some of the stars fall on the blind spots.  Also, there is quite a bit of light pollution.  Bubba73 You talkin' to me? 07:01, 17 January 2015 (UTC)


 * No, light pollution is when you can see your fingerprints 4 miles from downtown by cloud light :). Light pollution is when you're almost a hundred kilometres from downtown have only two thin strips of suburbs within 40 miles and the pink around the stars is merely "reduced significantly". Sorry about your eye problem, I sympathize. I guess you could try looking in spirals around the tails, this might make them appear to suddenly pop out of nowhere so having blind spots would make it easier. Sagittarian Milky Way (talk) 17:15, 17 January 2015 (UTC)

How farther apart in wavelengths do two lights have to be in order to appear like two distinct colors to the human eye?
Awkward phrasing, I know. But I am not sure of the term to describe this concept, so I write out the question like so. Anyway, I know that a normal human eye can certainly distinguish orange and yellow on the visible light spectrum, but how close do they have to be to be distinguishable? I mean, in my crayon box, there may be "Lemon", and there may be "Yellow", and they look very similar to each other until I use them to mark the paper and see a slight difference. 71.79.234.132 (talk) 05:40, 17 January 2015 (UTC)


 * Your phrasing is fine (except "farther" should have just been "far"). We recently had a similar question about how many colors the human eye can distinguish.  Let me see if I can find it... StuRat (talk) 05:47, 17 January 2015 (UTC)


 * ...I think this is it: Reference_desk/Archives/Science/2014_April_27. StuRat (talk) 05:50, 17 January 2015 (UTC)


 * There is no simple answer to this unless you are colourblind. Humans may have, develope and unfortunately also loose sensual abilities in a wide range. This range is more commonly known in the field of soundwaves, where for example an classical music concert to one person is not much more than "allot of noises" but in that same moment another person may be able to hear one single violin is not played perfect. Its part gift, part training. Graphic artists or printers for example are certainly trained to distince colour much better than average.--Kharon (talk) 14:32, 18 January 2015 (UTC)

Use of DNA in bodily substances to solve crimes
Let's say that we have a hypothetical crime scene. My understanding is that the perpetrator's DNA can be extracted if the perpetrator leaves behind any of the following at the crime scene: his blood, semen, feces, hair, or skin cells. Is my understanding correct on those five items? (I believe so, but I am not 100% sure.) Now, my real question involves two other items: perspiration and urine. Do those items also contain the perpetrator's DNA? Let's assume that the items mentioned above are of sufficient quantity for DNA testing. Thanks. Joseph A. Spadaro (talk) 07:13, 17 January 2015 (UTC)


 * Accoring to Urinary cast celluar debris is detectable in urine. (don't forrget salvia and tears) Another reference: http://www.nytimes.com/2010/11/02/science/02qna.html  --Digrpat (talk) 08:45, 17 January 2015 (UTC)


 * DNA is even present in your breath. 2A01:E34:EF5E:4640:5CFF:AF8:B79:73A8 (talk) 10:04, 17 January 2015 (UTC)


 * It used to be if you murdered a baby, you could frame it on the cat's natural tendency to eat that sort of thing. Not anymore. Well done, science. InedibleHulk (talk) 11:41, 17 January 2015 (UTC)
 * There has been some work on getting DNA from fingerprints but Google gives many false hits when searching on those terms. Rmhermen (talk) 17:02, 17 January 2015 (UTC)


 * One thing that always worries me when I hear about a murder being "solved" by finding one hair, etc., is how easily that could be innocently transferred. Anyone who has ever been in your home or met anyone in your family outside the home might very well have left some of their DNA in your home.  Possibly even further out, somebody who shook hands with an intermediary, who shook hands with you, might have their DNA on you.  So, as the sensitivity of our tests go up, to where we can analyze smaller and smaller samples, we may get more and more false positives.


 * I would think the first Q any defense attorney should ask the DNA analyst would be "how many unique DNA donors were you able to identify at the murder scene ?". The answer should make it clear if everyone in the neighborhood has left DNA behind there, just how meaningless the presence of any one person's DNA sample there is.   StuRat (talk) 17:01, 17 January 2015 (UTC)


 * Yeah, but they make DNA databases from criminals, i.e. anyone who is ever arrested, whether or not the charges stuck. Since the only hit in the DNA database is a criminal, the only criminal who was on the scene is the person in the DNA database, Q.E.D. he done it. Wnt (talk) 21:54, 17 January 2015 (UTC)


 * Yes, they have databases for the DNA of criminals. But, they can also compare the DNA profile to any person (for example, a suspect), whether that person is a criminal or not.  In other words, they don't only look at the criminal DNA database.  They can look at anyone's DNA, even if the person is not in the criminal database.   Joseph A. Spadaro (talk) 02:12, 18 January 2015 (UTC)


 * (I assume the small text is because you're kidding, but others might take you seriously.) StuRat (talk) 22:10, 17 January 2015 (UTC)
 * I thought it was funny. But then, I've never gone to prison for something the cat dragged in. They may not eat your soul, but they do lick your beard. Another good first question for a defender is "Where'd you find it?" A hair or drop of blood on a carpet or doorknob is far less damning than it is under the victim's fingernails or in her butt. InedibleHulk (talk) 22:22, 17 January 2015 (UTC)

Thanks, all. Joseph A. Spadaro (talk) 19:08, 20 January 2015 (UTC)

Skink ID


Can anyone identify this species? Someone else uploaded it, so all I know is that it's a skink in Australia: what part of the country, what exact size, etc. I can't tell. All I can suggest is (1) checking the uploader's contributions to see if there's a geographic pattern (i.e. if he has a bunch of Australian photos from a specific region), although I have to run and can't get that now by myself, and (2) perhaps this is in the country's northern regions, as EXIF says that this is taken in late September; it looks like a rather lush environment, not the kind of thing you'd expect to see at the end of winter in a temperate environment. Nyttend (talk) 12:05, 17 January 2015 (UTC)


 * Eastern blue-tongued lizard.  S n o w  talk 13:12, 17 January 2015 (UTC)


 * FYI,, I've taken the initiative in updating the file description on commons. I think it's a decent quality photo that should probably be added to the article for the lizard as well.  S n o w  talk 23:34, 17 January 2015 (UTC)

genetics (origin of somatic cell chromosomes)
in a human somatic cell, in the autosome pairs, is one of a pair totally from the mother and the other totally from the father? thx.72.183.121.78 (talk) 12:54, 17 January 2015 (UTC)
 * Not necessarily. Genetic recombination is best known in the context of meiosis, but it can also rarely occur in somatic cells during mitosis.  See https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3090628/. Looie496 (talk) 15:22, 17 January 2015 (UTC)

thx. that is very interesting. I guess my question should be: is most (or almost all) of one of a pair of autosomes from the mother and most of the other from the father (especially before a lot of cell divisions)?72.183.121.78 (talk) 15:58, 17 January 2015 (UTC)
 * I don't see how that is different from the original question, so I probably don't understand it. Looie496 (talk) 02:49, 18 January 2015 (UTC)

I really appreciate your patience. if I may: in the first few divisions after the egg is fertilized and absent the rare mitotic recombination, is one of the pair almost totally from the mother and the other almost totally from the father?72.183.121.78 (talk) 03:47, 18 January 2015 (UTC)
 * Yes, because chromosomal crossover occurs during meiosis, i.e. before the gametes exist. See homologous chromosome though it's not very clear, could use work.  This is particularly relevant in genomic imprinting of insects such as mealybugs, where the entire paternal genome can be turned off (heterochromatin) pretty much as a unit.  Wnt (talk) 04:07, 18 January 2015 (UTC)

thx much.72.183.121.78 (talk) 12:58, 18 January 2015 (UTC)

How and from what are hormones in pills/medical treatment created?
I've always wondered, with all the hormonal treatment given to lots of people in modern society, where does the hormones in pills etc. come from? Be it testosterone, estrogen or some other hormone, and be it in the form of pills or alcoholic gels etc.

It has to be artificially generated/created before put into pills or gels, right, but from where and how? It just seem so strange to me that they can create and put something like that into pills and the likes, something which are supposed to only be naturally generated inside an individual's body.. When it comes to other types of medicine, it is easier to understand how and from where the key ingredients come, because they are often natural resources that can be gathered.

So, to repeat my question; How, from where and from what do they make hormones used in medical treatment? 2A02:FE0:C711:5C41:1CEC:1194:53D:204E (talk) 13:36, 17 January 2015 (UTC)
 * Some are made by GMO, coping an appropriate set of genes into a suitable bacteria. Insulin is extracted from yeasts, it used to be extracted from pigs, Estradiol (part of the combined oral contraceptive pill is directly synthesised. Progestin (the other part of The Pill) doesn't indicate its synthesis/extraction. Testosterone-like hormones can be synthesised. It really depends on how complex the hormone in question is, and if there is a near-analogue already made by another species. LongHairedFop (talk) 14:38, 17 January 2015 (UTC)

"something which are supposed to only be naturally generated inside an individual's body." is an interesting comment. Chemicals don't know where they come from, they just exist, and have no really intrinsic difference based on their origin. It's something of a marvel of modern science that we can start from a non-biological chemical and make one, but total synthesis isn't a new field of productive research (and vitalism started to be disputed and disproven almost two centuries ago). DMacks (talk) 16:37, 17 January 2015 (UTC)

Thanks for answers. Today's education for me, that is. They say we all learn something every day.. :) I agree by the way that it is "something of a marvel of modern science that we can start from a non-biological chemical and make one." 2A02:FE0:C711:5C41:1CEC:1194:53D:204E (talk) 18:17, 17 January 2015 (UTC)


 * Premarin is extracted from the urine of pregnant mares. --TammyMoet (talk) 20:09, 17 January 2015 (UTC)

On an interesting historical note, the original source of the precursors for the hormones in birth control pills was yams. See our article. In the 1950s some yam species were found to be abundant sources of steroid compounds that could be converted to sex hormones. And another thing: in the Trobriand Islands, yams are a staple food, and the yams found there contain steroids with contraceptive activity. The regular consumption of these was a factor in the development of sexual mores that are very alien to traditional Western society. --71.104.75.148 (talk) 01:52, 20 January 2015 (UTC)

Main Battle Tank
When I read the information about tanks` maximum range, I noticed an issue which is that the M1 Abrams and all other tanks that use diesel fuel have almost the same range , but once a time I hear that the M1 Abrams refuel each four and a half hours while diesel fuel tanks refuel every 24 hours while watching a documentary film , so how can I understand this contradiction ? 46.185.161.90 (talk) 14:02, 17 January 2015 (UTC)
 * Simple. They almost certainly mean different things. At a guess, a tank can do 4 or 5 hours of heavy maneuvering before it runs out of fuel (there's your M1 answer -- how long can a tank drive at highway speed). At a guess, an army in combat plans to refuel its tanks daily so that they don't run out in combat the next day, whether or not they've maneuvered heavily the day before (there's your other tanks answer -- what an armored unit's logistics plan is). &mdash; Lomn 14:28, 17 January 2015 (UTC)
 * (ec)You may misremember ;-). The M1 Abrams guzzles fuel, but it also has a much larger tank than e.g. the Leopard 2 - the M1A gets 426 km out of 1900l (for 446l/100km, or about 100 times worse fuel economy than a modern compact car), the Leo 2 gets 550km out if 1200l, for more or less twice the fuel efficiency. How often either needs to refuel depends very much on how they are used. Driving either 420km or 550 km in a tank looks like a full peace-time job for one day to me, so normally you can fuel up in the morning and will run out when you are about to turn in anyways. With the M1A there is a somewhat larger chance that you need to refuel during the day... --Stephan Schulz (talk) 14:46, 17 January 2015 (UTC)
 * Anecdote alert: During the first Gulf War, the US armour couldn't get to Baghdad because they ran out of fuel. The reason was that they were employing local people to drive the fuel trucks. These people were using them to drive off to visit their families and would disappear for days, plus, even if they didn't do that, they had to pray five times a day, and would always turn up late. This problem was solved in the second Gulf War, by employing Europeans.  KägeTorä - ( 影 虎 )  ( Chin Wag )  05:01, 18 January 2015 (UTC)
 * Or they thought they did. But when they tried it, they found in practice the Europeans were arriving many days later. They found that the problem was the Europeans were demanding 15 minute tea breaks every few hours and similar for smoke breaks, 1 hour lunch breaks and stuff like that. And they would only work 8 hours or if you got lucky, 12 hours. The Iraqis may have prayed for 10 minutes 5 times a day and sometimes disappeared to see family for an hour or two, but otherwise they drove for 18-20 hours straight only taking a few minutes for lunch. Plus you could hire 30 Iraqi drivers for the price of 1 European, so they couldn't hire 3 per truck like they could when someone was concerned about the safety of driving 18 hours. And in any case, long hours aside, the Europeans didn't seem to know how to drive on roads where you may have random camels, motorcycles and whatever else appearing out of nowhere all time. After spending $30 million on several consultants trying to work out what they could do, an intern in the White House suggested they could just use more realistic timetables, and suddenly all was solved. Everyone was happy. The consultants made many many millions more of the years, the tank, fuel truck and other weapon and support system manufacturers billions. Well except may be the intern who went on to teach the children of these consultants and manufacturer CEOs and made about $80k a year until they got fired and blacklisted for saying something innocuous but which made it to the parents who didn't like, and now works at a public school making $30k. Nil Einne (talk) 07:36, 18 January 2015 (UTC)

Actually, as our article states, the U.S. military typically fuels the M1 with JP-8 jet fuel. The U.S. military uses JP-8 for all its ground vehicles as well as aircraft, to simplify logistics. Other users of the M1, like the Australian military, do use diesel. Also interesting is that the M1 is different from most tanks in having a turbine engine, instead of a reciprocating engine like what you would find in a car or truck. --71.104.75.148 (talk) 02:03, 20 January 2015 (UTC)

Mallard ducks in Britain
Do mallard ducks in Britain migrate for the winter, and if so, where?

Also, presuming they do migrate, is there documented behaviour of them returning to the same lakes, year after year? If yes, are these lakes the lakes by which they hatched?--Leon (talk) 16:01, 17 January 2015 (UTC)

The RSPB is your friend.--Phil Holmes (talk) 18:21, 17 January 2015 (UTC)
 * That article confirms my anecdotal American experience, which is that mallards usually stick around their specific habitat year-round, provided there's sufficient food. ←Baseball Bugs What's up, Doc? carrots→ 12:34, 18 January 2015 (UTC)
 * Backing that up with equally anecdotal British experience, it's common to see mallards standing on frozen ponds in winter. AndrewWTaylor (talk) 13:36, 18 January 2015 (UTC)

Road stabilisation
Are all roads stabilised either mechanically, or with a binder? Is it possible to have an unstabilised road other than a dirt road or roads with unbound bases. Can the term stabilisation also be used for the surface course which is normally bound with bitumen? 82.132.239.245 (talk) 18:56, 17 January 2015 (UTC)


 * No, some roads are stabilised with cement, which is not a binder.
 * No, no other public road types may be unstabilised.
 * Not sure.
 * This is based on New Zealand definitions. Plasmic Physics (talk) 03:10, 18 January 2015 (UTC)

Heat effect on skin: study of blow drier users versus non-users
So, I heard that basically the most damaging things to skin are the sun, and heat. Those who avoid the two (use sun-screen and don't take scalding showers) have fresh skin for longer. I've used this advice to good effect and can easily subtract a quarter of my age and be believed (say 24 at 32).

separately, I've always towel/air dried my hair. I've recently adopted a new look, and was taught to blow-dry for it. (Though not strictly necessary; but if I don't, if I air-dry, then it is wavy/curly instead of straight. I prefer the latter.)

So, here is my question: just how damaging is blow-drying (scalding hot) hair in the mornings, to skin, over a period of years (if I had this look for years)?

Best would be if I could simply see some comparison pictures. For example, here is a picture of someone half of whose face happened to be sunlit over a period of years: http://www.doobybrain.com/2012/06/04/unilateral-dermatoheliosis-the-effect-of-the-sun-on-human-skin/ (and there are many similar ones). It's a dramatic demonstration.

Are there some photos I could see of scalps and faces of blow-drier users versus air-drier users? I'd just like to know how strong the effect is. The blow-drier is scalding hot, but lasts just a couple of minutes. (I don't think drying on the cold setting produces the desired effect with the technique I've learned, and anyway I would catch a cold every morning I wash my hair. Towel/air drying produces totally different hair.)

Also, if you can't find any references, photos, I've thought of another way. If there are actors/actresses who obviously and for years wear a straightened, blow-dried look (that they obvoiusly repeat frequently) I could look at their faces versus ones with shorter/wavier hair or who have gone on record as air-drying. It is easy to follow actors' aging over a period of years (longitudinally) since they're always in the public eye. 212.96.61.236 (talk) 22:17, 17 January 2015 (UTC)


 * I can find nothing on the web about hair driers damaging skin, but having said that we can't give medical advice, so I can't tell you they definitely don't cause skin damage. You may be interested in this and this. I think finding pictures of actors with blow dried hair is a little outside the scope of the science reference desk :-) Richerman    (talk) 23:18, 17 January 2015 (UTC)


 * Yea, this is the first I've heard of hair dryers damaging skin. Are you sure you didn't hear somebody say they damage hair ?  To damage skin, they would need to leave a burn, I would think, and that seems more likely with a curling iron than a hair dryer.  Of course, a hair dryer might tend to dry out the skin, but that's nothing a little moisturizer won't fix. StuRat (talk) 01:20, 18 January 2015 (UTC)


 * (OP here). My very strong impression is that the two respondents are wrong and getting blown on by scorching hot air ages skin over time - I would just like to know the magnitude of the effect.  The idea that you can blow scorching hot air all over your scalp and delicate facial skin without aging them is obviously wrong on its face and counter to everything I've read or know about keeping from stressing skin.  I don't mean to a major extent or anything - just something that visibly ages you and causes wrinkles, etc.  If it really does cause no effect, I'd love to see this in a dermatology journal or something. 212.96.61.236 (talk) 02:07, 18 January 2015 (UTC)


 * Can you provide any sources for this belief ? The top layer of skin is dead, and removing it to get to the "fresh skin" below is what exfoliation is all about.  And just how hot is this air if you are actually creating burns on your skin ?  Obviously don't do that.  Sunlight causes damage by penetrating below the dead skin and damaging the DNA of the live skin below.  You can tell it is damaging the skin because excessive sunlight causes sunburns.  If excessive hair drying caused similar burns to the skin, then I would agree that you are damaging it, but that shouldn't happen unless the heat is way too high. StuRat (talk) 04:11, 18 January 2015 (UTC)


 * It's hot enough to scorch my ear if I'm not careful, I have to do it carefully. I guess I could use the next setting down, but the question was in general. I'll provide a source for the belief.  Google "heat damages skin" - https://www.google.com/search?q=heat+damages+skin     one article on a topic that happens to include heat (http://www.huffingtonpost.com/2010/10/04/warm-laptops-may-cause-sk_n_749049.html) says "Salkey, an assistant dermatology professor at Eastern Virginia Medical School, said that under the microscope, the affected skin resembles skin damaged by long-term sun exposure."  So it's not just UV exposure from the sun.  That is about laptop heat but heat is heat.  A hairdrier is waaaaaay hotter than a laptop. it would be uncomfortable if I held it too close or too long.  it's really hot!  Here is a whole article on heat-related skin damage: http://en.wikipedia.org/wiki/Erythema_ab_igne    so I think if you read through the Google search I linked, you can synthesize that there could be something going on here related to heat and heat alone.  By the way we're talking about a professional, very hot and very high airspeed blowdrier here. It's extremely hot. 212.96.61.236 (talk) 08:36, 18 January 2015 (UTC)


 * Turn the heat down dear, turn it down, it ain't rocket science. What kind of ***** uses a hair dryer that burns their ear. You could save the planet and your ear (have you got only one) by turning it down. Richard Avery (talk) 08:49, 18 January 2015 (UTC)
 * But I don't hold it close to my ear on that setting, I'm just mentioning that it gets hot enough that it would burn me (not literally) if I did. I hold it to my wet hair, obviously.  Other than blowing hot across my face for a few minutes, it doesn't bother me.  I'm fine with the result and the experience.  The only question I have is whether getting blown across the face by very hot dry heat every day or couple of days causes skin damage over the long term or not.... people's impressions were "no, only UV light does that" but my references seem to be "yes."  Also, as I mentioned earlier the style of hair I like now is made with very hot blowdrying (and using a round brush).  It's just very hot (doesn't bother me per se, unless I weren't careful.) 212.96.61.236 (talk) 09:07, 18 January 2015 (UTC)


 * On reflection, the references I provided at sturat's request are convincing to me. specifically our ab igne article "Prolonged thermal radiation exposure to the skin can lead to the development of reticulated erythema, hyperpigmentation, scaling and telangiectasias in the affected area".  I think I will try to avoid getting hot air on my skin.  212.96.61.236 (talk) 09:29, 18 January 2015 (UTC)


 * Those sources say the problem comes from elevated skin temps for hours at a time. Presumably it only take you a few minutes to blow dry your hair.  But yes, turn the heat down and the fan speed up, if possible, so as to reduce the risk of burns. StuRat (talk) 05:06, 19 January 2015 (UTC)