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December 13

Leadership skills

Does volunteering with listening services such as befriended or Samaritans teach you leadership skills? — Preceding unsigned comment added by 2A02:C7D:B901:CC00:7CE7:1D53:9581:45DA (talk) 09:30, 13 December 2015 (UTC)[reply]

It can do, much depends on the role you undertake as a volunteer and how you use your time there. --TammyMoet (talk) 10:06, 13 December 2015 (UTC)[reply]

For those unfamiliar with the organizations, we have: Samaritans (charity) & Befrienders Worldwide. -- ToE 14:32, 13 December 2015 (UTC)[reply]

Why can ethanol be used as a rocket fuel but gasoline can't?

^Topic ScienceApe (talk) 16:51, 13 December 2015 (UTC)[reply]

Kerosene has been used as a rocket fuel. I imagine it was preferred over gasoline because it is safer to work with and used to be cheaper. Jc3s5h (talk) 16:56, 13 December 2015 (UTC)[reply]

Gasoline _can_ be used as a rocket fuel - Robert Goddard's first liquid-fuelled rocket, "Nell" (1926), ran on gasoline and liquid oxygen. See RP-1 for our article on hydrocarbon rocket fuels - apparently, OTRAG, a 1980's German hobbyist organization, built a rocket that ran on diesel. Tevildo (talk) 18:33, 13 December 2015 (UTC)[reply]

The article says the fuel is, "The fuel was intended to be kerosene with a 50/50 mixture of nitric acid and dinitrogen tetroxide as an oxidiser." ScienceApe (talk) 19:09, 13 December 2015 (UTC)[reply]

This article (New Scientist, May 1976) states that the prototypes, at least, were diesel-powered. This site has a list of (presumably theoretical) specifications, which include the use of diesel fuel. Tevildo (talk) 20:04, 13 December 2015 (UTC)[reply]

This is more of an educated guess than a factual one but based on the characteristics of gasoline. Firstly, consider starting. Have you noticed that just before a LOX kerosene engine starts, little pyrotechnics come on to shower the exhaust nozzle with sparks to ignite the fuel. Imagine using petrol – it is explosive. It could easily over pressure the combustion chamber and blow it apart – or in astronautical terms, cause it to under go rapid disassembly. Say all engines do successfully fire up – what then. Gasoline does not burn smoothly. Both kerosene and alcohol have a lower octane rating... they want to burn as soon as they get hot enough in the presence of an oxidizer. The fuel to air/oxidizer ratio is less important. Petrol on the other hand may pause a moment and think about whether it wants to oxidise and having finally decided to oxidize.... it-can-do-so-sudden. So such an engine running on petrol will not run smoothly. It with stutter and cough. Should it burp in the process, the combustion chambers could well scatter bit of themselves all over the place. To run a petrol rocket engine one needs to run it very rich (i.e., much less fuel than the optimum amount of oxidizer and that lead to a lower SI). Even modern hydrogen/LOX engine are run a little fuel rich. Better to waste a bit of fuel than waste a whole rocket.--Aspro (talk) 18:57, 13 December 2015 (UTC)[reply]

^{[citation needed]} ? Nimur (talk) 19:08, 13 December 2015 (UTC)[reply]

Page five:
One odd aspect of Goddard's early work with gasoline and oxygen is the very low oxidizer-to-fuel ratio that he employed. For every pound of gasoline he burned, he burned about 1.3 or 1.4 pounds of oxygen, when three pounds of oxygen would have been closer to the optimum. As a result, his motors performed very poorly, and seldom achieved a specific impulse of more than 170 seconds.

Page 20

Malina and company started experimental work with RFNA and gasoline as early as 1941—and immediately ran into trouble. This is an extraordinarily recalcitrant combination, beautifully designed to drive any experimenter out of his mind. In the first place, it's almost impossible to get it started. JPL was using a spark plug for ignition, and more often than not, getting an explosion rather than the smooth start that they were looking for. And when they did get it going, the motor would cough, chug, scream and hiccup —and then usually blow anyway.

Ref: [1]

Yeah meant flame front propergation velocity not octane. Yeh got lean and rich mixed back to front too.--Aspro (talk) 22:51, 13 December 2015 (UTC)[reply]

Ethanol and especially methanol has a higher octane rating, not lower and less fuel would be lean not rich. Sagittarian Milky Way (talk) 19:40, 13 December 2015 (UTC)[reply]

@Aspro: It sounds as if your "just before a LOX kerosene engine starts, little pyrotechnics come on to shower the exhaust nozzle with sparks to ignite the fuel" is describing the Radial Outward Firing Initiators (ROFIs) used to burn off excess gaseous hydrogen during the start of LOX/LH2 engines, such as those used on the Space Shuttle, Delta IV, and SLS. Here is an NSF article discussing their operation. See Rocket engine#Ignition for a discussion of the ignition process. ROFIs are not used for engine ignition, and having the engine lit from an external source like that would result in a hard start. -- ToE 13:59, 14 December 2015 (UTC)[reply]

I'm highly skeptical that NASA rocket scientists can't figure out how to keep a gasoline rocket from exploding. I mean, the Nazis could play with hydrazine and concentrated hydrogen peroxide, and they're supposed to be dumb, right? I do note that kerosene has more energy per volume than gasoline [2] - 135 vs 125 kBTU/gal according to this. Then again, several grades of fuel oil have even more, but maybe NASA scientists couldn't... then again, there's also the matter of density... I'm seeing a figure of 0.71-0.77 for gasoline and 0.78-0.81 for kerosene ... thrills. I have no idea how that comes out, too much fog in the numbers, but fuel oil is 0.99-1.01, so that probably is out? Then again, the density also controls how big the rocket needs to be, which is also really important, so... well, at this point I admit I'm not a rocket scientist. Wnt (talk) 21:58, 13 December 2015 (UTC)[reply]

Aspro's reference is worth looking at. It's _possible_ to start a gasoline-fuelled rocket without it exploding - it's _much easier_ to start a kerosene-fuelled rocket. It's even easier to start a rocket with hypergolic fuel, but the cost of the fuel would be prohibitive for an orbital booster stage (as opposed to a short-range atmospheric vehicle, like the Me-163). I don't know how RP-1 compares in cost with a hypothetical rocket-rated gasoline blend, but I can't imagine it's significantly more expensive. Tevildo (talk) 23:15, 13 December 2015 (UTC)[reply]

Cost of fuel isn't the main thing against hypergolics (though they are more expensive), it's the poor isp. I assume you are aware that there are a number of hypergolic booster still flying (Proton, Long March), so cost isn't 'prohibitive'? That, and safety issues. Fgf10 (talk) 14:27, 14 December 2015 (UTC)[reply]

BTU's "per gallon" would be the wrong metric. "Per pound," though is a different story. Kerosene is about 7 pounds per gallon while gasoline is 6 pounds per gallon so gasoline would be a better weight to energy tradeoff though not a volume to energy tradeoff. I would think the problem would relate to compression with an oxidizer present. Kerosene in turbine engines behaves nicely. Gasoline engines have spark plugs because it does not behave well. Higher compression engines need purer gasoline to retard the spark as do piston aircraft but they never rely on compression itself as the igniter (so called "knocking" is bad). A rocket motor compressor would suffer the same problems I would think. --DHeyward (talk) 05:50, 14 December 2015 (UTC)[reply]

How do waves and winds interact?

Is there a science dedicated to the interaction of winds and waves on oceans or another big mass of water?--Denidi (talk) 19:55, 13 December 2015 (UTC)[reply]

There is - see Wind wave. Tevildo (talk) 20:12, 13 December 2015 (UTC)[reply]

Also note that waves formed in other ways, like tidal bores, tsunamis, and boat bow waves and wakes, may be affected by wind after formation, especially at the peaks. StuRat (talk) 23:16, 13 December 2015 (UTC)[reply]

Hydrology - "the scientific study of the movement, distribution, and quality of water on Earth and other planets"; hydrometeorology - "a branch of meteorology and hydrology that studies the transfer of water and energy between the land surface and the lower atmosphere". Gandalf61 (talk) 12:03, 14 December 2015 (UTC)[reply]

If you google the definition of either of those they are not really specific to waves. Hydrology is to do with the movement of water through land to the atmosphere[3] and hydrometeorology is to do with water in the atmosphere and its effects on the weather.[4] Physical oceanography and fluid dynamics (see Boussinesq approximation (water waves)) are the branches of science that would deal with to the processes of wave formation. Richerman (talk) 14:37, 14 December 2015 (UTC)[reply]

December 14

Were coalition troops prepared for/expecting an attack with chemical/biological weapons?

The question above made me curious about what the governments knew in 2003. Officially, the governments claimed there were MD weapons, but did they act coherently to this official position? During the invasion, were coalition troops provided with materiel to protect themselves against a chemical/biological attack? --Denidi (talk) 13:25, 14 December 2015 (UTC)[reply]

Yes: "Allied troops then invaded Iraq, taking great precautions in case chemical weapons were used against them." From Medical Aspects of Chemical Warfare, The Surgeon General Department of the Army, United States of America (p. 66). Alansplodge (talk) 14:06, 14 December 2015 (UTC)[reply]

In this particular case we can work out which you're talking about because you mentioned the year, but you do really need to give more details. Which government are you talking about? There were four countries involved in the initial invasion, and there was the Iraqi government on the other side. The poster above assumed you are talking about the US government, is this the case? Fgf10 (talk) 14:23, 14 December 2015 (UTC)[reply]

UK troops would also be of interest. The other two countries, Australia and Poland, sent only token troops.

The Australian contribution was small, but I wouldn't say it was only token. According to Australian contribution to the 2003 invasion of Iraq#The scale of the Australian force commitment, their contribution was 2.42% of (I think active duty) military personnel compared to 4.85% for the US. This is only slightly under half of the US, and it's difficult to argue the US contribution was close to token. Or to put it a different way, even if the US had only contributed 73,000, it would still be difficult to argue it was token. The relative size of the contribution by Australia was tiny but that's because Australia has a much smaller military, partially because they have a much smaller population. Post invasion, the Australian contribution was somewhat minor compared to the contribution from the US and others so could probably be called token, but your comments seem to be referring to the invasion only. Nil Einne (talk) 19:53, 14 December 2015 (UTC)[reply]

The United States military very much operated as if the threat from chemical or other unconventional weapons was real. This included provision of training and materiel, as well as operational, organizational, and doctrinal changes.

From the collection at United States Army's Combined Arms Research Library at Fort Leavenworth:

On Point : the United States Army in Operation Iraqi Freedom, by Col. Greg Fontenot et al., has extensive discussion of NBC preparations during the invasion. For example, Countering Iraqi WMD And Ballistic Missile Strikes (pg. 171) discusses plans and operations. In addition to lots of doctrine and organizational information, there are also anecdotes so you can see what "preparation" meant to ordinary front-line soldiers:

"On 28 March 2003, the platoon was in a blocking position near the “Airfield.” Both Horner and Jackson had just awakened and were eating MREs in the back of the company’s cargo truck. The unit received artillery fire, and an adjacent chemical unit’s alarms went off. It also received warning to don protective overgarments and masks immediately. As their masks had been destroyed [in the vehicle fire], their squad leader (Staff Sergeant Carver) had them run to the back of one of the M2s to have some protection. He also had them pull the hoods of the NBC suit as tightly as possible over their heads. By this time the entire company, as well as the chemical unit, was in MOPP 4."

On Point II : transition to the new campaign : the United States Army in Operation Iraqi Freedom, May 2003-January 2005, by Donald Wright and Col. Timothy Reese:

"Reorganization to meet the campaign’s requirements often meant huge growth in the number of commands under divisional authority. At one point, 1st AD added the 937th Engineer Group and the 18th Military Police Brigade, giving it the equivalent of 9 maneuver brigades and almost 39,000 Soldiers. The division accepted further reinforcements, such as a CA brigade, a chemical company, PSYOP companies, and an aeromedical evacuation detachment. Every division in theater underwent its own version of organizational transition as they rapidly adapted to the requirements of the new campaign in Iraq."

Prior to Operation Iraqi Freedom, an ordinary Army division would not normally include a chemical warfare company. This book also contains a photograph of U.S. Army chemical warfare soldiers preparing and reconditioning their equipment in Iraq, to keep it battle-ready.

Even outside of chemical warfare companies, ordinary troops were issued NBC suits. I am not sure if these were universally issued to all American soldiers.

Nimur (talk) 15:28, 14 December 2015 (UTC)[reply]

There was a bit of a rumpus when it was discovered that the British Army didn't have enough NBC equipment for everybody; see BBC News - UK troops 'left without key kit' (2003). I'm certain that the intention was for everybody to be protected, but as usual, it didn't go to plan. Alansplodge (talk) 16:32, 14 December 2015 (UTC)[reply]

Measuring the mass of non-detected dark matter

This source and our article Large Underground Xenon experiment both give the impression that, by failing to detect even a single dark matter collision, the experiment can place constraints on the mass that dark matter WIMPs must have. But how can anyone predict the likelihood that a WIMP with a given mass will interact with a xenon atom, never having seen one? Wnt (talk) 18:16, 14 December 2015 (UTC)[reply]

The weak interaction is fairly well understood, and predictions can be made about the statistical probability of a particle with specific properties (like the Lightest Supersymmetric Particle) interacting with bulk matter. Although absence of evidence is not evidence of absence, the lack of a single observed collision provides strong evidence that the particular predicted particle is not common (and hence that the whole theory might need re-thinking). Dbfirs 18:44, 14 December 2015 (UTC)[reply]

The article glosses over what exactly it is they are able to rule out. It's not really a range of masses, but a region in the 2D plane of mass and scattering cross-section. Other experiments had seen events that could be interpreted as a possible detection at low mass and a particular range of cross-sections. LUX was able to exclude those detection regions. You can see the exclusion region in Fig. 3 of the new paper. A different view, zoomed in on a low-mass region, including some other experiments' possible detection regions, and using older limits, is in the third figure here. --Amble (talk) 21:41, 14 December 2015 (UTC)[reply]

Bowel Movements

Do individuals hooked up to nutritional IV long term still have bowel movements. Additionally, if a person had their entire digestive system removed including colon, and they were kept alive with the nutritional IV would they still need to excrete, some how? — Preceding unsigned comment added by 24.215.64.134 (talk) 18:53, 14 December 2015 (UTC)[reply]

Despite lacking food, the body still produces matter to excrete as it breaks down red blood cells. In cases where the intestine is either removed or bypassed, the gut is attached to the skin and an opening is produced called a stoma, through which the matter is excreted. See for example ileostomy. --TammyMoet (talk) 19:39, 14 December 2015 (UTC)[reply]

[ec] See Parenteral nutrition and this factsheet from the NHS. According to the latter, "[t]he bowel will still produce mucus, cells and bacteria even though food is not being eaten and so you are likely to still have a bowel movement". I don't know of any surgical procedure that involves removing the _entire_ digestive system (from the oesophagus to the anus) which the patient is expected to survive; any remaining part of the digestive tract (after, for example, colectomy) will still produce some mucus which will need to go somewhere. Tevildo (talk) 19:45, 14 December 2015 (UTC)[reply]

I should add that, as if biology were determined to defeat our pretensions of simple causal logic, babies produce meconium before they ever eat. Wnt (talk) 16:18, 15 December 2015 (UTC)[reply]

It's not really the case that they don't eat...they swallow amniotic fluid in the womb. You try floating in something for nine months and not swallowing any of it. Of course, there isn't much nutrition to be had from it. --71.119.131.184 (talk) 23:48, 15 December 2015 (UTC)[reply]

Poorly designed battery: fire by discharging?

Can a poorly designed Li-ion battery catch fire by discharging too fast? Or, could another problem arise, like smoke or leaks?--3dcaddy (talk) 23:25, 14 December 2015 (UTC)[reply]

Yes. It can overheat, damage the separator between anode and cathode, cause a short-circuit, and explode. This is a situation known as thermal runaway.--Denidi (talk) 02:20, 15 December 2015 (UTC)[reply]

I'm actually not sure that "poor design" has anything to do with it. If you include "shorting them out" within the definition of "discharging too fast" then almost certainly you will see smoke and possibly fire. I've "disposed" of several such batteries by shorting them out, after they've out lived their useful life, and they've all been varying degrees of spectacular. Vespine (talk) 04:48, 15 December 2015 (UTC)[reply]

Indeed, for short-circuiting it, you won't need to be discharging, nor it is related to discharging. That's also why the FAA regulates how batteries can be carried by passengers. But I meant it as a process. When you are discharging the battery it can overheat > damage the membrane > short-circuit internally (=>more heat) > fire/explode. --Denidi (talk) 15:20, 15 December 2015 (UTC)[reply]

Gravity trains and the rotation of the earth

I was thinking about Gravity trains and realized that when you enter the train you are rotating one way, but when you exit you are rotating the opposite direction. That means that the entire trip would be spent with the train pressed first against one side of the hole and then the other, with an acceleration of about .04g, rather than, as said in the article: "During this entire trip, the train (and all passengers) would be practically weightless.". Am I correct? The article makes no mention of this at all. Ariel. (talk) 23:27, 14 December 2015 (UTC)[reply]

Indeed, you need to consider two factors: the coriolis force and the conservation of angular momentum, both of which considerably complicate the mathematical treatment of the trajectory. Although the first simplistic approximation you learn (by application of Gauss's law for gravity) is that the object in the hole is a "simple harmonic oscillator," the trajectory is in actual fact that an orbit through a non-uniform gravitational field.

I think there is a homework problem on this issue in Marion and Thornton, but I don't recall if they work the solution. I can check later today.

Nimur (talk) 23:47, 14 December 2015 (UTC)[reply]

The "tunnel through the Earth" oscillator was in fact Homework Problem 5-15, in the fifth edition, but it does not actually ask about the rotational effects. However, several problems in Chapter 10 (on rotating reference-frames) ask for re-calculation of earlier chapters' homeworks assuming a rotating Earth. If you can follow the math in these two chapters, you can correctly answer your question about the gravity-train. The calculus is non-trivial - there are a lot of vector cross-products in the equations - but as you intuitively guessed, there will be a non-vertical force that should not be neglected. Nimur (talk) 03:45, 15 December 2015 (UTC)[reply]

The tunnel could be dug with the curved path taken into account, allowing zero gee - specifically, you could emerge 42.2 minutes of rotation west of the antipodal point, which is to say 42 / (60*24) * 360 = 10.5 degrees. However, of course, that means that a reverse trip would either have double the acceleration, or have to use a whole different tunnel that ends up 21 degrees west of the original... Wnt (talk) 04:03, 15 December 2015 (UTC)[reply]

December 15

finding the work according to the blood pressure and the heart rate

I found on Facebook (later I found the same question -with the same typo- that looks like a source on Google) a very nice question and I decided to take advantage and to try to understand it. But before I'm going to do that, I would like to know if the answer (I found it also there) is correct or not. Afterward, I would like to understand where did the number 1300 come from to the solution. This is the question and the answer:

The pumping action takes place in less than 1/3 cardiac cycle while the heart muscle rests for over than 2/3 of the cycle .
Ex: - A patient of heart rate of (120/min) his pressure is 150/90 mmHg. Calculate the work done by the left ventricle for 2 seconds.
Sol:- W= p x ∆V
P= (150+90)/2 = 120 mmHg.
=120 x 1330 = 1.6 x 10⁵ dyne/cm²
∆V = 120/60 sec x 80 ml =160 ml/sec.
W=120 x 1330 x 160 =2.6 x 10⁷erg/sec
W/2sec = (120 x 1330 x 160) x 2=5.2 x 10⁷ erg/sec.
— Preceding unsigned comment added by 92.249.70.153 (talk) 00:01, 15 December 2015 (UTC)[reply]

Regarding the 1330 used in the solution (I assume that is the 1300 you are asking about), see millimeter of mercury (and Torr, which is essentially the same thing). 1 mmHg ≈ 133.3 Pa (where Pa is the unit of pressure Pascal). But your example problem appears to work with CGS derived units, where 1 barye (symbol: Ba) = 1 dyne per square centimeter = 0.1 Pa. So 1 mmHg ≈ 1333 Ba. Presumably the students were told to use the approximation 1 mmHg ≈ 1330 dyne/cm². -- ToE 03:46, 15 December 2015 (UTC) (I added linebreaks to the original question and repaired the exponential notation for readability.)[reply]

Regarding the problem itself, an unstated assumption is that the volume pumped each beat is 80 ml.

Also assumed is that the pressure increase imparted by the left ventricle is equal to the average of the systolic and diastolic pressures. This doesn't seem to account for the inlet pressure coming from left atrium, but perhaps that is insignificant.

Given those assumptions, calculating pumping power is easy, but their solution is sloppy with its units and confusion of work and power.

The work done on the fluid by a single stroke of a reciprocating pump is W = ∆p x ∆V (change in pressure times the volume displaced) and the average power of the pump is P = ∆p x Q (change in pressure times the volume flow rate).

So if your pressure increase really is equal to the average of the systolic and diastolic pressures, then yes, ∆p = 120 mmHg (133 Pa / mmHg) ≈ 1.6x10⁴ Pa (or 1.6x10⁵ Ba).

∆V = 80 ml, so the work done each beat is 1.6x10⁴ Pa x 8.0x10^-5 m³ = 1.3 J (or 1.3x10⁷ erg).

At 120 bpm, there are four beats in two seconds, so the total work done during that time is 4 x 1.3 J = 5.2 J (or 5.2x10⁷ erg).

Or, doing it their way, the average flow rate Q (not ∆V) is indeed 160 ml/sec. And the average power P (not W) is indeed 1.6x10⁴ Pa x 1.6x10^-4 m³/s = 2.6 J/s (or 2.6x10⁷ erg/s).

Thus the work done over two seconds is P x 2 s = 2.6 J/s x 2 s = 5.2 J (or 5.2x10⁷ erg).

Working CGS and getting your answer in erg saves you having to convert 1 ml = 1x10^-6 m³, but at the scale of this problem Joules seem more appropriate than erg. (You should pick up from context what units are expected in the particular field, though this may change over time.)

So their solution was particularly sloppy, and while their final numerical answer was correct, the units of that answer should have been erg (units of work) and not erg/s (units of power). If you make $10/hr, how much money have you earned after working 4 hours? $40, right, not $40/hr. -- ToE 15:37, 15 December 2015 (UTC)[reply]

Wow! this is very nice answer with complete explanation! I enjoy it (and I believe I can guess, too) Thank you very much! 15:23, 17 December 2015 (UTC) — Preceding unsigned comment added by 92.249.70.153 (talk)

A medium-size object

If the biggest thing is the universe and the smallest thing is a quark (or something like that), then how big is an object that is half way between? Does this question make any sense? Anna Frodesiak (talk) 00:07, 15 December 2015 (UTC)[reply]

We have an article, Orders of magnitude (length). The way you have phrased your question is a little bit difficult to answer - the question is valid English syntax, but it's not really the way physicists describe or compare sizes. You are not entirely correct in asserting that a quark is the smallest object we know about; nor in the implication that the universe is a single object. These details entirely depend on how you define "object," and subsequently how you choose to measure or define the size of an object. Universes and quarks are different types of entities, so it's strange to compare them; but we can use characteristic length scales to compare different types of objects. Finally, it's not clear how you want to measure "half way between" different length scales - we could use the arithmetic mean or the geometric mean; or we could look at some kind of logarithmic scale; and so on.

Nimur (talk) 00:18, 15 December 2015 (UTC)[reply]

Okay, I'm reading Orders of magnitude (length) and it sort of clears stuff up. I guess it is hard to ask such a question.

Anyhow, I'm pretty sure that if the observable universe sat down in a restaurant with a neutrino, the known universe would order a lot and the neutrino would probably have the small salad. Anna Frodesiak (talk) 00:31, 15 December 2015 (UTC)[reply]

But the universe would have to cover the check, because the neutrino has no charge. *groan* --71.119.131.184 (talk) 01:50, 15 December 2015 (UTC)[reply]

I suspect that joke was invented within a day or two of the neutrino's discovery. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:23, 16 December 2015 (UTC)[reply]

See the "Visualization" section under Planck length; you could sort of make the argument from that that it's a period. Wnt (talk) 03:35, 15 December 2015 (UTC)[reply]

Very nice, Wnt! Now that is something I can grasp. Many thanks. :) Anna Frodesiak (talk) 05:44, 15 December 2015 (UTC)[reply]

Anna Frodesiak, I have a clear memory of being stunned by the short documentary film Powers of Ten (film) (1968) when I first saw it as a college student in the 1970s. It makes the case that the realm of things that humans see and deal with every day is at the halfway point on the scale. Highly recommended. Cullen³²⁸ Let's discuss it 07:17, 15 December 2015 (UTC)[reply]

Thank you, Cullen328! I just watched it. I found it in my archives and actually remember watching it years ago. It is very good. Many thanks. :) Anna Frodesiak (talk) 08:04, 15 December 2015 (UTC)[reply]

The concept of "half way between" is not clearly defined. The arithmetic mean would be an object about half the size of the universe (if we could define such an object). The orders of magnitude approach leads to the Geometric mean, but there are other possibilities. Dbfirs 10:32, 15 December 2015 (UTC)[reply]

Does the universe really qualify as an "object"? However, if X represents the number of objects within that universe, then halfway would be approximately X / 2. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:38, 15 December 2015 (UTC)[reply]

You mean the size of the middle object when all objects are arranged in order of size? That would be the median which, I guess would be much smaller than the geometric mean ... probably ~~around the size of a proton~~ a neutrino since there are at least a million neutrinos for every proton. Dbfirs 17:24, 15 December 2015 (UTC)[reply]

No, I mean the size of half the total matter + energy in the universe. As to what the OP means, that's not altogether certain. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:34, 16 December 2015 (UTC)[reply]

I agree that half the total matter would be half the size. Usually, counting objects leads to the median, but we don't know what "objects" we are supposed to be counting here. Dbfirs 08:23, 16 December 2015 (UTC)[reply]

Miss Frodesiak^* is clearly asking about the geometrical mean, as Dbfirs has pointed out, and the movie and later book editions of Powers of 10, which Cullen mentions, demonstrate graphically that everyday objects lie around that mean. See YouTube μηδείς (talk) 17:13, 15 December 2015 (UTC) ^*Of no relation to the Passyunk Avenue Frodesiaks[reply]

This stands or falls on the definition of an "object". It's arguable that the universe isn't "an" object - but rather a collection of objects. Sadly, the same could be said of a rock or an atom or even of a proton. If you allow a "collection" to be an object - then should we consider the collection of all of the people named "Steve" to be "an object"? If not, then calling the universe "an object" seems wrong...but if you do include collections, then should we consider "The set of all people named 'Steve' who were born under a full moon" to be a different object than the larger set of all people named "Steve"? If the answer to that is "Yes" then we can count "Everything in the universe made of hydrogen" to be "an object" - which is nearly as big as the entire universe.

Worse still, it's perfectly possible that the universe is infinite - in which case, the thing that's halfway between its' size and that of a quark is still infinite.

So you need a stronger definition. You can ask "What is the tallest mountain?" and we stand a good chance of getting you an answer - but "object" is just too vague. SteveBaker (talk) 21:21, 15 December 2015 (UTC)[reply]

If you look at time however the human lifetime is quite large, and the total time of life is a large fraction of the age of the universe so far. Graeme Bartlett (talk) 21:14, 15 December 2015 (UTC)[reply]

I am referring to the geometrical mean. And when referring to the universe as an "object", just pretend it is a big ball the size of the universe. Anyhow, "everyday object"? Wow. Isn't that like standing on an ink dot and saying that the entire universe is inside? That seems odd to me. From my person-size viewpoint, big seems bigger than small seems small. Anna Frodesiak (talk) 00:51, 16 December 2015 (UTC)[reply]

You're criticizing the responders, but you have yet to define what you mean by "object". Is the earth an "object"? Is the sun an "object"? Is a galaxy an "object"? Is a given cluster of galaxies an "object"? Also, geometric mean of what? ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:39, 16 December 2015 (UTC)[reply]

Criticizing? Good heaven, no. I'm enormously grateful and just asking. I should have phrased it better. You see, this is why I always salt and pepper my posts with lots of smileys. :) It is so hard to judge tone. When I say "...Anyhow, "everyday object"? Wow. Isn't that...", I mean, really, wow. It is so cool that an everyday object is the "mean". And when I say "mean", as others have said above, I mean "mean" as in the middle or average sort of thing. I'm not even sure if that can be a thing considering it kind of means that half the objects are bigger and half smaller. I'm not too good at maths. :) With sincerity, plenty of smiles, gratefulness, humility, and deference to be sure, I would never criticize responses here. I am not qualified to do so. Best,

Anna Frodesiak (talk) 08:41, 16 December 2015 (UTC)[reply]

Anna Frodesiak, perhaps you can't imagine just how small the elementary particles really are? We can't see the millions of bacteria on our skin, but these are enormous on an atomic scale. Dbfirs 08:29, 16 December 2015 (UTC)[reply]

Absolutely right! I just can't get my head around the very small. I can feel the magnitude when I think of the universe, but with the very small, I just can't imagine it. I think, for me, this is all about perception. For me, a universe inside a dot of ink is inconceivable. :) Anna Frodesiak (talk) 08:41, 16 December 2015 (UTC)[reply]

All is well, except you did not answer my question. For example, is the earth an "object"? ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:00, 16 December 2015 (UTC)[reply]

An object is some physical object like a tangerine or planet or bunch of grapes or sure, a galaxy -- anything that is or can represent a particular size. :) I'm really looking for that cubic volume that is between the things with the biggest and smallest cubic volumes. Anna Frodesiak (talk) 11:56, 16 December 2015 (UTC)[reply]

So the earth itself is an object, and the solar system is an object (which contains the earth) and the Milky Way galaxy is an object (which contains the earth), and the cluster of nearby galaxies is an object (which contains the earth), and the universe itself is an object (which contains the earth). So the earth is being counted multiple times. What does that do to the mean calculation? ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:17, 16 December 2015 (UTC)[reply]

This might be a better example. Consider the state of Florida and pretend it's the universe. Consider one specific orange growing somewhere in Florida, and pretend it's the smallest object in that "universe". So there are multiple oranges on the tree, multiple trees in the grove, and multiple groves in Florida. What would be the mean, under your scenario? ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:23, 16 December 2015 (UTC)[reply]

Good question. I don't know. Maybe a mountain? How about an ant as the smallest animal and an elephant as the biggest. I'd say a cat would be the mean. Anna Frodesiak (talk) 13:22, 16 December 2015 (UTC)[reply]

I should further add that in my hypothesis, Florida contains nothing except oranges, growing on orange trees. There will be a finite number of those kind of objects. So what would the mean be? ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:34, 16 December 2015 (UTC)[reply]

But Elephants, ants and cats are "well-defined objects" - which makes it relatively easy...but atoms, solar systems and universes aren't...which makes it impossible.

Also, we have literally no idea how big the universe is. We only know how much of it we can possibly see (due to the limited age of universe and the finite speed of light) - it's almost certainly bigger than that - possibly very much bigger - and it's quite possible that the universe is infinitely big. Halfway between "tiny" and "infinite" is still "infinite" under any sane definition you can come up with. If it comforts you to take the "human-scale" answer - then by all means take it - but it's bullshit.

So, we can't (or at least "shouldn't") give you an answer...we just can't. This is the science ref desk and anything other than "There is no answer to this question" is scientifically untenable. SteveBaker (talk) 15:51, 16 December 2015 (UTC)[reply]

That's why "infinite" in the mathematical sense doesn't work. But for the sake of the example, let's suppose there is only one galaxy in the universe. What would the mean be? ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:37, 16 December 2015 (UTC)[reply]

But there are constraints we can set based on reasonable definitions (which we've agreed to constrain ourselves by, for the purpose of providing an answer). For obvious reasons, it isn't always helpful to throw up our hands and say "it can't be defined ever so don't bother". It's OK to say "there are no absolutes, so we can't give an absolute answer", but we should always be able to follow that up with "we can still come up with a workable answer so long as we all understand and agree upon the approximations or assumptions we are making." So, for example, while "The universe" is not a well defined set of dimensions, the Observable universe is, and it is a sphere 8.8×10²⁶ meters across. That's a reasonable upper bound to set (as long as we all know that it isn't the real upper bound, and we're OK with that). Likewise, there is a similar level of "lack of knowledge" regarding things at the small end. Most elementary particles are assumed to be point particles, which have a size of literally zero, but this is a convenient assumption, just as the state of the universe beyond the observable universe is unknowable (and thus assumed to be infinite because there's no difference between infinite and unknowable here), the dimensions of elementary particles like quarks and electrons and neutrinos are unknowable (though in this case assumed to be zero, because there is no difference between zero and unknowable here). If we take the smallest composite particle for which we have a measurable size, that would likely be the meson, of which there are many varieties and which have a size on the order of the femtometer (10^-15 meters) Assuming we're dealing in the average orders of magnitude here, the midpoint between 8.8×10²⁶ and 10^-15 is about 10⁶ meters, or 1000 kilometers, or about the size of the planet Pluto. So if we put reasonable constraints on the sizes we're dealing with, the "object" which comes "midway" (in a logarithmic sense) between the smallest "thing" we can measure (a meson) and the largest "thing" we can measure (the observable universe) is on the scale of small planet or large moon. --Jayron 32 16:31, 16 December 2015 (UTC)[reply]

You guys are too smart for me and this question I asked got out of my depth. I am sorry. I should have said "average", but even then, no. You must understand that I think of things so simply, like in terms of elephants and ants. I just figured there ought to be some sort of middle size. I agree that the question cannot be answered. If I ask what length is half way between the width of the smallest object and the width of the known universe, then it doesn't make sense either. I've go to learn to ask questions where I would have a reasonable chance of understanding the answer. I'm also asking unanswerable questions. Best wishes and a thousand thanks to all. Again, I am sorry. :) Anna Frodesiak (talk) 23:39, 16 December 2015 (UTC)[reply]

I don't think you need to apologize - it's a perfectly reasonable thing to ask - it just doesn't happen to have a clear answer. But you didn't know that when you asked - and in asking it, you provoked some very interesting replies - and lots of people learned stuff. We get these kinds of question all the time - and some of them are deeply fascinating. Take the classic: "How long is the coastline of England?" - the answer is (annoyingly) that there isn't an answer...but the reason that there isn't an answer is fascinating and takes us all for a stroll down some of the darker alleyways of mathematics.

So by all means, if you have a question - go ahead and ask it. SteveBaker (talk) 03:53, 17 December 2015 (UTC)[reply]

high blood pressure/donating blood

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

The reference desk will not answer, and will remove, requests for medical advice. Nimur (talk) 00:49, 15 December 2015 (UTC)[reply]

We cannot diagnose the OP, but it does no harm to point out that cannabis is a drug, and effects of cannabis include some cardiovascular side effects. A judge may have called it "safer than aspirin", but that's not actually saying much. See also [5]. Wnt (talk) 03:50, 15 December 2015 (UTC)[reply]

Don't forget paranoia. Now, if someone would just ask if donating blood has an immediate effect on blood pressure... 209.149.113.52 (talk) 19:43, 15 December 2015 (UTC)[reply]

Orangutan humor?

You may be familiar with that video of a young orangutan "laughing" when being shown a (pretty poor) "magic trick". I tried to find an analysis of what was going on a bit more serious (scientifically speaking) than what you usually get. All I could find was this. Have you seen anything by a bona fide ape specialist? It certainly didn't come up in my top Google results. Contact Basemetal here 12:05, 15 December 2015 (UTC) PS: I am aware that, unfortunately, Dan Zaleski (the American tourist who posted that video) showed the orangutan the trick "a few times" and then decided to post only "his best reaction" (rather than post the whole sequence) which might make it difficult for anyone to understand what's really going on: what if what we see was the tenth time he showed him the trick and the orangutan was laughing at him)? Contact Basemetal here 12:05, 15 December 2015 (UTC)[reply]

Wikipedia has a short article titled Laughter in animals and this article presents an overview of recent research in this area, with links to actual studies and other articles on the general question of humor in non-human animals. --Jayron 32 12:39, 15 December 2015 (UTC)[reply]

Thank you for these useful links. Has anyone seen anything relating specifically to this case though? Contact Basemetal here 17:01, 15 December 2015 (UTC)[reply]

Sunrise and sunset

I read the articles (sunrise and sunset), but I am still not exactly clear. So I ask my question here. The news will report sunrise and sunset as an exact time. Let's say that sunset is reported as 5:00 PM as a hypothetical example. So, what exactly is different from 4:59 PM and 5:00 PM? What exactly has happened at 5:00 PM that did not occur at 4:59 PM? Thanks. 2602:252:D13:6D70:14DE:69F5:F4C:EAE3 (talk) 20:21, 15 December 2015 (UTC)[reply]

See Sunrise equation for the calculation of sunrise (and sunset). 209.149.113.52 (talk) 20:29, 15 December 2015 (UTC)[reply]

Unless you are looking out to sea, or on a perfectly flat plain, your local sunrise and sunset are unlikely to be at the published times for your area. In theory, what happens at a 5 p.m. sunset is that at 4:59 p.m. you can just see a tiny part of the top edge of the sun, but at 5:01 p.m. all of the sun is below the horizon. Sagittarian Milky Way explains below why even in an ideal situation, the exact minute is unlikely to be observed. Dbfirs 21:17, 15 December 2015 (UTC)[reply]

(edit conflict) At sunrise the first point of Sun circle would appear if the Earth was free of obstructions (like buildings, mountains, and waves) and the same elevation everywhere. I believe that height is mean sea level but I'm not sure if anyone ever does it with the location's height (which would make more sense for Denver for example). The result is slightly wrong if the air isn't whatever temperature and humidity they use or doesn't have the same air density to altitude graph (coldness and to a small extent lower water vapor % makes astronomical objects appear higher in the sky). The Sun generally rises and sets slower the higher latitude you are (it takes many, many hours to at the poles) and temperature inversions happen when it's cold enough so high latitude sunrise predictions can be very wrong. If they don't calculate this every year (because of leap days and stuff) or use good enough formulas (because near perfect formula is very long) then that introduces some error. At midlatitudes everything happens about 5 seconds earlier for each mile east of the newspaper's spot. They might calculate for sea level eye height and if they do then even if they calculate for your point of beach exactly and that spot's mean sea level and the sea is glass smooth and the Sun is setting over it and the sunset tide is mean sea level and everything else I wrote till now is perfect it'll still be around a quarter minute too soon at midlatitude just because you're standing and 6 feet tall instead of swimming. If you moved your eyeballs to 9 inches above the glass sea then the prediction would be 5 seconds too soon. If you're up to you're nostrils in water and your eye is 2 inches above sea level that 2 inches still makes the sun set 2.5 seconds later. If you hold your breath and put your pupils 1 inch above sea level (this is some calm sea!) then the sun sets about 1.667 seconds later because of that inch. (Reference: [6], the horizon is what hides the sun so that's the important part and 1 minute of arc is 4 seconds of right ascension but the sun sets in a slanting path at midlatitudes so add a little time for that)). Also, even if eyeball is in the place of prediction and everything else is perfect if it's only to the minute then it'll be at least 30 seconds wrong some days just for that, which is important if you're wondering about what's so special about 5:00 am. Make it 60 seconds wrong if they truncate. Sagittarian Milky Way (talk) 21:38, 15 December 2015 (UTC)[reply]

More important is that the published times for your area are actually times for a specific location in your area (e.g. the town hall). So you have to consider how far you are from the town hall. 89.240.30.128 (talk) 09:25, 16 December 2015 (UTC)[reply]

I mentioned that when I said it's about 5 seconds earlier for every mile east (and west would have to be later obviously). Sagittarian Milky Way (talk) 16:58, 16 December 2015 (UTC)[reply]

These days the times are recalculated every year but that wasn't always the case. During the Second World War Whitaker's Almanac started printing sunrise and sunset times for a variety of locations across the UK. After four years they just recycled the data for four years before. This continued for most of the second half of the twentieth century. When the almanac went over to computer typesetting they started using the accurate times provided by the Royal Greenwich Observatory. 89.240.30.22 (talk) 09:36, 16 December 2015 (UTC)[reply]

As Dbfirs is introducing some inaccuracies in his reply at "Length of Day" below, just to clarify:

Dbfirs lives in the UK, so his responses purport to reflect the position as it is here.
Leap seconds are not officially used in the UK. Published times are in GMT (or possibly BST in the summer, neither of which uses leap seconds).
The only way that the general population will come into contact with leap seconds is if they listen to the "Greenwich Time Signal" broadcast periodically on BBC Radio 4.
Very few people listen to the BBC, and even fewer listen to BBC Radio 4. 89.240.30.73 (talk) 09:59, 16 December 2015 (UTC)[reply]

I don't know about your other points (though "Leap seconds are not officially used in the UK" seems implausible), but "Very few people listen to the BBC, and even fewer listen to BBC Radio 4" is simply untrue. From 2013 data: "we saw a record 11m tuning in to the station each week". More recently, the report linked from here for April-June 2015 shows "average weekly reach" for BBC radio as 35m, with 10.6m for Radio 4. (And that doesn't include the World Service, with an estimated audience of 210m.)

The UK doesn't use the leap second? - that seems incorrect too "At the last meeting in Norway in September, 20 countries voted in favor of dropping the leap second... but the U.K., Russia, and six other countries opposed the proposal, which was enough to quash it".[7] Richerman (talk) 17:18, 16 December 2015 (UTC)[reply]

It has to, otherwise it would be 13:00 in the UK and 12:59 or 12:58 in the rest of the world. We can't have that. The non-leap second time (I think GMT) is probably still used for almanacs, especially more technical almanacs so you don't have to screw with leap seconds when navigating with a sextant or calculating astronomy. Almanacs for farmers instead of astronomers and sailors probably mention leap second-less time little at most. Sagittarian Milky Way (talk) 17:31, 16 December 2015 (UTC)[reply]

89.240.30.73 seems to be making comments deliberately intended to provoke, in the same style as a known banned user from the same city. Is my suspicion justified? See our article Greenwich Time Signal for accurate facts, and note that millions of clocks in the UK are synchronised with the atomic clocks at the National Physical Laboratory through Time from NPL broadcast on a 60 kHz carrier from Anthorn Radio Station, and others use a Radio Data System for their time. All three systems broadcast Coordinated Universal Time, complete with leap seconds. Dbfirs 20:05, 16 December 2015 (UTC)[reply]

Thanks, all. 2602:252:D13:6D70:258E:2FDC:D3C8:55C9 (talk) 15:41, 17 December 2015 (UTC)[reply]

December 16

list of stars about 30000 ly distant please

Hi - it's for a novel - I need some sunlike stars that are about 30,000 lightyears away - ones with curious names/designations especially welcome. Thanks in advance Adambrowne666 (talk) 00:37, 16 December 2015 (UTC)[reply]

The thing is that modern astronomers don't generally give stars cute names - they're generally just numbered in some manner. Named stars tend to be the ones that have been known for a very long time - typically they are naked-eye objects. 30,000 ly is about a third the way across the galaxy - and stars that are that far away aren't usually visible without a telescope. There are also an immense number of stars out at 30,000 ly - at least 100 billion of them. Now, clearly we're not going to name any of them unless they are REALLY special - like maybe super bright. Why would be bother to name a boringly typical sun-like star out of the billions out there?

So the answer is "None" - there are no named stars out at those distances - and certainly no sun-like stars with names at anything like that distance. SteveBaker (talk) 00:56, 16 December 2015 (UTC)[reply]

Thanks, Steve - names would have been a bonus, but any sort of designation would do. Adambrowne666 (talk) 01:00, 16 December 2015 (UTC)[reply]

For example, if you take the text dump of the Guide Star catalogs, a set of "all-sky optical catalog(s) of positions and magnitudes of approximately 19 million stars and other objects" that are specifically used by scientists to aim the Hubble Space Telescope, you'll see things like:

N003-AAJE  46.13902  84.36855  0  99.999  99.999  3  16.759  16.685  3  16.082  16.086 
N003-AAAF  45.84270  84.48269  0  99.999  99.999  3  14.565  15.112  3  14.730  14.753
N003-AABF  45.75025  84.36574  0  99.999  99.999  1  16.999  17.003  1  16.262  16.315

...and so on, for 19 million entries. The "name" of one of these stars is, for example, "N003-AAJE."

Unless that specific entry is scientifically interesting for any other purpose besides its relative location, chances are very high that no scientist has ever bothered to study that star to determine its distance, or its spectral type, or anything else about it. A tiny fraction of the entries in these catalogs have been subjected to intensive scrutiny, but most of them are known only as dots with positions and approximate brightnesses.

What's more: if you use a different coordinate system, or even if you just a different sky catalog - that dot might be listed by a totally different designation. It might not even be listed in a different catalog.

Nimur (talk) 01:15, 16 December 2015 (UTC)[reply]

Only the first field seems like a designation. The next two seem like declination and right ascension in degrees in some order and the last four seem like magnitudes in some order (probably B, V, R, and I)? Sagittarian Milky Way (talk) 01:19, 16 December 2015 (UTC)[reply]

And the Guide Star Catalog II has 1 billion stars instead of 19 million (down to magnitude 21) and per absolute magnitude and interstellar extinction the average sunlike star that distance might be too dim to appear even there. Space is Big! If it did appear it would probably be unusually far from the galactic plane for a Sun-like star as the Sun is fairly metallic by star standards. Sagittarian Milky Way (talk) 01:27, 16 December 2015 (UTC)[reply]

To be honest, I'm not sure exactly how to interpret every column in the database. The text file I pulled those data from did not include a labeled header; and the database in this particular text-format does not seem to match the documentation in the published literature linked from the main website. This text-dump is evidently intended for consumption by a very specific computer program - it's really not aimed at human readers.

If you're very interested, you can read about this specific catalog at the The Guide Star Photometric Catalog I, from the Space Telescope Science Institute.

Anyway, for our OP: if you are writing a hyper-unrealistic Space Trek fictional story, you can just give your star a great name that will enthuse your readers (like Proxima Nimur VII) ; but if you're writing hyper-realistic fiction, you need to re-think the way you portray designated objects in deep space. Space is really big.

Nimur (talk) 01:29, 16 December 2015 (UTC)[reply]

Of course, if this is happening in the future we might be able to tell if it's interesting enough to name (if it has one of the most Earth-like planets known, for instance). That might be done with a telescope in space many miles wide with a spectroscope, or suspended animation and fast automatic spaceships that can function for ages so you could go there where it takes much less equipment to find out how Earth-like it is. Your list might be available to Earthlings before a few decades from now but you could give it an even more robot-sounding catalog number from a bigger alien or future human catalog if it seems likely that the characters would be using it. Sagittarian Milky Way (talk) 01:54, 16 December 2015 (UTC)[reply]

Or a smaller alien catalog from a planet much closer to the star than we are. Sagittarian Milky Way (talk) 01:58, 16 December 2015 (UTC)[reply]

Why 30,000 light years by the way? Any particular reason or cause it sounds good? Sagittarian Milky Way (talk) 02:02, 16 December 2015 (UTC)[reply]

Thanks, everyone. It's 30000 ly so that the protagonists on a world circling one of those billion unnamed stars can imagine looking back at Earth with a putatively perfect telescope and see something (in their imagination) happening 30000 years ago.Adambrowne666 (talk)

@Adambrowne666: You can check List of most luminous known stars - some are around 30,000 ly away. One that stands out is the Pistol Star -- if you're writing a culture of gunslingers influenced by American cowboy movies, I think you're in luck! :) Wnt (talk) 14:00, 16 December 2015 (UTC)[reply]

To be clear, I didn't say that there were no named stars out that far - only that there are no named SUN-LIKE stars that far away. Pistol Star is about as un-sun-like as it gets - it's a blue hypergiant and is one of the most luminous known stars in the Milky Way. That means that if your protagonists are anywhere remotely close to it, and your story is remotely believable, they are very, very dead. SteveBaker (talk) 15:42, 16 December 2015 (UTC)[reply]

D'oh, I forgot about that part! But as it happens the Pistol Star is "at least double" with much fainter "point sources" near the blue hypergiant [8] though apparently not confirmed (?). Of course, we have no idea what aliens can live on really, so I'm prone to stretch the sunlike requirement. I'll say one thing ... if the emanations of that hypergiant don't kill you, I imagine on the planets of any nearby sunlike companion, they must look pretty awesome. :) Wnt (talk) 20:33, 16 December 2015 (UTC)[reply]

I tell you, for all that we're stuffing up the world and each other, you people on the Wiki Ref Desks give me heart. Thank you. Adambrowne666 (talk) 02:00, 17 December 2015 (UTC)[reply]

Length of year versus length of day

It is somewhat of a "fiction" that the year is 365 days long. Actually, it is something like 365.25 days long (or so). And that is why we have the need for a leap year every four years. So, what about the length of the day? Is it exactly 24 hours? Or is that also a "fiction"? It seems a little too convenient to be 100% accurate, no? 2602:252:D13:6D70:14DE:69F5:F4C:EAE3 (talk) 02:28, 16 December 2015 (UTC)[reply]

Depends on what you mean by a "day". There's a Civil day, solar day, a sidereal day, etc. The civil day is defined as exactly 24 hours, and the sidereal day is defined a 1/365.24 of the year. The solar day varies slightly depending on the specific day of the year. All three days are within a few minutes of each other. --Jayron 32 02:51, 16 December 2015 (UTC)[reply]

To be more specific, the Julian calendar set 365 days with a leap day every four years, making 365.25 days. In the year 1582, Pope Gregory made an adjustment to correct an error that had accumulated to about 10 days. In that year, and for that year only, October 4th was followed by October 15th, thus advancing the date by 10 days. The intervening days (5th -14th) simply do not exist. There was also specified that 3 of every 4 centesimal years (ending in 00) would be common years, not leap years. Thus 1600 and 2000 were leap years but 1700, 1800, and 1900 were not. This is where the 365.24 length comes from, and it is this Gregorian calendar that we live under today. Most of Europe adopted the Gregorian calendar immediately in 1582. Great Britain and its colonies (including what is now the US) did not until 1752, by which time another day's error had occurred, so September 2 1752 was followed by September 14, an advancement of 11 days. Akld guy (talk) 03:17, 16 December 2015 (UTC)[reply]

The sidereal day is 1/366.25 (ish) of a year, rather than 1/365.25. —Tamfang (talk) 03:17, 17 December 2015 (UTC)[reply]

Hmmm. OK, now my head is spinning. I thought that a year was how long it takes the Earth to revolve around the sun. So, if the Earth starts at one point (Point A), makes a full revolution around the sun, and ends up at the same starting point (Point A again), that whole trip will take 365.25 days. I thought that a day was somehow similar. Something like how long it takes the Earth to rotate on its axis for one full spin (or something like that). And that was calculated to be 24 hours, which is where we get our "calendar day" from (e.g., the day we call December 15 versus the day we call December 16, etc.). Am I on the right track? In other words, our calendar "day" is derived by some celestial happenings (with the Earth or sun or moon or whatever). So is that celestial event exactly 24 hours? Or is it "off" by a bit, but we just use the "fiction" of 24 hours, for convenience? (Like, for example, in actuality it is really 24 hours and 3 minutes and 18 seconds, or whatever.) Thanks. 2602:252:D13:6D70:14DE:69F5:F4C:EAE3 (talk) 05:58, 16 December 2015 (UTC)[reply]

In basic terms, yes: a year is how long the earth takes to go round the sun, and a day is how long the earth takes to spin. The problems that make things a bit more complicated are:

1) How do you actually tell when the earth has got back to its starting position? There is more than one way of doing this (depending on what you use as a reference point), which give slightly different answers. Hence we have concepts like the stellar day and sidereal day

2) The earth/sun system isn't like a machine that does exactly the same thing all the time. Its a slightly wonky lump of rock being pulled round a big ball of plasma by gravity, while other lumps of rock and gas tug at them with their own gravity. This means things wobble a bit, and don't always move exactly the say way or at the same speed. Which means the time take to go round the sun or rotate on its axis can change slightly. This in turn means that - for people who need to define time really precisely, they need to use a consistent definition of year, day, second etc that aren't dependent on what the earth is doing right this moment. Iapetus (talk) 13:14, 16 December 2015 (UTC)[reply]

The day is currently 24 hours and 1 millisecond. It was 24 hours when the second was first defined to be something other than 1/86400th of a non-fictional day (the late corset era). We are now 1 minute and 8 seconds behind then as a result of the rotation slowing down until a day is 24 old hours and 1 millisecond. We can't change the second, it would screw up precise scientific work so we have to add leap seconds every so often. It takes 365.256 days for the Earth to revolve once but the axis isn't lined up as it wobbles very slowly (26,000 years per wobble) so the seasons (which is what we care about most) take under 365.2422 days to repeat (but well over 365.2421). Those are 365.2422 real days, not the 24 hour ones that're fictional now. Sagittarian Milky Way (talk) 06:15, 16 December 2015 (UTC)[reply]

The Earth actually takes 23 hours and 56 minutes and 4.091 seconds to rotate but by the time it revolves once it has "canceled" one rotation by the revolving so it needs to make up one rotation every year. This is why it's 24:00:00.00 on average between noons or midnights — it needs to make up 1 day's worth of rotating per year so it takes 24 hours. Sagittarian Milky Way (talk) 06:24, 16 December 2015 (UTC)[reply]

The "celestial day" you refer to is what is called the sidereal day, this is the length of time it takes for the earth to spin 360 degrees around it's own axis. This is equal to 23h56m. The "solar day", which is how human beings historically defined the day, is the length of time it takes the sun to reach the same position in the sky from one day to the next. Historically, this is how we defined the "day" that we cut up into 24 hours, so the solar day is exactly 24 hours long by definition (some complication: it varies because the earth's rotation and its orbit around the sun are not perfectly even, circular, or fixed). Why is the solar day slightly longer than the sidereal day? Because in the time it took the earth to rotate once around its own axis, it has orbited slightly along its path around the sun. Which means it needs to rotate slightly further for the sun to again be at the same point in the sky since yesterday. The earth's orbit around the sun has essentially caused the sun's position in the sky to "un-orbit" the earth by 4 minutes, so it is 4 minutes behind where it needs to be since yesterday. Thought experiment: if you play this through for an entire year, can you see that the earth's 1 orbit around the sun means that the sun has fully "un-orbited" the earth by 1 whole day over the course of the year? This means that for the 365.24 days we measure by the solar day, the earth has actually rotated exactly 366.24 times on its own axis. If you take 24h*365.24/366.24, you get the 23h56m number. I hope this helped and didn't confuse you further! Zunaid 06:19, 16 December 2015 (UTC)[reply]

Yes, the "real rotation" and "real revolution" is 23:56:04 and 365.256 days, but the "real day" and "real year" are 24:00:00.001 and 365.2422 day. The fake day and fake year are 24 hours and 365 days respectively. Sagittarian Milky Way (talk) 06:30, 16 December 2015 (UTC)[reply]

There are other types of days and years but those would just be good for confusing you. They're very specialised and trivia-like, like the human-powered underwater speed record. Sagittarian Milky Way (talk) 06:38, 16 December 2015 (UTC)[reply]

Thanks. So, the "real day" is not 24 hours, but is 23:56 (or, in other words, 4 minutes short of a full 24 hours). So don't all of those "four-minute deficiencies" build up and accumulate over time? So, after 2 days, we have an 8-minute deficiency. After 7 days (one week), we have a 28-minute deficiency. After 30 days (one month), we have a 60-minute deficiency. And so forth. And doesn't that accumulated "error" make the days/times get out of sync? Which is why we add that extra leap year, I think? So that the "accumulation" of that "extra" 0.25 of a day beyond the flat 365 days per year does not accumulate too much and throw the "year" off cycle. If we did not have a leap day, then every four years, we have an extra "day" accumulated that never gets accounted for. The way that we "account for" that extra accumulation is by adding a leap day. So, wouldn't it be the same idea for the 4-minute deficiency gap for the "day"? Thanks. 2602:252:D13:6D70:14DE:69F5:F4C:EAE3 (talk) 07:47, 16 December 2015 (UTC)[reply]

No, you have misunderstood. The 4 minutes per day add up to one full revolution per year, which is accounted for by the revolution of the earth round the sun. A day is the average time taken from one noon to the next (see Equation of time for why this isn't constant), and the only correction necessary is the occasional leap-second. The leap year is to keep the seasons from drifting from their usual dates (see Gregorian Calendar). Dbfirs 08:14, 16 December 2015 (UTC)[reply]

Some of Dbfirs' disingenuities have been corrected in "Sunrise and sunset" above. A day is the average time taken from one noon to the next as he says but this average is the "mean solar day" and no further correction is required for "leap seconds". Joe Public (i.e. the person to whom this resource is directed) does not use leap seconds. The only people who use leap seconds are scientists who need units of measurement which are not constantly changing in length, and have therefore devised an artificial "SI second" which is the length of the mean solar second as it was back in 1820. 89.240.30.73 (talk) 10:17, 16 December 2015 (UTC)[reply]

Hold the insults! I was simplifying to help the OP, but here in the UK, we use the SI second. It is broadcast by the Greenwich Time Signal, and an extra "pip" signifies the leap second for rare minutes that have 61 seconds. Many other countries use the same system. Dbfirs 19:30, 16 December 2015 (UTC)[reply]

The sidereal day is aligned with the stars. So if Taurus rises at a certain time within one sidereal day, it will rise at a certain time on any sidereal day. Problem is, the Sun might be in Cancer, Libra or Capricorn, so while you might know what time of sidereal day it is, you don't know if it's light or dark out! So people don't like the 23h56min day very much, even though it's always the same length.

The easy thing to do is to make up for how much the sun moves, but here's the trick... it doesn't move at the same rate all the time! Well, technically, it doesn't move much at all, relative to the barycenter of the solar system or whatever, but that's another story - what I mean is, the Earth's orbit is a tad elliptical and so sometimes the planet is whipping around the perihelion a little faster, sometimes further out and a little slower, so the Sun makes a whole analemma thing that can really confuse the hell out of you even if you actually understand everything I've written so far. But using the same average correction is the sanest way to do things so that your computer video plays back at the same rate regardless of what season it is. Wnt (talk) 14:09, 16 December 2015 (UTC)[reply]

Let's simplify this for the OP with a few key bullet points.

The second is a precisely defined unit of time. Other units you use (including minutes, hours, days, months, years, etc.) on a daily basis are defined precisely as multiples of the second. So the amount of time you mean when you say "a day" or "a year" in common usage is precisely defined and unchanging and means exactly the same thing. A day means "86400 seconds" and that's all it means, and it will never change, because the second is precisely defined in a way that it will never change.
There are other, highly specialized, meanings of words like "day" and "year" that always come with qualifiers(like "sidereal" or "solar" or "celestial" etc.) that let you know they are defining it in a different way than as multiples of the precisely defined second. Most of these are tied to the physical movements of celestial objects, and since those movements are NOT regular and repeatable (i.e. everything wobbles a bit, as noted above), those definitions are not immutable or precisely defined. Roughly speaking, the "day" is about equal to the amount of time it takes the Earth to spin once around its axis, and the "year" is roughly equal to the amount of time it takes the Earth to move a full orbit around the sun. However, because of the myriad of variables involved, defining the physical movement of the earth in terms of "days" and "years" results in numbers that are close to the precisely define times noted above, but which are neither exact nor repeatable forever in the way that the "second" and its derivatives are immutably defined.

I hope that helps a bit. --Jayron 32 15:06, 16 December 2015 (UTC)[reply]

For the sake of explanation, let's pretend that the earth stays still and the sun goes around us...yeah, I know...but let's pretend because it doesn't change the length of a day/year - and it makes understanding all of this much easier:

The time it takes for some distant star to rise above the horizon, go across the sky, sink back under the horizon, and then rise again is the 23 hours and 56 minutes and 4-ish seconds. That's how long it takes the earth to rotate through 360 degrees on it's axis.
But that's not "a day". We humans don't give a damn when stars rise and set - we need to know what time to get up and go to work...and that's to do with the sun - not the stars.
The time it takes for the sun to rise, go across the sky, under the earth and then rise again is 24 hours, zero minutes and zero-ish seconds...and THAT is what we call "a day".
The difference is because (in our imaginary geo-centric solar system) the sun orbits the earth every 365-ish days while the distant stars are "fixed" (ish). The direction that the sun "orbits" the earth is such that while we spend 23 hours and 54 minutes to spin 360 degrees, the sun has moved around it's orbit by 1/365th of 360 degrees...so it's a little bit below the horizon when the earth has spun 360 degrees - and the extra time it takes the earth to rotate the extra 1-ish degrees to get the sun to rise again adds 1/365th-ish to the length of a day.
The 23 hours 56 minutes is 1436 minutes - 1436/365 is 4-ish minutes - which *perfectly* explains the difference between 23 hours 56 minutes and the 24 hours we expect.
All of those "-ish" numbers conspire to make things a bit messier, leap years and so forth.
The fact that the earth doesn't spin precisely evenly (the moon, tides, global warming, volcanoes, weather, relativity (probably!))...explains the odd stray millisecond here and there - which we ignore until we get a whole second off, then we toss in a leap-second and half of the computers on the planet have a hissy-fit about it.
Of course the earth rotates around the sun and not the other way around - but that makes no difference whatever to the math. The ancient civilizations that worked all of this out had no idea that the earth orbits the sun and not vice-versa - and it takes a bit of science to figure that out - but it didn't matter because the answer comes out the same either way.

SteveBaker (talk) 15:31, 16 December 2015 (UTC)[reply]

There is no "gold standard" for intervals which track celestial events. There are various months ranging in length from 28 to 31 days and longer. Legally a "month" was 28 days. A synodic month (new moon to new) is longer than a sidereal month (star back to same star) is longer than a tropical month (equinox to equinox) is longer than an anomalistic month (nearest approach to Earth back to same) is longer than a draconic month (intersection with Earth's orbit back to same). None of these is "correct". It's the same with the year and the day. If you're grading the different varieties according to which is most useful then the synodic month comes out top, as does the tropical year (equinox to equinox) and the mean solar day (maximum elevation of sun to same). Same goes for hours, minutes and seconds. The day is always divided into 86,400 seconds of whatever timescale you're using. So the comment that the length of the second is "precisely defined" should be read in that context. What you must not do is mix units. To say the day is 24 hours and 1 millisecond is confusing and wrong. 86.151.51.24 (talk) 16:11, 16 December 2015 (UTC)[reply]

To clear up a possible misconception, the use of leap seconds to convert the grand total of atomic seconds accumulated since the system was devised about 1960 to the familiar hours, minutes and seconds recorded by our clocks is nothing to do with the occasional 29 February which adjusts for the difference between a fixed 365 - day year and the actual time between successive equinoxes. That four minutes per day you have to allow for if you are using the stars to tell the time when the sun is below the horizon actually amounts to two hours per day (24 hours over a year), which is why if you are using the star charts printed in newspapers to do some stargazing you have to correct to allow for the fact that the stars rise two hours earlier each month. 86.151.51.24 (talk) 16:43, 16 December 2015 (UTC)[reply]

A day is actually 24 hours and 1 millisecond near this decade and since OP wanted the "non-fictional day" then it has to be said. This is not unit-mixing, noone uses the 1/86400th of a real solar day second anymore. The 24 hour day isn't any more "real" than the 365 day year. If we kept using the fictional units then the seasons would be 1 month wrong in only a century and change and the time would be 8 hours off about 3 or 4 millenia ago or a similar distance in the future. A 24 hour day is clearly close enough most of the time, though. Sagittarian Milky Way (talk) 17:15, 16 December 2015 (UTC)[reply]

It seems clear 86 is using some weird definition of a second to be 1/86400 of a solar day. (I.E. The length of a second varies.) While 86 is free to use whatever weird definitions they want to, they shouldn't confuse the issue by pretending their definition is normal. It's not. The second which most people i.e. "Joe Public" use, including the UK government and people (and not just the BBC) is the SI one. On other words, this definition is not some weird definition that ony scientists use, it's the definition that nearly everyone uses. It is for example what nearly all modern clock (with the except of sundials) etc aim for. While I believe it's fairly unlikely a clock you're using has the precision that it makes a difference (although I'm not an expert on how long the length of a solar day varies), this doesn't mean such confusion is acceptable. Nil Einne (talk) 19:46, 16 December 2015 (UTC)[reply]

I don't think Nil Einne lives in Britain. There was a discussion a few days ago about what all those books are on the table of the House of Commons. They are law books. If you look up Halsbury's Laws or Halsbury's Statutes (which is basically what the clerks do) title "Time" you will see that this country has been on Greenwich Mean Time since about 1880. Now a mean time scale doesn't have a place for leap seconds, so there aren't any (don't need 'em). Everybody uses Greenwich Mean Time because that's the law of the land. Saying they use leap seconds implies that once every eighteen months or thereabouts the whole population rushes about adjusting its timepieces by one second and if you actually live in this country you will see that they don't. There is a mechanism for disseminating time which does involve leap seconds - the Greenwich Time Signal - but if you asked the BBC if they disseminate the legal time they will say "no, we don't." If you ask them why they don't disseminate the legal time they will say "just after we insert a leap second the time we disseminate is a fraction of a second behind the legal time, and just before we insert a leap second the time we disseminate is a fraction of a second ahead of the legal time. Clocks are made to run to mean solar time and the legal time is in line with what is displayed by clocks."

Some people are making a big issue of this and saying that there is a huge discrepancy between BBC time and legal time but this is simply not the case. Every century the number of days in a year reduces by about 1/2 - second. There are roughly 30,000,000 seconds in a year so after 100 years the length of the second increases by a factor of 1 in sixty million. After one year the second has grown by just one part in 600,000,000,000. Why are we getting het up about this? 86.151.51.24 (talk) 21:43, 16 December 2015 (UTC)[reply]

I agree that leap seconds are not a big issue since the discrepancy between UTC and UT1 is always less than one second. I disagree that clocks are made to run to mean solar time. They are synchronised to UTC. Perhaps you are thinking of sun dials? By the way, UTC is not just BBC time, it is understood world-wide, and often (incorrectly in your view) called GMT. UTC "is the primary time standard by which the world regulates clocks and time". I agree that GMT is taken to be UT1 for navigational purposes, but GMT is often considered identical to UTC for civil purposes, despite what old laws said. Why are we arguing over a fraction of a second? Dbfirs 23:01, 16 December 2015 (UTC)[reply]

I don't get this. If there is an EC directive relating to "apples" and a shop sells "apples", people coming in wanting to buy will ask for "apples". Nobody is going to call them pears. Mean time (without leap seconds) is as different from atomic time (with leap seconds) as apples are from pears. I note the weasel words creeping in:

"old laws".

The law against killing dates back to Biblical times. It doesn't matter how old it is - if you break it you go to jail.

"Nearly all modern clock".

How is my bedside quartz alarm clock going to assimilate a leap second? Or my wind - up alarm clock, come to that. Or my Apple watch, mobile phone or computer? Computers aren't programmed to accept a leap second. If you want them to do so you have to patch them, but nobody bothers. People adjust their clocks and watches primarily from their mobile phones, or a timecheck from a radio announcer, or a platform clock or (in London) the clock on a bus. If you look at these platform clocks you will see that the seconds displays are not synchronised, so the suggestion that they are influenced by leap seconds is ludicrous.

As for

UTC"is the primary standard by which the world regulates clocks and time"

that unsourced claim was removed from the article with the following result:

Another editor edit - warred it back in (with no source)
The Arbitration Committee protected the article for a very long time.

So what price "Wikipedia:The free encyclopaedia that anyone can edit" and "all contributions must be sourced"? 81.151.101.74 (talk) 14:09, 17 December 2015 (UTC)[reply]

Will global warming slow down or speed up the earth's rotation speed?

Some news outlets (for example [9], [10], [11]) affirm that global warming will speed up the earth's rotational speed while others (for example [12], [13], [14])affirm that it will slow it down. They can't very well both be right. Contact Basemetal here 03:51, 16 December 2015 (UTC)[reply]

First let's kill the echoes. The first two that say faster cite Felix Landerer at Max Planck Institute ( http://onlinelibrary.wiley.com/doi/10.1029/2006GL029106/full ) as of 2007; the latter four that say slower link to http://advances.sciencemag.org/content/1/11/e1500679 more recently. My assumption is the argument for slower is that glaciers are near the poles and when they melt the water has to go somewhere further out; the argument for faster is that the ocean overall expands, and water presently in deep basins ends up washing into the shallower Arctic Sea, North Atlantic etc. Both studies are what they are and we'd be hard pressed to settle the issue amongst ourselves. Wnt (talk) 04:45, 16 December 2015 (UTC)[reply]

They can't both be right, but they could both be wrong. Reminds me of National Lampoon's newspaper satire, in which articles on consecutive pages had different scientists claiming that we were on the virge of global boiling and global freezing. ←Baseball Bugs ^{What's up, Doc?} carrots→ 05:30, 16 December 2015 (UTC)[reply]

Global boiling: Only 1 billion more years. Global freezing: a few billion after that. Sagittarian Milky Way (talk) 05:35, 16 December 2015 (UTC)[reply]

Actually they can both be right. When melted, water becomes much more dense, but then it becomes less dense. Once the Antarctic ice is all melted, bringing rotation to its slowest rate, the oceans will continue to expand and thus redistribute themselves, speeding it up again. Whether it takes a a billion years or a hundred, I'd guess global boiling should reverse the sign of things a third time by moving the water far up into the atmosphere. Wnt (talk) 09:55, 16 December 2015 (UTC)[reply]

They might both be right at future points in time, but not at the same point in time. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:57, 16 December 2015 (UTC)[reply]

At the same time it can be true both that it "will speed up" and "will slow down". Wnt (talk) 13:54, 16 December 2015 (UTC)[reply]

Expands should correlate with slower. The mass doesn't change. When an ice skater puts her arms out she spins slower, when she brings them in by her side she spins faster. However looking at the arguments I think I agree the redistribution of the water would make a bigger difference than the ice melting so my opinion is on the faster side. I think it should just about be possible to measure the changes so far and figure out who is probably right. Dmcq (talk) 12:49, 16 December 2015 (UTC)[reply]

Why would redistribution of ice have any noticeable affect? It isn't like the ice on the surface amounts to much. Mt. Everest, the largest feature jutting out of the surface above sea level, sticks out 0.1% of the mean radius of the Earth. That is negligible. I feel that many people (even those who are very educated) picture the surface of the Earth as a very thick layer. It is more like the peel of an apple. If you add a few crystals of ice to the outside of an apple, the spin speed won't change significantly. Similarly, if you redistribute a very very thin layer on the outside of the Earth, it won't mean much as far as spin goes. 209.149.113.52 (talk) 13:42, 16 December 2015 (UTC)[reply]

The effect is, of course, exceedingly small; however, the length of day is something that can be measured with exceedingly high precision. It is not uncommon for people to write about the effect of an earthquake on the length of a day, and this is more than that. Because measurements really can be taken, it is also a way to probe or at least verify models of the distribution of the oceans, etc. It is only important in an academic sense. Wnt (talk) 13:54, 16 December 2015 (UTC)[reply]

<rant>This is the problem with popular reporting of science. It is particularly egregious with health and medical reporting (especially nutrition) but it clearly evident above. When science reports "cause X produces effect Y", the media reports this as "ONLY cause X produces effect Y, and there are no other causes or effects, and here's everything you need to know, and nothing else matters!!!". So you get reports like this complete and utter bullshit titled "A Glass Of Red Wine Is The Equivalent To An Hour At The Gym, Says New Study" No, it fucking doesn't, so stop that. The study showed that one ingredient in red wine, reservatrol, had certain physiological effects on a few body systems that mimic strenuous exercise. What the study does NOT SAY is "There is no difference in your body between drinking red wine and physical exercise, so just drink red wine and it's all the same thing". The science never said that, but the popular press comes out and basically says exactly that. Because journalists (as a subset of the entire population) have no idea how experimental science works. A properly constructed experiment " typically include controls, which are designed to minimize the effects of variables other than the single independent variable." to quote the Wikipedia article. That means, that when scientists publish a study, the study is almost always focusing on a single independent variable and carefully controlled to reduce, minimize, or control all other variables. So when scientists run an experiment as they did in the above studies regarding climate change and the speed of the earth, what they do is cafefully control for one aspect of climate change; or in these cases one aspect of warming oceans, and then see what the effect of that one single variable is on one single effect. In this case, the rotation of the earth. It turns out that depending on how you define your single variable, you can produce speeding and slowing effects. So which is actually happening? The answer is: both speeding and slowing, because both of those variables come into play, as well as probably dozens or hundreds of other variables that we didn't test for in these experiments" So, when you ask science a vague question like "Will the earth speed up or slow down because of climate change" the honest answer is either "It will do X so long as nothing else happens as well" or "We can't predict exactly because there are lots of factors at play, but we do know that this cause would lead to it speeding up because of XYZ, or this other cause could lead to it slowing down because of ABC." The sort of "tell us the future perfectly so we can stop worrying!" expectation of science is a complete misunderstanding of how knowledge grows...</rant> --Jayron 32 13:43, 16 December 2015 (UTC)[reply]

Not to lose sight of the elephant in the room, tidal friction dwarfs all other effects, so that in the long term the earth's rate of rotation always slows down. There are short - term fluctuations - unpredictable events such as earthquakes and tsunamis have an effect as also, I believe, do wind systems. In the 1920s the rotation rate speeded up quite considerably. If that were to be replicated, instead of leap seconds delaying our clocks they would speed them up. Thus headlines like "Wait a second, 1999 is going to be a little late" would change to something like "2019 is going to arrive a little early". 86.151.51.24 (talk) 17:02, 16 December 2015 (UTC)[reply]

Journal Articles

How to find journal articles for free about agriculture? Googled, but still hard to find. Any specific sites'd be much helpful... Thanks!

Learnerktm 10:14, 16 December 2015 (UTC)[reply]

Have you tried https://scholar.google.com/ ? It's not part of the regular google search, and google no longer advertises the service on their main page (they used to), so it is hard to find, but Google Scholar is where I go to search academic journals. --Jayron 32 12:52, 16 December 2015 (UTC)[reply]

Yes, google scholar is great, but it's also important to mention that many articles will be hosted behind the paywalls of academic publishers. So, when I search for e.g. /wisconsin corn/ [15], I see that some of the article listings say "[PDF] from (place)" on the right hand side. Those articles have PDFs that are freely accessible at places like researchgate, but you have to click on the PDF link, not the article title.

However, additional articles may also be free! For instance many journals have an "open access" option, wherein someone pays an additional fee to make sure the article is freely accessible. It is hard to tell which articles in a google scholar search have this property. One way is to click through to the journal, and then see if you can download it. Another (often better) way is to look at a specific journal. For example Agroecology and Sustainable Agriculture has an easy way to browse their open access content [16]. PLoS One and PLoS Biology are not focused on agriculture, but they do publish some agricultural research, and all their articles are freely accessible.

Taking this one step further, a regular google search for /open access agriculture journal/ [17] gives some good hits, and the open access journals search engine for agriculture [18] will probably be very useful.

Finally, if OP finds an article that is not accessible, they can ask for a copy at WP:REX. Sometimes, once you know the article you want, a full-text search of the title on regular google will find an accessible copy of the article. SemanticMantis (talk) 14:56, 16 December 2015 (UTC)[reply]

Let's not forget other sorts of interlibrary loan, whether conventional or via Sci-Hub or Libgen... Wnt (talk) 22:18, 16 December 2015 (UTC)[reply]

Energy expended per newton per second

Hello. Considering that human muscles are very inefficient, how many joules does an average human being have to actually expend to exert a force of 1 N for a duration of 1 second? Thanks.Leptictidium (mt) 14:01, 16 December 2015 (UTC)[reply]

Read the Wikipedia article Muscle#Efficiency, which has all the necessary figures to help you answer the question, and probably answers it directly anyways. --Jayron 32 14:07, 16 December 2015 (UTC)[reply]

What sense is my betta fish using to detect the arrival of food?

I put this on the science desk because I guess it's a biological question. My bowl is basically a large sphere about 10" in diameter and when the fish, which is about 2" in length is anywhere, even down at the bottom, when I drop its food, which is 3-4 pellets of betta fish food, each pellet being maybe 1mm in diameter, within about a second, the fish comes up to where the pellets are. Is it likely by smell, i.e., some molecules from the pellets propagating through the water, by sight (there's a fake plastic plant in the middle of the bowl that doesn't seem to slow it down), or by feeling that something has been dropped on the surface? 131.131.64.210 (talk) 14:08, 16 December 2015 (UTC)[reply]

I don't know directly (and it may vary between different species of fish), but I will direct you to reading the article lateral line. The first sentence of that article "The lateral line is a system of sense organs found in aquatic vertebrates, mainly fish, used to detect movement and vibration in the surrounding water." So, IF the fish is using the vibrations caused by the food hitting the water to know it is being fed, it would be the lateral line that is doing that. It could also be a combination of several senses, because you do this too i.e. you know dinner is coming BOTH because you saw your mom go into the kitchen, and you heard her rummaging in the cabinets for pots and pans, and you smelled the dinner cooking. It wasn't just one, but all of these senses that led to your conclusion. It could be the same for the fish. But the lateral line article is an interesting read, not the least of which is because it's a sense system unlike anything humans have. --Jayron 32 14:12, 16 December 2015 (UTC)[reply]

Any angler knows many a fish will bite at a shiny lure just after it strikes the water, so the scent is not, at least, required for all of them. But there are some kinds for which live fish bait seems to work better. Hearing among fish varies widely - some have inner ear and lateral line integrated in a way that suggests a common octavolateralis organ; others have otolith and lateral line separate. If a swim bladder is present, it may be used as a sort of tympanic membrane. I haven't looked into the betta fish at this point... from a first search, it looks like there might be some assocation of the labyrinth organ (a lung) and the lateral line, but I'm not sure yet. Wnt (talk) 14:47, 16 December 2015 (UTC)[reply]

What about sight? Fish can certainly learn to recognize when food is coming. My fish come to the top of the tank whenever I pick up the food container because they have learned that this (or some other visual cue) means they are about to get food. Maybe your fish is just seeing that something was dropped onto the top of the water and it knows this means dinnertime. Deli nk (talk) 14:55, 16 December 2015 (UTC)[reply]

I did some searching, and I'm convinced you won't find published results for this scenario with your type of fish, your type of bowl, etc. The above comments are all apt, but they don't tell us which sense is most important, or if all are used, or if some are not important at all. However, you can get empirical and do some experiments! You may not come up with a publishable, fully controlled scenario, but you can manipulate things like what the fish can see outside of the bowl, placing in unscented, inert pellets, blowing air on the surface to cause pressure waves without dropping anything in, etc. This is just a sketch, if you are actually interested in experimental design for this situation, let us know, and I think we could help with that too. My gut feeling (WP:OR) is that sight, sound/pressure, and scent are all used to varying degrees. So if you dropped in some dirt pellets, the fish may well come up to investigate, but no eat. Most animals use several sensory cues to find food, not just one. SemanticMantis (talk) 15:36, 16 December 2015 (UTC)[reply]

But I'd start by getting something bigger than 10" and replace the plastic plant with a real one, to make it more fun for the fish. Contact Basemetal here 17:12, 16 December 2015 (UTC)[reply]

Most likely it's mainly visual. Standard fish behavior is to investigate anything that looks like it might be food. If it still looks like food close up, the fish takes it into its mouth and tastes it. If it tastes like food the fish swallows it, otherwise spits it out. Many types of fish also have taste buds on their skin, but my guess is that they don't come into play in this situation. Looie496 (talk) 18:22, 16 December 2015 (UTC)[reply]

How did Races/ phenotype features originate?

I was wondering how humans from different parts of the world came about with different features. The answer probably isn't short and sweet and may deal with complex cellular interactions but I am interested in at least learning to gain some insight from someone on here or a at least a secondary source where I could gain more information.

I was wondering if changes in a person's DNA that leads to genetic expression of facial features, melanin regulation, skin folds around eye, etc. was factors of environment, diet, etc.

Say if I were to travel to Africa as a Caucasian male, what traits would I have a proclivity to acquire?

Thank you — Preceding unsigned comment added by 99.229.130.56 (talk) 16:52, 16 December 2015 (UTC)[reply]

None. Being in a different climate won't change your genetics. ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:55, 16 December 2015 (UTC)[reply]

He meant "his descendants", in the long run. Contact Basemetal here 17:08, 16 December 2015 (UTC)[reply]

His descendants will also be the descendants of the person(s) he has sex with. Their genetic make up (and the make up of whoever those descendants have sex with) will also come into play. Assuming no pedigree collapse, his grandchildren will only have 1/4th of his genes, great-grandchildren will only have 1/8th of his genes and so on. After several centuries, his unique contribution to the genetic pool of his descendants will be diluted to where his contribution becomes less and less relevant.--Jayron 32 17:41, 16 December 2015 (UTC)[reply]

You guys... What the guy wanted to know is what genetic traits would be tend to be acquired in the long run by a Caucasian population migrating to Africa. Is that clearer? Contact Basemetal here 17:50, 16 December 2015 (UTC)[reply]

If he meant that, he should have said that. I have no way to read his mind beyond what he typed. He used the singular pronoun "I" and repeatedly referred himself in the singular moving to Africa, not an entire population moving to Africa. If he wants to clarify, he can do so, but it is a disservice to him (and rather rude too!) to accuse him of saying something he didn't say, and not taking his question at face value. It is inappropriate to try to guess at what people mean, instead of what they actually say. --Jayron 32 18:00, 16 December 2015 (UTC)[reply]

You mean the OP is a proponent of Lamarckism and I am being rude? Contact Basemetal here 18:09, 16 December 2015 (UTC)[reply]

There you go again, saying words that someone else didn't say, this time me. I didn't say those words either. I said entirely different words. Please re-read them again. --Jayron 32 18:13, 16 December 2015 (UTC)[reply]

Some relevant articles - the general notion of races splitting apart is similar to that of speciation. So things like sexual selection could be involved in some cases, while things like allopatric speciation could be involved in divergence of other traits. This line of reasoning is in terms of Race_(biology), which is basically equivalent to subspecies.

However, keep in mind that Race_(human_categorization) is primarily viewed by modern scientists as a social construct. That is not to say that different lineages don't have different phenotypes, it just means that dividing people by skin color isn't biologically meaningful or useful (much like dividing dogs by coat color is not biologically meaningful. We all readily accept that a black lab is very different from a black poodle, and it would be silly to consider all black dogs as one breed).

Moving on, Afro-textured_hair#Evolution talks a bit about why that might be useful from an evolutionary perspective. Human_skin_color#Evolution_of_skin_color talks a bit about why we think there may have been evolutionary benefits to different skin colors in different places. Our article on white people mentions with references that it is whiteness that is the derived trait - Europeans were darker skinned rather recently.

For a more general perspective on variation in human traits, you might be interested in Recent_African_origin_of_modern_humans and Early_human_migrations - these set the stage for different lineages developing different phenotypes, and the resulting Human_genetic_variation. Just for fun, you might also take a look at Archaic_human_admixture_with_modern_humans, and notice that most of us have some Neanderthal or Denisovian alleles, in addition to our "modern human" alleles. SemanticMantis (talk) 17:44, 16 December 2015 (UTC)[reply]

The eye fold is called the Epicanthic fold and it is not known why some populations have them.[19] Richerman (talk) 18:57, 16 December 2015 (UTC)[reply]

Optometry

What's the difference between an optician and an optometrist?

❝Optometrists are trained to prescribe and fit lenses to improve vision [...]❞
❝Opticians determine the specifications of various ophthalmic appliances that will give the necessary correction to a person's eyesight.❞

The second sentence sounds like a complicated version of the first. What's the real difference? — Sebastian 20:09, 16 December 2015 (UTC)[reply]

As our articles sort of suggest, the precise difference varies from country to country. However optometrist normally have more training and would generally be better at assessing eye health and detecting diseases (often for referral to an opthamologist). In a number of countries, an optician may only be able to dispense an existing prescription from an optometrist. Nil Einne (talk) 21:13, 16 December 2015 (UTC)[reply]

In my experience in Canada, an optometrist prescribes what glasses (or contact lenses) you need, and an optician sells them to you according to the prescription. It is just like the relationship of doctor and pharmacist as regards prescription drugs. (You can also go to an ophthalmologist for the prescription; that's an actual doctor specializing in the eyes.) --76.69.45.64 (talk) 01:19, 17 December 2015 (UTC)[reply]

What you describe is what my ophthalmologist does; and that also fits to what Nil Einne writes. Does ophthalmology equal, include or overlap optometry? If it's true that an optician does not write prescriptions then I'd say we should delete that second sentence I quoted above. — Sebastian 02:19, 17 December 2015 (UTC)[reply]

Our article about opticians says:

Recent changes to the British Columbia Opticians regulations allow qualified opticians in that province to test a persons vision and prepare an assessment of the corrective lenses required for a client. Using the results of the assessment an optician is able to prepare and dispense eyeglasses or contact lenses. Opticians in Alberta are also permitted, under certain conditions, to refract and prepare and dispense eyeglasses and contact lenses.

Which seems to imply that they can actually determine what sort of correction is needed in certain conditions in certain places in Canada. I hesitate to say they can "write prescriptions". Although they sort of are, it may be that they are only able to test the vision, decide on what sort of correction is required and prepare the suitable appliances and then fit and test these appliances on the wearer. While they would have written a prescription internally, it may be that they aren't actually able to give this as a written prescription.

Our article doesn't seem to mention any other areas where opticians can assess and provide corrective appliances without an existing prescription, however it only mentions 3 other countries and in one of them (Ghana) it's not clear to me what opticians can do.

But anecdotally, I can say it's fairly common for opticians in Malaysia to carry out the assessement etc themselves. I haven't checked the law, and Malaysia is a place where stuff can happen despite clearly being against the law. But I wouldn't be that surprised if the law does allow this. I would expect some other developing countries have similar systems.

I probably should also mention that while in NZ, only optometrists can make prescriptions, there have been suggestions at various times that this should be changed and opticians should be allowed to tests the eyes and effectively make prescrptions albeit perhaps only after the patient has seen an optometrist (or I guess opthamologist) to assess eye health [20] [21] sometime recently. Nil Einne (talk) 15:23, 17 December 2015 (UTC)[reply]

Nil Einne (talk) 15:23, 17 December 2015 (UTC)[reply]

My experience is more or less Nils' and 76's:

an optician can make glasses and such, but not prescribe them.

an optometrist can prescribe glasses and such

an ophthalmologist is a physican qualified to diagnose diseases of the eye and treat them.

Anything an optician can do, an optometrist can do; anything an optometrist can do an opthalmologist can do.

I suspect the second statement and the first are not meant to be (or sound like) identical; I would guess that the second statement meands that opticians can, for example, determine the distance between pupils in order to fit glasses. - Nunh-huh 02:47, 17 December 2015 (UTC)[reply]

Why do progressive lenses have peripheral zones?

Zeiss states that peripheral zones are because of "aberrations" (presumably monochromatic aberrations, but which?) which in turn are caused when "the difference between the radii of curvature in the horizontal and vertical directions grows". Why does it grow to begin with? Can't they just make it so it doesn't grow? — Sebastian 20:09, 16 December 2015 (UTC)[reply]

A progressive lens tries to minimize the visible boundary between different regions, unlike a bifocal lens for example. So everything has to change gradually from one zone to the other ... I think. But optics is an art, and I'm not an artist. Wnt (talk) 22:17, 16 December 2015 (UTC)[reply]

Voice pitch of brunette and blonde women

I got an impression that naturally brunette women (roughly beyween ages 18 and 35) have slightly higher voice pitch than natural blondes of comparable age (regardless of language differences). Is it to a certain extant true or bullshit? 93.174.25.12 (talk) 21:10, 16 December 2015 (UTC)[reply]

I suspect this might be a case of confirmation bias. Not suggesting that it's completely impossible for two relatively disparate traits to be correlated, just that if they were, we'd probably have noticed by now. Googling what does voice pitch correlate with, it looks like it's mostly down to height, taller people have lower voices. Maybe most brunettes you know are shorter than average? Vespine (talk) 21:43, 16 December 2015 (UTC)[reply]

I'm thinking blondes are Nordic, Nordic is tall, etc., but ... it's not really science. I mean, because it matters what town you live in, where the blondes and brunettes came from, what their population structure is etc. You could probably find some lists of single nucleotide polymorphisms for these things in 23andme data and try to do a raw correlation coefficient, but all you'd get is the all too common sort of near-irreproducible result that links a genetic trait to something else in one experiment only. Wnt (talk) 22:14, 16 December 2015 (UTC)[reply]

I've recalled Wikipedia:Reference_desk/Archives/Science/2009_October_28#Voice_differences_between_blondes_and_brunettes. 23:49, 16 December 2015 (UTC)

Perception of own health in an isolated group

Let's say we have a person with some health defect from birth, such as congenital blindness, urinary incontinence, etc. For the sake of experiment, he/she is raised in a group isolated from the rest of society (similar to the Allegory of the Cave) and is being told that blindness or whatever he/she suffers from is normal, that everyone is like him, it's a normal state, etc. Provided the rest in the group suffers from the same defect and there's a continued isolation, would he/she realize by himself/herself at some point that he/she should actually see in case of blindness, contain his urine in case of urinary incontinence, etc? Maybe there were such experiments already? Brandmeister^talk 23:27, 16 December 2015 (UTC)[reply]

This idea was explored in The Country of the Blind, for example. ←Baseball Bugs ^{What's up, Doc?} carrots→ 01:38, 17 December 2015 (UTC)[reply]

In principle, such a collection of blind people could develop science, perform tests and experiments - and wonder why they have these organs in their heads that appear to have no function whatever - they might note that there are large nerve bundles and huge sections of the brain that connect to them. They might even notice that there is a light-focussing lens at the front of these two structures.

I don't think it's unreasonable that they might deduce that these organs were evolved to collect and focus light. If they had access to study animals that can see - then they might eventually come to some conclusions about their own deficiencies.

Sure, we can conclude that without vision, it might be much harder for them to develop this science - but it's clearly not impossible and if it's not, then I think they'd eventually realize that they've somehow failed to have all of the connections necessary for these organs to function properly.

SteveBaker (talk) 03:17, 17 December 2015 (UTC)[reply]

Does it mean that we indeed perceive our health through what healthy people around tell us or there's some innate, internal indicator thay may give us clues even in an isolated group? Brandmeister^talk 09:45, 17 December 2015 (UTC)[reply]

December 17

sodium iodide catalysis of SN2 reactions of diols on dichloromethane

I have an acid-sensitive catechol (which I believe is vulnerable to oxidation in acidic conditions) which I plan to methylenate under basic conditions. Reacting catechols with dichloromethane is discussed in the literature, but one way for me to increase yield would be to convert the dichloromethane into a more active form using an iodide catalyst. However, sodium iodide is not very soluble in dichloromethane. For various reasons, I plan to run the reaction in cyclohexanol with DCM dissolved in it, because the first step that leads to my catechol derivative relies on a ~1% catalytic impurity found in technical grade cyclohexanol (cyclohexenone). I shouldn't expect sodium iodide to be very soluble in cyclohexanol either.

If I produce diiodomethane using the Finkelstein reaction by dissolving DCM and sodium iodide in acetone, the problem is that even if I evaporate the acetone and any leftover DCM (leaving just the diiodomethane) I think the acetone will form an azeotrope with the diiodomethane, and this acetone will act as a surfactant and interfere with acid-base extraction during workup. (The octanol/water logP is -0.042, or an octanol/water partition coefficient of 0.9). At what points would diiodomethane and acetone form a zeotrope? (The liquid range of DIM is 6-182C, acetone -94 to 57C) Yanping Nora Soong (talk) 07:55, 17 December 2015 (UTC)[reply]

Diiodomethane is itself available (or can be made and isolated separately ahead of time). Why are you trying to make it in situ, with resulting complications from acetone? But thinking about separation process, I don't quite see why the data you have would necessarily leave acetone present. At say 60°C, most of it should evaporate easily. However, if it is a problem, there are azeotropes of acetone with cyclohexane and with hexane that could be used to drive out the acetone and leave instead a hydrocarbon that is much less water-soluble. DMacks (talk) 10:37, 17 December 2015 (UTC)[reply]

black holes, space physics stuff

(I don't really know how to word what I want to know properly and I'm a complete astrophysics layperson, so I apologize in advance if it's not clear and I'll try to clarify if need be.)

Been reading black hole and related articles because I want to understand how black holes "work", in a sense. One thing that's mentioned in the main black hole article here is that black holes don't actually suck in all objects around them unless those objects are within their "horizon" (I assume this means the event horizon); from a distance, it has the same gravitational field as normal objects of the same mass. At least, that's my understanding of what's written. What confuses me about this statement though, is that black holes have an enormous amount of gravitational pull (I think because of its incredibly high, dense mass, if I understood correctly?), and I would think that anything caught by its pull would get pulled in eventually. Galaxies are basically a ton of stars being slowly-but-surely pulled in by a black hole at the center, aren't they. Doesn't that mean that black holes do slowly suck in everything around them, or am I just misunderstanding something about how bodies orbiting a significantly greater mass works? Thanks, Drapsnagon (talk) 12:50, 17 December 2015 (UTC)[reply]

No, an object can orbit around a black hole in the same way as around a smaller object such as a star or planet. Basically if an object is not moving directly toward a black hole it has angular momentum, and needs to lose it in order to fall in. The usual way for an object to lose angular momentum is by collisions with other objects moving along different trajectories. Looie496 (talk) 13:15, 17 December 2015 (UTC)[reply]

(edit conflict) No, not really. Black holes operate under normal gravity, not magical "suck everything in" gravity. Consider the following thought experiment:

Q? What would happen to the earth if we replaced the Sun with a black hole of the exact same mass in terms of the Earth's motion?
A? Not a damned thing. Everything would work the same. All objects have a center of mass, which is the imaginary point to where its gravitational pull attracts other objects. If you replace one object with a different object of the same mass in the same location, its gravitational effects would be identical.

The ultimate fate of the universe depends greatly on the exact effects of attractive forces (mostly gravity) and repulsive forces (mostly the metric expansion of space due to inertia left over from the big bang. Again, since black holes don't have magical gravity, just normal gravity; taken in the bulk their gravitational effects are not greater on the whole universe than other objects. While there has been historically some debate over what will ultimately happen to the universe (it really depends on small differences in assumptions between how much various kinds of "stuff" exists that a) we don't know if it really exists and b) if it does, we're not entirely sure how much exists and what it does.), things like dark matter and dark energy. Consensus today is roughly that the universe will keep expanding forever, but evidence is not strong in any direction. Hope that all helps. --Jayron 32 13:25, 17 December 2015 (UTC)[reply]

(ec)"Galaxies are basically a ton of stars being slowly-but-surely pulled in by a black hole at the center, aren't they?" No they are not. Just like the moon is not falling onto the earth (in fact, it is getting further [22]), objects can orbit each other for all of eternity.

Thanks for the answers (and take it easy on me-- as I mentioned, astrophysics (and physics in general really) is a little difficult for me to wrap my head around, and I did mention having a feeling I had it wrong about how orbiting objects work...) Drapsnagon (talk) 13:50, 17 December 2015 (UTC)[reply]

Let me add a footnote that a black hole is not exactly the same as a smaller attractor, because for objects orbiting near it, the gravitational field can be so strong that general-relativistic effects come into play. In particular orbiting objects can radiate energy in the form of gravitational waves, and thereby fall into gradually lower orbits. But this effect is only significant for objects lying very close to the black hole. Looie496 (talk) 14:35, 17 December 2015 (UTC)[reply]
Not really that much of a footnote. General relativity (the modern theory of Gravity) operates on all objects equally, not just on objects near black holes. In close proximity to black holes, the effects of general relativity are more pronounced, but that's not different from saying that "near black holes, gravity is more pronounced" because for our purposes general relativity = gravity, and it's still not magic created by the black holes, simply expected increase of effects that happen everywhere. For example of general relativity effects showing up in a "smaller attractor", see Perihelion precession of Mercury. --Jayron 32 14:47, 17 December 2015 (UTC)[reply]
Yes -- but the rate of energy loss via gravitational wave radiation only becomes significant when the field is extremely strong. It's true that the effect exists for smaller attractors, but it is too weak to be meaningful. (I don't think we are disagreeing, just emphasizing different aspects of the situation.) Looie496 (talk) 14:56, 17 December 2015 (UTC)[reply]
- Or just say that the surface of the body interrupts the nice increase of the gravity and prevents the field from getting any stronger. Sagittarian Milky Way (talk) 15:30, 17 December 2015 (UTC)[reply]

Cloud seeding to prevent floods

Recently there was severe flooding in Cumbria caused by a storm. With weather forecasts giving a few days warning of a big storm's approach, would it be practical to seed clouds while they were still over the sea, and prevent dangerous levels of rain falling on land? I have read the cloud seeding article which doesn't seem to rule this out, but doesn't mention it happening either. 94.1.53.114 (talk) 15:19, 17 December 2015 (UTC)[reply]