Wikipedia:Reference desk/Archives/Science/2015 August 14

= August 14 =

Stealing electricity by manipulating apparent power
I have heard of someone stealing electricity by manipulating the apparent power of strip lights. The claim was that some component was removed. As I understand apparent power, it can only be greater than active power, and therefore this approach can only increase the amount of electricity for which an individual is billed. Am I missing something?--Leon (talk) 14:44, 14 August 2015 (UTC)
 * The obvious question is, why wouldn't bulbs have this component removed automatically? There are big advantages for a company that can put a better energy label on its box. A fluorescent light is an inductive load, so in theory you could reduce the apparent power at the meter by putting a capacitor into the system (but never to below the active power) which is what "power savers" claim to do. However, see "The real truth behind household power savers". Electricity meters in homes only measure active power, so whatever magic you try doing with inductors and capacitors, you will only ever increase the total power measured at the meter (bar a few very minor savings that you may get from reduced heat in your wires and better surge protection). (Some industries are billed on apparent power, but that's because a very large inductive load like an industrial motor could damage the power grid and make power spikes more likely.) 15:43, 14 August 2015 (UTC)
 * From your link: "The systems also automatically remove carbon from the circuit which also encourages a smoother electrical flow." Carbon? That sound like utter BS to me. Or do they mean something else? Sjö (talk) 07:23, 15 August 2015 (UTC)
 * I can't make any sense of that either. That's a quote of what the manufacturer said though, and given that the manufacturers are selling a useless product, I wouldn't try to look for too much sense in the explanation. Smurrayinchester 07:38, 15 August 2015 (UTC)
 * See power factor correction. You will be legal and more effective by using your own solar panel. -- Hans Haase (有问题吗) 18:47, 14 August 2015 (UTC)


 * Here is an authoritative debunking of these gadgets: NIST Team Demystifies Utility of Power Factor Correction Devices. --Heron (talk) 12:24, 15 August 2015 (UTC)


 * I still haven't wrapped my head around what this actually does. The current at the appliance is still alternating at the same voltage?  Is the waveform different??  Mostly what I'm wondering is:  do these devices have any potential to reduce the buzzing noise made by some electrical devices and equipment? Wnt (talk) 14:02, 15 August 2015 (UTC)


 * See AC power and power factor. For reactive loads on AC power, the current and voltage can alternate out of sync. And no, changing a load's power factor won't affect any buzzing you might hear. The buzzing is usually from components such as transformer windings vibrating. In turn, this is usually caused by the use of cheap materials and construction. --108.38.204.15 (talk) 04:23, 16 August 2015 (UTC)

Harnessing Light
What are the new possibilities and challenges in harnessing light energy (describe in very primary level concepts)Sayan19ghosh99 (talk) 15:30, 14 August 2015 (UTC)


 * We won't do your homework for you. Still, photovoltaics, phosphorescence and biofuel (which is an indirect form of solar power - when you burn wood or vegetable oil, you're releasing the light energy that was captured by plants during photosynthesis) might help. Smurrayinchester 15:48, 14 August 2015 (UTC)


 * Don't forget solar energy. Most forms of energy ultimately derive from the Sun, like hydroelectric energy, wind energy, and fossil fuels.  A few exceptions are nuclear energy, tidal energy, and geothermal energy. 18:23, 14 August 2015 (UTC)

E. coli long-term evolution experiment
In E. coli long-term evolution experiment, one sample evolved the ability to digest something new after about 33,000 generations. Is that considered a new species? Bubba73 You talkin' to me? 16:02, 14 August 2015 (UTC)
 * Defining species for bacteria is particularly problematic see the earlier articles and bacterial taxonomy + . Richard Lenski evidently believes it should qualify as a new species although I'm sure some bacterial taxonomists won't agree. Nil Einne (talk) 16:28, 14 August 2015 (UTC)
 * Thank you. Bubba73 You talkin' to me? 16:46, 14 August 2015 (UTC)


 * The definition of the word "species" is pretty vague. The Victorians liked the word and said that two organisms were considered to be of different species when they were sufficiently different that they could no longer inter-breed and produce viable offspring.  So all dogs are of the same species as wolves.  But lions and tigers can interbreed - so by that definition, they are technically of the same species.  Horses and donkeys can also interbreed - but only produce infertile mules - so they are of different species.  Then we have animals where group A can breed with group B and B can breed with C but C can't breed with A...so A and B are the same species and B and C are the same species but A and C aren't??


 * The traditional definition of this word breaks down if you push it too far.


 * So asking about "species" in this case isn't very meaningful...and especially so with bacteria. However, you'd have to say that if one group of bacteria are genetically equipped to thrive in some habitat where another group cannot survive at all - then something fairly major has happened - and that happened in this experiment.


 * Darwins' Galapagos finches were a similar deal - they'd evolved into different groups on different islands because of the different availability of food. Some "species" are able to eat nuts using short, powerful beaks - other able to get insects out of holes using long, thin beaks.  They could still interbreed with each other - but CLEARLY they should be considered to have become different "species".


 * If you want to use the "species" word informally, then that's fine...but it's not a hard-and-fast thing with a 'bright line' definition.


 * What we DO know here is that those bacteria changed beyond recognition. The change is permanent and breeds true.  They started as one very homogeneous group of bacteria, with one set of abilities, were exposed to altered  environmental conditions and thereby changed into two (or more, actually) distinct groups with very different abilities - and that, for sure, is evolution in action.


 * "Species" is just a word. What matters is what actually happened.  Sadly, those people who do not believe in evolution like to attach massive meaning to this very vague and outdated term - and that makes discussion difficult.  Scientists are not keen on saying that 'X and Y are different species', not because X isn't really different from Y - but because the word "species" is not amenable to 'bright-line' distinctions.
 * SteveBaker (talk) 15:50, 15 August 2015 (UTC)
 * Thank you. Yes, nature doesn't make beings of a certain speces, genus, etc.  Those are a classification used by people.  Bubba73 You talkin' to me? 23:14, 15 August 2015 (UTC)

A day in the solar system
I recently came across a diagram in the Facebook group I fcuking love science that listed the relative length of a day on a bunch of the planets:


 * Mercury: 175 days, 23 hours
 * Venus: 116 days, 18 hours
 * Earth: 24 hours
 * Mars: 24 hours, 37 minutes
 * Jupiter: 9 days, 56 hours <-- Actually this and the next four are hours and minutes. Bubba73 You talkin' to me? 16:54, 14 August 2015 (UTC)
 * Saturn: 10 days, 47 hours
 * Uranus: 17 days, 14 hours
 * Neptune: 16 days, 6 hours

Are these durations based on planet diameter, or distance from the Sun, or both or other things? Do we know and/or understand what causes such a discrepancy? Thanks!  DRosenbach  ( Talk 16:25, 14 August 2015 (UTC)
 * No, there is no good correlation between planet size, planet orbit ("solar year"), and planet rotation rate ("solar day"). Every one of these parameters appears to be independent.  From first principles, we can hand-wave about conservation of angular momentum, or tidal locking, or something, but we really don't have very many data points.
 * As always, my go-to reference is de Pater and Lissauer's Planetary Science, which is the most up-to-date textbook I've found on this topic. There's a chapter on the theory of planetary formation, which is informed by everything we know from fundamental physics, as well as observations within our solar system, and the very sparse new information that we've accumulated about extrasolar planets.  Nimur (talk) 16:37, 14 August 2015 (UTC)


 * Part of the discrepancy is because some of those numbers are wrong! The numbers you list for Jupiter, Saturn, Uranus, and Neptune are hours and minutes, not days and hours.  For example, the solar day on Jupiter is 9 hours 56 minutes.  These depend mainly on how fast each planet rotates.  However, each planet's orbit around the sun also makes a difference.  The day for Mercury is very long because it is in a tidal resonance where it rotates three times for every two orbits.  Venus has a very small rotation, although it's not known for sure how this came about.  You can find a table here along with an explanation of why one "day" is not the same as one rotation. --Amble (talk) 16:46, 14 August 2015 (UTC)


 * There does seem to be a correlation with larger planets rotating faster. Of course, this isn't the only factor, but it does appear to be the main one.  Now, why larger planets should rotate faster, I do not know.  (You've skipped Mars, so let me add that it has a sidereal rotation period of 24h, 37m.)  As for why Mercury and Venus rotate so slowly, Mercury is close enough to have a tidal resonance with the Sun, and I suspect Venus is somewhat affected by tidal forces from the Sun, too.  The Earth may be far enough away to avoid that effect, although the tidal forces from our rather large Moon may make a slight difference.  Pluto, classified as a dwarf planet now, has a sidereal rotation period of 6d, 9h, but it's big moon Charon is large enough to cause tidal locking, having a major effect.  StuRat (talk) 17:11, 14 August 2015 (UTC)


 * I have added Mars, which has a day almost the same as that of the Earth. As noted above, the periods for the outer planets should be in hours and minutes, so that they are spinning considerably faster than the Earth, which means that they have much greater angular momentum.  As noted, Mercury and Venus appear to be in tidal resonances with their solar orbits.  There is probably some reason why the smaller non-resonant rocky planets (Earth and Mars) spin slower than the giants.  Uranus is a strange case because it is doing a barrel roll.  The details of how the planets got their rotations is not well understood.  Robert McClenon (talk) 17:32, 14 August 2015 (UTC)


 * Pluto and Charon are tide-locked to each other; their day is their month. If "we would expect" that rotation rate from Pluto's size, we'd expect some other rate from Charon's size. —Tamfang (talk) 00:52, 15 August 2015 (UTC)


 * If we look at the sidereal period and equatorial radius of each planet from Earth to Neptune, it looks like the sidereal period is approximately equal to one day multiplied by the inverse of the cube root of radius (in Earths):

Sidereal                     Formula Rotation    Equatorial       Rotation Period    Radius           Period (Actual)                   (Predicted) =========== ==============   =========== Earth            1 d    1.000 Earths   1.000 d Mars      1.025957 d    0.533 Earths   1.233 d Jupiter  0.4135417 d   11.209 Earths   0.447 d Saturn     0.43958 d   9.4492 Earths   0.473 d Uranus     0.71833 d    4.007 Earths   0.630 d Neptune     0.6713 d    3.883 Earths   0.637 d


 * I'm sure that formula can be refined further, but of course it will never predict the rotation period precisely, because events like impacts in the early solar system have a random effect. StuRat (talk) 18:05, 14 August 2015 (UTC)


 * StuRat, you're conducting original research, and through this pseudoscience and numerology, you're carrying on the long and discredited tradition of applying arbitrary curve-fits to arbitrary sub-sets of astronomical data. For example, have a read at Titius–Bode_law.  You can fit some curve to some set of data, but that's not proper science: you don't have a theory to explain your curve-fit; you don't have enough data to validate the curve-fit on other solar systems; and there's no reason to pick these arbitrary parameters.  The issue is confounded further when you cherry-pick your data points: why did you choose not to include Mercury and Venus, or Ceres, Eris, or Pluto?
 * That kind of work is not science; and respectable (peer-reviewed) publications will not entertain it. Nimur (talk) 21:35, 14 August 2015 (UTC)


 * I didn't include Mercury and Venus because, as Robert McClenon said above "Mercury and Venus appear to be in tidal resonances with their solar orbits" (due to their proximity to the Sun). The others are not planets.  As for not having enough data points, maybe a mathematician can figure out the chances of 6 data points correlating as closely as those, assuming random distribution.  I would agree that it's not enough to define the precise formula, but it is enough to describe the general pattern. StuRat (talk) 23:23, 14 August 2015 (UTC)


 * Currently the giant impact hypothesis for Earth is fairly popular. According to that idea, much of the angular momentum of the Earth was established during a collision between two bodies.  As a result, one imagines that the Earth could have had a wide range of day lengths based solely on a seemingly random collision (though if Theia really formed as a sort of massive "trojan" at the L5 point, then it wasn't all that random).  Mercury is pretty well known to be affected by tidal locking and our article on Venus says it "may" be influenced by it (but opposed by other factors); apart from these, all the other planets listed fall in a fairly narrow range, as does Ceres (dwarf planet) with a 9h rotation, but Pluto has a 6-day rotation.  The Sun is also an outlier with something like 25 to 34 days rotation.  I wouldn't rule out some statistical explanation for the typical range of values... Wnt (talk) 23:23, 14 August 2015 (UTC)
 * Pluto's long rotation period is due to its being mutually tidally locked with its largest moon Charon. Double sharp (talk) 15:55, 15 August 2015 (UTC)

Gas giant day?
This makes me think of a sub-question. What is a day on a gas giant? I imagine "day" for a gas giant is defined by the apparent rotation of what we can see, but is that also the rotational frequency of the rocky core? Is that also the rotational frequency of a liquid metallic mantle? Do we have even the slightest idea of how these things correlate, or just theories? Someguy1221 (talk) 20:07, 14 August 2015 (UTC)


 * I think it's defined as when a point on the surface makes a complete rotation. This really is the case for all planets, and stars too. Any spinning object that isn't completely solid will have different parts that rotate at different speeds. You can see this if you spin a raw egg around and then stop it with your hand; the inside will keep spinning. The Earth's layers rotate at different speeds, and this is thought to be essential to the dynamo effect that generates Earth's magnetic field. Similarly, the differential rotation of stars is thought to be what gives rise to magnetically-driven phenomena such as sunspots and solar flares. --108.38.204.15 (talk) 20:46, 14 August 2015 (UTC)


 * For a gas giant, even the part we can see doesn't all go around in the same amount of time. It's about 5 minutes faster at the equator than at the poles.  The metallic hydrogen interior is believed to rotate at the same rate as the magnetic field and synchrotron radiation go around, which is about the same as the poles. --Amble (talk) 21:24, 14 August 2015 (UTC)


 * For Jupiter, the International Astronomical Union publishes several different conventions to define longitude. For example, here's a good review article: Coordinate systems of Jupiter (1983) and New Longitude System for the Jovian Magnetosphere (1989) that explains how it works.  It is mostly based on spectral analysis of periodic observations, both in visible and (more importantly) radio-frequency spectra.  Here's an even more recent paper, The Rotation Period of Jupiter (1995), which was published in GRL and is hosted by its author at the Institute of Geophysics and Planetary Physics, UCLA.  Nimur (talk) 21:54, 14 August 2015 (UTC)