Wikipedia:Reference desk/Archives/Science/2008 October 13

= October 13 =

Is our solar system flat ?
In all models and illustrations of our solar system that I have seen, the planets appear to be traveling in one plane. This seems strange to me. Don't the planets actually revolve in different orbital planes, and if so, is there some way that the distance between planets varies with time, maybe to the point of possible collision between two planets? —Preceding unsigned comment added by 58.167.231.238 (talk) 00:11, 13 October 2008 (UTC)
 * Solar system says: Most large objects in orbit around the Sun lie near the plane of Earth's orbit, known as the ecliptic. The planets are very close to the ecliptic while comets and Kuiper belt objects are usually at significantly greater angles to it., so yes, they're all basically on the same plane. This came about because the planets all formed from a spinning disk of stuff.  As for the second question, no the planets are too far away from each other to ever collide.  --Sean 00:18, 13 October 2008 (UTC)
 * Actually, if you ignore the now disgraced Pluto, they do all revolve in roughly the same orbital plane. Our articles on the solar system are actually some of the best at Wikipedia, most are featured or good articles. See Solar system and Planet for some broad overviews. As far as planetary inclination, which is the term for deviation from the mean orbital plane of the solar system, the largest is Mercury at 7o off center. All other planets are less than 3.5o off center. Now, lots of other objects do orbit at distinctly greater angles outside of the orbital plane, but none of the main planets do. See List of spherical astronomical bodies in the Solar System for a full list of planets and their stats.  The planets are all in fairly stable orbits, and stand no real chance of coliding with one another (even Pluto and Neptune, which swap place in terms of distance from the Sun, do not actually physically cross orbits, and would never collide). Objects in the Solar System do colide all the time, but this usually occurs because some of the smaller objectes, with more eccentric orbits, will collide with a planet.  There is no chance for two planet-sized objects to collide.  --Jayron32. talk . contribs  00:25, 13 October 2008 (UTC)
 * Pluto IS a planet, dammit. 67.184.14.87 (talk) 20:30, 13 October 2008 (UTC)
 * The distances between planets varies dramatically because they all orbit the sun at different rates. Mars (for example) goes around the Sun once every 1.9 earth-years.  So if Earth and Mars were as close together as they ever can be - then about a year later, they'll be on opposite sides of the Sun...and about as far apart as they can ever get.   But I presume that you are asking whether the radius of the orbits changes.  Well, things are a bit more complicated.  The planetary orbits are not circles - but ellipses - so the distance of the each planet from the sun varies slightly through the planetary-year.  Those ellipses are also slowly rotating - so each planet's path through the solar system looks a bit like a flowery spyrograph pattern.  While this pattern seems very stable and is unlikely to change much in the future, the solar system is an "n-body problem" - which is an unsolved mathematical problem - and is believed to exhibit chaotic properties.  That means that we can't reliably predict what will happen over the very long term - and it's possible that some strange combination of conditions could perturb the stability of the solar system.  While the planets seem to know where they're going - that's not true of moons.  It is known (for example) that our Moon is gradually spiralling away from the Earth and will eventually disappear off into space - it's unclear what the consequences will be when that happens.  One of Mars' moons is going to break up in the next million years and form an amazing ring system around that planet.  Pluto's orbit is thought to be somewhat unstable.  So things are not as stable and clear-cut as they seem.  SteveBaker (talk) 01:33, 13 October 2008 (UTC)
 * The moon is backing away from the Earth because it is increasing its orbital angular momentum by stealing from the Earth's rotational angular momentum via tidal drag. Given a long enough time the Earth rotation would slow to match the orbital period of the Moon, and the system would be doubly tidally locked (like Pluto and Charon are).  Once that happens the Moon will no longer recede from the Earth.  The mechanisms responsible for its recession don't allow the Moon to escape.  A back of the envelope calculation suggests that the orbit of the moon can grow to about 5 times it's present size before the Earth's angular momentum is entirely depleted, so that sets an upper limit on the ultimate size of the orbit.  Dragons flight (talk) 07:24, 13 October 2008 (UTC)
 * Actually, if it expanded to 5 times its current distance I think it would outside the Earth's Hill sphere (our article says the Earth's Hill sphere is about 1.5 million km and the Moon's orbital radius 0.384 million km, and 5*0.384=1.92>1.5), so it would be perturbed by the Sun and would eventually enter a direct solar orbit. --Tango (talk) 11:11, 13 October 2008 (UTC)

squid blood
I was watching a tv show about colossal squid. The narrator said that the squid's blood was blue. I have read through the articals on squid, giant squid and colossal squid but can't find any information as to why the blood is blue. Why is this? Also, are there any other animals that do not have red blood?

Thanks. —Preceding unsigned comment added by 216.154.17.55 (talk) 03:30, 13 October 2008 (UTC)


 * It's bluish. All your questions are answered in hemolymph and hemocyanin articles. --Dr Dima (talk) 03:46, 13 October 2008 (UTC)


 * short answer: it uses copper instead of iron to grab the oxygen. rust is red, but copper oxide is green. see articles mentioned above for details.Gzuckier (talk) 00:23, 14 October 2008 (UTC)

to know mechanism
please give me satisfactory mechanism of how blood cells come out from the bone marrow? which mechanism do they follow to come out?

i also want to know that through which respiration method RBC respire?

please send me answers of all this questions. i am a biology teacher. thanking you. —Preceding unsigned comment added by 117.196.0.122 (talk) 04:59, 13 October 2008 (UTC)


 * For the record, you sound like a biology student. I'd suggest consulting your teachers manual and colleagues for answers. If you can't find them there, read Red blood cell and Bone marrow. In reponse to your second question in particular, consider the following: What enzymes or cellular machinery does a cell require to perform aerobic or anaerobic metabolism? What do RBCs have/lack? --Shaggorama (talk) 07:28, 13 October 2008 (UTC)

Orthogonal translation
Wikipedia doesn't have an article for this. What is it? --M1ss1ontomars2k4 (talk) 05:50, 13 October 2008 (UTC)
 * Some context would be useful here. Is this phrase just the "plain-English" sum of its parts, i.e., approximately "Orthogonal translation--motion at a right angle to some other direction"? DMacks (talk) 05:57, 13 October 2008 (UTC)
 * I agree, context is needed to answer this question properly, but orthogonal transformation might be meant if this is a mathematical concept, and the Maths desk might be able to help more]]  Sp in ni ng  Spark  07:08, 13 October 2008 (UTC)
 * My bad; I intended this question to be in the biological sense. "Orthogonal translation" is noted in several places in my lecture slides but no definition is given. --M1ss1ontomars2k4 (talk) 16:43, 14 October 2008 (UTC)
 * Alright, so it's translation (biology), and "orthogonal" meaning "completely different of or independent from each other". Consider :"'Notably, each module is mutually orthogonal with the other modules such that there is little unintentional cross-talk. For example, the lac repressor acts on promoters containing the lac operator sequence but does not repress transcription from the tet or the cI operator sequence; a similar relation exists among other repressors and promoters.'" So you either have orthogonal conrols over translation of a certain gene or different pieces of the transcription machinery that only act on certain pieces of genetic code (instead of a single all-purpose ribosome, for example). DMacks (talk) 13:40, 15 October 2008 (UTC)

quantum mechanics
de broglie predicts that matter is a wave, and hence has a wavelength, right? when my teachers explained this, they usually used a baseball or something to show that the effects were small for large objects. well, let's say that plancks constant was large, like 1 J*second. would the baseball have a discernable wavelength? well, the equations of quantum mechanics say that λ=h/p, and so, since the baseball has momentum, it would have a wavelength. but the baseball is just a myriad of electrons, protons, and neutrons. so wouldn't it be those particles which have the large wavelength, rather than the baseball. this question can also be generalized to other concepts like the uncertainty principle: are analogies with macroscopic objects valid? —Preceding unsigned comment added by 65.92.231.82 (talk) 09:32, 13 October 2008 (UTC)
 * Both the baseball and each constituent would have a wavelength. An experiment has been done with a very small balls, in fact with buckyballs of 60 atoms (see Quantum Mechanics in that article), and the complete balls produce a diffracton pattern just like electrons. Dmcq (talk) 10:04, 13 October 2008 (UTC)
 * The de Broglie wavelength of any object is given by the simple equation:


 * $$\lambda = \frac{h}{p}$$


 * where h is Planck's constant and p is the object's momentum. Since momentum is directly proportional to mass, then the wavelength is inversely proportional to mass; i.e. the more massive an object is, the shorter the wavelength.  For any significantly large object, the wavelength of its DeBroglie wave will be so small as to be meaningless, like wavelengths smaller than the diameter of a proton. --Jayron32. talk . contribs  18:13, 13 October 2008 (UTC)

Clockwise or Anti-Clockwise
I know our solar system travels around the our galaxy the milky way. But I do not know if it travels clockwise around the core of the galaxy or Anti-clockwise. By that I mean if the direction pointed by the north pole of the Earth is defined as up, are we traveling around the core, in a clockwise manner or anti-clockwise manner? 122.107.229.49 (talk) 09:40, 13 October 2008 (UTC)

For that matter, I don't even know if the Earth travels clockwise or anti-clockwise around our Sun. —Preceding unsigned comment added by 122.107.229.49 (talk) 09:42, 13 October 2008 (UTC)


 * Using the Right-hand rule with north in the direction of the thumb, the earth rotates counterclockwise as can be seen from the sun rising in the east. We go around the sun anticlockwise as well, but that axis is tilted by 23 degrees relative to the north pole. (Warning: Tilting causes seasons)


 * According to the sun rotates around the galactic centre with an axis that's tilted 117 degrees relative to the earth's north. So we're basically going clockwise around the galaxy. According to the sun article, that's at 220 km/s so it takes the sun 8 days to move a distance equal to the distance between us and the sun. Adding the speed of the milky way with respect to the rest of the universe, we're going at a comfortable 370 km/s.


 * The milky way you can see in the sky are simply stars along the galactic plane, which gives you a bearing on where we are. You can see the 117 degree tilting in that the milky way is never aligned exactly east-west in the sky. (If it had been tilted 90 degrees, it would have run north-south and east-west if by 0 degrees) EverGreg (talk) 10:37, 13 October 2008 (UTC)


 * As an aside, the shadow on a sundial travels "clockwise" (in the northern hemisphere). Clock hands just copy the motion of the shadow.  Saintrain (talk) 16:50, 13 October 2008 (UTC)

FISH
In fluorescent in situ hybridisation, how many fluorescent entities must converge on a point to make it visible? How small a point is it likely to be for a typical probe and its unique recognition sequence?


 * I don't have an answer to your question, but we do have a page on the technique: Fluorescent in situ hybridization (U.S. English spelling) --Scray (talk) 11:01, 13 October 2008 (UTC)
 * I've created a redirect. --Tango (talk) 11:14, 13 October 2008 (UTC)
 * I consulted the article before coming here. It was not helpful in this case. :( Seans Potato Business 15:25, 13 October 2008 (UTC)


 * I can't speak to what is typical for the FISH technique, but there is no reason why with the right probe and a sufficiently sensitive sensor that the answer couldn't be one. In general it helps both for visibility and background rejection to have a brighter signal, so FISH may be designed to operate with a greater abundance, but from a technical perspective detecting an isolated fluorescent tag is certainly possible.  Dragons flight (talk) 16:52, 13 October 2008 (UTC)
 * Yup, all you need is one. In FISH, a filter is used on the microscope to exclude all light that isn't within the range emitted by the flourescent tag, so it is an extremely sensitive technique. It is often used to locate individual binding sites on a chromosome, which are tiny! Poke around google for some images. --Shaggorama (talk) 18:13, 13 October 2008 (UTC)


 * The article is actually a pretty good description of how FISH works. Since the technique is based on hybridization of a unique probe sequence to the target chromosome, only one "fluorescent entity" can be present at a single point on the chromosome.  Usually this is a large (50-300 kb) piece of DNA (a bacterial artificial chromosome or fosmid which can be propagated in bacterial culture and purified in large quantities) that is labeled with fluorescent nucleotides so that multiple fluorophores are incorporated into the probe.  The size of the probe largely determines the sequence specificity (i.e. whether the probe binds to only one position in the genome), and the sensitivity (brightness) of the fluorescent signal.  There will almost always be some background non-specific hybridization that comes from repeated sequences within the probe or low complexity sequences in the genome that are just "sticky", which requires optimization for each given probe.  The spatial resolution will depend highly on the conformation of the chromosomes you are using -- the highly condensed mitotic chromosomes will give much lower spatial resolution than interphase ones or the stretched out "fiber FISH" technique (which can supposedly give a resolution of around 1 kb).  From a theoretical perspective, one might be able to identify a 16-20 base pair sequence that is present only 1x in the genome of interest, label an oligonucleotide probe and use some fancy tricks to amplify a fluorescent signal so that it could be detected by a highly sensitive microscope.  The smallest reported probe is around 50 bp (see this), but from a practical standpoint it isn't done this way very much.  —Preceding unsigned comment added by Medical geneticist (talk • contribs) 20:35, 13 October 2008 (UTC)

Questions about massive sqid
1. Is there a theoretical maximum possible size for squid?

2. Would it be possible to capture a giant/colossal squid alive to place on display in an aquarium? —Preceding unsigned comment added by 84.71.115.30 (talk) 12:10, 13 October 2008 (UTC)


 * Tthere are some theories on how large an animal can get. A predator for instance, may be limited by the size of its prey . But according to Deep-sea gigantism, there may be advantages to being big in the deep ocean. But noone has calculated an exact maximum size. In it is speculated that an unusually large squid had messed-up hormones so in any case there'd always be giant freaks that didn't fit into the theories. As for the second question, it's probably easier to catch a young one and raise it to adulthood in captivity. EverGreg (talk) 12:33, 13 October 2008 (UTC)


 * Squid belonging to the 'large' species decompress and die if you haul them up from the deep to the surface, don't they? --Kurt Shaped Box (talk) 22:36, 13 October 2008 (UTC)
 * I get this, ...with the extreme change in pressure, and environment in general, these creatures can't survive for very long, if at all, on the surface. from the article Deep sea creature. Julia Rossi (talk) 09:51, 15 October 2008 (UTC)

composite aircraft
Good Day,I would like to know how many composite (carbonfiber/fiberglass) Federal Aviation Administration certified aircraft were built every year from 1998 to the present.Please if possible list by manufacturer. I would also like to know if any projections are made by the manufacturers or the F.A.A. for the future of composite aircraft.65.15.124.92 (talk) 18:44, 13 October 2008 (UTC)

O-ring and G-ring
I'm confused by the term O-ring; it seems to have one or two additional meanings beside the one found here, referring to metal rings. Is there a 2nd meaning to the term "O-ring" that means the kind of double-looped steel ring that is commonly used as a keyring? I found this meaning e.g. here. My theory is that people don't know how this type of ring is properly called and make an analogy to the related G-ring - "it's like a G-ring but in the shape of an O". Is that right, or is "O-ring" a proper name for this thing? The 3rd possible meaning of the term "O-ring" can be found in items of jewellery such as necklaces and earrings. If my interpretation of the pictures I found via Google is correct, here the term means something like "a bigger decorative circular ring sideways attached" - is that right? --84.155.219.241 (talk) 19:22, 13 October 2008 (UTC)


 * I have always only heard O-ring to mean a big rubber gasket or washer of some sort. Though it certainly may have other uses.  --Jayron32. talk . contribs  19:27, 13 October 2008 (UTC)


 * Sorry, I need to rephrase the 2nd part of my question. I'm also wondering whether there is a 2nd meaning to the term G-ring, found in items of jewellery such as necklaces and earrings. If my interpretation of the pictures I found via Google is correct, here the term means something like "a bigger decorative circular ring sideways attached" - is that right? 84.155.219.241 (talk) 19:30, 13 October 2008 (UTC)
 * Sounds to me like in jewellery, an O-ring would be a solid ring such as one found at one end of a necklace; and a G-ring would be an O-ring with that little opener thing (i.e. a clasp) that you pull back to fasten the necklace. By my interpretation, when you pulled open the little clasp-thingie, it would look exactly like a "G". Franamax (talk) 05:07, 16 October 2008 (UTC)


 * Sounds plausible but does not really correspond to the images that Google finds. 84.155.220.228 (talk) 12:07, 19 October 2008 (UTC)

How does NASA calculate trajectories?
When NASA calculates the trajectory of an interplanetary space probe, do they use Newton's formula's (classical physics) or Einstein's (relativity)? 67.184.14.87 (talk) 23:07, 13 October 2008 (UTC)


 * Newton is plenty good enough for trajectories. The systems that provide the thrust and measure the position/velocity aren't accurate enough to show the consequences of relativity at the speeds that current spacecraft move. SteveBaker (talk) 23:53, 13 October 2008 (UTC)


 * It's true that the probe will usually get close enough to its target without relativity, but to take the question literally, "they" (JPL) do actually "use ... relativity" in the detailed calculations. According to this blog, the Messenger's voyage to Mercury requires relativistic corrections. --Heron (talk) 18:14, 14 October 2008 (UTC)


 * I wonder if that's for all space probes or just Mercury. I've read that Newton's equations don't accurately predict the orbit of Mercury.  67.184.14.87 (talk) 17:12, 15 October 2008 (UTC)
 * The precession of Mercury's orbit is greater than Newtonian physics would predict and requires GR to get it right. I'm not sure how big a difference that would make over the length of time required for the probe's journey, but it might be enough to warrant including in the calculations. Missions to Mercury will probably require more relativistic corrections that elsewhere in the solar system, since you're closer to the Sun, but I don't know if you just need less for other missions or none at all. --Tango (talk) 17:33, 15 October 2008 (UTC)


 * The extra 43"/century is about .5 km/day, so significant. Saintrain (talk) 18:33, 15 October 2008 (UTC)


 * Yes, there are effects like that - but they are negligable compared to the errors due to the inaccuracy of the rocket burn power and duration - and the inability to point the rocket with enough precision. Hence course corrections are needed - and those unpredicatble corrections totally swamp the magnitude of any relativistic effects.  In the case of Mercury - you may need relativity to figure out where it will be in 10 years time when your rocket is intended to get there - but the path the rocket takes to get to that point at that time is an entirely Newtonian calculation.  The errors due to the speed of the spacecraft causing time & space dilation is nothing compared to the unpredictability of photon pressure from the sun, inaccuracy in your initial launch, etc, etc.  It's negligable.

What is the theoretical wavelength upper limit for electro-magnetic waves?
Extremely low frequency waves have a wavelength of ~ 10,000km - 100,000km. Is there an upper limit? The size of the Universe?, or as the Universe is unbounded is the upper limit infinite? Jooler (talk) 23:04, 13 October 2008 (UTC)


 * There is no natural limit, though the size of the antenna one can operate and other factors do impose many practical limits. Dragons flight (talk) 17:43, 15 October 2008 (UTC)


 * (ec (who cares about ec's anyway? :-)) It appears that there is no theoretical upper limit to wavelength. From Planck constant (and a little rearranging) $$\lambda = h c / E$$, where $$\lambda$$ is wavelength, $$h$$ is Planck's constant, $$c$$ is the speed of light and $$E$$ is the energy of the photon.  Since there's no lower limit to E, there's no upper limit to $$\lambda$$.  There is probably a minimum actual energy (steps between electron energy bands, say) that puts a practical limit on the wavelength of a photon that can be emitted.   Saintrain (talk) 17:52, 15 October 2008 (UTC)
 * The expansion of the universe has stretched the wavelength of light in a (so far as we know) continous manner. The microwave background radiation for instance, started out with shorter wavelengths. And if Planck's law is to be taken literally, black-body radiation contain photons of arbitrarily long wavelengths, since the wavelength distribution has no cutoff for large wavelengths. In that case, name a wavelength and it's all around us, though in small amounts.
 * But with analogy to the quantum well which enforces a maximum wavelength, you can probably find a cutoff invoking the size of the visible universe and inflation theory. If I recall correctly, there's also some low-frequency waves reflected in the upper atmosphere, that have their wavelengths limited and quantized by the circumference of the earth. EverGreg (talk) 08:54, 16 October 2008 (UTC)

What triggers a missile to explode?
What, exactly, is it that causes a missile, specifically a surface-to-air missile, to explode? Does it have guidance built in so that when it reaches a specific point in space, it goes "I have now reached my target; I shall explode now", or does it have sensors to detect that, or a mechanical trigger which goes off on impact? (Could you theoretically grab a missile (gently) out of the air and hold it without setting it off?) What happens if the conditions for exploding are not met and the missile gets lost or starts running out of fuel to keep seeking the target? Does it explode, or become inert/safe? SamSim (talk) 23:11, 13 October 2008 (UTC)


 * We'd tell you but then, well you know... ;)  hydnjo talk 23:30, 13 October 2008 (UTC)
 * Well, that scuppers my plans for stealing SAM's and asking on Wikipedia how to set them off. I guess I won't post my question on how to launch them either. Anyone know a good place to sell unused surface-to-air missiles? eBay? Franamax (talk) 04:08, 14 October 2008 (UTC)


 * Its called a # Fuse_(explosives), If missile goes wrong and is heading back to you, there is a thing called a Break up system that, well, breaks up the missile without detonating the warhead.

--GreenSpigot (talk) 01:04, 14 October 2008 (UTC)
 * Clearly one could build a missile to explode due to the passage of time, due to altitude, due to impact, or due to proximity to a possible target, as well as due to triggering by the party who launched it. Edison (talk) 05:17, 14 October 2008 (UTC)


 * For guided missiles, the same system that's doing the guidance is likely to be the trigger. A radar-guided missile (for example) can use the radar returns to set itself off when very close to the target. SteveBaker (talk) 09:43, 14 October 2008 (UTC)


 * No, sorry. Guidance system and fuzing are completely separate parts of a missile: the fuze is in the warhead. If our articles combine them, they're wrong to do so.--GreenSpigot (talk) 02:44, 15 October 2008 (UTC)


 * Maybe I'm nuts, but I've always had the impression that most missles were actually designed to physically impact their targets, and hence would generally be expected to have fairly dumb impact driven triggers. That's different from same a cluster bomb or area-effect artillery that simply wants to get close and then detonate in the air.  Dragons flight (talk) 10:24, 14 October 2008 (UTC)


 * For manouvering air targets the chance of a direct impact is relatively small, so relying solely on an impact fuse would not be a wise thing. Also I'm not sure if using the main guidance is generally done. I always thought most *-to-air missiles had a seperate proximity fuze, because the explosion (see continuous-rod warhead) is most effective to the side (where the main guidance system cannot scan, though it could possibly estimate). To answer the second part of your question: the K-13 and Sidewinder articles have a nice paragraph about your theoretical situation. Ever since then, air-to-air missiles self destruct if they miss their target. I'm not sure if it's also true for surface-to-air missiles, but something tells me they do, after all, you don't want your own missile coming down on your troops. - Dammit (talk) 10:44, 14 October 2008 (UTC)


 * Correct. Physical impact is not required as proximity fuzes of one type or another are almost always used. In fact I think achieving physical contact would be rather difficult in the case of a missile trying to shoot down another missile.--GreenSpigot (talk) 02:44, 15 October 2008 (UTC)
 * Actually, the Aegis Ballistic Missile Defense System is a direct impact missile to missile system. The impactor is a "kinetic kill vehicle" (see kinetic projectile) and has no explosive at all.  This works, in part, because ICBMs are largely unpowered during their sub-orbital arc, and hence don't dodge.  Dragons flight (talk) 17:55, 15 October 2008 (UTC)

Why can pulse be normally abnormal?
I'm a little confused, after reading the article on the pulse as it relates to the body. I understand it's not always the same as heart rate - so is that it? Because, I'd been under the assumption one would just check for 10 seconds or so and multiply by 6, or at least 15 and multiply by 4. Does this mean that pulse rate can have a few little skips, and if so, why? Is it slight movements - the hand moving a bit while trying to measure at the wrist? is it the different things that cause the waves in the heart's normal sinus rhythm? Or, what? —Preceding unsigned comment added by 209.244.187.155 (talk) 23:44, 13 October 2008 (UTC)


 * Pulse rate and heart rate are identical under most circumstances (the exceptions mainly occurring when the heart is pumping abnormally). But neither is as regular as, say, a CPU. It's not a clock. It speeds up, it slows down, based on a variety of variables: exertion, rest, drugs, stress, emotion, vagal nerve stimulation, etc. So 10 seconds is too short a time for a reliable estimate of heart rate. Count for 30 seconds and multiply by 2, or for a full 60 seconds. And you should expect the pulse to fall within the normal range (60-100) rather than to be the same each time you take it. - Nunh-huh 23:57, 13 October 2008 (UTC)


 * Perhaps the OP is asking about regularly irregular pulse, e.g. second degree AV block. These rhythms are irregular, but beat patterns can be grouped in a way that can be described as regularly irregular.  In particular, for these rhythms one should count for a few cycles of the beat group, or about a minute, before estimating the heart rate. --Scray (talk) 02:34, 14 October 2008 (UTC)
 * To rephrase, they are irregular at regular intervals. They follow a clear pattern, but the pattern is an irregular. --Shaggorama (talk) 16:39, 15 October 2008 (UTC)