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March 12

Track position of something

How can you tag something cheaply, to track its position? I mean, you could put an iPhone into something and report the position, but I need something much cheaper and simple, for tagging some expensive tools and maybe recover them if they get lost within a building, or even stolen. XPPaul (talk) 01:29, 12 March 2012 (UTC)[reply]

Well, you can place RFID tags that can track things fairly cheaply, per item, for a large number of items, as they pass scanners at the exits. However, trying to track things after they have left the building would be quite expensive, requiring cell phone technology at the least, and satellite technology if you need to be able to scan for items away from cell towers. StuRat (talk) 01:46, 12 March 2012 (UTC)[reply]

But can you track cheaply the location within a building of something tagged with RFIDs? Or only when they pass a threshold? XPPaul (talk) 01:56, 12 March 2012 (UTC)[reply]

They do make portable scanners, but you would then need to walk through the building until you get close enough (a few meters) to read it. Placing a network of scanners every few meters would likely be prohibitively expensive. StuRat (talk) 02:00, 12 March 2012 (UTC)[reply]

There are also key-finders, where you press a button on the base unit and the unit attached to the item selected starts beeping. Unlike RFID, these have batteries that need to be changed on each item. This is more economical for a very small number of items, though, although not good at preventing theft, because, unlike tiny RFID chips, these tags aren't easy to hide, so the thief would just remove them. The cost here is around $10 per item tracked initially, then maybe $5 a year in batteries each. StuRat (talk) 02:07, 12 March 2012 (UTC)[reply]

There are commercial GPS locators that sell for $150 or so. Depending on the cost of the tools, that might be a worthwhile investment. --Mr.98 (talk) 02:09, 12 March 2012 (UTC)[reply]

If you tell us more about your situation, like how many items you want to track, the average cost of the items, how large the area is where you need to track them, your annual loses from theft, etc., we can tailor our suggestions accordingly. StuRat (talk) 02:15, 12 March 2012 (UTC)[reply]

I have a non-technical solution for theft:

1) Keep tools locked up.

2) When somebody needs to use them, have them sign for them, with the understanding that if they don't return them, they will be charged for them (whether they lost them or they were stolen doesn't matter).

You might find they take better care of them, in this scenario. StuRat (talk) 02:28, 12 March 2012 (UTC)[reply]

To follow on that, it is often helpful to attach identifying information i.e. Property of XYZ (555-5555), or similar. This helps guard against accidental losses (e.g. people forgetting where an item came from) and in addition, identifying info may discourage theft if the information is sufficiently hard to remove. Not a guarantee obviously, but simple strategies like this can be helpful in decreasing the rate at which things go missing. Dragons flight (talk) 02:58, 12 March 2012 (UTC)[reply]

The tools are mechanical and electrical for apprentices going through vocational training. Having a tracking system could make it easier to just let them access the tools to play/learn as much as they want, maybe taking the tools outside the school. And they are not really expensive, just for the school they would be expensive, specially if they go missing. XPPaul (talk) 03:19, 12 March 2012 (UTC)[reply]

Put on RFID or simple barcodes, and require students to check them in- and out at a scanner, just as in a modern library. Do occasional spot checks to find out if procedure is followed. It's a hassle, but then, nearly everything would be. You might want to restrict this to power tools, and just eat the loss on plain screwdrivers and hammers... --Stephan Schulz (talk) 07:49, 12 March 2012 (UTC)[reply]

A cheap way is to install mobile phone tracking on a cell phone, and attach the phone to whatever or whoever you want to track. See also tracking system and vehicle tracking system.--Shantavira|^{feed me} 09:10, 12 March 2012 (UTC)[reply]

Register the student who checks out an item, or give each student his own set of tools, those are the two systems usually used in my experience. Or make them available at one location for all students attending but check if all is returned at the end of each lesson. Students who borrow tools for outside the classroom would still be registered. There are always risks, I remember a student who got all his gear stolen on his first day. 84.197.178.75 (talk) 12:27, 12 March 2012 (UTC)[reply]

I !vote for a "library" system. Each idem has an individual identity (engrave a number on it) and students can check them in and out the same way as library books. If the cost can be justified install an RFID system with a scanner at the exit of the tool storage room - similar to the anti-shoplifting scanner systems used in retail stores. Roger (talk) 14:37, 12 March 2012 (UTC)[reply]

Journey time with constant acceleration drive

In the article on Space travel using constant acceleration, it is my understanding that the traveler will not see himself limited by the speed of light (if I remember my first year physics, the universe relatively moving at close to the speed of light will appear squashed to him, effectively making his journey shorter). But is the stronger statement, that from his perspective all the relativity cancels out and that he can treat his distance calculations a Newtonian, correct?

For example, setting aside all the other issues with interstellar travel, if I wanted to fly to a star 10 light years away, I would constantly accelerate for the first 5 light years and constantly decelerate for the last 5 light years. Assuming I accelerate at 1G, could I simply solve t from 0.5 * g * t^2 = 5 (light years), and double it for total journey time? If not, what is the formula for the travel time, as measured by the traveler's watch? 41.164.7.242 (talk) 13:40, 12 March 2012 (UTC) Eon[reply]

Distance traveled: (see Time dilation )

x(t)={\frac {c^{2}}{g}}{\sqrt {1+{\frac {\left(gt\right)^{2}}{c^{2}}}}}.

from that formula you can get t (duration as seen on earth) as a function of (half of) the distance, and put that into the next one:

Time in spaceship:

\tau (t)={\frac {c}{g}}\ln \left({\frac {gt}{c}}+{\sqrt {1+\left({\frac {gt}{c}}\right)^{2}}}\right)={\frac {c}{g}}\operatorname {arsinh} \left({\frac {gt}{c}}\right).

total time (with deceleration) will be double that...

~~Oops, forgot the actual question: no, he can not calculate his travel time the 'newtonian' way, he would get the same result at the start as an observer.~~ I forgot, his calculated speed would go beyond the speed of light, but a quick calculation shows that doesn't give him the right traveling time... 84.197.178.75 (talk) 18:07, 12 March 2012 (UTC)[reply]

Verrucas

The article on Verrucas does not give any mention of the long lasting effects of the wart. It skips straight from cause to diagnosis and prevention, but does not say anything about what can actually happen. Do they just stay there for years and never give you any problems? What exactly are the effects of them? Rcsprinter (talkin' to me?) 16:40, 12 March 2012 (UTC)[reply]

Unless one's immune system is deficient in some way, it will finally clear the infection. Then as the skin layer grows the wart drops off and one becomes immune to getting any more for quite some time. Agreed, the article really should explain this too.--Aspro (talk) 16:57, 12 March 2012 (UTC)[reply]

Fan

what would a fan look like if it spins in the speed of light? 203.112.82.2 (talk) 18:52, 12 March 2012 (UTC)[reply]

good question, like to know that too. Ehrenfest paradox seems to give no answer... 84.197.178.75 (talk) 19:33, 12 March 2012 (UTC)[reply]

Hang on a mo. Lets brake this hypothetic question down into digestible chunks. If this hypothetical fan made of super high tensile Wikimetal was able to rotate fast enough – only its very tips would be able to reach c or near as dam it. In this case the reflected light (which has a velocity of c ) it would still be reflected off of it at c thus giving the same appearance of slower fans, i.e. a transparent disk with a discernible thickness. Now for augments sake: If we consider a disk of pure Wikimetal, then we can do a thought experiment and consider the tips as being able to go at more than c. Some photons would not be able to touch the tips as they would move away faster than the light could approach. Some photons would hit it at an angle and get reflected. How they then get reflected together with those that pass by would be dependant, in part - on mass. Since the tips of Wikimetal fan are travelling at c or c + then mass is err.. extraordinary large! Some-where-in-between these two extremes, suggests to me that light will be bent by the mass of the tips to form a halo around said fan. Of course this would have to be done in a high vacuum, otherwise one's lab notes would be blown all over the place. Why can't you ask the more usual questions like why is the sky blue?--Aspro (talk) 22:13, 12 March 2012 (UTC)[reply]

because google can answer that and i go to wikipedia for intelligent answers. =) 203.112.82.2 (talk) 23:41, 12 March 2012 (UTC)[reply]

Wouldn't the blades of the fan simply appear to an observer, to twist into a spiral. The above explanation does not follow special relativity sense. For instance there is never a c+ instance. Plasmic Physics (talk) 23:03, 12 March 2012 (UTC)[reply]

Yes, but I didn't want to complicate a hypothetical question as one could probably not be able to observe the spiral anyway – unless a Femto strobe light or something was at hand. I was also counting on the special properties of rigidity that Wikimetal has, to allow the tips to reach c in the first place. In which case I think it would be just the effect on light that one would notice. Yes, there can never be a c+ It was all a thought experiment. I tend to find its easier to answer questions like does my bum look big in this but I am a bit of a masochist I suppose.--Aspro (talk) 23:29, 12 March 2012 (UTC)[reply]

Ignoring the practical difficulties of this experiment, and assuming "the speed of light" means "slightly less than the speed of light", the blades would appear thinner (with respect to simultaneous measurement in the lab frame), and that's about it. The blades would not twist into a spiral unless the fan was (angularly) accelerating or decelerating. -- BenRG (talk) 23:51, 12 March 2012 (UTC)[reply]

Remember, that the spped of light is not an angular quantity. Ordinarily, a point positioned at a further radial distance sweeps through a larger arc length, meaning that Lorentz contraction should be more pronounced towards the tips of the fan blades.

Wouldn't the length of the blades also contract, because they are undergoing acceleration towards the axis of the fan? Plasmic Physics (talk) 00:04, 13 March 2012 (UTC)[reply]

That's a good point. The point I wanted to get across, is that if this hypothetical situation could be approached without regard to the practical limitations due to the strength of materials and energy required to spin it up to speed, then the observed effects or as the OP put it ”what would a fan look like” the likely appearance -I think- would be a development of a halo due to Gravitational lensing. Maybe an astrophysicist can chip in as to whether a rapidity spinning black hole also shows astigmatic lensing or whether its spheroidal shape and speed of rotation causes it to deforms and cancel it out. --Aspro (talk) 00:14, 13 March 2012 (UTC)[reply]

I'm going to have to come back to this tomorrow. I can understand the fan's cord getting smaller but acceleration towards the axis requires me to to think in terms of π and I can't do that at the moment. If only the Op has asked about the colour of the sky; we would have had this polished off by now!--Aspro (talk) 00:33, 13 March 2012 (UTC)[reply]

It has a cord, here I thought it was battery powered. Plasmic Physics (talk) 00:49, 13 March 2012 (UTC)[reply]

Don't be an ignoramus. Cord as in Chord (aircraft) the OP is talking about a fan. And a thought: Isn't acceleration towards the axis just Newtonian mechanics. Its not absolute (in this frame). I still don't see how it applies here.--Aspro (talk) 01:26, 13 March 2012 (UTC)[reply]

Yes, the blades would be thinner at the tips, but there's no relativistic contraction in the radial direction. If anything the blades would be longer since they're under (ridiculously huge) tension. Gravitational effects would depend on the mass of the blades, which could be made arbitrarily small if you wanted to ignore gravity (since this is unrealistic anyway). -- BenRG (talk) 01:14, 13 March 2012 (UTC)[reply]

"(ridiculously huge) tension" This is why (for this thought experiment) I have chosen to use Wikimental, which will not elongate so much as half an Yoctometer under whatever any ridiculously huge tension one subjects it to. --Aspro (talk) 02:40, 13 March 2012 (UTC)[reply]

Why would there be no Lorentz contraction in the radial direction? Plasmic Physics (talk) 01:20, 13 March 2012 (UTC)[reply]

@Aspro: I've genuinely never heard of "chord" being used in that sense, and I haven't studied aircraft in such detail. Which way is acceleration then? Special relativity is just amended Newtownian mechanics to take the limiting factor c into account, there is no reason why Newton's first law of motion should no longer apply. Plasmic Physics (talk) 01:37, 13 March 2012 (UTC)[reply]

That's OK, I don't know how to mix a Manhattan cocktail. Have you hear of the Voyager space probe 'sling shot' manoeuvres. It didn't get 'accelerated' (gain extra momentum) rather it got its angular velocity converted. Gravity assist. Therefore, the blades are not really increasing their velocity due to rotation about their axis. I haven't put that very well but that is all that comes off the top of my head right now and my ISP has gone all fluttery on me and so my connection keep going down so I can't keep up with the comments.--Aspro (talk) 01:56, 13 March 2012 (UTC)[reply]

I have heard of slinghot manoeuvres however, your statement contradicts a sentance in the leading paragraph of that article. Plasmic Physics (talk) 03:03, 13 March 2012 (UTC)[reply]

The acceleration while at constant angular velocity is purely centripetal. But this doesn't imply any centripetal velocity since "change in velocity" is permitted to be a change in direction component of the vector, rather than the magnitude (which is indeed what centripetal acceleration is). While the fan is speeding up, there is indeed a component of the acceleration that is perpendicular to the radial. As for why there is no radial contraction, that's because there is no radial component to the velocity vector of any atom on the fan. Someguy1221 (talk) 02:57, 13 March 2012 (UTC)[reply]

Oh, so as a vector quatity, only the direction changes, not the magnitude. And only the magnitude is limited by the speed of light? Plasmic Physics (talk) 03:45, 13 March 2012 (UTC)[reply]

Yup. Someguy1221 (talk) 01:52, 14 March 2012 (UTC)[reply]

Aircraft and Faraday cages

Most of us probably know that it's easy to make a cell phone call from inside an airliner while it's on the ground, taxiing before takeoff, where it's well within range of, presumably, multiple cell phone towers. But an aircraft seems to me to be a perfect Faraday cage with the exception of the windows. Are our electromagnetic signals when making a cell phone call really just the result of the signal that travels through the plane's windows? Comet Tuttle (talk) 19:35, 12 March 2012 (UTC)[reply]

Faraday cages, per the article intro, are only effective if gaps are smaller than the wavelength of the radiation in question. Modern cell frequencies are ~2GHz, which gives them wavelengths of ~15cm. That's smaller than airliner window openings, so that's enough to prevent the aircraft from operating as a Faraday cage. Whether and how much the airframe is responsible for signal attenuation, I can't say. — Lomn 22:05, 12 March 2012 (UTC)[reply]

(ec)A Faraday cage cannot have holes bigger than about the wavelength of the electromagnetic wave its supposed to protect against. Notice how e.g. light easily comes in through the windows of an aircraft ;-). IIRC, cell phones use frequency bands somewhere between 800MHz (~40cm) and 2100MHz (~15cm). Thus, they signals can also simply come in through the plastic windows. --Stephan Schulz (talk) 22:12, 12 March 2012 (UTC)[reply]

Yes, it it simple the windows. Astronaut Dr. Owen K. Garriott ( call sign W5LFL) who stuck his antenna on a space shuttle window and with only 5 watts transmitting power, I could hear him better than if he was standing right next to me speaking into a tin can telephone.--Aspro (talk) 22:48, 12 March 2012 (UTC) .[reply]

Excellent, thank you. Comet Tuttle (talk) 23:08, 12 March 2012 (UTC)[reply]

Gut flora in poop

My question is about the undignified subject of bacteria that live in feces. How long does gut flora live in feces that has already been pooped out? How much of a difference does it make when the feces is immersed in water as opposed to drying out on the ground? (I'll preemptively stop one or two sniggering comments by suggesting we consider this to be gut flora of a dog rather than of a human.) Comet Tuttle (talk) 19:46, 12 March 2012 (UTC)[reply]

One of the first things to happen will be that the CO2 will diffuse out and so the pH will increase. But much of the faces is made up of dead bacteria and so lysis of those cells will create ammonia. This complicates trying to guesstimate the actual conditions as this chemical is not always a proton donor but I guess that it will also increase the pH. Becoming more acidic and with more oxygen diffusing in, the bacterial and fungal gut flora will then find their 'poop' environment becomes less than hospitable and some will turn into dormant spores. On dry ground I think this take just a few hours. In wet conditions it depends a lot on the pH and things. Even mildly acidic conditions don't favour Asiatic Cholera and those types of bacteria. Therefore, I don't think any definitive answer can be given – at least by me - as it depends on temperature, moisture, oxygen availability and pH..--Aspro (talk) 20:08, 12 March 2012 (UTC)[reply]

One of the bacteria that is prevalant in poo (and of particular interest because it can cause food poisoning) is ecoli, maybe that article might help a little. Specifically this paragraph Cells are able to survive outside the body for a limited amount of time, which makes them ideal indicator organisms to test environmental samples for fecal contamination.[8][9]. There is, however, a growing body of research that has examined environmentally persistent E. coli which can survive for extended periods of time outside of the host. Unfortunately, "limited time" and "extended periods" are not very descriptive. Vespine (talk) 03:17, 13 March 2012 (UTC)[reply]

I probably shoulnd't have used "prevalant" since it's only 0.1% of the bacteria which makes up 60% of the dry weight of poo, from the gut flora article. Just call it "present". Vespine (talk) 03:21, 13 March 2012 (UTC)[reply]

Ok, last post, promise:) The reference for the "extended period" claim is available to [[read online for free. It might have more specific details if you're interested in reading it. Vespine (talk) 03:27, 13 March 2012 (UTC)[reply]

E. coli is a good example of one of the bacterium that can tolerate a wide range of conditions. [1] both temperature and pH. So, now wash your hands. --Aspro (talk) 03:36, 13 March 2012 (UTC)[reply]

laws on cell towers

Are there any laws in the United Kingdom about the building of cell towers near schools? 72.129.183.133 (talk) 23:06, 12 March 2012 (UTC)[reply]

Cell towers are called "mobile phone masts" in the UK. This page says that in 2001, the Government issued guidelines for Local planning authorities called "...'Planning Policy Guidance 8: Telecommunications'," which "reinforced public consultation arrangements for small masts, increased the prior approval period to 56 days, and insisted that school governors must be consulted on any proposals for masts on or near schools or colleges." The following year there was "A Code of Best Practice on Mobile Phone Network Development". So although it's unlikely that planning permission would be granted close to a school, it's not actually prohibited. See this current case about permission being granted for a mast next to a church which hosts a pre-school kindergarten. Alansplodge (talk) 00:43, 13 March 2012 (UTC)[reply]

Why is there a problem putting transmission masts near schools? If it is because there is a "radiation" issue can you take the time to find a reputable citation. Richard Avery (talk) 23:04, 13 March 2012 (UTC)[reply]

I know of a number of schools here in South Africa that have cell towers on their property. The rental income is put to good use. Roger (talk) 06:39, 14 March 2012 (UTC)[reply]

There is a widely PERCEIVED danger from mobile phone radiation following some early research. For example Mobile phones 'alter human DNA' and 2-Year Study Finds Possible Cell Phone Danger To Brain. We have an article Mobile phone radiation and health with a section on Health hazards of base stations. Here is the UK Government's advice about masts, health issues and planning. Since local authorities are responsible for planning permission, and since they are also elected by people who perceive a risk from these structures, most play it safe and won't site masts near schools. For example, Phone firms appeal over mast rejection. But not all - see the press report linked above. Alansplodge (talk) 16:58, 14 March 2012 (UTC)[reply]

This Fact Sheet on Cell Tower Health Studies lists research that suggests that there IS a health risk. The main one seems to be The Naila Study, Germany (November 2004). Cancer Research UK's page: Mobile phones and cancer, highlights a major Danish study on mobile phone use which said: "We found no evidence for an association between tumor risk and cellular telephone use among either short-term or long-term users. Moreover, the narrow confidence intervals provide evidence that any large association of risk of cancer and cellular telephone use can be excluded.". However, this research was about phone use and not proximity to a phone mast. Alansplodge (talk) 17:51, 14 March 2012 (UTC)[reply]

That fact sheet is from a highly POV source. A couple of the articles cited are clearly nonsense. The others cite things like "increased fatigue" and "nausea" with people living less than 100m from a tower, but not one of them seems to compensate for the fact that almost everyone living that close to a tower is living in a dense urban area, and virtually everyone not living that close is out in the suburbs or other more rural areas. It's well understood that the poor air quality of a big city can damage your health.

The first study has 14% of participants living within 10m of a transmitter. I have to assume that most of those were lower-power urban transmitters. Probably transmitting at less power than your average handset. Now, notice the journal that it's published in. "Electromagnetic Biology and Medicine Journal" Someone correct me if I'm wrong but this seems to be a fringe journal entirely dedicated to this sort of scare story.APL (talk) 09:32, 15 March 2012 (UTC)[reply]

Dominant solar system plane inside a galaxy?

Hi

I see that the galaxies are rather 'flat'. Not entirely so that all solar systems share the same position in height (z-axis), but with a clear predominant tendency towards a plane. Now, is the tendency for solar systems inside the galaxy to share this plane? Ie that we look at the Milky Way in each solar system as though it is level with the orbital patterns of most other planets inside it.

If you could help me with this I would be much obliged!

83.108.140.82 (talk) 23:16, 12 March 2012 (UTC)[reply]

There might be a very weak association, but for the most part planetary systems are believed to be randomly oriented with respect the galactic plane. Our solar system makes a 60 degree angle to plane of the galaxy, if I recall correctly. Dragons flight (talk) 23:23, 12 March 2012 (UTC)[reply]

For reference, you might read Protoplanetary disc and Formation and evolution of the Solar System. It seems the 'local' forces of the protoplanetary disc outweigh the over all 'galactic' influence. Vespine (talk) 00:16, 13 March 2012 (UTC)[reply]

And for each planet with rings and/or moons, those orbits aren't necessarily aligned with either the solar system plane or galactic plane. StuRat (talk) 03:44, 13 March 2012 (UTC)[reply]

They are unless something weird is going on. Moons that formed with the planet, rather than being captured later, will orbit in roughly the equatorial plane of the planet, which will normally be roughly the same as the orbital plane (all the angular momentum comes from the same source - the net random movements in the cloud of dust and gas that collapsed to form the solar system - so it all has roughly the same axis orientation). You get exceptions like Uranus, where some kind of close interaction or collision with another body moved its axis considerably. You also get moons that were captured later, which can have pretty much any orbit. The norm, though, is for everything in a solar system to rotate and revolve in roughly the same plane. --Tango (talk) 12:30, 13 March 2012 (UTC)[reply]

However, over the course of 4.3 billion years, nearly every object in the solar system has had ample opportunity to be so disturbed. Axial_tilt#Axial_tilt_of_selected_objects_in_the_solar_system shows that most objects in the solar system to not align that way, the one exception being Mercury (planet). This suggests, to me, that Mercury is close enough to the Sun for some gravitational effect similar to tidal locking to have had a major effect. Surprisingly, even the Sun itself has a tilt of 7.25 degrees, so there must have been an interaction with quite a large object (larger than any current planet) at some time in it's history. StuRat (talk) 16:01, 13 March 2012 (UTC)[reply]

Though individually quite negligible, I wonder if the small stochastic impulses from coronal mass ejections might be enough to introduce a small tilt to the sun after 4.5 billion years. Dragons flight (talk) 16:22, 13 March 2012 (UTC)[reply]

Wouldn't they tend to balance out ? StuRat (talk) 18:35, 13 March 2012 (UTC)[reply]

That's like saying, if you take a random walk shouldn't you stay near zero? In a certain sense it is true, but the longer it goes on the higher your odds of finding the walker far from the origin. Dragons flight (talk) 19:10, 13 March 2012 (UTC)[reply]

Having run some numbers, the impulse per event seems to be too small to appreciable effect the sun's orientation, even after billions of years. Dragons flight (talk) 02:23, 14 March 2012 (UTC)[reply]

Why does the Sun have a 7.25 degree tilt ?

OK, I'm going to break this off as a new question. As per the discussion above, what caused the Sun to have this obliquity/axial tilt, relative to the ecliptic plane ? StuRat (talk) 05:39, 14 March 2012 (UTC)[reply]

This particular one? Probably not a lot. But if it was any different, would you be less likely to ask the question? I'm no astrophysicist (obviously), but it seems to me that even if on average the axis of rotation of a star tends to aligned with the axis of rotation of the planets around it, being seven degrees or so off doesn't seem particularly implausible - at least without data to the contrary. If the (local) universe had been perfectly uniform in all directions before the Sun formed, it wouldn't have. It wasn't, so it did. As to why the universe isn't perfectly uniform in all directions, I've no idea (I'm no... well, I've said that already), but if it was, you wouldn't be here to ask the question. AndyTheGrump (talk) 06:33, 14 March 2012 (UTC)[reply]

Sorry, but that's not much of an answer. The Sun would presumably have to have had zero tilt relative to the planets when the solar system was formed, so what caused it to change ? StuRat (talk) 06:38, 14 March 2012 (UTC)[reply]

Why do you presume that? AndyTheGrump (talk) 07:09, 14 March 2012 (UTC)[reply]

All rotation of the Sun and planets and moons must have come from the rotation of the proto-planetary disk. The planets and moons could fairly easily have been disturbed since then by gravitational interactions with each other and other passing objects, explaining their tilts, but it would take a massive object to cause the Sun to tilt. StuRat (talk) 07:15, 14 March 2012 (UTC)[reply]

If the planets all started off in the same plane, gravitational interactions with each other couldn't move them out of this plane - which leaves your 'passing object', presumably quite massive. Maybe it changed the tilt of the sun as it passed, maybe it only changed the tilt of the planets (though maybe it hit the Sun?). Once the planets have been perturbed out of their original plane, gravitational interactions will tend to realign them again - but not necessarily in the same plane as they were originally. AndyTheGrump (talk) 15:37, 14 March 2012 (UTC)[reply]

If everything was exactly in the same plane, that's true, but whatever tiny variations exist can be greatly magnified over time. Pluto, for example, was thought to have been in the same plane as the rest, until many near misses with Neptune knocked it out of the plane. StuRat (talk) 22:49, 14 March 2012 (UTC)[reply]

Not an answer, but I did make the observation that the rotational angular momentum of the sun is approximately 3% of the total angular momentum of the solar system. About 60% of the total is the orbital angular momentum of Jupiter. I suppose one possibility is that the very early solar system could have contained some extra protoplanets. If they was scattered out of the disk in the right way, the remaining angular momentum for the disk might have been shifted by the right amount relative to the sun. Dragons flight (talk) 22:07, 14 March 2012 (UTC)[reply]

Have scientists proposed any theories as to what sized objects might have perturbed the Sun, and when ? StuRat (talk) 22:30, 14 March 2012 (UTC)[reply]

Why are you assuming that it is the Sun that has been perturbed, rather than the planets? AndyTheGrump (talk) 22:51, 14 March 2012 (UTC)[reply]

Because, as noted above by Dragon's Flight, it would take far more to move all the planets, especially Jupiter, into an orbit 7.25 degrees out of the original plane, since the Sun's angular momentum is only some 3% of the total. (Even though the mass of the Sun is far more, the distance from the surface to the center of rotation is far less.) StuRat (talk) 23:06, 14 March 2012 (UTC)[reply]

Actually, if you consider the torque required, it would seem much easier to perturb the planets since the effective lever arm would scale as the orbital radius, while for the sun you only have the solar radius to work with (and really not even that, due to the high symmetry). If it is an outside influence, then my bet would be on something skewing the planetary disk. Even so, it wouldn't be that easy. Dragons flight (talk) 00:12, 15 March 2012 (UTC)[reply]

But a single object slamming into the Sun could do it (a star at low speed or a gas giant at high speed), making that a simpler scenario than objects slamming into each and every planet. StuRat (talk) 00:44, 15 March 2012 (UTC)[reply]

I don't think anyone is suggesting that objects were hitting each planet - I'd assumed we were talking about a massive object perturbing them with its gravitational field as it passed by. AndyTheGrump (talk) 00:48, 15 March 2012 (UTC)[reply]

I wouldn't expect it to perturb each item in the same way, you'd end up with a rather chaotic system, methinks. StuRat (talk) 00:55, 15 March 2012 (UTC)[reply]

On long timescales the orbits of the planets interact with each other. I would guess that there is a tendency for the planes of the various orbits of the major planets to drift towards each other if perturbed. If there is such a tendency then a large perturbation for one planet could eventually cause the plane of all the planets to shift. Dragons flight (talk) 01:58, 15 March 2012 (UTC)[reply]

I don't think that's right. To bring each other into the same plane the objects actually need to strike each other, as they do in a proto-planetary dust cloud or a ring around a planet. Once you have large objects with empty space in-between, gravitational perturbations are just as likely to move objects farther out of the plane as back into it. Just look at the orbits of the moons of Jupiter to get an idea of how chaotic they are: [2]. Saturn's moons are almost as bad, despite the rings: [3]. StuRat (talk) 02:39, 15 March 2012 (UTC)[reply]

For Jupiter's moons, >99.99% of the mass is in the four large moons, which all have inclination less than 1 degree (as do all four of the moons that orbit inside of the radius of the Galilean four). For Saturn, the 13 largest moons each have inclination less than 7.5 degrees (11 of 13 are less than 2 degrees), though one of the 13 is retrograde. I still think settling is plausible, though the objects involved would have to be large enough to have appreciable mutual interactions. The irregular moons of Saturn and Jupiter have such a tiny fraction of the total mass, that they probably can't do much to influence the other orbits. Dragons flight (talk) 16:58, 15 March 2012 (UTC)[reply]

There does seems to be a pattern, both with objects orbiting the Sun and the planets, that the innermost objects orbit in a plane, while the outer objects orbit at random. In the solar system, the Oort Cloud is where the most of the randomly aligned orbits fall. StuRat (talk) 19:04, 15 March 2012 (UTC)[reply]

Note that the article on the ecliptic gives a table of how inclined the planets are relative to the Sun - Earth is the most inclined of all the orbits. The gas giants and Mars are all at 5.5-6.5 degrees, the inner two planets at about 3.5 degrees. This is not my field and I don't know the answer to this question, but I'm thinking that because the outer planets fall into such a close range the protoplanetary disk must have been at about 5.5 degrees relative to the Sun, and the Sun is what was twisted for some reason. Did the same thing twist Mercury and Venus, or were they somehow entrained into the same plane as the Sun afterward? I have no idea. Earth should have an excuse though - it was whacked hard enough to make the Moon, after all. Wnt (talk) 23:20, 14 March 2012 (UTC)[reply]

To clarify, Ecliptic#Planets lists the inclination of the planet's orbits about the Sun. If you include the minor plants, as noted in the article, you get some much higher values. And the angle of rotation of each planet about it's own axis is also wildly variable, especially for Venus and Uranus, and, if we include dwarf planets, Pluto: Axial_tilt#Axial_tilt_of_selected_objects_in_the_solar_system. StuRat (talk) 23:36, 14 March 2012 (UTC)[reply]

On the subject of the alignment of planetary orbital planes

I assume everyone here has noticed Jupiter and Venus playing footsie in the evening sky. [4]. Even with misty cloud cover, and much of the London suburbs polluting the night sky darkness, they were unmissable earlier tonight. AndyTheGrump (talk) 03:46, 15 March 2012 (UTC)[reply]