Take your right hand out. Stick your thumb up. Curl your fingers around. Your thumb represents a planet's N pole, and your fingers point in the direction that the planet is spinning. (The Earth moves from W to E, and the result is that it looks like the Sun rises in the E. Sit down a globe and a flashlight if this comment makes no sense.)
For any spinning thing we can do the same exercise. Just wrap your fingers of your right hand around in the direction of the spin, stick your thumb up, and that is the North pole of that spin.
Now for the fun fact. Most of the stuff in the Solar System rotates roughly the same way. It doesn't matter whether you take the rotation of the Earth, the rotation of the Moon, the orbit of the Moon around the Earth, the orbit of the Earth around the Sun, the orbit of Saturn around the Sun, the rotation of Saturn, the orbits of Saturn's moons around Saturn - the north poles of all of these are reasonably well aligned.
They are not exactly aligned. For instance the Earth's rotational axis is tilted 23.5 degrees from the axis of its orbit around the Sun. (Hence our seasons.) And not everything follows the rule. Uranus is the best-known exception. But most of it lines up fairly well.
The only actual use that I've ever found for this fact is being able to explain to my son why the Moon rises later every night, but I've always thought that it was pretty cool.
EDIT: glurgh below corrected my understanding. It happens that for most of the planets, North corresponds to the right hand rule as I described. But that's not actually the way it is defined and Venus in particular does not work that way.
I tend to pick up fun trivia, but I'm not an expert, and always appreciate when someone corrects mistakes in my understanding.
However across the Milky Way there are again a whole lot of things roughly moving in the same direction.
I think I may have just exceeded my recommended daily nerdallowance of reading about spinning things in the sky.
I have found that to be endlessly fascinating - that the reason the planets dance together in harmony is because of their common and violent birthing process.
But not entirely - the amount of axial tilt turns out to be a chaotic system. About 20 years ago I ran across an estimate that if the Earth did not have the Moon, then every so often we would randomly wind up with a sufficient tilt to be extremely difficult for life. Therefore our Moon may have been critical for sustaining life as we know it.
See http://www.nytimes.com/1993/03/02/science/moon-may-save-eart... for confirmation of that tidbit.
The seasonal variation of warmth from the sun leads to differences in atmospheric and surface temperatures.
The atmosphere warms faster than the oceans, creating a temperature gradient. This is the primarily mechanism that energises the water cycle. i.e. evaporation, cloud formation, rain, rivers etc.
And it isn't coincidence that stuff tends to spin the same way. Because when you don't then tidal forces try to pull you back into alignment. Of course, being basically frictionless tops, the main effect is that the rotation precesses. (The Earth's rotation takes about 26,000 years to precess.) However there is a tiny tidal friction component that slowly tends to bring things into alignment, and which is trying to lock all spins to each other.
And the operative word here is "slowly". If the Moon had been thrown off, spinning the opposite way from the Earth, it would have remerged. Instead the Earth's rotation is being transferred into throwing the Moon into a higher orbit at about 4 cm/year. (For comparison, this is a bit under twice the rate that the North American Plate is moving.)
The main consequence here on Earth is that the UTC system that we all use is going to have to add leap seconds more and more often over time, and in a few thousand years either we'll need to reconsider either the length of the second, or our tying the measurement of time to astronomy. (My vote would be to remove the astronomical definition. Humans seem to be OK living with time zones that do not match the sky. Having to move those time zones every few centuries does not seem like that big a deal. There won't be an observable issue in a normal human lifespan from this until after longer than human civilization has existed so far.
Astronomers are in charge of UTC right now, and they would hate the change. But when you consider how much it would cost astronomy to cope compared with the real costs of software bugs that tend show up when they insert leap seconds in UTC, right now the tail is very much wagging the dog.
This one is done - the definition of the second is not based on astronomical observations.
"Since 1967, the second has been defined to be:
the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom"
The accuracy of this kind of measurement is so high it's also used (along with the speed of light) as the basis for defining the meter. Earth-time is a complicated and messy business but the base unit, the second, is pretty much nailed down and independent.
You are right in how we define the second. It was chosen so that on average the number of seconds from midnight to midnight is 606024 = 86,400. At this point a ton of stuff depends on it - the only change that I think likely is to something that we can measure even more precisely than the current standard.
But we have set up UTC such that the first second of every year starts close to midnight for the Royal Observatory at Greenwich, London. This sometimes requires having minutes with 59 or 61 seconds (usually 61).
These weird minutes have real costs. For instance the June 30, 2012 leap second crashed Linux machines around the world, taking down quite a few websites. And the costs are only projected to increase as we have more programs that make assumptions about UTC, and the slowing day requires more leap seconds to be added.
Therefore logically we have 3 choices. Change the meaning of a second (not feasible), continue putting up with leap seconds (costly, and serves no purpose unless you're an astronomer), or give up the UTC peg to an astronomical fact. Unfortunately astronomers control UTC right now, don't want to give it up, and don't care how much their leap seconds cost everyone else. But this can't last forever.
Given the way that things work, I don't think that it will change until there is some disaster that is too big to ignore. For instance a leap second bug causes some critical control software to fail, leading to a industrial accident, which brings the attention of politicians and the general public to this ridiculous situations. (Or crashes critical aviation software. Or something else on that scale.)
If the current situation maintains, it is just a question of time until something on that scale happens. But until that happens, I don't think that astronomers will understand the costs that they are imposing on the rest of the world.
My thinking is that since it is obvious that we'll lose the astronomical peg eventually, we should lose it now. Before someone dies.
Even in your example, Linux machines didn't actually crash - some processes spinlocked. And it wasn't even all Linux machines, if you were running a mildly old kernel (say, the one that came with debian etch and derivatives) nothing happened whatsoever.
Beyond that, there is no shortage of time standards that are both based on SI seconds and free of leap seconds - Terrestrial Time, International Atomic Time, GPS Time come to mind -
Google's solution is 'leap smear' and they, similarly, did not run into the problem
Leap smear is a good solution, as is TA1; sadly the posix/unix standards do not permit it (which makes it difficult to use on e.g. government projects).
I think 'btilly is right - it's an unpleasantly difficult problem.
I suppose my point is 'it just happens to be unpleasantly hard problem' - given that a great number of specialists have put serious time in thinking about it trying to solve it, I have a very difficult time imagining that the solution (or satisfactory answer) is as simple as 'just blame astronomers'.
Having _two_ or more slightly different units that measure the base unit of time (which would be the case if we defined seconds in terms of (siderial? some other?)) year seems like a far greater potential source of cock-ups than just having a well-defined unit that might not quite, but more often than not, matches astronomical detail.
As far as I can tell the proposal before the ITU (replace leap seconds with leap hours, with a view to abolishing leap hours once any incompatibilities with national laws have been resolved) solves all the problems quite nicely. I'm not entirely clear why they voted to defer a decision until 2015, but I'm not aware of any serious objections to the proposal.
The only objections that I've ever heard about are astronomers who are annoyed that this piece of traditional authority is being taken from them. My obviously unsympathetic attitude is that they used to serve an important role, but their once critical role in precision timekeeping has been obsolete since the development of the atomic clock. It is time to recognize that.
As http://queue.acm.org/detail.cfm?id=1967009 notes, fear of encountering leap second bugs ALREADY causes many factories to schedule downtime around leap seconds because of how serious the potential consequences of not doing so could be. It is just a question of time until someone who had such a bug doesn't realize it, doesn't schedule downtime, and suffers the consequences.
And what's the consequence of eliminating leap seconds? In the next few decades the Earth and our clocks will drift out of alignment by about 1% of the amount that they are already forced to be out of alignment for most of us by the fact that time zones are an hour wide. Which very few people will notice.
If the bug had been introduced during a longer period without leap seconds - not long ago there was one that lasted 7 years - then its impact would have been more widely felt. And it is true that it wasn't technically a crash, but many websites did suffer outages because internal services stopped responding. In common usage that was a crash.
Beyond that, there is no shortage of time standards that are both based on SI seconds and free of leap seconds - Terrestrial Time, International Atomic Time, GPS Time come to mind...
UTC is the standard for time in C, all languages derived from C (eg Java), and all languages written in C (eg Perl, Python, PHP, etc). It is also the standard in all Unix operating systems (including OS X), POSIX, Linux in all variations including Android, and has even been adopted by Microsoft. It is also the standard in widely used protocols written on top of that, like HTTP, and inside of any software built on top of them, such as web browsers.
Yes, there are other definitions of time that you can use. But UTC as published by NIST and distributed by the NTP utility is "the time" as far as the computer world cares. If you use anything else, people will ask - repeatedly - why you have the wrong time.
P.S. See you've now mentioned it in your response to another comment. That and this comment apparently passed in space without aggregating (into a combined rotation).
It sucks that I really do think the non-false color image is boring, because that should be really exciting to someone who enjoys thinking about the universe like I do. Although I still think my mind would fucking explode if I ever got to go deep into space.
It's an amazing image to be sure, but why all that nonsense?
If you're sending a camera from here to another planet, it makes no sense to send a camera that takes pictures in the same wavelengths that we see so you can claim true color. Instead you pick wavelengths that for whatever scientific reasons you think will be most informative.
And then once you have that information, for humans to understand it, it makes no sense to leave it as raw binary data. Instead you map some of the wavelengths that you've got onto wavelengths that our eyes can see, and trained human eyes can identify and understand features very quickly. But at that point you've got a false color picture.
"Images with red, green and blue spectral filters were combined to create this natural-color view, which is what the human eye would see if we were there at Saturn."
Comparing natural color and false color, it is clear to me that false color is more convenient for trying to pick out features in the picture.
In Earth this is powered mainly by the temperature differences caused by the Sun.
"Saturn has a very hot interior, reaching 11,700 °C at the core, and the planet radiates 2.5 times more energy into space than it receives from the Sun. Most of this extra energy is generated by the Kelvin–Helmholtz mechanism of slow gravitational compression, but this alone may not be sufficient to explain Saturn's heat production. An additional mechanism may be at play whereby Saturn generates some of its heat through the "raining out" of droplets of helium deep in its interior" [Wikipedia]
Strange -- the storm is both larger and smaller than I would have expected.