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Earth Travel On Time, Again
burgburgburg writes "The NY Times has an interesting article about a rather puzzling phenomena: for the fifth year in a row, the Earth's travel through space is right on time. The rate that the Earth travels through space has slowed ever so slightly for millenia. To compensate for this, since 1972, scientists have added a "leap second" at the end of each year. The problem: Since 1999, the Earth has been on time. The recognition of a need for a leap second was an unintended consequence of the invention of the atomic clock. Suggested reasons for the unexpected punctuality: the tides, weather and changes in the Earth's core."
OK so help me out here. Pardon the pun, but how on earth do they figure out that the earth is in the exact same position as it was a 'year' ago? Do they use the background of stars, or some other mechanism? How can they reduce the error in such a measurement so that they can be sure that a second has been 'lost'?
before the atomic clock the Earth was always on time.
It's good to know that the fudge factor isn't always necessary too, what with a leap second occurring every year at some point the slop has to be soaked up in the system. Were the powers that be planning to save up a leap day? If they had, where would they have put it? Frankly, just letting the extra second add onto the end of the year and letting 43200 years swap noon and midnight would have been an interesting social experiment. Assuming mankind hasn't destroyed itself by then, of course.
Now that we've established that the article mistakenly talked about annual rotation instead of daily rotation, it seems plausable that a smaller rotational intertia is to credit.
If the core settled down even a tiny bit, so heavier elements rested slightly closer to the core, the planet's axial rotation would speed up like an ice skater pulling in their arms.
Alternatively, the wearing down of mountains (buildings?) could have the same effect.
If the Earth is speeding up, perhaps the terrorists have already won.
Maybe that's why they're all carrying almanacs!
Kevin Fox
Just a thought and I know it's a miniscule mass by comparrison but we have sent some of Earth's mass to the Earth Sun L1 lagrange point which should slightly speed our orbit shouldn't it. The dates may coincide, it was launched in 95 but when it reached it's current orbit is unclear, some time towards the end of 1998 seems to be when some the instruments were first switched on. The on orbit dry mass of SOHO is 1350 kg.
So how about some back of the envelope calculations. How much mass at the Earth Sun L1 Lagrange point would it take to influence our orbit by one second per year?
I fully expect to be out by several orders of magnitude but can anyone answer?
No, and physicists physicists do admit that they are not perfect. They also have a plan to use pulsars to see just how imperfect the atomic clocks are.
One second per year is about 32 parts per billion. Changing the rotation of the Earth by that amount could be accomplished by moving approximately 8260 cubic miles of "Earth" (i.e., material with the same average density as the planet) from the equator to the poles. Moving the material to the mid-latitudes would require moving more material to create the same rotational speed change. For example, we could move about 28,000 cubic miles of Earth from the equator to the 45 degree latitude belt.
28,000 cubic miles of Earth seems like a lot until you spread it out around the Earth. If it were removed from a 1000 mile wide band around the equator, it would be only 6 feet thick. But this still seems like a lot to me because it would have to include changing the mean sea level by 6 feet too and this would be very detectable from orbiting altimeters such as TOPEX.
Hmmm.... Either I've done these calculations incorrectly, or a great deal of material has been moved, or somebody hasn't published their data on changes in the planet's shape.
Two wrongs don't make a right, but three lefts do.
which is the year that this week falls into, and according to ISO standards the 1st week of the new year is the week that contains the first thursdays in the new year.....
so welcome to week 1 of 2004
Other way round. If an ice cap melts, it will release water into the ocean. Generally speaking this is away from the axis of rotation (think: the geographical poles) Overall this should mean more mass further from the axis of rotation, hence slower rotation (conservation of momentum).
On the other hand, if we have the ice caps growing, there should be more mass closer to the axis of rotation, and through the same principal, the Earth should rotate faster.
Of course, I would tend to question how much of an affect the the melting or growth of ice caps has on the Earth. Consider that all of the ice in the world is a very small fraction of the total mass of the Earth. Technically, if all of it became concentrated at the poles or equator there may be a mesurable difference, but I seriously doubt it would amount to a 1 second difference in rotational speed throughout the year. But then, I've not bothered to do the math, so I could be wrong.
Necessity is the mother of invention.
Laziness is the father.
Tidal slowing is also magnitudes more important than anything you'd see from mountain building, earthquakes, or any other surface phenomenon. The earth is BIG. But tides take out a LOT of energy. Tides are the major reason the Earth's rotational period slows over geological time.
So right now, the Earth is not slowing; this must mean a shorter-acting phenomenon is supplying the rotational energy that the tides normally suck out. Again, there is only one thing big enough -- turbulence in the Earth's liquid core. Like the Earth itself the core is BIG so little changes in the fluid flow there can actually affect the Earth noticeably, and that flow is known to be chaotic -- because the magnetic field caused by that flow reverses periodically.
My money would be on a near-term magnetic field polarity reversal. Of course "near term" probably still means it will be ten thousand years before it's a problem. Sucks to be a man-made satellite, though, especially when flying over the South Atlantic, an area where the Earth's magnetic field is already starting to do strange things.
Brackets contain world's first nanosig, highly magnified:[.]
If the Earth is assumed to be a homogeneous sphere and the rotational axis is assumed to be the straight line passing through the north and south geographic poles, the moment of inertia of the Earth is I = MR^2 where M is the total mass of the Earth and R is its radius. The kinetic energy of a rotating Earth is given by K = 1/2 I w^2, where w is the angular velocity.
The energy associated with a 1-second shorter-than-expected day is equivalent to an extra 1.6e22 Joules of energy or 40 times the annual energy consumption of mankind (DoE 1999). The matlab script is here.
Michael.
Linux : Mac
Global dimming.
To slow down in its orbit, it has to get farther from the sun (otherwise it'd fall in closer to the sun, and it doesn't).
Light can exert pressure. That's the idea behind solar sails.
The sun has put out 3% less light per decade for the last 50 years. It may have been pushing the Earth farther out, and with less light now, it's not.
"I may be synthetic, but I'm not stupid." -- Bishop 341-B
It could be, of course, that there's actually some merit to Barry Setterfield's theory that the speed of light is not constant, but rather has been decreasing throughout history.
I recently had to implement code to convert terrestrial time (TT) to martian solar day (MSD). Some interesting tidbits in that research follow.
As you might guess, the extra days in leap years help keep our calendars synchronized with our actual position about the sun (heliocentric longitude). This is called intercalation, and the general rules governing the gregorian calendar cover 400 year periods. Other methods exist which are in a sense more "accurate," but less useful for predicting future dates. Fortunately, the earth is pretty regular in its movement around the sun.
The 0 degree mark for heliocentric longitude occurs at the vernal equinox, an event that can be easily determined from earth, and has been for centuries. In the Iranian calendar, the new year begins on the day of the vernal equinox. Since this event occurs later in the day each year, eventually an extra day must be added. Such calendars are based on observation rather than rule-based model and consequently are implicitly self-calibrating.
Leap seconds, as pointed out, are an entirely different beast, and are meant to shore up the discrepency between our actual rotation and the atomic clocks we use. The current offset is 22 seconds slow officially. Oddly enough, a NASA document from 1997 uses a value of 63 seconds as the offset between TT (terrestial time) and UTC (Greenwich Mean Time). Another from 2000 shows a 32.184 second offset from TT to TIA (atomic). It doesn't exactly correlate or add up, and I'm not precisely sure why that is. Perhaps someone could enlighten me on the matter.
Curiously, our leap years follow the mathematical model while our leap seconds follow the observation method of calibration. Consequently, you can determine the correct date in the future, but not the correct second.
-Hope
On a more serious note, maybe were seeing the Quantum Zeno effect on a global scale.
Something like this was actually tested with a large group of English schoolchildren, I believe; it made a small blip on the Richter scale, but certainly nothing noticable. Fun, but as the StraightDope article says, fairly silly and pointless, as the effects can be estimated fairly easily with some physics.
--- Bwah?
Which is why soldiers march out of step over bridges, interesting java applet showing why.