Earth Travel On Time, Again 361
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."
It's Obvious (Score:5, Funny)
Re:It's Obvious (Score:2, Funny)
Damn, and I _just_ bought that stinking atomic clock so I could be the most precise on the block and I'm going to be off by a freaking second now! I couldn't be happy with the Bart Simpson watch from Burger King...
It's a tough life being an ubergeek.
Re:It's Obvious (Score:2)
Re:It's Obvious (Score:3, Interesting)
Re:It's Obvious (Score:5, Funny)
Re:It's Obvious (Score:5, Funny)
Re:It's Obvious (Score:4, Funny)
All wrong... (Score:5, Funny)
No. God just likes to screw with us.
The Core? (Score:4, Funny)
Re:All wrong... (Score:2, Insightful)
NO... God just likes to *fuck* with us.
Strange days (Score:4, Funny)
Well, everyone keeps saying the world moves faster these days. I guess they are right.
Full Text of Article (Score:3, Informative)
The Associated Press
BOULDER, Colo. Dec. 30 -- In a phenomenon that has scientists puzzled, the Earth is right on schedule for a fifth straight year. Experts agree that the rate at which the Earth travels through space has slowed ever so slightly for millennia. To make the world's official time agree with where the Earth actually is in space, scientists in 1972 started adding an extra "leap second" on the last day of the year.
For 28 years, scientists repeated the procedure. But in 1999, they discovered the Earth was no longer lagging behind.
At the National Institute for Science and Technology in Boulder, spokesman Fred McGehan said most scientists agree the Earth's orbit around the sun has been gradually slowing for millennia. But he said they don't have a good explanation for why it's suddenly on schedule.
Possible explanations include the tides, weather and changes in the Earth's core, he said.
The leap second was an unexpected consequence of the 1955 invention of the atomic clock, which use the electromagnetic radiation emanated by Cesium atoms to measure time. It is extremely reliable.
Atomic-based Coordinated Universal Time was implemented in 1972, superseding the astronomically determined Greenwich Mean Time.
Leap seconds can be a big deal, affecting everything from communication, navigation and air traffic control systems to the computers that link global financial markets.
Re:Full Text of Article (Score:2)
Maybe not as reliable as they thought?
Re:Full Text of Article (Score:4, Informative)
I got this value from the web site for the Time and Frequency division of NIST.
Re:Full Text of Article (Score:5, Insightful)
Let's do some math and see how big of a distance difference a leap second is. Rough estimate of 93 million miles on average for r. 2*pi*r = 584,309,935 miles for the circumference of the orbit -- assuming a circular orbit. 60*60*24*365.25 = 31557600 seconds on average per year. circumeference/seconds ~= 18 miles. Interesting. But hardly seems like much.
On time? (Score:3, Funny)
If we all run in one direction fast enough... (Score:4, Funny)
Let's do it!
Reminds me of the classic "if all Chinese jumped.. (Score:2)
Re:Reminds me of the classic "if all Chinese jumpe (Score:4, Interesting)
Re:Reminds me of the classic "if all Chinese jumpe (Score:2)
Regardless of that though, we can still pick up the ground noise of construction equipment completely on the otherside of campus.
Basically, anything hitting/movi
Maybe Cyclical? (Score:2)
Slightly more informative story (Score:5, Informative)
Next on Tom's Hardware - OC'ing the earth (Score:5, Funny)
Re:Next on Tom's Hardware - OC'ing the earth (Score:2)
Re:Next on Tom's Hardware - OC'ing the earth (Score:5, Funny)
clueless reporter (Score:5, Informative)
Re:clueless reporter (Score:3, Informative)
Intercalation, Calendar Calibration, Leap Seconds (Score:5, Interesting)
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 [wolfram.com], 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 [nasa.gov] from 1997 uses a value of 63 seconds as the offset between TT (terrestial time) and UTC (Greenwich Mean Time). Another [nasa.gov] 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
Lots of long words... (Score:5, Informative)
Each day, the sun rises and sets a little more to the north or little more to the south depending on the season. The days of the year where the sun reaches the most north or most south are solstices. When the sun crosses the middle, they're equinoxes. The official "spring equinox" is when the sun crosses the middle moving north. If you were to call that the first day of the year and beginning counting days, you will total up 365 days between equinoxes. After about four years of that though, you'll be off by one, so you'll need to add an extra day. This is called "intercalation."
One could make a rule to add an extra day every four years, but after 100 years or so, they would be foward one day too many. Skip the 100th year, and after 400 years, they'd be 1 day behind. The rule as it stands is every fourth year, except years ending in '00, plus every 400th year. Easy enough, but still not quite right.
Because the rule is not quite right, it will never be perfectly accurate. But if you follow the rule exactly, you can tell that January 1, 1601 was Monday for instance. You can also tell exactly how many days are between now and January 1, 2400 because you know which years are leap years.
The method of watching the sun and adding leap years as necessary is a great way to stay exactly on time, but really inconvenient if you need to predict exactly how every year will fall for the next 100 years or so.
Some people say so what, just live. Who cares if your birthday in 20 years is on a Tuesday. Tax collectors care... Money lenders care... Hallmark greeting cards cares... Calendar makers care... The Vatican cares... So we use the 400 year rule and call it the Gregorian Calendar. It works well enough.
As for TT, UT, UTC, TIA, ET, and a number of other time standards, well... the important thing is that we're now using very accurate clocks for counting seconds and we've determined that the earth does not spin all the way around in exactly 24 hours no matter how closely we've measured it. In fact, it had slowed down for awhile and now seems to have gotten back up to speed.
We determine the difference between the atomic clock and the earth by watching the stars go by, and after spinning, spinning, spinning, we watch the atomic clock and the sky, and if it doesn't come out just right, we assume the clocks are right and the earth is wrong. To make up the difference, we throw in an extra second once every 6 months as necessary. It hasn't been necessary since 1999 which was the crux of the article.
-Hope
It's Because the Moon is Gone (Score:5, Funny)
Physics for the rest of us (Score:5, Interesting)
Re:Physics for the rest of us (Score:5, Funny)
Duh. They use GPS.
Re:Physics for the rest of us (Score:5, Interesting)
I really hope that was sarcasm...
Why? GPS is great for this.
The length of each day has typically been 2-3 milliseconds longer than the day before. And the equatorial rotational velocity is 1670 km/hr. That means that at midnight, a point on the equator can be 90-130 cm away from where it was at midnight on the night before. After a week, the apparent motion is 7-10 meters, and after a year of this, you've moved 300-500 meters due to changes in rotational velocity. That's very noticeable.
The only thing that GPS directly measures is the exact location of a receiver relative to orbiting satellites. It doesn't know anything about the rotational position of the earth itself beneath your feet. So GPS has to be continually calibrated so that stationary receivers at fixed points on the earth's surface don't appear to be slowly drifting. The apparent position of a fixed reference receiver is uploaded to the satellites as a correction or else any stationary GPS receiver would show a very noticeable drift as the weeks went by and people would notice. It should be trivial to calculate the drift (and the necessity of a leap second) based on the necessary GPS corrections that had to be made during the year.
Re:Physics for the rest of us (Score:2, Interesting)
then by your logic in 5600 a day will be ~25 hours, which will leave us with 350 days a year, basically a bunch of februaries.
Re:Physics for the rest of us (Score:5, Informative)
Re:Physics for the rest of us (Score:3, Insightful)
You're assuming that the GPS satellites don't orbit at the exact same speed of the spin speed of the Earth; you're assuming that they in fact orbit a little faster than the Earth--that they orbit at a speed that is the exact same as the length of an ideal day.
I don't know which speed they orbit at, but it's not hard to think that they orbit exactly as fast as the Earth spins, so they don't need to be corrected as you mention. I would be interested to know which is true.
Re:Physics for the rest of us (Score:3, Informative)
Re:Physics for the rest of us (Score:2)
Re:Physics for the rest of us (Score:3, Informative)
Re:Physics for the rest of us (Score:3, Informative)
The "punctuality" they're referring to (and the "leap second" correction) have to do with the rotational speed (length of a day) of the earth, not its speed of revolution around the sun (which leap days correct for).
Re:Physics for the rest of us (Score:5, Informative)
For more info, browse here: http://hpiers.obspm.fr
Note: IAAA (I am an astronomer)
this sucks (Score:5, Funny)
Re:this sucks (Score:2)
I really could use that extra second of partying on new year's eve.
good point (Score:3, Funny)
Its even worse! (Score:2)
It's funny... (Score:3, Interesting)
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.
Re: It's funny... (Score:3, Funny)
> before the atomic clock the Earth was always on time.
Maybe we should set it 5 minutes fast, to allow a little extra time.
Re:It's funny... (Score:2)
> would they have put it?
Feb 29h, every four years?
The article is wrong, should be rotation (Score:5, Informative)
It is somewhat odd that the rotation has stopped slowing down. Some have speculated that as more and larger dams are built, creating large lakes far from the equator, that there's a net movement of mass closer to the axis -- causing the earth's rotation to increase in speed slightly.
On the other hand, global warming and the melting icecaps and warming oceans should move mass away from the axis, slowing down rotation.
It will be very interesting to see what happens over the next few years. I'd be curious if there's any relationship between the non-slowing of the earth's rotation and the decrease in the earth's magnetic field, mentioned in Slashdot a couple of weeks ago.
thad
Re:The article is wrong, should be rotation (Score:2)
Re:The article is wrong, should be rotation (Score:4, Interesting)
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.
Re:The article is wrong, should be rotation (Score:2)
If there are electric conductors around, then this is pretty obvious (from a physicists's POV :). You can try this by waving a magnet next to a nonmagnetic conductor (e.g. copper plate). The induced currents will tend to slow down the motion; if the magnetic field is weaker, the effect is less pronounced.
The only obvious co
Re:The article is wrong, should be rotation (Score:2)
Re:The article is wrong, should be rotation (Score:2)
Re:The article is wrong, should be rotation (Score:2)
Re:The article is wrong, should be rotation (Score:2)
We haven't put much stuff into space when you think about it. Certainly less than a million tons.
I'm guessing things l
Bad for United (Score:3, Funny)
Smaller Rotational Intertia? (Score:4, Interesting)
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!
0.1 second irregularity and Modern Time Standards (Score:5, Informative)
Re:0.1 second irregularity and Modern Time Standar (Score:4, Informative)
Heh (Score:2)
Damn! (Score:2, Redundant)
Ha Ha! FART Strikes Again (Score:3, Funny)
It's good to see our efforts to fuck with those atomic timekeeping twits succeeding!
here is a plot of the length of day (Score:4, Informative)
Do atomic clocks keep perfect time? (Score:5, Insightful)
IANAP, so perhaps a professional could explain why the atomic clocks must be right -- why a 32 ppb variation in them is impossible (i.e. would manifest itself in other more obvious ways).
Re:Do atomic clocks keep perfect time? (Score:3, Interesting)
Re:Do atomic clocks keep perfect time? (Score:3, Funny)
Terrific. So how do they check the pulsars? Or is it just turtles all the way down?
Belloc
Re:Do atomic clocks keep perfect time? (Score:3, Insightful)
Terrific. So how do they check the pulsars? Or is it just turtles all the way down?
Ultimately, it's *always* turtles all the way down when it comes to measurements. Sooner or later, you have to pick *something* and say, "This is my standard against which all things are measured." Sadly, we have (and can have) no truly absolute metrics of physical quantities against which to measure. Witness continual redefinitions of
its not perfect (Score:4, Informative)
Re:its not perfect (Score:2)
We're starting to measure things so exactly that any misunderstanding of the laws of physics should start yielding strange measurements. Suppose some prop
Re:Do atomic clocks keep perfect time? (Score:2, Informative)
We count seconds by coun
SOHO at the L1 Lagrange point? (Score:4, Interesting)
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?
Re:SOHO at the L1 Lagrange point? (Score:4, Informative)
T^2/a^3 = 4 * pi^2 / ( G * M),
where M is the mass of the Sun. Neglecting the gravitational attraction between the L1 mass and the earth (the L1 mass will be pulling the earth while its position remains constant since its pull towards earth is balance out by the pull toward the Sun), no change in Earth's mass will change its orbital period.
It's a conspiracy and Bush is responsible (Score:2, Funny)
Required Mass Movement for 1 sec/year (Score:3, Interesting)
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.
Re:Required Mass Movement for 1 sec/year (Score:2)
Re:Required Mass Movement for 1 sec/year (Score:2)
Already 1st week of 2004 (Score:3, Interesting)
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
It's all about tides and the core (Score:5, Interesting)
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.
Rotational Kinetic Energy (Score:3, Interesting)
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-forman.com].
Michael. [michael-forman.com]
A different God? (Score:5, Funny)
Another Possible Reason: (Score:2, Interesting)
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.
Re:Another Possible Reason: (Score:4, Informative)
First, I believe "Global Dimming" refers to less visible light reaching the planet's surface, independent of any variation in the Sun's output. This is thought to be due to an increase in airborne particulates. I'd have to check, but I think average solar output has been relatively constant over the last 50 years. If solar output dropped 15.9% in 50 years, (as your 3%/decade number suggests), we'd all be popsicles by now.
Second, I'm pretty sure that the Earth is too massive for reemission of solar radiation to generate enough thrust to cause a 1 second per year change in our orbit.
Third, if the suggested causes involve changes in the Earth's core, the article is probably referring to changes in the length of the day (the Earth's period of rotation), and not the length of the year. I can think of no way, short of ejection of significant mass at escape velocity, that the Earth's core could affect the planet's orbit in any way.
Holleywood Anyone? (Score:2)
"What? Nothing's wrong? But that can't be right! We've got to try and break it again!"
Other alternatives (Score:2, Interesting)
Re:Other alternatives (Score:2)
Earth orientation and the leap second (Score:4, Informative)
The dominant force behind the slowing is "tidal braking" from the moon. Basically, just as the moon exerts forces on the ocean, the ocean exerts forces on the moon. As a result, the moon is getting thrown gradually into higher and higher orbits because of force from the earth. The energy has to come from somewhere, and that somewhere is earth's rotational inertia.
Leap seconds were implemented as a result of branch of astronomy known as earth orientation. Basically, Earth Orientation is astronomy backwards. By looking at distant quasars constantly and monitoring atomic clocks, astronomers can see minute changes in earth's rotation. Quasars are observed because they are bright (in the radio part of the spectrum) and are far enough away that any physical motion over time would be negligible in the night sky. Correcting for leap seconds and other rotational issues like precession and nutation allows for the accurate functioning of GPS.
For more information, check out USNO's Earth orientation web site [navy.mil]
This is caused by global warming (Score:2)
Your SUV will be responsible for the n
Re: (Score:2)
Three Gorges Dam (Score:2)
Last month, New Scientist had an article about some GPS receivers having a bug related to the fact that 256 w
Re: (Score:2)
AOL CDs (Score:2)
And all that energy to matter conversion has increased the mass of the Earth. Which has increased its gravatational field, and the effects of everything elses field on it. Thus the earth is moving faster.
Or possibly space dust.
Actually (Score:2)
Re:No more Feb 29th? (Score:2)
Re:No more Feb 29th? (Score:2, Insightful)
Re:It's those d*mned Republicans! (Score:5, Funny)
Re:27 years. good statistical sample.... (Score:2)
The really scary thing with all that is that we are all going to die faster than expected! We now loose 1 second of existence every single year!!!!!!
Talk about a WMD! 5 sec lost * 5 billion people = 792 years of life destroyed in 5 years. It's like if Earth just killed 10 people. We should invade right now, before next year when all that will happen again.
Re:27 years. good statistical sample.... (Score:4, Funny)
We here at HaulmarkCards.com think about Dooms Day a lot. An awful lot. We've been trying to come up with some catchy verses and clever phrases for a new line of Dooms Day greeting/sympathy cards. We have three problems:
1. We're not sure exactly when Dooms Day will fall, so getting cards to retailers will be a logistical nightmare,2. We won't have much time afterward to spend the profits, and
3. Well, gosh! We just don't know how to "read" the public on this whole Dooms Day issue. We don't want to come off all tacky with something like, "Life was Swell, See you in Hell!" Then again "Best wishes for a Brighter Tomorrow" just doesn't give us that warm fuzzy glow that your granny has come to expect from Haulmark Cards.So we're asking you, the movers and shakers in the feel-good arena to offer up some suggestions. (In keeping with our policy of not paying for anything, these would be considered free-as-in-"free advice".)
TIARe:Well now... (Score:2)
Re:Leap second NOT every year... (Score:2)
No, they don't add (or subtract) a leap second every year; they do it whenever it's needed. And up until 1999, it had been needed every year or two, which is why it's a bit unusual that we haven't needed one in 5 years. See the complete list of leap seconds [navy.mil].