According to a story on CNN:

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.

http://www.cnn.com/2004/TECH/science....ap/index.html

So I pose the question to you all, what things could affect us enough to make the Earth keep time?

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Science--can't live without it, but it makes everything so much more boring.

I don't know, but can't help guessing. 8-[

Since we are talking very small changes (less than a second per year, or less than one part in about 60x60x24x356.25, since they are using a leap second as the smallest change, the true difference might actually be less than one second.) perhaps small effects could cause it. I'm thinking the influence of Venus or Jupiter, and how that changes from year to year due to the elliptical orbits. Or the Sun as it gets yanked around by Jupiter and actually orbits a spot slightly outside the photosphere.

Leap seconds are added because of slowing of the earth's rotation. The main effect is the tidal friction with the moon, and conservation of angular momentum means that the moon is receding from the earth (~ 4cm/year)

We haven't had a leap second in a few years because of other effects. Again, due to conservation of angular momentum. Weather patterns and atmospheric effects store angular momentum - a big spinning hurricane got its angular momentum from the earth - and there is some speculation that the heavier rainfall we've had in North America lately is redistributing water away from the equator, reducing the moment of inertia (which would tend to speed us up). Also, the oblateness has decresed somewhat, again reducing the moment of inertia; I'm not sure the time constant on this, but I thought it was from the polar icecaps melting, reducing the weight at the poles.

Part of the long gap between leap seconds is coincidence. The rate of slowdown decreased right about the last time a leap second was announced, and the difference between universal time (UTC) and earth rotation time (UT1) was (IIRC) about 0.3 seconds. (Usually the change is made when there is half second difference, so they did it a little early. But given the trend of the 1990's, waiting might have made the difference very large over the next year) So after the leap second was inserted, the difference was around -0.7 seconds. The diference is now approaching ~0.4 seconds, so we've slowed ~1.1 seconds in the interim.

The values are given here (look for UT1-UTC) in the IERS bulletin B.

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Wow did they ever give some BA! :roll:

The leap seconds haven't been added every year, and some were added at the end of June. It's due to the rotation rate slowing, not the orbit. And, as I already posted, we're still lagging. It's just that we add integral seconds, so the annual slowdown is currently below that resolution.

Dollars to donuts NIST got it right and the reporter screwed it up. They should ask the USNO to check their work.

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S. Baldrick

CNN are slow! I read this in a New Scientist story about two months ago!

Anyway, it's perplexing and will no doubt be very irritating in the future.

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No kidding!!! What do you say at this point?

Maybe I've missed something, but I thought that the adding of leap seconds is to account for the earth being precisely in the exact same spot in the orbit around the sun each year. Not slowing in rotation. Are these two issues linked, if so can some one enlighten me how one affects the other.

Thanks.

No, it has nothing to do with the year, it has to do with the Earth's rotation being just slightly slower than 24 hours because the rotation has slowed slightly since the length of the second was established.

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Everything I need to know I learned through Googling.

A little bit of a nit-pick here, but the Earth is never "... precisely in the exact same spot in the orbit around the sun...". The inclination, eccentricity and argument of perhelion (and maybe other elements of the orbit) are all perturbed by the other planets (especially Jupiter).

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Hey thanks to everyone, I was hoping to get some interesting possibilities on this because I hadn't really been aware of this phenomena before. I'm going to learn more about it, thanks again!

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Science--can't live without it, but it makes everything so much more boring.

Oh No! Planet X must being screwing up the Earth's orbit!!!!

So that's why we have'nt seen it yet then? Nancy didn't take iton account the erractic orbit of the earth!

Hmph! Next you'll be saying the space shuttle Columbia wasn't travelling at 18 times the speed of light when it broke apart.

Thanks swansont,

The CNN article did not make sense and has been misconstrued by many.

IIRC Leap Year was set up to not only add one extra day every four years but in addition to that we are supposed to add one extra day every 400 years. Whats up with that?

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My initials are on the moon, my name is on Mars and Earth is my planet of origin.

Nope, we add one day every four years but we remove three of those extra days every 400 years.

A 400 year period has 97 leap days, not 100 (or 101).

What's up with that is that 365 days a year is not enough, but 365.25 days a year is a little too much.

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SeanF

"Ask to understand, but don't challenge unless you have the knowledge."--NEOWatcher

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