Leap Second to be Added to Clock

Saturday night will be just a little longer than usual, as a "leap second" will be added to the clock. That adjustment comes around every once in a while to keep our clocks on track with the sun.

A leap second has been scheduled for June 30, 2012. A leap second is an adjustment to the atomic clock-based Coordinated Universal Time (UTC) to bring it more closely in line with Universal Time (UT), which is based on the rotation of the earth. The two time standards do not agree because the earth’s rotation is ever so gradually and unpredictably slowing down.

I don't know about you, but "unpredictably slowing down" doesn't sound all that reassuring. But no far, I don't see any scientists and chronologists panicking. Link

(Image credit: Flickr user Alan Cleaver)

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Are you sure the Earths slow deceleration is unpredictable? I thought it has been calculated. The Moon's gravity slows Earths rotation by about 2 m/s every 100 years.

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I'm not at all sure, but that's what it says at the link. This stuff is way beyond me!

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It is unpredictable as it can also be affected by remodeling in the Earth's crust that alters the planet's mass distribution. These change the planet's rotational inertia which can speed up or slow down rotation slightly.