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## December 9, 2008

Aren’t we lucky? We get a whole extra second this year.

The official Keepers of Time will add a leap second to the world’s master clocks (in the U.S., that’s the U.S. Naval Observatory) on December 31 at 23:59:59 UTC. This extra second is necessary because official time depends on two timescales—one that uses atomic clocks and another that is dependent on the earth’s rotation—and they don’t match up perfectly.

An atomic clock (Credit: NIST)

Atomic clocks (that’s a NIST atomic clock on the left) use the internal resonance frequency of atoms to measure time. The atoms generate pulses at regular intervals. Count the pulses, and you have a clock that is constant and very accurate.

Earth’s rotation is the traditional form of timekeeping. It is what defines a day. However, while we call a day 86,400 seconds, it is really 86,400.02 seconds. All those .02 seconds add up over time. In addition, the earth’s rotation is not constant (it has been slightly slowing, and 900 million years ago a day was only 18 of our hours). Time as we know it changes.

To remedy the discrepancy between the two timescales, extra time is periodically added to the atomic clock; this is the 24th leap second since 1972.

What time is it? Check the official time at time.gov

***

Posted By: Earth |

1. Me says:

I would argue that http://www.time.gov is the official time for the US Government run by folks at NIST, and the Naval Observatory is the official time for the military.

2. jan says:

second!ed

3. [...] your cesium clocks! The world’s official time keepers will be adding an extra “leap second” to the atomic clocks that keep “official” time at 23:59:59 UTC on December 31st. Yes, that means you get to sleep an extra second on the [...]

4. [...] always wanted more time in my day. Well according to NASA, the atomic clock people, and trusty science, if I can just live another 900 million years or so, I’ll have an extra 6 [...]

5. [...] Wednesday, December 10th, 2008 | Fun Tech On December 31, at 23:59:59 UTC, a leap second will be added to the official timekeeping clocks of the world. That’s because the timescales of atomic clocks and the earth’s rotation aren’t perfectly in synch. The last leap second was added in 2005. From Smithsonian: Earth’s rotation is the traditional form of timekeeping. It is what defines a day. However, while we call a day 86,400 seconds, it is really 86,400.02 seconds. All those .02 seconds add up over time. In addition, the earth’s rotation is not constant (it has been slightly slowing, and 900 million years ago a day was only 18 of our hours). Time as we know it changes. “Leap Second Added to Your Calendar“ [...]

6. [...] leap second will be added at 23:59:59 on December 31st (the last one was added in 2005). (via the Smithsonian) Comment (RSS) [...]

7. [...] Leap Second By annnee From the Smithsonian: [...]

8. [...] The Smithsonian: Earth’s rotation is the traditional form of timekeeping. It is what defines a day. However, [...]

9. Dave Bush says:

Two nerdish questions:
1/ What will the second be “known” as? 23:59:60 ?
2/ How do unix / linux systems, which keep the number of seconds since 1980, cope?

10. [...] Smithsonian.com (via Boing [...]

11. WILL JOHNS says:

This is science. Thank you all.

12. [...] news, dear reader – come the end of the month, you are getting an extra second of sleep or new-year celebration to enjoy Earth’s rotation is the traditional form of timekeeping. It is what defines a day. [...]

13. Thomas Vinciguerra says:

Greetings, all–

I am writing a piece for the Week in Review section of The New York Times and would appreciate hearing from anyone about how leap seconds unnerve, disrupt, inspire, or otherwise affect you. Please e-mail me at vinciguerra@theweekmagazine.com. Thank you!

–Tom Vinciguerra

14. Crazy26 says:

It involves rethinking the purpose and usage of our physical and virtual spaces. ,

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