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Links for 2011-12-16

By drorzel on December 16, 2011.
  • Mellowmas | Popdose

    Your go-to guys for Christmas songs that DO suck...

  • The 20 Unhappiest People You Meet In The Comments Sections Of Year-End Lists : Monkey See : NPR

    7. The Self-Punisher. "I always hate your tastes, so I knew this would be a miserable and useless list before I decided to click on it and read the whole thing, and now I know I was right."

  • [1112.3004] Time in the 10,000-Year Clock

    The Long Now Foundation is building a mechanical clock that is designed to keep time for the next 10,000 years. The clock maintains its long-term accuracy by synchronizing to the Sun. The 10,000-Year Clock keeps track of five different types of time: Pendulum Time, Uncorrected Solar Time, Corrected Solar Time, Displayed Solar Time and Orrery Time. Pendulum Time is generated from the mechanical pendulum and adjusted according to the equation of time to produce Uncorrected Solar Time, which is in turn mechanically corrected by the Sun to create Corrected Solar Time. [...] This paper describes how the clock reckons time over the 10,000-year design lifetime, in particular how it reconciles the approximate Dynamical Time generated by its mechanical pendulum with the unpredictable rotation of the Earth.

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I'll have to check that last one out, especially considering the surprising, to me, use of the phrase "the unpredictable rotation of the Earth." Sure, I know about precession of the Earth's axis and that after 10,000 years it will point far from Polaris, but that is still "predictable." Enough noise, chaotic system effects in Earth-Moon relation, diddling by Venus and Mars, etc to make "unpredictable" worth saying?

The unpredictable rotation of the earth shows up in the fact that leap seconds are not inserted in a predictable fashion, recall that leap seconds are used to keep atomic time more or less in sync with solar time. In addition at the millisecond level big plate boundries by changing the moment of inertia of the earth slightly change the length of the day (See 2011 Japan quake). So it does depend on how accurate you want the clock to be over 10k years if sub second accuracy is desired, then you do have unpredictable rotation.