Designed by Danny Hillis, this solid metal prototype cam just arrived from the Long Now Foundation. She has a lovely, lithe and sinuous shape that emerges from the precise encoding of a fundamental future for Earth’s next 10,000 years.
In the design of a clock that will run for 10,000 years, the Long Now Foundation decided to use the passage of the sun as a feedback loop on the precision of the mechanical mechanism. Every year, the timing of the sun varies with the seasons; the solar clock repeats an annual pattern as the Earth, with its tilted axis of rotation, circles the Sun. But over thousands of years, it changes in two major ways:
1) the Earth’s rotation slows by 1.8 msec/day, and this adds up to a 16 hour error over 10,000 years.
2) the axis of rotation itself wobbles over a 26,000 cycle. In 8,000 years, we will have a new North Star — Deneb instead of Polaris.
So, the cam encodes both, the steady lengthening of the day and the cyclical shift of Earth’s axial angle.
Here is a writeup with more details and diagrams of the curves:
“The equation of time cam is a piece of the clock that converts solar noon to absolute noon. The cam represents 12,000 years of this equation, with one rotation per year. While the Clock’s day to day time-keeper is a slow pendulum, a solar synchronizer and cam like this one are needed to correct drift over the long haul. On any sunny day, when the sun lines up with this mechanism, light is focused onto a piece of nickel-titanium wire that reacts when heated by the sun. This motion is used to synchronize the Clock to solar noon. The synchronization is also modified slightly by the equation of time cam, which accounts for the +/- 15 minute difference of solar to absolute time. Due to meteor impacts and volcanic eruptions, the clock may not see the sun for several years, so it must be accurate enough to stay within the range of this correction during those times.”
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