[ntp:questions] A Suggestion For Abolishing the Leap Second

Richard B. Gilbert rgilbert88 at comcast.net
Wed Jun 6 12:19:57 UTC 2007

Rob van der Putten wrote:
> Hi there
> jlevine wrote:
> <Cut>
>>    Yes, this idea was proposed some time ago, and it is currently
>> being
>> pushed pretty hard by the folks who need to plan for going to Mars.
>> Some
>> version of this idea will probably be adopted if/when space travel
>> becomes
>> more common. However, the idea that the rotating geoid (which is the
>> basis for the current SI defintion) is the center of the universe will
>> not
>> be easy to overcome.
> I was at high school in the 70's. At that time the definition of a 
> second wasn't linked to the earth's rotation at all.
> I still have a list of SI units somewhere, but I can't find find it 
> right now. However, I remember it having something to do with caesium 
> and a number of periods. I think this page uses a similar definition;
> http://www2.nict.go.jp/w/w114/next-generation/One-Second/One-Second-E.html
> BTW, the metre is defined in a similar way.
> <Cut>
> Regards,
> Rob

The original definition of a second was linked to the earth's rotation. 
  The original clock was the position of the sun in the sky!  As we 
became better at measuring time we learned that the earth's rotation is 
not particularly stable.

The cesium standard was adopted because it's the most stable thing we 
know of that can be used as a clock.  When you goose a cesium atom, it 
emits a five note "chord" in the microwave frequencies.  The middle note 
of that chord is the frequency that defines the second.  The technology 
is fantastic but the principle is much the same as we have used for 
measuring time for several centuries now; you design an oscillatory 
system such that when you add some energy you get that energy back in a 
very regular and predictable way. That's what a pendulum does, or a 
tuning fork or a slice of quartz crystal.

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