[time-nuts] Why 9,192,631,770 ??

[Don Lewis]

Thanks, all ...this thread has helped me a lot.

It reinforces my beliefs of what a 'second' is ...what we were taught from
day 1 in school:

One solar day/86,400 (A 'solar' day being an earth solar day)
  
So as I try to rationalize all this in my mind, ...a good cesium unit is
just a sophisticated 'counter'.  The counter gate is just the solar day.

It's interesting to note (to ask?): When did someone get smart enough to
start measuring 1/86thousthanth of a day, ....That starts needing a standard
in itself.

-Don
Austin, TX

(When we go to Mars we'll need a few more cesium 'counts' , btw.)








----------------------------------------------------------


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf of J. Forster
Sent: Wednesday, May 09, 2012 11:31 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Why 9,192,631,770 ??

This issue came up when I was involved in SETI work. One big question was
"How do you know what frequency to listen at?"

Any earth-centric system is essentially arbitrary. There is nothing
'universal' about the Meter, Kilogram, or Second. (or any of their
equivalents in other systems of units).

And, all other units are derived from those fundamental units.

The only things, thought to be anything like universal, are fundamental
properties of atoms, like hyperfine transitions. Hence the defined second.

-John

=================



>
>>It is interesting that the leap seconds correction is always a positive
>> number.
>
> But less so now than 40 years ago according to:
> http://en.wikipedia.org/wiki/Leap_second
> So does that mean the earth is speeding up?  Maybe the cause is all the
> DARK ENERGY out there speeding everything up  :)
>
>
> A good and simple explanation of why they CHOOSE to make the second wrong
> is at:.
> http://www.nist.gov/pml/div688/leapseconds.cfm
>
> "There are two main reasons that cause leap seconds to occur.
> The first is that the duration of the atomic second was measured and
> defined by comparing cesium clocks to the Ephemeris Time (ET) scale, an
> obsolete time scale that defined the second as a fraction of the tropical
> year.  The duration of the ephemeris second was slightly shorter than the
> mean solar second and this characteristic was passed along to the atomic
> second.
> If the atomic second had been defined with respect to the mean solar
> second, it is likely that leap seconds would have been required much less
> frequently.
> The second reason for leap seconds is that the speed of the Earth's
> rotation is not constant.  It sometimes speeds up, and sometimes slows
> down,
> but when averaged over long intervals the trend indicates that it is
> gradually slowing.
> This gradual decrease in the rotational rate is causing the duration of
> the mean solar second to gradually increase with respect to the atomic
> second."
>
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