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Author Topic: How do we define the second?  (Read 13977 times)

Offline Geezer

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How do we define the second?
« Reply #25 on: 28/03/2010 16:55:48 »
The Atmos is a good example of what I'm on about. (Actually, it's not really a good example because it does not keep very good time.) Anyway, its pendulum has a full one minute period. It rotates around a torsion spring - 30 secs in one direction, then 30 secs in the other direction.

So it goes tick.............................................tock................................................tick.......
 

Online Bored chemist

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How do we define the second?
« Reply #26 on: 28/03/2010 18:07:00 »
Incidentally, the NIST clock doesn't define time. No single clock does; they use an average of a group of clocks round the world.
 

Offline yor_on

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How do we define the second?
« Reply #27 on: 28/03/2010 18:36:20 »
I read that one should send it in for cleaning every twentieth year, The clock I mean, not times arrow. How old is it?
 

Offline Geezer

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« Reply #28 on: 28/03/2010 20:47:21 »
The Atmos? (Not the NIST I suppose  :D) It's been going strong for almost forty years. Never had to wind it up once!

Maybe a cleaning would help, but it's never really kept very good time. Mind you, some of that might just be perception. Because I never have to wind it up I hardly ever adjust it, so it's probably going for many months between adjustments.

BTW - for anyone that's wondering what we are yakking on about - http://www.atmosadam.com/

Probably more a piece of kinetic art that a great timepiece, but possibly a bit more interesting than a quartz digital clock!
 

Offline gem

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« Reply #29 on: 28/03/2010 22:22:22 »
The ATMOS as manufactured by Jaeger LeCoultre, the makers of world famous Reverso wrist watches, is a time piece that for generations has represented the wonders of science, technology and remarkable Swiss craftsmanship. Possessing one signifies belonging to an exclusive group of world leaders, famous celebrities, business professionals, and, put more simply, people with exquisite taste.

so geezer to which category do you most identify with?

on a serious note on the fractions of a solar day something that soul surfer touched on the leap seconds that are used are not all in one direction [I will exspand on later but will have to go in new theorys]
 

Offline Geezer

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How do we define the second?
« Reply #30 on: 28/03/2010 22:31:34 »

so geezer to which category do you most identify with?


Gosh! It's hard to say really. Can I only select one?

(It's one of the rather basic ones from the early 70's. Wedding present from my Mum and Dad.)
 

Offline gem

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« Reply #31 on: 28/03/2010 22:40:16 »
On behalf of your wife i think it must have been a person with exquisite taste.
 

Offline Geezer

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« Reply #32 on: 28/03/2010 23:16:51 »
It's not etirely clear Mrs G would agree with that statement  ;D
 

Offline yor_on

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« Reply #33 on: 29/03/2010 03:48:06 »
Ah your mum and dad found a excellent present for you both my man. I read that you can expect it to work for hundred of years :) Up to a thousand if lucky, and cleaning it, nota bene. I was looking for one here in Sweden (curiosity:) But there were none for sale. People that have them seems to want to keep them too.



 

Offline syhprum

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« Reply #34 on: 29/03/2010 07:34:27 »
One of the characteristics of clocks seems to be the higher the frequency of the basic oscillator the more accurate they are.
The 'Atmos' that Geezer uses has a torsion oscillator working at .033 Hz and is incredibly inaccurate where as most clocks today use 32768 Hz crystals and are pretty accurate while really stable clocks use microwave Cesium transitions.
The only exceptions that I can think of are gravitational ones based on the rotation of planets etc that use periods of about .000078 Hz and quite accurate. 
 

Offline LeeE

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« Reply #35 on: 29/03/2010 09:15:44 »
Quote
The only exceptions that I can think of are gravitational ones based on the rotation of planets etc that use periods of about .000078 Hz and quite accurate.

Heh! - I hadn't thought of that.  Hmm... Jupiter, in its orbit, would make a pretty massive oscillator, and if I've done my maths right, it would have a frequency of 2.672026246839270841e-09 Hz.  Moving even further out, to use Neptune, would result in a frequency of 1.922923089229784694e-10 Hz  ;D
 

Offline Geezer

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« Reply #36 on: 29/03/2010 17:16:59 »
Good points! Funny thing about the frequency. I wonder if there is some intrinsic law at work there, or is it more a case of the technology?

Of course, it gets even more complicated, because, the second is really defined by a rather large and very slow pendulum called the Earth  ;D. The SI second is a very good thing for science and engineering of course, but we always end up having to finagle things to line up with our one year pendulum.
« Last Edit: 29/03/2010 18:29:44 by Geezer »
 

Offline yor_on

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« Reply #37 on: 29/03/2010 19:58:09 »
Syhprum you sure have a way with thinking :)
That was a very cool idea.

Now we just wait for LeeE to finish it. I'm putting myself first in the queue for buying one, when you finished your work Lee :)

A stellar watch :)
A very sweet idea.

(or is it a planetary?)
 

Offline Geezer

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« Reply #38 on: 29/03/2010 20:07:48 »
I'm pretty sure I could rig up something that regularly adjusted the Atmos to keep it reasonably in sync with the RF time signal from Boulder CO, but it might tend to screw up the aesthetics, don't you think?

Synchronizing it with Neptune might be a wee bit trickier.
« Last Edit: 29/03/2010 20:18:51 by Geezer »
 

Offline yor_on

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« Reply #39 on: 29/03/2010 21:03:24 »
Why stop at Neptune?
 

Offline Geezer

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« Reply #40 on: 29/03/2010 22:55:28 »
I know what your trying to do. You're trying to get me to say that Pluto is not a planet so we have to debate that for the next ten years!

Ho no! I'm not falling for that one.  ;D
 

Offline LeeE

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How do we define the second?
« Reply #41 on: 30/03/2010 08:56:33 »
Actually, a solar orbit clock wouldn't be much good for measuring durations less than the orbital period because the orbits are all slightly eccentric.
 

Offline syhprum

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How do we define the second?
« Reply #42 on: 01/04/2010 19:29:56 »
Before the development of the marine chronometer by Harrison et al the chief source of timekeeping for navigation was the passage of the Moon thru the star field.
As Lee points out the eccentricity of the orbit causes a lot of problems and prediction tables had to be prepared so that adjustments could be made.
When I suggested that large bodies made good time keepers I had in mind their rotational periods not of course their orbital time about other bodies.   
 

Offline Geezer

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How do we define the second?
« Reply #43 on: 01/04/2010 20:00:12 »
Before the development of the marine chronometer by Harrison et al the chief source of timekeeping for navigation was the passage of the Moon thru the star field.
As Lee points out the eccentricity of the orbit causes a lot of problems and prediction tables had to be prepared so that adjustments could be made.
When I suggested that large bodies made good time keepers I had in mind their rotational periods not of course their orbital time about other bodies.   

So here's the thing. Does the second define the period of the "Earth pendulum", or does the period of the "Earth pendulum" define the second?

(I think it's really the latter, but I suspect I'll get some heat for saying that!)

 

Offline LeeE

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« Reply #44 on: 01/04/2010 23:59:22 »
It's the former: as I thought we'd already agreed, the second is defined by the "transition between the two hyperfine levels of the ground state of the caesium 133 atom" and most definitely not by the Earth's rotational and/or orbital periods (which are subject to stuff like earthquakes etc.).

The Earth's rotational and orbital periods are defined in terms of the second.
 

Offline Geezer

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« Reply #45 on: 02/04/2010 01:17:32 »
It's the former: as I thought we'd already agreed, the second is defined by the "transition between the two hyperfine levels of the ground state of the caesium 133 atom" and most definitely not by the Earth's rotational and/or orbital periods (which are subject to stuff like earthquakes etc.).

The Earth's rotational and orbital periods are defined in terms of the second.

As I said, I'll probably get some heat  ;D

As you say, today, the second is defined in terms of atomic activity. However, originally the second was a subdivision of the period of Earth's orbit. We still have to make adjustments to reconcile the two.
 

Offline syhprum

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« Reply #46 on: 03/04/2010 05:35:14 »
Geezer

No the second was never defined with reference to the Earths orbital time it was defined with reference to the Earths rotational period relative to the distant stars.
 

Offline Geezer

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How do we define the second?
« Reply #47 on: 03/04/2010 05:49:13 »
Geezer

No the second was never defined with reference to the Earths orbital time it was defined with reference to the Earths rotational period relative to the distant stars.

Thanks Syhprum. If I understand correctly, that means the second is a fraction of the time it takes for the Earth to rotate 360 degrees on its axis.

Who came up with the concept of the second first?
 

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