[time-nuts] Determination of the placement of the first pps

J. Forster jfor at quikus.com
Mon Jan 23 12:45:30 EST 2012


The fundamental problem is our system of units is not defined rationally.
What is universal about a meter or a second or a kilogram? Nothing!

If you were suddenly transported elsewhere in the universe bareassed,
could you replicate the standards we use?

If you lived on another planet, perhaps Klingon, would the second make any
sense?

This problem was faced maybe 50 years ago by the SETI folks. How do you
know what frequency an ET might be transmitting on? 1.000000000 GHz? And
if their unit of time is different, what then?

The only purpose of a transite instrument is to determine the relationship
between two, essentially arbitrary, and essentially unrelated time scales.

YMMV,

-John

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



> Hi
>
> I think the key point is that they are still using a gizmo made in the
> 1800's and it works "good enough". There are certainly better ways you
> could
> set it up today, but they use what they have.
>
> Bob
>
> -----Original Message-----
> From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
> Behalf Of Attila Kinali
> Sent: Monday, January 23, 2012 11:57 AM
> To: Discussion of precise time and frequency measurement
> Subject: Re: [time-nuts] Determination of the placement of the first pps
>
> On Mon, 23 Jan 2012 08:43:01 -0800
> Chris Albertson <albertson.chris at gmail.com> wrote:
>
>
>>
>> It's a transit telescope (one that looks up at the local meridian) but
>> they don't use the sun.  It looks at every start that passes in front
>> of it, thousands of them every night.  Then they reduce the data by
>> knowing the exact location of every star and the time is pasted
>> directly overhead.  This way they get thousands of measurements every
>> day.  If you use the Sun you get only one per day.
>
> Not to mention the solar noon varies by +/- 15min over the year
> (don't ask me how this is called...old knowledge from my high school days)
>
>> A transit solar scope would be a fun Time Nut project.  I think a
>> primitive one would be a photo cell and a length of wire.  Measure the
>> time when the shadow of the wire sweeps across the cell.  The trouble
>> is that with only one measurements per day it would time years to
>> build up uSec level data.    Even if you placed the cell behind a pin
>> hold mask and used a fine piano wire, shades and baffles and so on.
>
> Why not use a real telescope with a CCD and get more reliable data?
> A friend of mine is into hobby astronomy and uses special type CCDs
> for it (ie not even the hobbist look directly into the telescope anymore).
> I guess it shouldn't be too hard to rig up some gear, a PC that collects
> the pictures at precise instances and calculates the ephemeris time to
> UTC/GPS difference. The only issue is that you'd need to put that
> telescope
> somewhere with little light polution, otherwise you'll only get the
> brightest
> stars.
>
>
> 				Attila Kinali
>
> --
> The trouble with you, Shev, is you don't say anything until you've saved
> up a whole truckload of damned heavy brick arguments and then you dump
> them all out and never look at the bleeding body mangled beneath the heap
> 		-- Tirin, The Dispossessed, U. Le Guin
>
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