[time-nuts] On Setting the Astronomical Time
Brooke Clarke
brooke at pacific.net
Sun Jun 10 17:38:00 EDT 2007
Hi Tom:
Couldn't find the key to reading that series 7 data, but did find this weekly
one: http://maia.usno.navy.mil/ser7/bulb.dat where there are column headings.
I think I'm seeing a 100 ms change in the last 3 months. On your Frequency
Stability plot (Max TI error) at 1 day the point is at 4.3E-3. Can you help me
understand this Allan plot? For example what can be said about the variation
in a one day period measurement? What is the slope and is it of a known noise
type?
I'd like to see a replot of the Log PSD graph where the X axis is days. That
way the peak at 4.133E-7 Hz would be more like 28 days and it would be
interesting to see where the others were.
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.precisionclock.com
Tom Van Baak wrote:
>>Setting your clock using GPS time, or with the known offset UTC is straight
>>forward. Offsetting UTC using the posted value of DUT1 gets you UTC1 good to
>>0.1 seconds. But that's 8 orders of magnitude away from the precision of UTC.
>
>
> Correct. See plots of earth accuracy and stability:
>
> http://www.leapsecond.com/museum/earth/
>
>
>>Is there some way to get TT to better than a tenth of a second, or is the earth
>>just too sloppy of a time keeper?
>
>
> Don't know for sure but the following may help you:
>
> http://maia.usno.navy.mil/
> http://www.iers.org/MainDisp.csl?pid=36-9
> http://maia.usno.navy.mil/ser7/finals.daily
> http://maia.usno.navy.mil/search/search.html
>
> My recollection is that using VLBI, UT1 is measured to
> sub-millisecond even microsecond levels.
>
> For example, yesterday UT1-UTC was -148.709 ms, today
> it is -149.996 ms, and tomorrow it will be -151.172 ms.
>
> /tvb
>
>
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