[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 

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

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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