[time-nuts] Sidereal Time and Lady Heather.

Neville Michie namichie at gmail.com
Thu Dec 20 03:39:21 UTC 2012

I have just found out how to get sidereal time from Lady Heather.
(You put t=GMST in the command line, or alias target line, and 
the Lady comes up in Sidereal Time, ticking away in Sidereal seconds.)
(Also you can get LMST, LAST or GAST.)
Now, as a time nut, I have questions. How is a leap second handled?
Sidereal time is time observed by watching stars rather than the sun.
In fact it is the source of all knowledge about how fast our planet rotates,
and the basis for all our time scales.
A sidereal second is shorter than a physical second by about one second in six minutes,
so as to fit 366.25 sidereal days into the year of 365.25 solar days.
At the Vernal Equinox there is a situation where Solar seconds exactly match
the Sidereal second count, as zero, but how can a time nut know if this 
is in error? How accurate is it? In microseconds, nanoseconds?
My interest in Sidereal time is because I have two pendulum clocks mounted 
on the same brick wall and they interfere with each other.
By running one one sidereal time they are independent.
The problem is to get a source of sidereal time to measure the performance of the 
sidereal clock. It is no problem to divide 10 MHz down to sidereal seconds, but how do you synch.
the seconds? This is where the Lady helps. But I do not know how I can get really accurate 
seconds markers as convenient as the PPS from my Thunderbolt.
Neville Michie

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