[PLUG] Calculating the correct UTC time

[Mike Chirico <mchirico@comcast.net>]

UTC sometimes has 61 seconds in a minute. These seconds
are introduced so that (UTC - UT1) is never off by over
0.9 seconds.  UT1 is the mean number of seconds in a day, which
is increasing because of the tidal friction from the sun and moon.

This is not to be confused with the revolution of the earth around
the sun (which is a mean tropical year of 365.2422). This revolution
of the earth around the sun is less variable. 

Since it's easier to adjust the atomic clocks, verses adjusting the
rotation of the earth, leap seconds were introduced.  Some systems,
GPS (time of Global Positioning System satellites), do not adjust for
leap seconds ... that is why there is a difference of about 18 seconds
between GPS and UTC.

The UTC time is important for astronomical observations - everything is
relative to the position of the observer. Linux and most operating systems
rely on UTC.  This data is collected here - which shows the difference 
between UTC and UT1.  

ftp://maia.usno.navy.mil/ser7/ser7.dat


So, this means there is no way to calculate the correct time, the time
that one's Linux computer, that is correctly set with NTP, exactly 5
years into the future.  One has no way of knowing how many leap seconds
need to be added.  Reference the following for a graph:
http://www.ucolick.org/~sla/leapsecs/dutc.html#atomic.png

It also means before the time of telescopes, we have no way of figuring the
time down to the second. The mean length of the day was much shorter 1000 and
2000 years ago.

My question is -- does anyone know of any open source packages that will
give the correct UTC time, both going forward with the best approximation of
when leap seconds will be added, plus, the exact time for all seconds, going
back to 1972?  By the way is data is available at the following link:
ftp://maia.usno.navy.mil/ser7/tai-utc.dat

I have Steffen Beyer's DateCal, which does a pretty good job of calculating
the Julian Date.  But before making changes, there must be something else
out there, since I assume astronomers must make use of this data.  Any help
in the right direction would be greatly appreciated.

Thanks,

Mike Chirico
   

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