[ale] OT ntp - leap second - how many knew what this was 3 weeks ago

Michael H. Warfield mhw at WittsEnd.com
Wed Jul 4 12:31:04 EDT 2012


On Wed, 2012-07-04 at 11:34 -0400, Michael H. Warfield wrote:
> On Wed, 2012-07-04 at 10:39 -0400, Ron Frazier (ALE) wrote:
> > Hi all,
> 
> > Around the beginning of this year, I was doing quite a bit of research
> > into ntp and gps and eventually set up my own gps based ntp time
> > server in both Linux and Windows. At the end of June, a leap second
> > was inserted into the time sequences of the clocks on Earth. For those
> > that may not know what that is, the atomic clocks are coordinated with
> > the earth's rotation, so, for example, when the clock says noon, the
> > sun is always roughly overhead. However, the earth's rotation speeds
> > up and slows down at times. So,sometimes, we have to tweak the clocks
> > to match the earth again. At the end of June, an extra second was
> > inserted. Normally, the seconds go 58 ... 59 ... 00. This time, they
> > went 58 ... 59 ... 60 ... 00. As it turns out, this crashed a number
> > of servers.
> 
> It crashed (really just interfered with) a few someone high profile
> servers.  The vast majority were unaffected.
> 
> > I find this very interesting, and somewhat scary as a potential
> > programmer. Since I'm thinking of learning programming again, and
> > since I have an interest in timekeeping, I have considered writing a
> > world clock program etc., to show the time in different parts of the
> > world. However, prior to my NTP research, I never knew about the leap
> > second. So, there would have been a good possibility, had I written
> > the program prior to this year, that my program would have crashed as
> > well.
> 
> > So, my question is, how many of you knew about leap seconds prior to
> > this incidence of it and prior to my describing it. If you were
> > writing a clock program, would you have known to account for this?
> 
> Known about it for decades.  Just about anyone involved with time and
> timezones and such, particularly if they have a strong interest in
> astronomy, should know about them and the difference between UTC and UT1
> (astronomical time).  Normally, though, it's on the 1st of the year they
> make that adjustment.  I was surprised they were doing it when they did
> this year.  They must have had been too close to their critical boundary
> and realized they wouldn't make it to Dec 31 before it was too far out.
> Astronomers tend to be a pissy lot.
> 
> I think the first time I remember about "leap seconds" I actually
> listened to WWV out of Boulder, probably on 10MHz which generally gave
> me the best reception up in Michigan on a long-wire antenna, for it.
> One December 31 night I listened and counted down the seconds as they
> ticked through 60 and ticked 61 before the top of the minute chime.
> This was lllooonnnggg before GPS and the Internet.  This would have been
> back in the 70's.

> Interesting thing about the time signals from WWV (Boulder) and WWVH
> (Hawaii) is that they also indicate the .1 seconds offset between UCT
> and UT1 as well.  It will tick off the 1/10 second lead or lag by
> "double ticks" on the seconds before and after the minute mark.  Up to a
> second or so lead could be heard with the double ticks after the minute
> and up to a second or so lag could be heard by ticks before the minute.
> Obviously, you could tick off up to several seconds plus or minus using
> that method but they don't.  When it approaches around one half second
> to one full second is when they would have to kick in or,
> (theoretically) pull out a second.  When they throw in that leap second
> you can hear them go from +.5 to -.5 from one minute to the next as
> well.  I don't know that I recall them pulling a second, though it is
> possible.  The drift is not linear and varies subtly over the years as
> the earth's axis wobbles slightly.

Corrected details on UTC vs UT1 and leap seconds...

http://www.nist.gov/pml/div688/grp40/wwv_format.cfm

Under UT1 Time Corrections, second paragraph...

== 
You can obtain UT1 from the time signals broadcast by WWV and WWVH. UT1
is available at two levels of accuracy. If you need UT1 with an
uncertainty of 1 s, you can simply use UTC, since the two time scales
are always kept within 0.9 s of each other. Occasional corrections of
exactly 1 s are inserted into the UTC time scale to keep the two time
scales in agreement. These corrections, called leap seconds, are
coordinated under international agreement by the International Earth
Rotation Service. Leap seconds can be either positive or negative, but
so far, only positive leap seconds have been needed. A positive leap
second is normally added every 1 or 2 years, usually on June 30 or
December 31.
== 

So, it's +- .9 seconds before an adjustment and it will be on June 30 or
December 31.  There have been 25 adjustments, always positive, to date
with the first two both back in 1972.

Now, I puzzle you a puzzle.  If, as they say, this happens once every
year or two, why did these sites suddenly crash this time and not the
last time (which was just a few years ago on Dec 31 2008)?  Did these
sites not exist 3-1/2 years ago?  Plausible, I suppose.  Just as
plausible that some chump introduced a bug along the way.  :-P

> There were some proposals put out recently (again) to do away with "leap
> seconds" entirely and shift back to astronomical time as the standard
> and compensate in "atomic time" by just letting it drift, but that
> discussion pops up every couple of years and then goes nowhere.  When I
> heard about it again, yearly this year, they sounded seriously in
> earnest about changing our time standard but then it dropped out of the
> news yet again.

Proposal to do away with leap seconds has been postponed.  They kicked
the can down the road to the World Radio Conference in 2015.  Plus I had
it backwards.  The idea is to do away with leap seconds and let the
astronomers fend for themselves (letting the drift exceed .9 seconds).
Needless to say, that pissy lot are not happy with the idea.

http://en.wikipedia.org/wiki/Leap_second

That article has some nice points in dealing with the leap seconds.

> > Sincerely,
> 
> > Ron
> 
> Regards,
> Mike
> 
> > --
> > 
> > Sent from my Android Acer A500 tablet with bluetooth keyboard and K-9 Mail.
> > Please excuse my potential brevity.
> > 
> > (To whom it may concern. My email address has changed. Replying to former
> > messages prior to 03/31/12 with my personal address will go to the wrong
> > address. Please send all personal correspondence to the new address.)
> > 
> > (PS - If you email me and don't get a quick response, you might want to
> > call on the phone. I get about 300 emails per day from alternate energy
> > mailing lists and such. I don't always see new email messages very quickly.)
> > 
> > Ron Frazier
> > 770-205-9422 (O) Leave a message.
> > linuxdude AT techstarship.com
> > 
> > _______________________________________________
> > Ale mailing list
> > Ale at ale.org
> > http://mail.ale.org/mailman/listinfo/ale
> > See JOBS, ANNOUNCE and SCHOOLS lists at
> > http://mail.ale.org/mailman/listinfo
> 

-- 
Michael H. Warfield (AI4NB) | (770) 985-6132 |  mhw at WittsEnd.com
   /\/\|=mhw=|\/\/          | (678) 463-0932 |  http://www.wittsend.com/mhw/
   NIC whois: MHW9          | An optimist believes we live in the best of all
 PGP Key: 0x674627FF        | possible worlds.  A pessimist is sure of it!
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 482 bytes
Desc: This is a digitally signed message part
Url : http://mail.ale.org/pipermail/ale/attachments/20120704/b23bcf82/attachment.bin 


More information about the Ale mailing list