
No leap second will be added tonight - ColinWright
http://hpiers.obspm.fr/iers/bul/bulc/bulletinc.dat
======
srean
Poul-Henning Kamp's article "The One-second War (What Time Will You Die?)" [0]
is a great read. I certainly was unaware of the background, and how it can
affect actual systems.

[0]
[http://queue.acm.org/detail.cfm?id=1967009](http://queue.acm.org/detail.cfm?id=1967009)

~~~
deisner
Another great article on the topic, from American Scientist: "The Future of
Time: UTC and the Leap Second", available either from the magazine (behind
paywall):
[http://www.americanscientist.org/issues/feature/2011/4/the-f...](http://www.americanscientist.org/issues/feature/2011/4/the-
future-of-time-utc-and-the-leap-second/1) or on arXiv.org:
[http://arxiv.org/ftp/arxiv/papers/1106/1106.3141.pdf](http://arxiv.org/ftp/arxiv/papers/1106/1106.3141.pdf)
.

~~~
JadeNB
I'm not sure about the etiquette of arXiv links, but I have always preferred
being taken to the abstract, so that I can decide whether I want the paper:
[http://arxiv.org/abs/1106.3141](http://arxiv.org/abs/1106.3141). It's just a
click from there to the PDF (or other formats, if there are any).

------
gee_totes
I did not know that the speed of the Earth's rotation is affected by
earthquakes[0] and the weather[1], and thus the need for a leap second.

0:[http://en.wikipedia.org/wiki/Earth's_rotation#Changes_in_rot...](http://en.wikipedia.org/wiki/Earth's_rotation#Changes_in_rotation)

1:[http://en.wikipedia.org/wiki/Fluctuations_in_the_length_of_d...](http://en.wikipedia.org/wiki/Fluctuations_in_the_length_of_day)

~~~
datenwolf
Another important effect is the transfer of angular momentum of the Earth to
orbital momentum of the Moon by tidal forces.

------
bryanh
A fun, related read on what Google does when they must introduce a leap second
to their fleet of servers: [http://googleblog.blogspot.com/2011/09/time-
technology-and-l...](http://googleblog.blogspot.com/2011/09/time-technology-
and-leaping-seconds.html)

~~~
anon4
Interesting that they don't keep them in TAI. I would expect having the hw
clock of the PC be in TAI to be the most pain-free option. Or is that not
possible?

~~~
lmm
There's very little OS- or application-level support for it. Adding support
would probably take more effort than convincing governments to abolish leap
seconds.

~~~
gpvos
Abolishing leap seconds is a terrible option. In a few thousand years' time,
official time will have shifted noticeably from solar time, which is not
acceptable to society. It's just code. We should draw up a transition plan to
using TAI in computers.

~~~
giovannibajo1
In software engineering, batching changes is almost always good, because once
you look at some code, migrate a database, profile a section, it's very
convenient (economically speaking) to flush any similar task of reasonable
size in the same area.

Leap seconds are the opposite; they try to spread the time changes as much as
possible, adding single seconds whenever possible. If they went for minutes
instead of seconds, it's possible that a leap minute would be added once per
century (or less); entire generations of computer scientists would not have to
deal with it and Google could come and go (for good) without ever having to
shift their clocks.

Humans don't really care if you add a minute at midnight of new years eve, in
fact, it could even be fun to countdown twice for the new year, but for
computers it would be a massive saving of engineering effort.

~~~
gpvos
You have valid points there. But in that case, I think using the existing
system of time zones (i.e., leap hours) may be a better idea than introducing
a somewhat new mechanism of leap minutes. Also because leap seconds are
accelerating, in a few thousand years' time we'd have leap minutes every
month, so it's better to postpone any problems even further into the future.

------
derefr
A great little bit of fiction, if you want to revel in the sense of how weird
it is that our measures of time are effectively "by fiat":
[http://slatestarcodex.com/2013/11/03/the-witching-
hour/](http://slatestarcodex.com/2013/11/03/the-witching-hour/)

~~~
marcosdumay
Dates are decided by fiat (always with a bias of keeping astronomical events
at sync), timespan is very well defined and does not change at all.

~~~
aaronblohowiak
Elapsed time does not change, but the current time is. We measure elapsed time
based on a presumably stable measure -- the vibration of cesium under exposure
to microwaves -- but we want 'now' to be based on the earth's rotation and
location with respect to the sun, which is gradually decaying. Atomic vs
Astronomical time.

------
joerick
One thing I've never understood is why we have to shift computer time to match
celestial bodies. We have a definition of the second (in terms of a Caesium
atom) and we've agreed on the epoch, so why can't we just leave it be?

I understand that if we want to know the time in 'human language' (in terms of
the earth's rotation around the sun, and the specific timezone that we're in)
we then have to apply these corrections. Surely that's simpler than every
timekeeping device on the planet having to adjust a second? Electronic devices
are much more likely to be sensitive to a second's difference than us humans
are.

~~~
gnur
[https://news.ycombinator.com/item?id=7965881](https://news.ycombinator.com/item?id=7965881)
Sums it up pretty well.

------
johnnymonster
I think more of the internet should be displayed in plain text like this!

~~~
TazeTSchnitzel
One of the nicer things about RFCs.

------
kintamanimatt
Is there a reason why a leap second wouldn't be added if the difference
between TAI and UTC is 35s?

~~~
taejo
Leap seconds are added to UTC to keep it within one second of UT1; the drift
from TAI is unbounded.

In TAI, each second is the same length, and each day lasts the same number of
seconds; UT1 is (conceptually, approximately) the solar time in Greenwich, so
the length of seconds depends on the position of the earth; UTC has seconds of
fixed length, like TAI, but occasionally has more or (potentially) fewer
seconds in a day, to keep synch with UT1.

If you used TAI, eventually the sun would not be overhead at noon -- and after
many millennia, the sun would be up during the "night" and down during the
"day" (after around 70 000 years if leap seconds continue to be added at the
same rate, but the whole point is that they aren't -- at the moment they seem
to be accelerating).

~~~
ggreer
Thank you for explaining the various time standards concisely. I think a lot
of people don't know about TAI, but would prefer it to UTC if they did. Leap
second handling has been responsible for some pretty serious software bugs.
It's so bad that Google doesn't use them internally.

I think it makes the most sense for computers to use TAI internally, and have
UTC as a time zone on top of that. Whenever there's a leap second, just push
out a TZ update. Most applications don't have special code for time zone
updates, which means a lower likelihood of bugs.

Using TAI internally would have another advantage: Computers with GPS
receivers could just add 19 seconds to GPS time to get a very accurate TAI.
(GPS time is defined to be 19 seconds behind TAI. That was UTC in 1980.)

~~~
gpvos
Using TAI internally would be much better than what we have now. But another
problem is that leap seconds are only announced 6 months in advance, which is
not enough to update all computing devices (including embedded ones, etc.).
See Poul Henning Kamp's article linked elsewhere in this discussion for an
idea on how to address that.

------
cgtyoder
Do not upset the authorities responsible for the distribution of time.

~~~
twic
Oh, this lot don't just take care of time.

Seriously, check the heading on that memo. You know how people say "money
makes the world go round", or sometimes "love makes the world go round"?
False. Why do you think they're called the International Earth Rotation
Service?

------
a_c_s
Given the immense cost of leap-seconds, why not just wait for 60 of them to
accumulate and add a leap-minute every 60ish years or so?

Being almost a minute behind would have far less impact than all of these
unpredictable, tiny changes to UTC.

------
mrgriscom
Can anyone explain why leap seconds exist vs. a gradual skewing of atomic time
to match the earth's rotation. Like say, "from date X to Y, civil time will be
atomic time slowed by Z parts-per-billion". It just seems like such a better
solution than this discontinuity that occurs once every few years and _surely_
everyone would have prepared and tested for. Civil time just doesn't require
the accuracy where it actually matters, and if it does matter to you, use a
continuous timescale like TAI or compute the current skew offset using a
simple formula. Really, I love leap seconds as geeky trivia, but they seem so
impractical.

~~~
drzaiusapelord
Whose algorithm do we use? How much time has deviated is arguable and ties in
with things like rotation, earthquakes, inertia, tidal forces, etc. Would your
proposal be yet another buggy and heavily patched update we need to worry
about constantly being updated on the world's IT infrastructure? Incorporating
a simple leap second via fiat seems to be a simple and sane solution.

Then what of high accuracy computing? If my clock randomly adds or substracts
2ms a day, that could fuck up my calculations. Better to have things work in a
classical sense and to just tack on or remove a second once in a while and be
prepared for it in advance. 25 leap seconds have been added since 1972,
according to wikipedia. Why make this harder than it needs to be?

Atomic clocks are right and human calendering is arbitrary/wrong. Trying to
merge the two automatically can only cause more problems as our arbitrary
political and cultural nature could spill over into our scientific nature. See
trying to legislate the value of pi in Indiana for an example. The current
method works the other way. We push science into our calendering. We keep them
nice and separate.

~~~
mrgriscom
You would continue to use the IERS as the authority on what the true solar
time is. They would continue to declare when leap seconds are, but instead of
inserting them as a discontinuity, you would simply amortize them slowly over
a long period.

Like I said, if you demand high accuracy, use a timescale like TAI where
seconds are really SI seconds. But very few people need that kind of accuracy.
My computer clock probably already drifts more than 2ms a day. Anyone tracking
time for civil purposes is just syncing from a more authoritative source
anyway. My computer talks to upstream ntp servers. They could/should hide the
fact that leap seconds exist from me entirely. Some of Google's ntp servers
already do this.

------
zaroth
Clearly the proper solution is some space-elevator type device with a rocket
on the end to speed up/slow down the rotation as needed and keep our pesky
planet turning on schedule!

Would love to see this as a candidate for XKCD 'What If'.

~~~
luminiferous
It's already been done. [https://what-if.xkcd.com/26/](https://what-
if.xkcd.com/26/)

------
izzydata
Thank you for the service announcement. I will continue to go about my day
expecting the second to not be 1 off.

Edit: No need to get so worked up over a joke people.

~~~
bpicolo
These things matter a lot for time libraries.

~~~
tomp
But probably not at such short notice.

~~~
edwintorok
Doesn't seem short at all: "Paris, 16 January 2014 [...] NO leap second will
be introduced at the end of June 2014."

