
UTC might be redefined without Leap Seconds - privong
http://www.ucolick.org/~sla/leapsecs/
======
brownbat
The rotation of the Earth is a terrible timekeeper. We used to have 6 hour
days. Now it wobbles. Major earthquakes throw it off. On the other hand,
ignoring this leads to weird results. In Rome, the priests used to control the
Calendar, and they had to decide how many leap days to put into the cycle.
Senators served through the end of the year, and they had influence over the
priests. By the time Julius Caesar implemented a new calendar, this sort of
political drift in the calendar had January in the middle of summer.

I guess people don't like mid-summer January because it makes historical
comparisons more difficult. Not impossible, just awkward.

It's a horrible messy dilemma. Leap seconds don't seem as dramatic as the
Roman intercalary days, but there's the same battle between synchronicity and
simplicity (where simplicity = something short of insane perturbations).

Maybe none of this matters for radio broadcast time signals. Maybe you just
want a fixed counter everyone's synchronizing to, and people should convert to
the Earth's messy system at the last possible moment.

Fun story about the awesome 13 month Calendar that we could have adopted
(except for Hitler): [http://99percentinvisible.org/episode/the-
calendar/](http://99percentinvisible.org/episode/the-calendar/)

[http://www.livescience.com/38083-earth-core-day-length-
patte...](http://www.livescience.com/38083-earth-core-day-length-pattern.html)

[http://www.scientificamerican.com/article/earth-rotation-
sum...](http://www.scientificamerican.com/article/earth-rotation-summer-
solstice/)

[http://news.nationalgeographic.com/news/2011/03/110316-japan...](http://news.nationalgeographic.com/news/2011/03/110316-japan-
earthquake-shortened-days-earth-axis-spin-nasa-science/)

[https://www.uwgb.edu/dutchs/PLATETEC/RotationQk2004.HTM](https://www.uwgb.edu/dutchs/PLATETEC/RotationQk2004.HTM)

[https://en.wikipedia.org/wiki/Julian_calendar#Motivation](https://en.wikipedia.org/wiki/Julian_calendar#Motivation)

~~~
contravariant
Do earthquakes also change how long it takes for the earth to rotate around
the sun? Because it seems like the earth's orbit should be more or less
constant (ignoring relativistic effects).

~~~
pavel_lishin
I don't believe so - earthquakes should only affect the number of days
(rotations) that occur during an orbit.

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Hyperborian
If I'm reading the linked projections correctly, even the worst predicitions
put us at less then three minutes off from the earths rotation by the year
2100, and it will take somewhere in the area a _thousand years_ to be off by
an hour.

I'll be frank: if we haven't progressed to the point that those offsets
generally don't matter by those points in time, we've probably already failed
as a species.

I say we drop leap seconds.

~~~
Trombone12
It is the heavens that set the time for humanity, all else must either imitate
or pick another name. Abandoning the leap seconds means breaking the
connection between utc and what the people consider time to mean.

It is not so much that the actual times drift apart very fast, it is that the
clock tries to corrupt the meaning of the word "day".

If leap seconds cause problems for your application, you probably should find
another source of synchronisation signal.

~~~
yellowapple
Yeah, another source like... seconds.

Plenty of applications need to know a precise number of seconds (or
milliseconds or nanoseconds) between the present and a past or future
date/time. Leap seconds throw a wrench in that. Whether UTC should serve the
role of an unaltered time source is indeed a matter of debate (and for good
reason), but it's pretty clear that we do need an unaltered stream of seconds
(upon which UTC - or an intermediate between UTC and various timezones should
UTC fill this role as advocated - would base itself, as would any other
applications that require said unaltered stream of seconds).

This isn't even mentioning more far-fetched things like space travel (at which
point the non-constant rotational parameters of an arbitrary planetary body
are neither relevant nor appropriate for system-wide/galaxy-
wide/universal/multiversal timekeeping).

------
lisper
At root, this is all just a quibble over terminology. The fundamental problem
is that there are two reasonable time standards for different applications:
mean solar seconds for ordinary day-to-day timekeeping, and cesium seconds for
applications that require a precision of more than a second per year. These
two standards drift, so you have two choices:

1\. Let them drift

2\. Introduce a computational complication (leap seconds) to synchronize them

But the dispute is not over which of these is "right", the dispute is over
which of these two options gets to go by the label "UTC". This could be easily
resolved by simply defining two UTCs, one with leap seconds, and the other
without. You could call them UTC-L and UTC-N (or UTC-S and UTC-N if you wanted
to mollify the French ;-).

~~~
SEMW
"Like UTC but without adding leap seconds" already exists; it's called TAI
([http://en.wikipedia.org/wiki/International_Atomic_Time](http://en.wikipedia.org/wiki/International_Atomic_Time))

~~~
lisper
Then what is really at issue here? Is it really a dispute about whether WWV
broadcasts (what is currently known as) UTC or TAI?

~~~
gpvos
Basically, yes. (Not only WWV, but also DCF77 et al., of course.) Several
countries have enshrined UTC in law, so it's a pretty big thing.

~~~
gpvos
...and just to add that this enshrining in law was most likely done with the
general expectation that UTC would keep a close relationship with solar time.

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IvyMike
Whenever I read about leap seconds, somewhere in my mind I wonder if wouldn't
just be easier to blow up a bunch of "booster" nukes every few years. ;)

~~~
pavel_lishin
Would that actually alter the spin of the Earth? I assumed that you'd be more
likely to have more success by making a few passes past the planet with a
sizable asteroid.

~~~
chc
IvyMike's plan is silly, but it sounds a lot more feasible than this one.

~~~
pavel_lishin
I don't know enough about any of this to judge which one is more feasible.
Detonating nukes on the surface is "easy", but would it be effective? How much
energy and money would it take to divert some asteroids? I haven't done the
research, and almost certainly won't :P

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politician
OT: Does anyone know what sort of calendar Martian rovers use? Is there a NASA
calendar for solar system operations?

~~~
termain
I can't speak for the rovers, but in my experience you start with the UTC time
and the convert to a UT1 for space launches. We have to correct for the
difference, which is called DUT1:
[https://en.wikipedia.org/wiki/DUT1](https://en.wikipedia.org/wiki/DUT1)

------
kozak
Why don't they just use TAI time in places where leap seconds are not
practical?

~~~
regularfry
Because that's _everywhere_. Whether _everywhere_ should "just use TAI" is
exactly the question (only they're not talking about TAI as far as I can see,
but a new standard which would I _think_ map 1:1 to it).

~~~
sp332
Right, so why make a new standard that looks just like this old one?

~~~
vilhelm_s
TAI currently differs from UTC by 35 seconds, so if you literally switched to
it, every clock in the world would jump 35 seconds. If leap seconds are
abolished, UTC and TAI will remain 35 seconds apart forever.

~~~
kozak
And then that time will be neither UTC not TAI. Either we'll have to call it
something different (like GPS time: always offset from TAI by certain number
of seconds), or a different name will have to be made for what used to be
called UTC (time tied to earth rotations, from which zoned wall time is to be
delivered). Great. That's exactly what
[https://xkcd.com/927/](https://xkcd.com/927/) is about.

~~~
vilhelm_s
I don't know if that's true. We already have a name for the time that is tied
to Earth rotation, "UT1". Users who care about positions of astronomical
objects can refer to that. UTC was always a bit of a compromise, which partly
tracked UT1, but only up to the nearest second.

On the other hand, I think the idea of abolishing leap seconds is to no longer
derive wall time from earth rotation, and to derive it from atomic time
instead. So "UTC" would still refer to "the source of wall time". As I
understand it, this is the point of changing the derivation of UTC: there are
lots of laws in different countries that say that wall clock time is tied to
UTC, so if we want to switch from earth rotation to atomic time, it is easier
to change the definition of UTC than to change the laws in all those
countries.

------
gpvos
I see that the solution the author proposes on the "right+gps" subpage is
basically the same as what Dan Bernstein has proposed for many years now,
except using GPS time rather than TAI (which only differs in the seconds
offset). Sounds like the sanest approach to me.

~~~
sla29970
Dan Bernstein proposed it and Bradley White wrote the code in the time zone
package used by Unix-like systems. The point of "right+gps" is that all of the
pieces needed to implement such a scheme are already deployed and tested and
with appropriate caveats anyone can decide to use that to avoid leap second
issues.

------
acqq
Even if UTC were redefined the number of the time-related bugs wouldn't
decrease.

