## An important update from the International Earth Rotation Service

Bulletin C 52:
To: authorities responsible for the measurement and distribution of time

A positive leap second will be introduced at the end of December 2016. The sequence of dates of the UTC second markers will be:

2016 December 31, 23h 59m 59s
2016 December 31, 23h 59m 60s
2017 January  1,  0h  0m  0s

The difference between UTC and the International Atomic Time TAI is:

from 2015 July 1, 0h UTC, to 2017 January 1 0h UTC: UTC-TAI = - 36s
from 2017 January 1, 0h UTC, until further notice : UTC-TAI = - 37s

This means that tomorrow, 3:59:59 PM PST will be followed by 3:59:60 PM PST prior to the advent of 4:00:00 PM PST.

The leap second's stay of execution has been extended until at least 2023. Whew!

Tags: ,

### 11 Responses:

1. robert_ says:

Link is b0rked - should be:
https://datacenter.iers.org/eop/-/somos/5Rgv/latest/16

PDT? Don't you mean PST?

3. Nick Lamb says:

The leap second is a tiny but perfect example of mankind's insistence on kicking every possible can down the road rather than ever once deal with something before it becomes a complete disaster. The thing that makes humans remarkable isn't Language, or Tool use, or Late Night Talk Shows, it's Procastination.

• NT says:

You have a long term solution to rounding error? Or a proposal to speed up the earth's rotation a bit? Can we terraform the earth into a sphere while we're at it? Does your solution generalize to handle leap years?
Time has been indexed to astronomy since the beginning: one second is 1/86400 of a mean solar day. Unfortunately that's not a physical constant. So a bunch of physics PhDs decided to redefine it in terms of something you can only measure with an exotic device and now it's easy to confuse calendar seconds with physical seconds. It's interesting to imagine a world in which they chose a new unit for scientific measurement of time along with the new units for distance and mass. I remember wondering when I was taught metric units why the day was still divided 24*60*60 instead of into thousandths.

• Nick Lamb says:

The "new units" you learned about are from the French revolution, and have nothing to do with any Physics PhDs until, as you complain of with the second, they "decided to redefine it" almost a century later by constructing the prototypes. You complain that you can only measure a second using "an exotic device" and I presume you don't consider a stopwatch to be exotic so it must be that you demand to be able to determine these units from first principles. The prototypes, being by definition singular, were far more exotic than the equipment needed to measure a second, they were (for the kilogram still are) locked in a vault in France.

If you don't sweat the small stuff, as I suppose you don't, then it wouldn't bother you at all that civil time drifted along with TAI. It would take many years to make as much difference as simply happening to stand in a different part of the city to take your observations of the sun.

Long term, which is why I spoke of "kicking the can", your insistence upon 86400 seconds in one solar day becomes obviously laughable, as the planet's rotation decays. That's why we should bite the bullet, fasten UTC directly to TAI (or just abolish UTC) rather than keep trying to correct it to match UT1. If some places insist upon having their local civil time tied to the sun for some reason they can tweak their timezone as often as they like to track it.

• Steve Allen says:

Feel free to use TAI for your applications. ITU-R and POSIX painted the rest of the world into a corner decades ago. Now it is much harder to get consensus on a change through the process of re-examining UTC in radio broadcast time signals. It's almost 7 more years before the issue will be reconsidered at ITU-R WRC 2023. During the 16 years the process has gone on and failed to get consensus most of the principals who were trying to get consensus have retired and/or died.

• Ronald Pottol says:

Here, here! Let's abolish time zones while were are at it. Gah. But, definitely kill leap seconds.

4. JH says:

I have always wanted to my name on an International Earth Rotation Service business card. Think of all the taglines.

5. Steve Allen says:

If you prefer to work with the IERS but not for them then apply to become Director of Time at the International Bureau of Weights and Measures
https://www.iers.org/SharedDocs/Publikationen/EN/IERS/Publications/messages/IERS_Message_No_319.txt?__blob=publicationFile&v=2
This follows the impending retirement of one who tried to abolish the leap second but failed because there are three factions who cannot agree on which two of three priorities are most important for time
http://www.ucolick.org/~sla/leapsecs/picktwo.html

• NT says:

That last link has some important notes explaining why handling leap seconds is more confusing than it has to be. --posix-me-harder indeed.

6. Steve Allen says:

About the clock in the picture, those stopped being able to do precision time just after the 2012 leap second when NIST changed the modulation of WWVB so that the Chinese-made "atomic clocks" that people buy to hang on their walls would work better.