[time-nuts] Negative leap second

[Tom Van Baak]

Hi Adam,

 > I've read several articles lately claiming that the Earth is spinning 
much
 > faster since 2020.

Yes, quiet, then many articles in a few days, then quiet. It's been 
fascinating to see how technical news morphs and scary how fast it 
spreads. Some of the headlines are creative to the point of sensational.

 > I didn't see anything definite directly from IERS about this,

That's because there isn't much to say. IERS creates data. They do it 
very well. At the millisecond level the earth is always quite variable 
and you get used to it. There are always highs and lows, always cycles, 
trends, and predictions. The same as any oscillator. Earth is a clock 
too. [1]

That said, there has been an uptick in postings on the LEAPSECS list the 
past few years. [2] We have been watching earth rotation trends 
carefully since the last time this happened, back in 1999-2006, when 
there was no leap second (not positive, not negative) for a record 
breaking 7 years. It might happen again. You can get the same excitement 
watching GPS sawtooth error unfold before your eyes. ;-) By analogy the 
Earth seems to do a hanging bridge every ~20 years.

 > but I was wondering if the systems are ready for a negative leap
 > second some time in the future?

Of the recent news articles, the more prudent ones are quick to point 
out that this does not mean there will be a negative leap second. The 
only observation right now is that the earth, on average, is closer to a 
true 86400 s day than in recent years or decades. It will take some time 
before the actual outcome is known.

It takes a lot of sub-milliseconds before it accumulates enough to be 
adjusted with a (positive or negative) leap second. As I mentioned, a 
similar thing happened 20 years ago and it didn't lead to a negative 
leap second. This time it might. Or might not. I would not bet on the 
Earth; there are so many factors involved, many of which are deep inside 
the planet and there isn't a lot of understanding at that level.

As far as negative leap seconds, its useful to remember that UTC, from 
day one, was designed to handle either +1 or -1 corrections at the end 
of a month. Most of the systems I know are fine either way, or a problem 
either way.

That said, and to address your comment, I'm sure there will be s/w bugs 
here and there; that is the nature rare events like leap seconds. It's 
also one reason why there is serious consideration to just get rid leap 
seconds altogether, but that's a topic for [2].

/tvb

[1] http://leapsecond.com/museum/earth/

[2] https://pairlist6.pair.net/mailman/listinfo/leapsecs



On 1/9/2021 3:56 AM, Adam Kumiszcza wrote:
> Hi.
>
> I've read several articles lately claiming that the Earth is spinning much
> faster since 2020. I didn't see anything definite directly from IERS about
> this, but I was wondering if the systems are ready for a negative leap
> second some time in the future?
>
> https://phys.org/news/2021-01-earth-faster.html
>
> Adam