[LEAPSECS] earth speeding up

[Rob Seaman]

Hi Tom,

I see Steve and Demetrios have also responded.


> I know it's a risk making trend lines, but those of us who work with clocks, oscillators and frequency standards find it irresistible to peek ahead sometimes and guess what's coming. This applies to my favorite clock, the earth.


My favorite clock, too :-)  Although the Laplace resonance of the Galilean moons is a close second:

	http://commons.wikimedia.org/wiki/File:Galilean_moon_Laplace_resonance_animation.gif

And New Horizons is just 15 Earth-Moon months away from closest approach to the Pluto-Charon clock:

	http://pluto.jhuapl.edu/mission/missionDesign.php

where the month and the day are the same thing, making it one of my favorite calendars, too...


> See attached inverse length of day plots (that is, frequency error rather than excess LOD, or period error). This started with Stable32 (the standard tool we all use for time & frequency metrology) but I reformatted them with Excel to make them clearer.

> 

> This plot is for 1 July 1972 to the present. Those of you who follow DUT1 like the stock market recognize the characteristic periodicity, bumps, and trends. Note especially the stable period starting 1999, with many days of the year longer than 86400 seconds, and consequently no leap second for 7 years (roughly MJD 51000 to 54000).


I think you mean many days shorter than 86400 seconds, not longer?

(All days have 86400 seconds, just differing numbers of SI-seconds ;-)


> Any betting person would say the plot shows an upward trend over the past 40 years. A simple linear fit suggests the earth will be back to an honest 86400 second day within a few years, around MJD ~59000 (year ~2020).


The question is what the behavior was to the left of the plotted points.  A 40-year trend would be hasty even on a 6000-year old Earth.  Some people make long-term bets:

	http://longbets.org

I don't know about "honest", but every quirky day on Earth is perfect just as it is.


> I realize this is just for fun, and the serious geology, astronomy, and climate professionals on the list will raise valid concerns. But there's no doubt that since the 1970's the earth is generally speeding back up. If this trend continues, within a decade, we will have another long stretch of no leap seconds and this time it will be followed by our first negative leap second.


Your plot is Steve's (per Morrison & Stephenson), upside down:

	http://www.ucolick.org/~sla/leapsecs/ancient.pdf

The recent trend is indeed flatter than either historically observed or the value from lunar tides, but you're suggesting that flatter will turn upside-down.  Evidence from the long term trend suggests otherwise.

Rob