UTC, with leap seconds as we define it now, is doomed.
On Thu 2003-04-10T22:39:45 -0700, Steve Allen hath writ:
> DUT1 calendar year grace interval
> 0.5 hours 2603 600 years
> 1.5 hours 3152 550 years
> 2.5 hours 3533 380 years
> 3.5 hours 3844 310 years
> 4.5 hours 4113 270 years
> 5.5 hours 4354 240 years
> 6.5 hours 4574 220 years
This used the Stephenson & Morrison millennia-long deceleration of 1.7
ms/day/century. The deceleration since 1620 has been less, and that
would push the calendar years farther into the future. If global
warming causes the ice caps to melt then the deceleration will be
somewhat larger. If melting ice caps shut down the Gulf Stream and
cause a new ice age then the deceleration could be somewhat smaller.
If a supervolcano erupts or asteroid strikes, all bets are off.
It is, nevertheless, interesting to take a cue from Rob Seaman at
http://iraf.noao.edu/~seaman/leap/
and estimate when UTC is doomed.
The current rules for leap seconds require that they happen at the end
of a month, with primary preference for semiannual scheduling in June
& December, and secondary preference for quarterly scheduling in March
& September.
So far, only the semiannual primary preference has been exercised.
When LOD has increased such that two leaps are needed every year, then
the secondary preferences will begin to be needed. When LOD has
increased such that 4 leaps are needed every year, then the monthly
options will begin to be needed. When LOD has increased such that 12
leaps are needed every year, then UTC as we know it is doomed.
avg. recurrence of leap seconds calendar year
1 / yr 1981
2 / yr 2142
1 / qtr 2464
1 / month 3752
(Note that the recently decreased deceleration already invalidates
the long term prediction that we should already be experiencing
more than 1 leap per year.)
So, in 1700 years UTC as we now define it will become unworkable. If
our descendants still choose to keep time using a Babylonian
sexagesimal scheme of 24 hours/60 minutes/60 seconds they will have a
choice to make. They might choose to keep civil time using TAI
seconds with leaps happening really often. They might choose to
employ two kinds of clocks, one using TAI for time-tagged events and
one using mean solar seconds for scheduling social events.
Under the current scheme for UTC even the primary preferences
should be adequate for over a century. There's no need to rush.
--
Steve Allen UCO/Lick Observatory Santa Cruz, CA 95064
sla_at_ucolick.org Voice: +1 831 459 3046 http://www.ucolick.org/~sla
PGP: 1024/E46978C5 F6 78 D1 10 62 94 8F 2E 49 89 0E FE 26 B4 14 93
Received on Tue Apr 22 2003 - 23:58:52 PDT