Re: [find_orb] Delta-T data used by Find_Orb

Rob Seaman Jul 4, 2018

Hi Bill,

Wiping a bit of spittle from my eye, full disclosure requires acknowledging having served as a member of the IAU Working Group on Coordinated Universal Time. UTC and leap seconds do indeed provoke strong opinions, and that was true on the WG itself, as one might infer from the careful wording of the final report that resulted:


There are a lot of nuances to timekeeping, enough for a couple of meetings specific to UTC, the Colloquium on Decoupling Civil Timekeeping from Earth Rotation in 2011:


and Requirements For UTC And Civil Timekeeping On Earth in 2013:


The chairs' report from 2011 covers most of the issues:


With copious background material (click through to Lick Observatory’s resources in particular):

All that said, modern reference clocks (at least our Meinberg M1000) can sync to different time scales: UTC, GPS, TAI, and thus TT. No one time scale is sufficient to all purposes and ceasing leap seconds would not improve access to time scales that are already devoid of leaps.

UT1 is not distributed other than from one experimental NTP server at NIST. IERS Bulletin A provides predictions of UT1, which formally is not known except retrospectively (Bulletin B):


Rob
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On Jul 4, 2018, at 8:52 AM, Bill Gray pluto@... [find_orb] <find_orb@yahoogroups.com> wrote:


(*) (Getting on my soapbox here; picture the following delivered as a
red-faced harangue, with spittle being sprayed over the first few rows.)

The claim is made that leap seconds are needed to provide a civil time
system that will stay in synch with the sun, to within +/- 0.9 seconds..
That claim is made, but then actual local civil time (the sort we use when
telling someone we'll meet them for a beer at 5:30 PM) is divided into
time zones, introducing a casually accepted half-hour error; then further
mangled with Daylight "Saving" Time by another hour. You never really
know when a local government will change zones or DST rules.

I see no need for _two_ levels of unpredictable, arbitrary time
mangling. Drop leap seconds, and leave UTC fixed relative to atomic
time. As the earth's rotation requires it, governments may decide,
a millennium or two from now, that clocks need not "spring ahead"
in their jurisdiction, in order to stay at least somewhat in synch
with the sun, to the same minimal degree that they currently do.

(OK, I'm getting off my soapbox. Thank you; I feel better now.)