Re: "Secular"
John Cowan wrote on 2005-02-24 20:07 UTC: > Rob Seaman scripsit: > > > Not silly - and not secular. Astronomers (at least) use the term > > "secular" to imply monotonic - and therefore cumulative - effects. > > Ah, I didn't grasp that point, and was merely using it to mean "not > periodic". The way I understood the word "secular" to be used in astronomy, it it can be defined formally as: Given two time-varying functions g(t) and f(t), with g(T_0) = f(T_0) for some time T_0, we say that g(t) features a "secular deviation" from f(t), if for any b > 0, there is a time T > T_0 such that for all t >= T the inequality || g(t) - f(t) || > b holds, where || x - y || is a suitably chosen distance measure. In other words, a secular deviation grows beyond any constant bound. TAI(t) and UT1(t) feature a secular deviation. [Outside astronomy, there is of course the far more widely used political meaning "non-religious" for the same term, as in "Irak's secular government versus Iran's Islamic government".] Markus -- Markus Kuhn, Computer Lab, Univ of Cambridge, GB http://www.cl.cam.ac.uk/~mgk25/ | __oo_O..O_oo__
Re: GMT -> UTC in Australia
On Fri 2005-02-25T09:24:56 +0100, Poul-Henning Kamp hath writ: > It semantically would make a lot of sense to retain the name UTC > and get rid of the leapseconds. Except that we already have another name for that time scale TAI In the long run it will be interesting to see how or whether various disciplines and user groups distinguish between TAI and GST. Galileo system time will be guaranteed to be within 50 ns of TAI for 95% of the time. To whom is that a difference that will make a difference? Sociologically, it makes sense to wait for the understanding brought by the answer to that question before redefining UTC. -- Steve Allen UCO/Lick Observatory Santa Cruz, CA 95064 [EMAIL PROTECTED] Voice: +1 831 459 3046 http://www.ucolick.org/~sla PGP: 1024/E46978C5 F6 78 D1 10 62 94 8F 2E49 89 0E FE 26 B4 14 93
Re: GMT -> UTC in Australia
In message <[EMAIL PROTECTED]>, "Clive D.W. Feather " writes: >* "Universal" Time is a *really* stupid name for a time scale based on > the variable rotations of one small piece of rock. Indeed. But back when UTC was named the universe was a lot smaller :-) It semantically would make a lot of sense to retain the name UTC and get rid of the leapseconds. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 [EMAIL PROTECTED] | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.
Re: GMT -> UTC in Australia
Rob Seaman said: > No reasonable standard can be based on constraining the behavior of our > descendants 600 years hence. In what way is the requirement "|DUT| <= 0.9s" not "constraining the behaviour of our descendants 600 years hence"? While I understand your argument about the name UTC: * *EVERY* approach requires constraining the behaviour of our descendants 600 years hence, just in different ways; * "Universal" Time is a *really* stupid name for a time scale based on the variable rotations of one small piece of rock. -- Clive D.W. Feather | Work: <[EMAIL PROTECTED]> | Tel:+44 20 8495 6138 Internet Expert | Home: <[EMAIL PROTECTED]> | Fax:+44 870 051 9937 Demon Internet | WWW: http://www.davros.org | Mobile: +44 7973 377646 Thus plc||
