Re: "Secular"

From: Markus Kuhn <>
Date: Fri, 25 Feb 2005 12:41:43 +0000

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 Kuhn, Computer Lab, Univ of Cambridge, GB | __oo_O..O_oo__
Received on Fri Feb 25 2005 - 04:41:59 PST

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