Re: [LEAPSECS] what time is it, legally?

From: Tom Van Baak <tvb_at_LEAPSECOND.COM>
Date: Tue, 12 Dec 2006 13:17:10 -0800

> But this needs a clarification. Standard time replaced local
> apparent solar time in several steps. First, clock (mean) time
> replaced apparent time for civil purposes. As you can see from the
> proliferation of railroad standards, these were both still local to
> one place or another. Later, local time was referenced to standard
> localities such as Greenwich. Still later, a loose international
> consensus was formed regarding a common time zone system with a
> single standard prime meridian.
>
> All of these remained solar time. Mean solar time of some remote
> location is still a flavor of solar time because there is no secular
> drift. The important issue is the continuity of still recognizing
> mean solar time as the foundation of civil time. Leap seconds are
> simply one possible mechanism for achieving this. The notion of a
> leap hour fails to preserve mean solar time in any practical fashion.
>
> Rob Seaman
> NOAO

Rob,

Is there a technical definition of the "mean" in "mean solar
time" that would help guide the discussion?

One could argue that adding 50 or 100 leap milliseconds a
few times a year (as was done in the 60's) to preserve the
mean is just as valid as adding a couple of leap seconds
every few years (as is done now) is just as valid as adding
a couple leap hours every few thousand years (as has been
proposed).

I'm not arguing for one over the other but it seems to me
all three models achieve a mean. All prevent noon drifting
to midnight. All are a form of solar time. None of them
scale well to the extreme past or the extreme future. All
of them have practical limitations. None of them prevent
secular drift.

/tvb
Received on Tue Dec 12 2006 - 13:22:01 PST