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


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

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.

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

This archive was generated by hypermail 2.3.0 : Sat Sep 04 2010 - 09:44:55 PDT