[LEAPSECS] Fractured fairy tale

[Warner Losh]

On 12/23/2010 08:09, Rob Seaman wrote:

> Which is to say that mean solar time is a requirement.  Leap seconds as we currently know them are one possible way to implement that requirement.  The latter is negotiable.  The former is not.


Mean solar time is not a requirement.  It is merely a tradition.  As has 
been noted before, there has been a steady march away from mean solar 
time.  Time originally was governed by the local solar time.  Then, it 
was governed, for those in cities, by whatever the clock in the center 
of town said.  Then timezones of the 1850's expanded the notion nations, 
and then internationally.  We moved further away from the sun with the 
adoption of the second as based on the mean second of 1900, away from 
the second of the current era.  Then we moved to atomic time kept in 
sync at first by its varying frequency.  The most recent change has been 
to tick at a constant frequency but insert leap seconds into the labels 
we put on the seconds that tick by to keep things more or less in 
alignment to the earth.

Based on this history, it is far from clear that mean solar time is an 
absolute requirement.  Mean solar time is another way of saying that 
time must measure the angle of rotation of the earth.  Time keeping has 
moved beyond that one property.  It is merely tradition at this point as 
many of the motivating factors for keeping UTC and UT1 in close harmony 
have changed.

While you make many good points, this point I think is the fundamental 
source of disagreement in this list...

Warner