[LEAPSECS] Back to Basics

[Finkleman, Dave]

Recalibrating to get to the point.

1.  Universal Time is a set of time scales related to the mean diurnal
motion of the Sun.    So defined in many places and first recommended by
the IAU in 1935.  Different flavors have been defined and redefined
since, but the connection with motion of the Sun is consistent and
essential.  

The IAU is the enduring authority.   So, it is not a matter of the
convenience of one sector relative to the other or any religious,
psychological, or biological matter.  It is a matter of definition.
Anything "Universal" by definition must be related to the mean motion of
the Sun. 
 
2.  UTC is an international time scale approximating Greenwich mean
solar time with the precision of the SI second and matching UT1 to
within one second.  (From Seidelmann with supporting references.)   It
was precipitated by adoption of the SI second based on the properties of
Cesium 133.  

3.  The ITU is constituted under the UN as a regulatory agency without
the force of law.  The relationship with ISO is collaborative, but ITU
recommendations do not carry the force of international standards unless
implemented by ISO under ISO rules and procedures.  ITU-R 460-x are not
normative international standards.  A normative standard can be
referenced in contracts as a binding requirement.  Furthermore, the ITU
relationship is through ITU-T, not ITU-R. 

These are the basis of our discussions.

My goal is not necessarily to save the leap second.  It is to assure
consistent definition and implementation of time intervals and time
scales for a broad range of applications.  UTC was conceived and
implemented to correlate with Earth rotation to a degree sufficient for
many processes time accrued in constant atomic seconds.  Without leap
seconds, it is no longer UTC.  We require guidance in implementing for
different purposes different degrees of correlation with Earth rotation
-- and mechanisms for providing timely information that is precise
enough for each element of that spectrum.  

Dave Finkleman
Senior Scientist
Center for Space Standards and Innovation
Analytical Graphics, Inc.
7150 Campus Drive
Colorado Springs, CO 80920
 
Phone:  719-510-8282 or 719-321-4780
Fax:  719-573-9079
 
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outreach events at www.CenterForSpace.com.
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