[LEAPSECS] Back to Basics

[Rob Seaman]

Well stated.  I'm not sure about the intended meaning of the final sentence beginning "We require guidance" and ending "element of that spectrum".

Rob
--

On Nov 3, 2010, at 9:39 AM, Finkleman, Dave wrote:


> 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

> 

> Discover CSSI data downloads, technical webinars, publications, and

> outreach events at www.CenterForSpace.com.

> ***********