[LEAPSECS] How good could civil timekeeping be?

[Rob Seaman]

There are a lot of timescales.  Astronomers are as heavy users of even  
interval time as of Earth orientation time.  I guess the answer to  
your question lies in the explanatory supplement to the astronomical  
almanac.  Recent IAU standards changes have yet to appear in a  
similarly normative form.  Steve Allen may also comment.

But the issues focus on the requirements of civil timekeeping, not the  
various precision timekeeping users like astronomers.  I won't repeat  
my argument about why civil time is mean solar time, but I assert that  
it is.  In addition, we all grasp the various issues regarding even  
interval timekeeping for computing.  That adds up to two types of  
civil time.

UTC does a pretty good job of capturing both flavors of time into a  
single mechanism.  It's ok by me, however, if there is a initiative to  
split them.  It is not ok if we try to pretend that one does not exist  
and I assert this will become obvious to all in the fullness of time.

Rob
--

On Feb 14, 2008, at 7:07 AM, Tony Finch wrote:


> On Wed, 13 Feb 2008, Rob Seaman wrote:

>>

>> The "day" is a key concept in our civilization. The "mean solar  

>> day" is

>> the natural way to implement this. Sundials have nothing to do with  

>> the

>> mean solar day, but rather the apparent solar day.

>

> How does the mean solar day relate to ephemeris time? Between the  

> period

> where time signals were based on observing solar transitions and the

> period where time signals were based on atomic clocks, official time  

> was

> ephemeris time. ET is more uniform than the Earth's rotation so a  

> second

> of ET is not 1/86400 day any more than an SI second is - and of  

> course the

> final definition of the SI second was chosen to match ET.

>

> If we can imagine what things might have been like if essens had a

> different period, can we imagine how astronomers would have handled  

> the

> discrepancy between ET and UT1 in the absence of atomic clocks?

>

> Tony.