[LEAPSECS] LEAPSECS Digest, Vol 51, Issue 7

Rob Seaman seaman at noao.edu
Wed Feb 2 14:23:13 EST 2011

I'm trying not to comment on every one (of the very many) issues I see with this thread. The point of the exercise is to seek consensus. As Stephen said at the very beginning, this group is very good at identifying points of disagreement.

Note that Descartes started with a single observation, "Je pense donc je suis". We aren't necessarily seeking a vastly long and detailed list. What are the key pivot points of agreement?

As others are doing, I will however comment on vocabulary.

Warner Losh wrote:

> Also, what is meant by mean solar X? what is the averaging time? what are the requirements for smoothing?

The word "mean" here doesn't refer to averaging statistically independent observations. Mean solar time is simply time based on the synodic day, that is, the underlying sidereal rotation period of the Earth adjusted by one day per year from lapping the Sun. It is the sidereal rate, measured against "fixed" stars or cosmologically distant quasars, that is varying due to tidal and other geophysical effects. The synodic day, and thus "mean solar time", go along for the ride.

As Warner implies, an area ripe for consensus-building progress is the "smoothing", i.e., the tolerance for the intercalary adjustments that will continue to be needed (whatever mechanism is implemented and whether or not the ITU has anything to do with the design of the mechanism). Whatever workflow is being followed to deliver a 5-month lookahead window for leap-seconds could be modified to extend the lookahead very significantly, perhaps by relaxing the DUT1 tolerance by a modest amount.


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