[LEAPSECS] Universal Time works

[Rob Seaman]

On Mar 12, 2015, at 1:04 PM, Warner Losh <imp at bsdimp.com> wrote:

> So why is keeping us inline with solar days so desirable? The rate of
> change is so slow and the number of people already out of sync with
> solar time on the second level is so large it seems like a lot of hassle
> for not much benefit when DUT1 can be known.

“Seems like a lot of hassle” is not a coherent engineering argument.  Proponents of change to such a fundamental standard should quantify the trade-offs and risks before conducting a politicized vote.  Few communities have been consulted even now.

> Apart from telescopes, nothing really breaks.

Even in astronomy this isn’t true:

	http://www.cacr.caltech.edu/futureofutc/2011/preprints/36_AAS_11-677_Seaman.pdf

And the reason the American Astronautical Society sponsored two meetings on this topic is that there are serious concerns about the impact of redefining UTC on space operations.  "The Space Community needs to develop a plan for upgrading operational software in case leap second discontinuance goes into effect”:

	http://www.cacr.caltech.edu/futureofutc/2011/preprints/30_AAS_11-674_Storz.pdf

Perhaps the notion is that GNSS makes the obvious air, sea and land navigation issues obsolete, but GNSS itself would incur significant costs.  "The costs and time needed for the required changes to the operational software and ICDs are unknown at this time, but they are expected to be significant”:

	http://www.cacr.caltech.edu/futureofutc/2011/preprints/32_AAS_11-675_Malys.pdf

If a timescale is created without leap seconds it should be called something other than UTC, as discussed in Torino in 2003.  This would preserve UTC (and the widespread concept of Universal Time as an approximation to mean solar time) for backwards compatibility.  Many other issues are discussed in:

	http://www.cacr.caltech.edu/futureofutc/2011/preprints/01_AAS_11-660.pdf

Rob Seaman
National Optical Astronomy Observatory