seaman at noao.edu
Mon Jul 2 13:04:49 PDT 2007
On Jul 2, 2007, at 11:04 AM, Steve Allen wrote:
> I am going to plead that this discussion be stayed until Arnold Rots
> returns from vacation. STC already has several representations for
> reference date-time and offset date-time, and Arnold is also taking
> the lead for the FITS WCS paper on time.
Rather, let's agree to stay any final decisions until Arnold and
other STC and FITS authors can comment, but I see no advantage to not
attempting to make progress in the mean time.
> STC has a list of time scales which may have any sort of precision
> meaning. For precision purposes its structure acknowledges the
> situation that has been discussed over the past two decades by the
> IAU Working Group on Relativity, Celestial Mechanics, Astrometry
> and Metrology (RCMAM) which was (just last year at IAU Prague 2006)
> elevated to full status as IAU Commission 52 Relativity in Fundamental
And for how many astronomical purposes - transient alerts or
otherwise - is point-by-point absolute precision of this sort
necessary? A typical time series will have a reference epoch in some
standard timescale plus a number of data points with relative
offsets, both with modest errors. For much of the science the
absolute epoch is beside the point except for observational
logistics. Simple cases must be simple to express and interpret
without having a prodigy like Arnold on staff at either end.
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