[fitsbits] communique from the leap second wars

[Steve Allen]

On Fri 2005-01-21T08:11:52 -0800, seaman at hanksville.org hath writ:
> Summary:  We should make plans now about how FITS would support UTC
> should the issuance of leap seconds be halted.

Rob Seaman suggests preparing to redo the FITS documents to replace
UTC with UT1.  The original motivation for having UTC be the default
time scale in FITS was that UTC is the most practically available time
scale.  For practical purposes it is my impression that most things
writing FITS files will not actually have access to a suitably
accurate value of UT1.

It has been opined that FITS and VO are destined to merge.  In some
cases the VO has been following FITS, but in this case I think that
Arnold Rots has taken the VO to an appropriate solution first with his
Space-Time Coordinate Metadata for the Virtual Observatory document as
seen at
http://www.ivoa.net/Documents/latest/STC.html
When it comes time to have a FITS WCS Paper V (VI?  VII?) with a title
like "Representations of temporal coordinates in FITS" I see no
reason to expect that it will not follow the lead of the Virtual
Observatory document.

I expect that FITS will continue to specify UTC as the default,
because (despite many valid objections) that will probably remain the
name of the time scale most practically available to most writers of
FITS files.
For unambigous (but not precise) historical purposes I expect that
UT will remain the best time scale.
For unambiguous precision purposes of observations near earth
I expect that Arnold Rots is right to have TT be the default.

--
Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064
sla at ucolick.org      Voice: +1 831 459 3046     http://www.ucolick.org/~sla
PGP: 1024/E46978C5   F6 78 D1 10 62 94 8F 2E    49 89 0E FE 26 B4 14 93