WFC: Year-2000 issue

[sla at ucolick.org]

teuben at astro.umd.edu wrote:

>      The European FITS Committee suggests
>
>        1) that the use of UTC time scale is made mandatory for all
>           DATExxxx keywords including DATE-OBS both for date and
>           date/time representations (i.e. 'ccyy-mm-dd' and
>           'ccyy-mm-ddThh:mm:ss[.sss...]Z' formats),

I am concerned that mandating UTC may prove too restrictive.  Whenever
pre-1972 (pre-UTC) data are encoded as FITS this European mandate
would force a dilemma on FITS writers and an ambiguity on FITS readers
who want to specify accurate time.  The Bunclark proposal denotes UTC
as "preferred", and permits it to be specified explicitly by use of
the 'Z' suffix.  This seems quite adequate for solving the FITS Y2K
problem before Y2K happens.

It does not make sense to mandate that the time be UTC without also
mandating that the calendar date be expressed in the Gregorian
calendar.  There is currently no FITS specification of the calendar
system.  UTC and TAI are often expressed in counts of seconds and MJD
counts of 86400 seconds; if there is any specification for the use of
Gregorian calendar for either timescale it is not widely enough known
that it can be presumed.

In short, I believe that the specification of a time system should not
precede the specification of a calendar system.  These are items which
should be "preferred" and not "mandatory" for the initial adoption of
the Bunclark proposal.  They can be resolved at a later date when
other time system issues are considered.

--
Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064
sla at ucolick.org      Voice: +1 408 459 3046     http://www.ucolick.org/~sla
"You should know better than to trust a strange computer." -- C-3PO to R2-D2