[fitsbits] DATE-OBS versus TIME-OBS

[Steve Allen]

On Tue 2002-01-22T21:54:32 +0000, William Thompson hath writ:
> How are other groups handling this?

snips from the header of our soon-to-deliver instrument

DATE-OBS= '2002-01-04'
UT      = '13:11:43.12'

DATE_BEG= '2002-01-04T13:11:43'
DATE_END= '2002-01-04T13:11:44'

The explanation for this is that DATE-OBS and UT are traditional
keywords which are generated by an existing system that provides date
only and time only.  Our traditional usage of DATE-OBS provides no
more precise a definition of its meaning than was in the original FITS
paper.

For the sake of better documentation we have coined the new keywords
which do have precise definitions and which are guaranteed to
correspond closely to the shutter action.  Those use the new FITS date
format.

In particular, for our systems there has been no demand for the DATE
or UT values to correspond closely to the shutter action.  The two
keywords may actually be queried on different sides of a day boundary
(albeit an unlikely event given the longitude of our telescopes).  The
UT value may actually be outside the BEG-END range.

In effect, we deem DATE-OBS to be broken/deprecated and aren't
spending any engineering time fixing how we handle it.

--
Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064
sla at ucolick.org      Voice: +1 831 459 3046     http://www.ucolick.org/~sla
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