WFC: Year-2000 issue (again)

[Don Wells]

"AR" == Arnold Rots <arots at xebec.gsfc.nasa.gov> writes:
AR> Any file in the XTE archive will do.  The archive is at:
AR> 	ftp://legacy.gsfc.nasa.gov/xte/data/archive

I selected one at random, and copied it to directory
http://www.cv.nrao.edu/fits/data/samples/xte/; I used my tool
'listfits' to produce a nice listing of the header at:

http://www.cv.nrao.edu/fits/data/samples/xte/FIHX_587412a-5874264.txt

The FITS file I selected contains one BINTABLE, which says that it is
a "HEXTE INDEX". The keyword choices, comments and layout of this
header make it easy to read.  The header line "TIMESYS = 'TT' / XTE
time will be TT (Terrestrial Time)" is certainly quite explicit.

I heartily approve of the use of CHECKSUM and DATASUM; this should be
made a general practice in all astronomy archives, and probably in all
astronomy data acquisition systems. The precise references to the FITS
literature which appear early in the basic header are commendable;
this too should be made a general practice in all of our archives and
data acquisition systems.

If some programmer is assigned the problem of decoding the syntax of
this file 50 years (or maybe even 100 years) from now, he/she is
likely to succeed with very little trouble. My bet is that an
astronomer who examines the information decoded by that programmer
will be able to infer quite a lot of the semantics of the file too,
even without paper documentation.

My compliments to the XTE chefs! 

AR> A good document on time systems is:
AR> 	http://tycho.usno.navy.mil/systime.html

Yes. It is precise and concise. A nice feature of this page is that it
contains URL links to machine-readable leap-second and UT1 tables. It
would be possible to fetch and install these automatically, hands-off.

AR> ..  It's
AR> utterly deplorable that GPS introduced yet another system; TAI
AR> would have served them just fine.

I agree.   

Thanks for your help,
-Don
-- 
  Donald C. Wells         Associate Scientist         dwells at nrao.edu
                    http://fits.cv.nrao.edu/~dwells
  National Radio Astronomy Observatory                +1-804-296-0277
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