[Aavso-photometry] FITS Keyword standard

[Michael Newberry]

Don't bother worrying about dictionaries of FITS keywords---there's only one 
standard and one "dictionary" for all the important keywords that would 
probably be of importance to you. FITS involves a very specific header 
structure, keyword names, data types, and formats for how the quantities are 
stored by the keywords. Just use software that follows the FITS standard.

The only cacophony that may exist is if a piece of software does not follow 
the standard. FITS format basically sets up 3 classes of keywords: standard, 
conventional, and private. The standard keywords are those that must use 
particular names, such as NAXIS, EXPTIME, and OBJECT. The conventional 
keywords are those which are not forced to have specific names but which 
have names that are more or less universally adopted within the professional 
community of observatories and institutions, such as RDNOISE, GAIN, and 
IMAGETYP. A "true" conforming FITS reader is required to understand the 
standard keywords and should, as a matter of professional ettequite, 
understand the conventional keywords. The 3rd set, the private keywords. are 
those that anyone can create for their own use but which no other FITS 
reader is required to understand. The standard and conventional keywords are 
to be used when appropriate and may not be replaced by private keywords for 
the same quantity---a common error of this type being to use EXPOSURE for 
EXPTIME, EGAIN for GAIN, or NOISE for RDNOISE. Two pieces of software that I 
do know follow the FITS standard strictly are IRAF and MIRA.

Michael Newberry

----- Original Message ----- 
From: "Mark Munkacsy" <Mark_Munkacsy at alum.mit.edu>
To: <aavso-photometry at mira.aavso.org>
Sent: Wednesday, January 02, 2008 7:53 PM
Subject: [Aavso-photometry] FITS Keyword standard


> Does the AAVSO endorse any particular dictionary of FITS keywords?
> One of my long-term projects is to clean up the cacophony of FITS
> keywords that I've used in the various software packages I've written to
> manage my own observing sessions. I've discovered several FITS keyword
> dictionaries (see http://fits.gsfc.nasa.gov/fits_dictionary.html), but
> none seems appropriate off the shelf for AAVSO observing programs. Is
> there anything approaching a "standard" in use by the VSO community?
> - Mark
>
> --------------------------
> Mark Munkacsy (MMU)
> Portsmouth, RI, USA
>
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