			    Standard FITS Keywords

This is an alphabetical listing of standard FITS keywords, with a particular
emphasis on keywords used within solar physics.  Users developing their own
keywords can examine this list to see if a proposed keyword already has a
standard or widely recognized meaning.  The list also includes keywords that
have been used in the past, but are no longer recommended for use--such
keywords are marked as "deprecated".  (See footnote 1.)

The following references are for keywords published in the literature, or
officially recognized by the IAU FITS committee.

[1] Hanish, R.J. et al., 2001, A&A 376, 359-380
[2] Greisen, E.W. and Calabretta, M.R., 2002, A&A 395, 1061-1075
[3] Calabretta, M.R. and Greisen, E.W., 2002, A&A 395, 1077-1122
[4] Greisen, E.W. et al., 2006, A&A 446, 747-771
[5] Thompson, W.T., 2006, A&A 449, 791-803
[6] Calabretta, M.R. et al., "Representations of distortions in FITS world
    coordinate system", draft, http://www.atnf.csiro.au/people/mcalabre/WCS/
[7] Thompson, W.T., "Error sources for solar image_coordinates", draft, 
    http://achilles.nascom.nasa.gov/~thompson/papers/coord_errors.pdf

The following references are for keywords from less official sources.  Users
should be aware that the meanings of keywords from the lettered references may
not be used in a consistent manner by all members of the solar or astronomical
community.  That's particularly true of those keywords marked as deprecated.

[A] Commonly held convention
[B] Howard, R. and Thompson, W, "Proposed keywords for SOHO", 2002,
    http://achilles.nascom.nasa.gov/ (only selected keywords listed)
[C] SolarSoft conventions, http://www.lmsal.com/solarsoft/ssw_standards.html
[Y] Mink, D., "The WCSDEP convention", http://www.ucolick.org/~sla/fits/
    (These keywords are expected to be folded into reference [6].)
[Z] Inferred from other keywords

Conventions used in the list

#	= Integer, generally in the range 0-999
##	= Two single-digit integers in a row
@	= Optional single character A-Z
$	= Required single character A-Z

<blank>		[1]	Any ASCII text (can be multiple)
##CD#@		[2]	Same as CD* for binary tables
##PC#@		[2]	Same as PC* for binary tables
#CDE#$		[2]	Same as CDELT* for binary tables (alternate)
#CDLT#		[2]	Same as CDELT* for binary tables
#CNA#@		[4]	Same as CNAME* for binary tables
#CROT#		[2]	Same as CROTA* for binary tables
#CRP#$		[2]	Same as CRPIX* for binary tables (alternate)
#CRPX#		[2]	Same as CRPIX* for binary tables
#CRV#$		[2]	Same as CRVAL* for binary tables (alternate)
#CRVL#		[2]	Same as CRVAL* for binary tables
#CSY#@		[2]	Same as CRDER* for binary tables
#CTY#$		[2]	Same as CTYPE* for binary tables (alternate)
#CTYP#		[2]	Same as CTYPE* for binary tables
#CUN#$		[2]	Same as CUNIT* for binary tables (alternate)
#CUNI#		[2]	Same as CUNIT* for binary tables
#DP#@		[6]	Same as DP* for binary tables
#DQ#@		[6]	Same as DQ* for binary tables
#S#_#@		[2]	Same as PS* for binary tables
#V#_#@		[2]	Same as PV* for binary tables
#V#_X@		[2]	Coordinate parameter array
ANGLE		[B]	Angle of observation			[DEPRECATED]
AUTHOR		[1]	Author of data
BITPIX		[1]	Bits/pixel, negative for floating point
BLANK		[1]	Value signaling undefined integer data
BLOCKED		[1]	True if file block size = N*2880	[DEPRECATED]
BSCALE		[1]	Multiplier for data values
BUNIT		[1]	Data units
BZERO		[1]	Offset for data values
CARX_OBS	[7]	Carrington X coordinate of observer
CARY_OBS	[7]	Carrington X coordinate of observer
CARZ_OBS	[7]	Carrington Z coordinate of observer
CAR_ROT		[5]	Carrington rotation number
CD#_#@		[2]	Dimensioned transformation matrix
CDELT#@		[2]	Pixel spacing along axis #
CNAME#@		[4]	Name of coordinate axis #
COMMENT		[1]	ASCII comment (can be multiple)
CPDIS#@		[6]	Prior distortion function type
CPERR#@		[6]	Max value of prior distortion correction for axis #
CQDIS#@		[6]	Sequent distortion function type
CQERR#@		[6]	Max value of sequent distortion correction for axis #
CRDER#@		[2]	Random coordinate error along axis #
CRLN_OBS	[5]	Carrington heliographic longitude of observer
CRLT_OBS	[5]	Carrington heliographic latitude of observer
CROTA		[Z]	Unofficial equivalent of CROTA#		[NON-STANDARD]
CROTA#		[1]	Coordinate rotation (see footnote 1)	[DEPRECATED]
CRPIX#@		[2]	Reference pixel along axis #
CRVAL#@		[2]	Reference value along axis #
CTYPE#@		[2]	Type of coordinate axis #
CUNIT#@		[2]	Units along axis #
DATAMAX		[1]	Data maximum
DATAMIN		[1]	Data minimum
DATE		[1]	FITS creation date
DATE-AVG	[4]	Average date of observation
DATE-END	[A]	End date/time of observation
DATE-OBS	[1]	Date of observation, usually start time
DATE_AVG	[Z]	DATE-AVG with light travel correction	[DEPRECATED]
DATE_END	[B]	DATE-END with light travel correction	[DEPRECATED]
DATE_OBS	[B]	DATE-OBS with light travel correction	[DEPRECATED]
DAVG#		[4]	Same as DATE-AVG for binary tables or pixel lists
DAY		[C]	Number of days since 1979-1-1		[DEPRECATED]
DETECTOR	[B]	Detector used to acquire the data
DIST_OBS	[5]	Reserved but not used
DP#@		[6]	Parameter for a prior distortion function
DQ#@		[6]	Parameter for a sequent distortion function
DSUN_OBS	[5]	Distance between the observer and Sun center
DVERR@		[6]	Max value of all distortion corrections combined
END		[1]	End of header
EPOCH		[1]	Deprecated, use EQUINOX instead		[DEPRECATED]
EQUI#@		[3]	Same as EQUINOX for binary tables or pixel lists
EQUINOX@	[3]	Floating point year associated with coordinate system
EXPTIME		[B]	Exposure time in seconds
EXTEND		[1]	FITS file may contain extensions
EXTLEVEL	[1]	Level of extension in hierarchy
EXTNAME		[1]	Name of extension
EXTVER		[1]	Version of extension
FILENAME	[B]	Name of the data file
GCOUNT		[1]	Size parameter for extra (heap) data
GEIX_OBS	[5]	Geocentric equatorial inertial X
GEIY_OBS	[5]	Geocentric equatorial inertial Y
GEIZ_OBS	[5]	Geocentric equatorial inertial Z
GEOX_OBS	[5]	Geographic X
GEOY_OBS	[5]	Geographic Y
GEOZ_OBS	[5]	Geographic Z
GROUPS		[1]	True if random groups are present	[DEPRECATED]
GSEX_OBS	[5]	Geocentric solar ecliptic X
GSEY_OBS	[5]	Geocentric solar ecliptic Y
GSEZ_OBS	[5]	Geocentric solar ecliptic Z
GSMX_OBS	[5]	Geocentric solar magnetic X
GSMY_OBS	[5]	Geocentric solar magnetic Y
GSMZ_OBS	[5]	Geocentric solar magnetic Z
HAEX_OBS	[5]	Helicentric Aries Ecliptic X
HAEY_OBS	[5]	Helicentric Aries Ecliptic Y
HAEZ_OBS	[5]	Helicentric Aries Ecliptic Z
HCIX_OBS	[5]	Heliocentric Intertial X
HCIY_OBS	[5]	Heliocentric Intertial Y
HCIZ_OBS	[5]	Heliocentric Intertial Z
HCPA_OBS	[5]	Reserved but not used
HECH_OBS	[5]	Radial distance from the solar surface of observer
HECR_OBS	[5]	Reserved but not used
HEEX_OBS	[5]	Heliocentric Earth Ecliptic X
HEEY_OBS	[5]	Heliocentric Earth Ecliptic Y
HEEZ_OBS	[5]	Heliocentric Earth Ecliptic Z
HEQX_OBS	[5]	Heliocentric Earth Equatorial X
HEQY_OBS	[5]	Heliocentric Earth Equatorial Y
HEQZ_OBS	[5]	Heliocentric Earth Equatorial Z
HGLN_OBS	[5]	Stonyhurst heliographic longitude of observer
HGLT_OBS	[5]	Stonyhurst heliographic latitude of observer
HISTORY		[1]	ASCII history record (can be multiple)
HPLN_OBS	[5]	Reserved but not used
HPLT_OBS	[5]	Reserved but not used
HPRZ_OBS	[5]	Reserved but not used
HRLN_OBS	[5]	Reserved but not used
HRLT_OBS	[5]	Reserved but not used
INSTRUME	[1]	Name of instrument
LATP#@		[3]	Same as LATPOLE for binary tables or pixel lists
LATPOLE@	[3]	Native latitude of celestial north pole
LONP#@		[3]	Same as LONPOLE for binary tables or pixel lists
LONPOLE@	[3]	Native longitude of celestial north pole
MAGX_OBS	[5]	Geomagnetic X
MAGY_OBS	[5]	Geomagnetic Y
MAGZ_OBS	[5]	Geomagnetic Z
MJD		[C]	Modified Julian Day			[DEPRECATED]
MJD-AVG		[4]	Average Modified Julian Date of observation
MJD-OBS		[3]	Modified Julian Date of observation
MJDA#		[4]	Same as MJD-AVG for binary tables or pixel lists
MJDOB#		[3]	Same as MJD-OBS for binary tables or pixel lists
NAXIS		[1]	Number of axes
NAXIS#		[1]	Dimension along axis #
OBJECT		[1]	Name of object
OBJ_ID		[B]	Object identifier, e.g. active region number
OBSERVER	[1]	Name of observer
OBSGEO-X	[4]	Geographic X location of observatory (m)
OBSGEO-Y	[4]	Geographic Y location of observatory (m)
OBSGEO-Z	[4]	Geographic Z location of observatory (m)
OBSGX#		[4]	Same as OBSGEO-X for binary tables or pixel lists
OBSGY#		[4]	Same as OBSGEO-Y for binary tables or pixel lists
OBSGZ#		[4]	Same as OBSGEO-Z for binary tables or pixel lists
OBS_MODE	[B]	Observing mode
OBS_PROG	[B]	Name of the observing program
ORIGIN		[1]	Responsible organization or institution
PC#_#@		[2]	Transformation matrix
PCOUNT		[1]	Size parameter for extra (heap) data
PS#_#@		[2]	ASCII coordinate parameter
PSCAL#		[1]	Equivalent of BSCALE for random groups	[DEPRECATED]
PTYPE#		[1]	Name of parameter # for random groups	[DEPRECATED]
PV#_#@		[2]	Coordinate parameter
PZERO#		[1]	Equivalent of BZERO for random groups	[DEPRECATED]
RADE#@		[3]	Same as RADESYS for binary tables or pixel lists
RADESYS@	[3]	Reference frame
REFERENC	[1]	Reference to publication for data
RESTFREQ	[4]	Line rest frequency (synonym of RESTFRQ)
RESTFRQ@	[4]	Line rest frequency (Hz)
RESTWAV@	[4]	Line rest wavelength (m)
RFRQ#@		[4]	Same as RESTFRQ for binary tables or pixel lists
RSUN_REF	[7]	Value of Rsun (meters) used in determining coordinates
RWAV#@		[4]	Same as RESTWAV for binary tables or pixel lists
SCI_OBJ		[B]	The science objective of the observation
SC_ROLL		[B]	Spacecraft roll				[DEPRECATED]
SIMPLE		[1]	True if conforming FITS file
SM_X_OBS	[5]	Solar magnetic X
SM_Y_OBS	[5]	Solar magnetic Y
SM_Z_OBS	[5]	Solar magnetic Z
SOBS#@		[4]	Same as SSYSOBS for binary tables or pixel lists
SOLAR_B0	[B]	Solar B0 angle
SOLAR_L0	[A]	Solar L0 angle
SOLAR_P0	[B]	Solar P0 angle
SOLI_OBS	[5]	Reserved but not used
SOLX_OBS	[5]	Reserved but not used
SOLY_OBS	[5]	Reserved but not used
SOLZ_OBS	[5]	Reserved but not used
SPEC#@		[4]	Same as SPECSYS for binary tables or pixel lists
SPECSYS@	[4]	Spectral reference frame
SSRC#@		[4]	Same as SSYSSRC for binary tables or pixel lists
SSYSOBS@	[4]	Spectral reference frame fixed during observation
SSYSSRC@	[4]	Spectral reference frame for SOURCE cases
TBCOL#		[1]	Column number for ASCII table field #
TC#_#@		[2]	Same as CD* for pixel lists
TCDE#$		[2]	Same as CDELT* for pixel lists (alternate)
TCDLT#		[2]	Same as CDELT* for pixel lists
TCNA#@		[4]	Same as CNAME* for pixel lists
TCROT#		[2]	Same as CROTA* for pixel lists
TCRP#$		[2]	Same as CRPIX* for pixel lists (alternate)
TCRPX#		[2]	Same as CRPIX* for pixel lists
TCRV#$		[2]	Same as CRVAL* for pixel lists (alternate)
TCRVL#		[2]	Same as CRVAL* for pixel lists
TCSY#@		[2]	Same as CRDER* for pixel lists
TCTY#$		[2]	Same as CTYPE* for pixel lists (alternate)
TCTYP#		[2]	Same as CTYPE* for pixel lists
TCUN#$		[2]	Same as CUNIT* for pixel lists (alternate)
TCUNI#		[2]	Same as CUNIT* for pixel lists
TDIM#		[1]	Dimensions of binary table field #
TDISP#		[1]	Format for displaying binary table field #
TDMAX#		[B]	Same as DATAMAX* for binary tables
TDMIN#		[B]	Same as DATAMIN* for binary tables
TDP#@		[6]	Same as DP* for pixel lists
TDQ#@		[6]	Same as DQ* for pixel lists
TELESCOP	[1]	Name of telescope
TFIELDS		[1]	Number of fields in ASCII or binary table
TFORM#		[1]	Format of ASCII or binary table field #
THEAP		[1]	Byte position of start of binary table heap area
TIME		[C]	Milliseconds of day			[DEPRECATED]
TIME-OBS	[A]	Time of observation (see footnote 3)	[OBSOLETE]
TIME_OBS	[Z]	TIME-OBS with light travel correction	[DEPRECATED]
TNULL#		[1]	Null value for ASCII or binary table field #
TP#_#@		[2]	Same as PC* for pixel lists
TS#_#@		[2]	Same as PS* for pixel lists
TSCAL#		[1]	Equivalent of BSCALE for ASCII or binary tables
TTYPE#		[1]	Name of ASCII or binary table field #
TUNIT#		[1]	Units of ASCII or binary table field #
TV#_#@		[2]	Same as PV* for pixel lists
TWCS#@		[2]	Same as WCSNAME for pixel lists
TZERO#		[1]	Equivalent of BZERO for ASCII or binary tables
VANG#@		[4]	Same as VELANGL for binary tables or pixel lists
VELANGL@	[4]	Angle of true velocity from tangent to line of sight
VELOSYS@	[4]	Radial velocity wrt standard of rest (m/s)
VSYS#@		[4]	Same as VELOSYS for binary tables or pixel lists
WAVELNTH	[B]	Wavelength of observation (character or Angstroms)
WCAX#@		[2]	Same as WCSAXES for binary tables
WCDP#@		[Y]	Same as WCSDEP for binary tables
WCSAXES@	[2]	WCS coordinate dimensionality
WCSDEP@		[Y]	WCS dependence parameter
WCSN#@		[2]	Same as WCSNAME for binary tables
WCSNAME@	[2]	Coordinate system name
WCST#@		[2]	WCS cross-reference target
WCSX#@		[2]	WCS cross-reference
XCEN		[B]	X coordinate of array center
XTENSION	[1]	Name of extension type
YCEN		[B]	Y coordinate of array center
ZSOU#@		[4]	Same as ZSOURCE for binary tables or pixel lists
ZSOURCE@	[4]	Redshift of source for SOURCE cases

===============================================================================
Footnotes

1.  The CROTA# keyword requires some special comment.  This keyword is now
considered deprecated in favor of the PC* (or CD*) transformation matrix.
However, it's still widely used, and both [3] and [5] give official definitions
of its meaning.

Officially, one cannot combine CROTA#, PC*, and CD* keywords in the FITS
header.  However, some people have expressed the wish to have the same
information in the header in an easily readable form.  The non-official keyword
CROTA can be used for this purpose, although it skirts the edge of what the
standard allows.

2.  All DATE_* keywords are deprecated in favor of the standard DATE-* form.

3.  TIME-OBS is a widely used keyword, but it should be considered obsolete in
light of the fact that DATE-OBS can now include time information (since 1997).
