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 [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).