FITS Keywords
The table below lists all FITS keywords that may be recognized by Mira. This table does not include the myriad of keywords used by the FITS World Coordinate Standard, but see World Coordinate System Keywords for the list.
FITS Keywords
Keyword |
Type |
Definition |
(blank) |
none |
This keyword is used to enter a blank line into the header, usually to group sections of related information. |
ABG-VAL |
real |
Specifies the value used by the Anti-Blooming Gate (ABG) circuitry of the camera hardware. |
AIRMASS |
real |
Specifies the airmass. at the midpoint of the exposure. |
APERTURE |
real |
Specifies the aperture of the telescope. |
AUTHOR |
string |
Specifies the name of the author of the image. |
BIAS |
real |
Specifies the electronic offset, or Bias, of a CCD detector. This is specified in units of counts, or digital numbers in the image pixel values. |
BIASSEC |
region |
Specifies the column and row region containing the detector Bias value. The value is read as a character string and then interpreted as a MIRA region in the form [column1:column2,row1:row2] |
BITPIX |
integer |
Specifies number of bits per pixel and the pixel type are encoded as a single number that is the value of BITPIX. The magnitude (absolute value) of BITPIX gives the number of bits in each pixel and a negative value signifies floating point pixels. Thus, BITPIX= 8 for byte data, 16 for integer data, 32 for long integer data, and -32 or -64 for real data. A 24-bit RGB image is represented internally to MIRA as BITPIX = 32. For color images, the MIRATYPE keyword distinguishes the pixel type even though BITPIX = 32 as in a 32-bit integer image. A 24-bit image cannot be saved in FITS format. |
BSCALE |
real |
Specifies a scaling factor used to pack large dynamic range or floating point data into an integer pixel representation. This packing follows the rule: True value = BZERO + BSCALE x (pixel data value) |
BZERO |
real |
Specifies an offset used in packing large dynamic range or floating point pixel data into an integer representation. The relationship between packed and actual values is given above for the BSCALE keyword. |
BUNIT |
string |
Defines brightness units used by the pixel data. In optical work this is almost always counts but may be jansky or other units. FITS format files, especially those of raw, unprocessed data, are usually stored in count units if the data originated from a digital detector. |
CCDBINn |
integer |
Specifies the binning value for the axis n, with n=1 referring to the most rapidly changing subscript (the x axis direction). |
CCDSEC |
region string |
Specifies the column and row region containing the unbinned subframe position on the detector. The value is read as a character string and then interpreted as a MIRA region in the form [column1:column2,row1:row2] Compare with binned coordinates in the DATASEC keyword. |
CCDSUM |
integer |
Specifies the number of on-chip summed exposures. |
CAMTEMP or CCD-TEMP |
real |
Specifies the temperature of the detector, usually a CCD, at the time of the exposure. |
CCDTEMP1 |
real |
Specifies the temperature of the detector, usually a CCD, at the time when the exposure started. |
CCDTEMP2 |
real |
Specifies the temperature of the detector, usually a CCD, at the time when the exposure finished. |
CCD-TREQ |
real |
This is an antiquated keyword; see SET-TEMP. |
CCDBINn or COL_BIN |
integer |
Specifies the pixel binning for axis n at the time a CCD image was produced. The COL_BIN keyword is antiquated. |
COPYRIGH |
string |
Specifies a copyright statement pertaining to the image. |
COMMENT |
string |
Includes a comment that describes some characteristic of the image or the data. Note that COMMENT and HISTORY keyword lines do not use single quotation marks, ' ', to delimit the character string. The lack of quotation marks to delimit the string is unique to the COMMENT and HISTORY keywords. |
CLABELn |
string |
Specifies the text label for the n-th axis. |
COPYRIGH |
string |
Copyright statement for the file. |
CRDELTn |
real |
Specifies the scaling factor in physical coordinate units per pixel for axis n of an image. |
CRPIXn |
real |
Specifies the reference pixel for the physical coordinate system for image axis n. The physical coordinate at image location CRPIXn is CRVALn. |
CRTYPEn |
string |
Specifies the type of physical coordinate system used for axis n. |
CRVALn |
real |
Specifies the zero point of an optional coordinate system for axis n. |
CUNITn |
string |
Specifies the units of measurement on the n-th axis. |
DARKTIME |
real |
Specifies the time in seconds that characterizes the build up of dark count in the sensor that produced the image. |
DATAMAX |
real |
Specifies the maximum pixel value in the image. |
DATAMIN |
real |
Specifies the minimum pixel value in the image. |
DATASEC |
region string |
Specifies the column and row region containing the binned subframe position on the detector. The value is read as a character string and then interpreted as a MIRA region in the form [column1:column2,row1:row2] Compare with unbinned coordinates in the CCDSEC keyword. |
DATE-MID |
date+time |
Specifies the UT date and time at mid exposure. This keyword is added or updated by the Combine Image Set command. It gives the weighted average time of mid exposure based on the exposures of the images combined as well as the combining method and the normalization method. See the DATE-OBS keyword for a description of the format. |
DATE-OBS |
date+time |
Specifies the Universal Time ("UT") date and time at the beginning of the exposure. Before 1999, the FITS standard expressed this in the format dd/mm/yy and did not specify whether the date and time applied to the beginning, middle, or end of the exposure. Beginning in 1999, the FITS standard revised the format to solve the Year 2000 (Y2k) problem and specified that the time shall apply to the beginning of the exposure. The new format uses a 4 digit year and it includes the time value from the TIME-OBS keyword. The letter T is used to separate the date and time information. The format of the new DATE-OBS keyword is yyyy-mm-ddThh:mm:ss.sss |
DATEFITS |
date+time |
Specifies the UT date and time when the image was most recently written to FITS format. See the DATE-OBS keyword for a description of the format. |
DEC |
degrees |
Specifies the declination at the center of the image specified in units of decimal degrees. |
DETECTOR |
string |
Specifies an identification string for the sensor used to acquire the image. |
DWELL |
real |
Specifies the dark integration time. Also used sometimes to specify the lag time between beginning to flush the CCD and the actual beginning of the exposure. |
END |
none |
This keyword is required to signify the end of the header. This tells the FITS reading program that the pixel data begins at the next 2880 byte offset from the beginning of the file. |
EPOCH |
real |
Specifies the decimal year of observation of the image. The positions of moving objects are strictly correct only at the epoch of the image. |
EQUINOX |
real |
Specifies the coordinate reference time for the system of right ascension and declination used by the image. Modern catalogs use the J2000 equinox. |
EXPTIME |
real |
Specifies the exposure time in seconds. |
FFT-COMP |
string |
Specifies the type of components of an image that is a Fourier Transform. |
FFT-TYPE |
string |
Specifies the status of an FFT image. If the value of this keyword is FFT, the image is in the Fourier transform domain. If the value is Inverse FFT, the image has been inverse transformed from an FFT'd image. |
FILE |
string |
Specifies the name of a disk file that was turned into a FITS file. The time this was done may be reflected in the value of the DATEFITS keyword. |
FILTER |
string |
Specifies the name of the filter used in the observation. |
FOCALLEN |
real |
Specifies the focal length of the telescope. |
GAIN |
real |
Specifies the detector gain, often referred to as the inverse gain in units of electrons per count. |
HISTORY |
string |
Includes a comment that describes how the data have been changed by image processing operations. MIRA makes profuse use of HISTORY keywords. Note that HISTORY and COMMENT keyword lines do not use single quotation marks, ' ', to delimit the character string. The lack of quotation marks to delimit the string is unique to the HISTORY and COMMENT keywords. |
IMAGETYP |
string |
Describes the type of observation in the image. This is intended for automated data reduction operations. The typical options are IMAGETYP= 'normal ' 'flat ' 'dark ' 'zero ' or 'bias ' |
INSTRUME |
string |
Specifies a name or description of the instrument (telescope, spectrograph, etc.) used in obtaining the image. |
MIRAPROC |
string |
A string of codes used to monitor image processing steps. Used internally by Mira. |
MIRATYPE |
string |
Specifies the pixel type of the image as a character string. |
MIRAFITS |
date+time |
Specifies the Universal Time ("UT") date and time Mira saved the image to a FITS file. This keyword uses the same format as the DATE-OBS keyword: yyyy-mm-ddThh:mm:ss.sss |
MIRAVERS |
string |
Specifies the Mira product name and version used to save the image. |
NAXIS |
integer |
Specifies number of coordinate dimensions. MIRA supports 1 and 2 dimensional image data. |
NAXIS1 |
integer |
Specifies number of pixels along the image axis whose subscript changes most rapidly from pixel to pixel. This corresponds to column number in a 2-D image. |
NAXIS2 |
integer |
Specifies number of pixels along the image axis whose subscript changes next most rapidly after NAXIS1. This corresponds to row number in a 2-D image. In a 1 dimensional image, the NAXIS2 keyword has either a value of 1 or is not present in the image header. |
NAXISn |
integer |
Specifies the number of pixels along the n-th axis. |
NPHOTSTD |
integer |
Specifies the number of objects used to calculate the photometric quantities in ZERO-PT value and ZERPTERR |
NSKYPIX |
real |
Specifies number of pixels used to estimate the background. |
N-COADDS |
integer |
Specifies the number of image frames that were summed to produce the image. Antiquated, replaced by the CCDSUM keyword. |
OBJECT |
string |
Specifies the name of 7 other descriptive information about the image. |
OBSSTATE |
string |
Specifies a state flag that describes the operating mode of the detector at the time of the observation. |
ORIGIN |
string |
Specifies the software that created the original image. |
ORIGIN-C |
integer |
Specifies the column number origin of a sub-image. |
ORIGIN-R |
integer |
Specifies the row number origin of a sub-image in its parent image. |
OBSERVER |
string |
Specifies the name or a description of the observer who obtained the image. |
OBSRVTRY |
string |
Specifies the name of the observatory where the data were taken. |
OBSTYPE |
string |
Describes the type of observation in the image. This is intended for automated data reduction operations and is software specific. This is antiquated and has been replaced by IMAGETYP. |
PALETTEn |
string |
Identifies the n-th line of the saved palette and display information. The value of n is in the range 0 to 3. |
PSF-FWHM |
real |
Specifies the FWHM of the point spread function for the image. MIRA saves this value to the header when the FWHM is computed as consequence of a Radial Profile Plot. |
PROCESS |
string |
Specifies a series of flags that describe the processing done to the image. This is implementation dependent. |
PTIMEREF |
string |
Indicates whether the time reference for the AIRMASS was taken to be the beginning, middle, or end of the exposure. |
RA |
degrees |
Specifies the right ascension at the center of the image in units of decimal degrees. |
REFBIAS |
string |
Specifies the reference bias value for a CCD frame that was obtained shortly after the end of the exposure. |
ROW_BIN |
integer |
Specifies the row direction binning of physical pixels into image pixels at the time a CCD image was produced. Use CCDBIN2, as the ROW_BIN keyword is antiquated. |
RDNOISE |
real |
Specifies the detector readout noise in units of electrons per pixel. |
REFERENC |
string |
A bibliographic reference. |
SKYCOUNT |
real |
Specifies the zero point term in the polynomial fit to the background of an image. If a polynomial of order higher than 1 is used for the background, this is the value of the lowest order (constant) term. |
SKYSIGMA |
real |
Specifies the standard deviation of the fit to the background in units of counts. |
SIMPLE |
boolean |
Specifies whether the pixel data adhere to standard FITS format, with values T or F. The value T (true) means that every aspect of the data is FITS standard. The value F (false) indicates that the image is non standard in some way, and that your software must how to handle it. |
SITEELEV |
real |
Specifies the elevation of the observing site in units of meters. |
SITELAT |
degrees |
Specifies the latitude of the observing site in units of degrees. |
SITELONG |
degrees |
Specifies the longitude of the observing site in units of degrees. This value follows the geodetic convention that longitude west of Greenwich, England is negative. For example, all locations in the Americas have a negative longitude. |
SITESYS |
string |
Specifies the coordinate system used for the SITExxxx keywords. The standard value is NAD83, referring to the geodetic coordinate system definition of 1983. |
TELESCOP |
string |
Specifies the name or a description of the telescope used for the observation. |
TIME-MID |
time |
Specifies the mid exposure time for a combined image (one made by combining the pixel intensities of more than 1 image). See the DATE-MID keyword for details. |
TIME-OBS |
time |
Specifies the Universal Time at the beginning of the exposure. This is specified using the format hh:mm:ss.ssss. Beginning in 1999, the FITS standard merged the TIME-OBS value with the DATE-OBS value as part of a solution to the Year 2000 problem. See the description under the DATE-OBS keyword. |
TIMEFITS |
time |
Specifies the time when the image was most recently written to FITS format. This is specified in Universal Time in the format hh:mm:ss.ssss. Beginning in 1999, the FITS standard merged all TIMExxxx values with the DATExxxx values as part of a solution to the Year 2000 problem. See the description under the DATE-OBS keyword. |
TRIMSEC |
region |
Specifies the region of a CCD image which should remain after trimming away the under-scan and/or over-scan bias region. The value is read as a character string and then interpreted as a MIRA region in the form [column1:column2,row1:row2] |
WCOEFTYP |
string |
Specifies the wavelength solution type for which the WVCOEFn keyword values pertain. The most common value is polynomial. |
WCOEFORD |
integer |
Specifies the numerical order of the wavelength solution contained in the WVCOEFn keywords. |
WVCOEFn |
string |
Identifies the n-th line of wavelength calibration coefficients. The value of n is in the range 0 to 9. |
X-OFFSET |
integer |
Specifies the column offset of the subimage on the detector. This is obsolete, replaced by CCDSEC keyword. |
Y-OFFSET |
integer |
Specifies the column offset of the subimage on the detector. This is antiquated, replaced by CCDSEC keyword. |
XTENSION |
boolean |
Specifies that the file contains FITS extensions, T or F. |
ZERO-PT |
real |
Specifies the photometric zero point of the image expressed as a magnitude. |
ZERPTERR |
real |
Specifies the uncertainty in the value of ZERO-PT. |
FITS Format, World Coordinate System, FITS Header Editor, Modify Keywords, Comment Keywords, History Keywords, MIRAPROC Keyword, WCS Keywords, Photometry Keywords