Unfortunately, only the first seven keywords in the FITS headers of the ESI image data files contain any descriptive text. Fortunately, most of the undocumented keywords are not important in the context of the purpose for which these images were taken. The important keywords are described in this document. DATE-OBS Year-Month-Day on which the observations were made (UT) DATE same as DATE-OBS UT Coordinated Universal Time at exposure start AIRMASS path length through the atmosphere in units of the vertical TARGNAME target name TARGEPOC target epoch (year) TARGEQUI target equinox (year) TARGDEC target declination (radians) TARGRA target right ascension (radians) TARGFRAM target reference frame RA right ascension in hours:minutes:seconds format DEC declination in degrees:arcminutes:arcseconds format RAOFF right ascension pointing offset DECOFF declination pointing offset EQUINOX equinox of the coordinates (year) FRAME reference frame of the coordinates AZ azimuth (degrees; 0 is north, positive to the east) EL altitude (degrees; 0 is horizon, 90 is zenith) HA hour angle in hours:minutes:seconds format ST sidereal time at exposure start LATITUDE latitude of observatory (degrees) LST local sidereal time (degrees) MJD obviously NOT the Modified Julian Date MJD-OBS same comment as for MJD PARANG parallax angle (degrees) [direction of atmospheric dispersion] TELFOCUS telescope focus setting TUBETEMP telescope tube temperature (Celsius) TELESCOP name of telescope CURRINST current instrument OBJECT name of object OBSERVER name of observer DETECTOR name of detector INSTURME name of instrment FRAMENO frame number OBSNUM observation number EXPOSURE exposure duration (seconds) PREPIX number of prescan pixels PRELINE number of prereadout lines POSTPIX number of postscan pixels POSTLINE number of postreadout lines BINNING binning in pixels and lines CCDPSIZE dimensions of data area (pixels)