***** File FITS_IHW.TXT                                                       
                                                                              
                                                                              
                        FITS Format Information                               
                                                                              
                                                                              
    All data were submitted to the International Halley Watch Lead Center on  
magnetic tape, written in standard FITS format.  There are three primary      
references to basic FITS (Wells et al, 1981) and its extensions (Greisen and  
Harten, 1981, Harten et al, 1988).  Although commonly viewed as a magnetic    
tape format, the actual FITS specifications can be interpreted to describe a  
general byte stream.  As such, FITS files may be written on any storage       
medium, including CD-ROM.  Note that there is no inherent record structure    
called for in the FITS agreements, only a blocking structure for block        
oriented media such as magnetic tape.                                         
                                                                              
    The basic FITS agreements call for only a few required keywords (SIMPLE,  
BITPIX, NAXIS, END must be present; EXTEND may appear; keywords NAXIS1, ...,  
NAXISn appear as defined by the value of NAXIS).  We have also followed       
recommended conventions for the representation of values of keywords (dates in
the format 'dd/mm/yy', SI units used where possible, etc.).  The IHW has      
defined an additional set of mandatory keywords for all submissions to the    
Lead Center.  These are presented in the table below:                         
                                                                              
                                                                              
                                                                              
    OBJECT   - Name of the object in the data file, a text string.            
    FILE-NUM - Unique 6-digit number of the file submitted to the Lead Center.
               The first digit identifies the discipline, the other digits are
               assigned by the individual Disciplines, but must uniquely      
               identify the file.                                             
    DATE-OBS - UT Date of mid-observation, in the format 'dd/mm/yy'.          
    TIME-OBS - UT Time of mid-observation, as fractional day.                 
    DATE-REL - IHW internal release date for data, as date string.            
    DISCIPLN - Name of the network submitting the file, a text string.        
    LONG-OBS - Longitude of the submitting observatory, in the format         
               'ddd/mm/ss', with degrees from 0 to 360, increasing in the     
               eastward sense.                                                
    LAT--OBS - Latitude of the submitting observatory, in the format          
               'sdd/mm/ss'.                                                   
    SYSTEM   - An 8-digit coded character string identifying the Discipline,  
               observatory and instrument which supplied the data. The first  
               character identifies the network, the next three identify the  
               observatory (by IAU code number, where one is assigned, 500    
               otherwise). The next four digits either identify the           
               telescope/instrument combination (if there is an IAU number for
               the observatory) or the country and observatory (if no IAU     
               number).                                                       
    OBSERVER - Name of the observer(s) who took the data, a text string. The  
               notation "ET AL." indicates that there were more than two      
               observers, and the names of the additional observers are given 
               in a COMMENT later in the header, with the subkeyword "ADD.    
               OBS."                                                          
    SUBMITTR - Name of the person submitting the data to the Lead Center, a   
               text string.                                                   
    SPEC-EVT - A logical value indicating that the observation is a special   
               event.  Either T or F.                                         
    DAT-FORM - A character string defining the form of the data, e.g.,        
               'ASCII', 'NODATA'.                                             
                                                                              
                                                                              
                                                                              
    The individual Disciplines have written appendices which describe the     
keywords used in addition to the mandatory ones.  Refer to the text files in  
the \DOCUMENT\APPENDIX directory on these discs.                              
                                                                              
                                                                              
                                                                              
                                                                              
                                REFERENCES                                    
                                                                              
Greisen, E. W. and Harten, R. H.: 1981, Astron. Astrophys. Suppl. Ser.        
  44, 371.                                                                    
Harten, R. H., Grosbol, P., Greisen, E. W. and Wells, D. C.: 1988,            
  Astron. Astrophys. Suppl. Ser. 73, 365.                                     
Wells, D. C., Greisen, E. W. and Harten, R. H.: 1981, Astron. Astrophys.      
  Suppl. Ser. 44, 363.