Function:     JULIANDAY

Purpose:      Convert a date in the Julian or Gregorian calendars into the
              corresponding Julian Day number.

Category:     COORDINATES

File:         julianday.c

Author:       M.G.R. Vogelaar

Use:          DOUBLE JULIANDAY( DAY,         Input      DOUBLE PRECISION
                                MONTH,       Input      DOUBLE PRECISION
                                YEAR,        Input      DOUBLE PRECISION 
                              )

              DAY     Day (with decimals) of input data
              MONTH   Month of input data
              YEAR    Year of input data. If year is entered with 
                      decimals, take DAY=0.0 and MONTH=0.0
                      
Example:      DOUBLE PRECISION   JD
              JD = JULIANDAY( 0.0, 0.0, 1950.0 )
              JD = JULIANDAY( 22.5, 9, 2000.0 )
              
             
Notes:        The Julian Day begins at Greenwich mean noon that is at 12h
              Universal time (or 12h Ephemeris Time).                     
              After 15 October 1582, the Gregorian Calendar is used.

Updates:      Nov 6, 1992; VOG, Document created.