FUNCTION abstime(year, day, time)

      REAL*8    abstime
      INTEGER*4 year,day,time
      
c-Julian day on 1/0/yyyy, from 1975 to 2025 (0.0 hours GMT)
c
c   +------------------------------------------------------------+
c   | LET:  yyyy be the four digit Gregorian year, and           |
c   |       doy  be the day number of the year (1= Jan. 1), and  |
c   |       tod  be the time of day (hours, GMT)                 |
c   |                                                            |
c   | To compute julian day number for a date (yyyy, doy, tod),  |
c   |                                                            |
c   |     JD= jd_ny(yyyy-1974) + doy + tod/24.                   |
c   +------------------------------------------------------------+
c
c-Numbers checked against USNO's online MICA system. (EAC, 10/97)
c-  These numbers have been changed to modified Julian dates,
c-   (MJD= JD - 2400000.5).  This is (1) a slight simplification;
c-  and (2) a correction from the previous version that had the
c-  MJD different by 0.5 days. (EAC, 6/98)
c
      REAL*8 jd_ny(51) /
     &   42412.0, 42777.0, 43143.0, 43508.0, 43873.0,
     &   44238.0, 44604.0, 44969.0, 45334.0, 45699.0,
     &   46065.0, 46430.0, 46795.0, 47160.0, 47526.0,
     &   47891.0, 48256.0, 48621.0, 48987.0, 49352.0,
     &   49717.0, 50082.0, 50448.0, 50813.0, 51178.0,
     &   51543.0, 51909.0, 52274.0, 52639.0, 53004.0,
     &   53370.0, 53735.0, 54100.0, 54465.0, 54831.0,
     &   55196.0, 55561.0, 55926.0, 56292.0, 56657.0,
     &   57022.0, 57387.0, 57753.0, 58118.0, 58483.0,
     &   58848.0, 59214.0, 59579.0, 59944.0, 60309.0,
     &   60675.0    /

      REAL*8 a, f

      f= dble(time)/86400.d0

      a= jd_ny(year-1974) + day + f 

      abstime= a

      RETURN
      END