code: def gcal2jd(year, month, day):
      year = int(year)
      month = int(month)
      day = int(day)
      a = ipart((month - 14) / 12.0)
      jd = ipart((1461 * (year + 4800 + a)) / 4.0)
      jd += ipart((367 * (month - 2 - 12 * a)) / 12.0)
      x = ipart((year + 4900 + a) / 100.0)
      jd -= ipart((3 * x) / 4.0)
      jd += day - 2432075.5
      jd -= 0.5
      return MJD_0, jd