code: def jd(date = self)
        index = (12 * (date.year - 1)) + date.month - 16260
        mcjdn = date.day + HijriUmmAlqura::UMMALQURA_DAT[index - 1] - 1
        mcjdn = mcjdn + 2400000 - 0.5
        return mcjdn
      end
docs: Hijri to julian