'Convert a time tuple from this calendar to Gregorian calendar
@param timetuple: time tuple (y, m, d, hh, mm, ss)
@return: time tuple (Gregorian)'

def _gdate(self, timetuple):

    if (self.name == 'Gregorian'):
        return timetuple
    (y, m, d, hh, mm, ss) = timetuple
    jd = self.to_jd(y, m, d)
    (y, m, d) = self._jd_to_gregorian(jd)
    return (y, m, d, hh, mm, ss)
