def cweek
      start = Date.civil(year, 1, 1)
      ((jd - start.jd + start.cwday - 5) / 7.0).ceil
    end
def cweek
      start = Date.civil(year, 1, 1)
      ((jd - start.jd + start.cwday - 5) / 7.0).ceil
    end
Returns the calendar week number (1-53).