code: def compute_delta(lambda, beta, eps)
        a = Math.sin(beta) * Math.cos(eps) \
          + Math.cos(beta) * Math.sin(lambda) * Math.sin(eps)
        return Math.asin(a)
      rescue => e
        raise
      end
docs: =========================================================================
   δ の計算
  
   * δ = arcsisn((sinβ cosε + cosβ sinλ sinε )
  
   @param:  lambda  (unit: rad)
   @param:  beta    (unit: rad)
   @param:  eps     (unit: rad)
   @return: delta   (unit: rad)
  =========================================================================