A clear day model for the beam transmittance of the atmosphere is presented. The clear sky is modeled because this condition generally produces the maximum energy available. This maximum established the criteria from which engineers can design solar cells, space and process water heating equipment and estimate the thermal loading on buildings, etc. The model is based on five-years of daily global radiation data assembled from measurements at the Solar Energy Research Center at Baghdad, Iraq. The model offers the prediction of clear day hourly values of direct normal and global solar radiation for any day of the year at a given location with no required meteorological inputs. Modeled data are compared with observations, demonstrating good agreement for several days from different seasons. This model provides a baseline for solar energy researchers and is utilized for quality control of solar radiation parameters.