||This study was used two detectors only i.e., the human eye and photometer of Sky Quality Meter (SQM-LU) during the time of sunrise and sunset. The human eye used to determine the moon's phase. The measurements of sky brightness, by using SQM-LU, performed via two locations that covered Baghdad and Karbala in Iraq from December 2016 through March 2017 intermittently. The research focused only on light perceived by detectors and not how it happens. The aim of research is to find a mathematical formula (i.e . brightness contrast) between the sky brightness against the solar altitude by taking moon illumination as the standard reference. Analytical software based on the Python's PyEphem astrometry library was developed to calculate the solar altitude at the two locations. Finally, the formula of sky brightness obtained from this work is an important key that contributed to finding the simulated sky brightness, when the sun's altitude is known.