This article is an study with study of Hisab and Ru’yah, utilized by Islamic people (Muslims) in religious practice especially salat, fasting and religious service of Haji. It includes of the fundamental solution of science execution in determining early time of salat, instructing Kiblat, and early month; for Qamariyah moon precisely. Thereby, the writers elaborate them for theoretically and practically in this article, about how the these sciences used in determining early time of salat, instruct kiblat, and early month of Qamariyah at one particular place. Their validity and correctness can be proved pursuant to specified formula by pertinent science. Specially time awal of salat, instruct kiblat. In term of determination of early month; the moon of Ramadan and early month of Syawal, for the fasting day of Ramadan, Idul Fitri, result of Ru’yah and hisab that can be earn and justified scientifically.
