HILAAL-CTM: Algorithm to Determine and Visualize the First Visibility of Lunar Crescent Using Contrast Threshold Model

Introduction: The determination of the beginning of the Hijri month depends on the visibility of the new moon after conjunction Objectives: This study develops an algorithm based on a contrast threshold model to determine the first moment of new moon visibility at selected locations in Malaysia. Methods: Key factors influencing new moon visibility, such as atmospheric attenuation, light pollution, twilight sky brightness, and human eye sensitivity, are also considered in this model. Results: This algorithm can generate windows of opportunity that provide the best time for new moon sighting. Conclusions: The study also validates the model by comparing it with observational data from several locations, including Aceh, Indonesia, and Tindouf, Algeria, for the determination of the beginning of Ramadan 2025. The findings indicate that this algorithm can aid in aligning the rukyah (moon sighting) method with scientific models, thereby contributing to the unification of the Islamic calendar.