George Saliba, professor of Arabic and Islamic Science at Columbia University, will present a talk focused on the ritual of Islamic prayers (which believers perform five times a day) and the fact that those prayers are defined by the interplay between light and shadow. From the dawn prayer, before sunrise, to the dusk prayer, before the stars become visible, to the noon and afternoon prayers, which are defined by the length of shadows on the ground, light and shadow play a crucial role in determining the times of these prayers.