The article is an attempt to answer the question why Wednesday has the status of a holy day in Yezidism. Wednesday can be seen as a commemoration of the fourth day of creation, when the life on earth began and the Peacock Angel became its ruler. The article points to the Yezidi worship of the Moon and the Sun and related angels (Melek Fakhradin and Melek Sheikh Shams) and connects it with the Pythagorean concept concerning the movement of the planets and the Music of the Spheres. Two sacred Yezidi instruments, def and shibab, appear as allegories of celestial bodies in the Yezidi sacred hymns in the cosmogonic context of the creation of the macrocosm and microcosm (Adam). The article also points out the meaning of Wednesday in Judaism as the day when God created the sun, moon and stars and briefly discusses relationships with planet worship in Harran, Zoroastrianism and Mandaeism, especially in the context of the Yezidi Çarşemiya Sor festival which takes place on the first Wednesday of the month of Nisan.