The Sun's Day in Practice

Classical and medieval astrology reads each day of the week through the character of its ruling planet, and Sunday carries the Sun's own significations: vitality, the conscious self, authority, honour and new undertakings. A working timed to Sunday, in the older magical and astrological literature that pairs planetary days with planetary hours, was considered strengthened when it also fell within an hour ruled by the Sun, the doubled attribution reinforcing rather than merely repeating the day's own character.

Because Sunday opens the seven day cycle, it also carries associations of beginning that have less to do with the Sun's specific nature and more to do with its position: the first day of a new week inherits some of the symbolism of any first thing, a fresh start set against the six days that follow and complete the cycle before it starts again. That double association, solar vitality on one hand and simple positional primacy on the other, is why Sunday appears in astrological and folk tradition alike as an auspicious day for beginnings even in traditions that do not otherwise emphasize planetary rulership.

Sources A History of Western AstrologyNicholas Campion with Grimoires: A History of Magic BooksOwen Davies