The Islamic week is derived from the Jewish week, as was the medieval Christian week, all of which have numbered weekdays in common. All three coincide with the Sunday through Saturday planetary week. The Islamic and Jewish weekdays begin at sunset, whereas the medieval Christian and planetary weekdays begin at the following midnight. Muslims gather for worship at a Masjid or mosque at noon on "gathering day", which corresponds to the sixth day of the Jewish and medieval Christian weeks, and to Friday of the planetary week.