A friend of mine recently sent me this picture of a calendar wheel, which is part of an astronomical clock in the cathedral of St John the Baptist in Lyon, France. (The clock was built in 1661 to replace earlier one destroyed by the Huguenots in 1562; it has been restored several times.) The outer part is the current liturgical calendar, printed on a card that is supposed to rotate a little bit clockwise every day; on the left side of the frame, there is a metal hand hand with a finger that points to the current date (not shown here). On the inner part, within the metal grill, are indicated the calendar year, the number of Sundays after Epiphany, the dates of Septuagesima (still useful even in the post-Conciliar Rite for the dating of Carnival), Ash Wednesday, Easter, Ascension, Pentecost and Corpus Christi, then the number of Sundays after Pentecost, the date of the First Sunday of Advent, the dominical letter, the golden number, the epact, the indiction, and the letter of the martyrology. The rotatable card currently in place is good until 2089.
Above it is this astrolabe, which indicates the position of the Earth, sun and moon, and various stars.
The complete structure; the calendar wheel is on the lower part of the front.
