The Sion astronomical clock is an astronomical clock at the town hall of Sion in the canton of Valais, Switzerland. The clock was first installed in 1667–68; the present mechanism dates from 1902.^[1][2]

The clock has five dials: on the two lateral sides of the clock tower, there are 12-hour dials. The principal dial on the front of the tower indicates, from the outer to the inner ring:^[2]

• the hours, on a chapter ring numbered I to XII twice, indicated by a double-ended fleur-de-lys hand;
• the signs of the zodiac;
• the months;
• the minutes, indicated by an arrow hand.

The position of the Sun in the zodiac and the month are both indicated by a hand with a golden sun. The other end of this hand, with a star, indicates the constellation which passes through the meridian at Sion in the middle of the night.^[2]

The two smaller dials underneath the principal dial indicate the day of the week, represented by an illustration of its classical deity, and the lunar phase by means of a rotating moon ball.^[1][2]