A lunar phase display mechanism includes an upper disc which is the lunar display disc and a lower disc mounted concentrically to this disc. One of the discs is mounted so that during normal operation of the mechanism that one disc rotates relative to the other disc, and the other disc is mounted in a stationary position during normal operation of the mechanism while this position can be changed by a rotary motion. The gear train driving the rotating disc allows that the direction of rotation of this disc can be reversed so that the different appearance of the lunar phases at the latitudes of the earth and, in particular, in the northern and southern hemisphere can be taken into account in the display.