The moon is a ball of papiermaché. It is painted half black, half white, and has a black background. The wheel has 59 teeth (that is 2 x 29.5.) Every 12 hours it is nudged to the left, one tooth at a time, by the horizontal wire which is driven to and fro by an eccentric on the hour hand of the clock. On the far side of the wheel, not visible in the picture, is a pawl which prevents the wheel turning backwards.
      A lunar month is actually more than 29.5 days, (more precisely 29.530587981 days.) So the display looses about 30 seconds a day, that is, about one day in 2 ½ years.

Another moon: this one is made of wood. (I was previously concerned that wood might be too heavy for the clock to turn, but it works fine.) And now the pawl is at the front, where it can be seen. Otherwise, the same as before.


Having made my moon display, I frequently checked it by visiting moon-phase websites. They also have information about up-coming eclipses.

The moon in the picture below is not a "waxing sickle" as one might think, but a partially eclipsed full moon, as seen from Berlin at about 4.45 am on the 16.05.22. It was touted as a "blood moon" (illuminated by rosy twilight from the Earth) and the left edge was indeed a delicate shade of pink. Having got up at 3.30 in the morning to see it, I was certainly interested but slightly disappointed. The pink effect is presumably more pronounced when it is provided by a complete ring of refracted rosy glow from the Earth during a total eclipse.

The geodesic domes on the left are the ruined remains of a US National Security Agency listening station on the Teufelsberg, built during the Cold War in 1963 in what was then West Berlin.