The Munari is the first of the Montessori Mobiles, it can be used with children that are just a few weeks old.
The Munari's time tested design with black and white geometrical patterns and a glass sphere helps the baby develop his ability to explore the world visually. He practices focus, concentration, tracking of a moving object and depth perception as the mobile moves gently on natural air currents and reflects the light.
The mobile should be hung at 20-30 cm distance from the child's eyes. It is meant to be observed, not grasped. The baby should be alert and awake while 'working' with the mobile, so it's best to hang it over the movement area, not the sleep area or the changing station.
After a few weeks, the baby moves on to the octahedron mobile.
I make these mobiles completely by hand.