Taken from the back of the box:
Rotates silently on its own when exposed to ambient light! The MOVA™ globe is the first member of a new family of objects that come quietly to life when touched by light, without wires or batteries. The globe floats at a point of perfect balance between buoyant forces and gravitational forces, and slowly turns as it feels the force of the earths magnetic field and the energy carried in light. Its perpetual, quiet motion brings a tranquil point of focus to a room.
From the user manual:
How Your MOVA™ Globe Works The inner globe floats in an almost friction free environment, much like the earth itself. This globe has the same average density as the fluid it floats in, so there is no force or contact between the inner globe at the north and south poles and the inside surface of the outer shell. The rotation of the globe creates forces in the fluid that center the inner ball and prevent contact at the equator, so the inner globe is not actually touching the outer shell. At these low speeds the fluid friction is very low. Use and care instructions are included in this manual as well as information about the warranty that you receive (so keep your invoice). The globes offered here are 4 ˝ inch in diameter. It comes with its own tripod acrylic stand and I have added a small flat one with it. So you will have a choice of how your globe is displayed. On the tripod stand, the globe stands about 7 inches high. On the flat base, the globe stands about 5 ˝ inches tall. To see them in motion, check out the web site of Turtle Tech Design, Inc.