This lovely present spins very fast in the sunshine but more slowly in the shade. I had an idea that it worked due to photons changing momentum on reflection but that couldn't be correct because it would mean that the shiny sides move away from you but in fact the black ones do. It works because it is not a full vacuum inside. There is a tenuous amount of air. The black absorbs infra-red radiation from the Sun best and becomes warm. This thermal energy transfers to the air in the bulb which expands next to the black surface and pushes it.
