Shengdong Lu

Take a child's spinning top and set it on the table. It spins steadily, with all its parts moving in the same direction. Now toss a handful of beads onto the floor and blow on them: each bead will fly its own way. That's roughly how astronomers distinguish two types of large galaxies: 'spinning tops' (fast rotators) and 'beads' (slow ones with chaotic stellar motion).

A potter sits down at the wheel, and the first movements of the hands set the fate of the future vessel. If the lump of clay stays flat and wide, it will spin for a long time, gaining mass and heat. If the potter squeezes it into a dense ball, the wheel slows down and the piece hardens quickly.