Turbulence is the wild, chaotic motion of air and water. At first blush, turbulence has no structure. But if constraints, like rotation, are added, a sharp transition appears between structureless turbulence and the growth of large-scale vortices. Such vortices are prominently visible in the atmosphere and oceans on our rotating planet. Researchers will study this effect in computer simulations to better understand and predict this transition. These insights are crucial for the modelling of large-scale natural flows like the motion of liquid iron in the core of the Earth, the source of its magnetic field.