text: The Magnetic Prandtl number (Pr) is a dimensionless quantity occurring in magnetohydrodynamics which approximates the ratio of momentum diffusivity (viscosity) and magnetic diffusivity.  It is defined as:
  where:
  * Re is the magnetic Reynolds number
  * Re is the Reynolds number
  * &nu; is the momentum diffusivity (kinematic viscosity)
  * &eta; is the magnetic diffusivity
  At the base of the Sun's convection zone the Magnetic Prandtl number is approximately 10, and in the interiors of planets and in liquid-metal laboratory dynamos is approximately 10.