convection

Convection is the movement of fluid and heat within a fluid body due to the reduced density of heated fluid, along with buoyancy, i.e., gravitational force drawing the remaining fluid under its less dense counterpart. It is a common phenomenon on Earth in the air above a flame or hot object. The heat represents energy and convection is one of the means by which energy is transmitted outward from a stellar core toward a star's surface: most stars undergo convection at some point in their life and many (e.g., the Sun) have a convection zone during their main sequence, a layer within which convection persists.

Convection is chaotic and a challenge to model: one simplified model based upon mixing length aims for approximate answers for the questions of when convection will occur, how much energy will be transmitted, and where it places the energy.

Convective overshoot is the occurrence of material convected rising higher than material of the same density, typically due to its upward momentum. It has been presumed in models of some stellar phenomena. The term may also be used for higher-density sinking material to continue past the level where the density is the same. In either case, the layering of temperatures are affected, with more mixing.