Convection is the circular movement in a liquid when it is in a non-uniform temperature which is based on gravity and the difference in its density. While convection is generally most noticeable in liquids the same movement applies to gases. In astronomy convection generally refer to the movement of gases due to heat and gravity. This movement involves both the transfer of heat and mass. In stellar bodies convection happens when the warmer. This movement of gases also involves the transfer of energy.

Convection in large stellar bodies like stars happens when hotter gasses from the core move outwards and release their energy while the cooler gases from the outer region of the star move back into the hotter core area. This phenomena account to how stars radiate heat and energy.

Convection is also noted in the atmospheres of planets where large pieces of atmosphere routinely move from hot areas and colder areas. In this case the hot air or gases rise up due to decrease in density and eventually cool when it uses up its heat and energy and moves downwards again to be heated up by the surface beginning the cycle anew. A key concept in understanding convection is the combined gas law which establishes the relationship between temperature, pressure and volume.

Experimenting with Convection