Answer:
Radiation can move through empty space to transfer heat; convection cannot.
Explanation:
For convection to occur, a propagating medium, usually fluid (liquid or gaseous), must exist, because convection cannot move through empty spaces. This process of heat propagation happens due to the emergence of convection currents in the fluids. Convection currents arise by the difference in particle density in the fluid. Generally, warmer particles are less dense and tend to rise, while colder particles are denser and tend to do the opposite motion.
This happens, for example, when heating water in the stove. The deeper molecules near the fire heat up faster, becoming less dense than the molecules closer to the surface.
Unlike convection, radiation does not need a medium to occur, because the thermal energy in this process is transferred by electromagnetic waves, which are able to propagate in a vacuum.
All bodies emit energy by radiation at all times. At temperatures close to the environment, this phenomenon can usually not be perceived by human eyes, but can be seen when the body is at very high temperatures, such as a glowing ember.
