How does the sun's heat get to earth if heat needs a medium?
Light does not need a medium to travel but heat does. Since heat energy cannot travel in a vacuum and space is mostly a giant vacuum, how does heat from the sun get to earth?
The heat does not get to Earth. Instead the Earth absorbs some of the radiation from the Sun, and that absorption results in heating of the substance that absorbed the radiation. Some of that heat is radiated back outward into the atmosphere.
heat could be transferred by electromagnetic radiation,, its like the heat u feel from a really bright (and hot) object, that's not all transferred by a medium but through the electromagnetic radiation which doesn't need a medium/
this might help: http://en.wikipedia.org/wiki/Stefan%E2%80%93Boltzmann_law
Radiant heat needs no medium, it is nothing more than long wavelength light... infrared light as a matter of fact. This is the heat you get on your skin when standing out in the noon day Sun. Further, as the meteorologist indicated, a lot of Earth's heat comes from absorbed electro magnetic energy from the Sun that is turned into lower frequency, infrared energy that is radiated back into the atmosphere.
The heat requiring a medium is convection and conduction heat. Convection is where the air moves about distributing the heat it contains. Your central house heater does this when its fan blows. Conduction is where the heat is transferred in solids, like between the burner of your electric stove and the bottom of the fry pan on top of that burner.