The third mechanism of heat transfer is radiation.Radiation travels out in all directions from its source.Unlike convection or conduction,which needs a medium to travel through, radiant energy easily travels through the vacuum of space. Radiation is the heat-transfer mechanism by which solar energy (energy from the sun) reaches our planet.Of the 100% of the solar energy that leaves the sun,about 50% of it is directly absorbed by land and sea.What happens to the other 50%? Well, 20% of solar radiation is absorbed by the atmosphere and clouds.Another 20% is reflected from the clouds and sent into space.5% is backscattered to space by the atmosphere,and a final 5% is reflected from land-sea surfaces.