(3) Radiation Explanation: The radiation (light, heat, etc.) travels through the intervening 150,000,000 kilometers in 8 minutes. Radiation is a process in which energetic particles or energetic waves travel through vacuum, or through mattercontaining media that are not required for their propagation. Waves of a massive medium itself, such as water waves or sound waves, are usually not considered to be forms of "radiation" in this sense.