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What is radiation?. Radiation is energy that is transmitted in the form of rays, waves, particles. Light, heat and sound are types of radiation. . All matter (solid, liquid, gas) absorbs and emits radiation in precise ways determined by its physical and chemical makeup.. Radiation travels through a vacuum (empty space) at the speed of light (usually the letter c" is used to designate this value": 3 * 108 m s-1, resulting in energetic connections" across time and space. .
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28. a rule of thumb:
When the sky is clear, the photosynthetically active part of the total solar spectrum accounts for about HALF of the total solar energy (but it is NOT half of the photon flux density from the sun!)