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TheSource of Energy A summary of the physical and chemical nature of life must begin,not on the Earth, but in the Sun; in fact, at the Suns very center. It is herethat is to be found the source of the energy that the Sun constantly pours outinto space as light and heat. This energy is liberated at the center ofthe Sun as billions upon billions of nuclei of hydrogen atoms collide witheach other and fuse together to form nuclei of helium, and in doing so, releasesome of the energy that is stored in the nuclei of atoms. The output of lightand heat of the Sun requires that some 600 million tons of hydrogenbe converted into helium in the Sun every second. This theSun has been doing for several thousands of millionsof years. The nuclear energy is released at the Suns center ashigh-energy gamma radiation, a form of electromagnetic radiationlike light and radio waves, only of very much shorter wavelength. Thisgamma radiation is absorbed by atoms inside the Sun to be reemitted atslightly longer wavelengths. This radiation, in its turn is absorbed and reemitted. As the energy filters through the layers of thesolar interior, it passes through the X-ray part of the spectrumeventually becoming light. At this stage, it has reached what we call the solarsurface, and can escape into space without being absorbed further by solaratoms. A very small fraction of the Suns light and heat is emitted in such directions that after passing unhindered throughinterplanetary space, it hits the Earth. | 
