Canned Sunlight

The concept of energy has always fascinated me, and this web log will discuss aspects of it often. Everyone realizes that the ultimate source of energy for most of mankind’s activities on Earth is our Sun. The exceptions are nuclear energy and hydrothermal energy which results from radioactivity deep within the Earth. A friend of mine who has no knowledge of science or any interest in it, made a comment while sitting before my fireplace "those flames are ancient sunlight being released from the wood." I found it a remarkable observation coming from him, and, of course, he was absolutely right. All our fossil fuels, coal, wood, petroleum, and natural gas, result from solar energy stored in now fossilized ancient plants. These plants used solar energy to combine the simple ingredients of carbon dioxide from the air and water from the soil into more complex hydrocarbon molecules that make up our fossil fuels. Energy must be used to create more organized things (hydrocarbons), and is released again when these organized things are broken down again by combustion. This is nature’s way, and we call it the law of conservation of energy.

Getting back to the Sun. Why is it hot and where did the energy which it so freely radiates come from? If you are science savvy, your immediate answer might be the nuclear fusion in the Sun’s core. Yes, there is a controlled hydrogen bomb like explosion going on continuously in the Sun’s center. Atoms of hydrogen are fused into those of helium with the release of lots of energy. In fact, this nuclear fusion actually keeps the Sun cool. The Sun, like all stars, condensed out of an immense, diffuse cloud of cool gas. As the cloud collapsed toward its center under the pull of its own gravity, the potential energy of the gas is converted into increasing velocity of its atoms resulting in higher and higher temperatures. Eventually, the core temperature becomes hot enough to kindle thermonuclear reactions. Now, the radiation pressure from nuclear burning balances the force of gravity and stops the Sun from contracting further--preventing it from getting any hotter. So the initial gravitational collapse of the Sun is what makes it hot.