by Chet Raymo
"Deep in the belly of the Sun, where the temperature is 10 million degrees, protons- the nuclei of hydrogen- are fused together to form the heavier nuclei of helium. By a marvelous magic of nature, the helium nuclei weigh about one percent less than the total weight of the four protons out of which it was made. Mass has vanished from the universe. And in its place- energy.
Every second at the Sun's core, 660 million tons of hydrogen is converted into 655 million tons of helium. The missing 5 million tons is turned into an amount of energy equal to the vanished mass times the speed of light squared. The rate of conversion is prodigious, but the amount of hydrogen in a Sunlike star is virtually inexhaustible. The Sun will burn for another 5 billion years before it has exhausted the hydrogen at its core.
All of that energy produced deep in the Sun takes several million years to make its way to the surface, up through a half-million miles of roiling plasma. At the surface, it is hurled into space as heat and light. Eight minutes later, a tiny fraction of this flux bathes the Earth- to warm the planet and sustain photosynthesis.
Imagine the Sun as a basketball. On this scale, the Earth would be a pinhead about 85 feet away. The Sun pours out its energy in every direction. Only that part that falls upon the pinhead can we count as ours. It would be nice to think that the Sun burns for us alone, but the vast majority of its bounty is destined for deep space. We catch what we can. Every second, about a millionth of a millionth of an ounce of the Sun's depleted mass falls onto my body as I lie on the sand. I consume the Sun.”