This illustration shows the layers of the Sun. It generates energy through nuclear fusion reactions in its core. The energy follows a long, torturous path before reaching the Sun's visible surface, the photosphere. The corona is the Sun's million-degree outer atmosphere. [NASA]
For those of us in the United States and other northern latitudes, the Sun makes itself scarce at this time of year. In fact, the shortest day of the year — the winter solstice — is coming up on Friday.
Despite the colder, shorter days, the Sun still warms our planet just as it’s done for the past four-and-a-half billion years. That warmth is the result of nuclear reactions deep in the Sun’s heart, known as the core. The core accounts for about a quarter of the Sun’s diameter, so it’s hundreds of thousands of miles below the surface.
The Sun’s powerful gravity squeezes the core so tightly that it heats it to millions of degrees. At those temperatures, the hydrogen that makes up most of the core consists not of atoms, but of individual electrons and protons — the building blocks of atoms.
As these particles zip around, some of the protons fuse together through nuclear reactions to form the nucleus of a helium atom. There’s so much material in the core that this process adds up. Every second, in fact, the Sun converts about 700 million tons of hydrogen to helium.
But a little less than one percent of the mass of the original hydrogen is converted to energy — about four million tons per second. It’s this process that causes the Sun to shine.
Yet the energy produced in its core isn’t what we see from the Sun’s surface. The Sun’s light is the result of a long and twisting path from the core to the surface — and we’ll talk about that tomorrow.
Script by Damond Benningfield, Copyright 2012
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