March 6, 2010

The sun: driver of all weather, climate

"Ra" is the name ancient Egyptians called their sun god.

It represented light, warmth and growth, and while its meaning changed somewhat over the millennia it was always central to their culture. Today the sun is still central for scientists trying to understand how it creates and changes Earth's weather and climate over time. While it may appear to us to be a constant, in fact, some scientists consider our sun to be a variable star.

The sun is a maelstrom of activity. Solar flares explode from its surface on an irregular basis with the power of a billion nuclear bombs. Clouds of magnetized gases spew from the sun's surface almost daily and are large enough to swallow planets. Million-miles-per-hour gusts of solar wind emanate from its surface into space. And ours is just an average star. But I am getting ahead of myself. First let's take a quick look at its origin.

Astronomers and physicists agree that a huge molecular cloud of gas, a nebula, collapsed and began to spin, a process caused perhaps by a shock wave from a nearby exploding star. Most of this collapsing mass collected in the center, forming the sun, and the rest formed a flattened disc out of which formed the planets, moons and other small bodies. All of this happened between 4.55 billion and 4.56 billion years ago. And yes, modern instrumentation and knowledge of different element forms allow such precision in that time measurement.

The sun, with 99.86 percent of the mass of the solar system, consists mostly of hydrogen and helium. The enormous energy emitted from the sun comes from the fusion of hydrogen nuclei into helium. This is caused by the extreme pressures and high temperatures within that body. It is literally undergoing continuous thermonuclear explosions not unlike those we might remember seeing pictures of on islands in the Pacific Ocean decades ago. The energy output is prodigious but the sun's enormous gravity holds it all together. It has "burned" through about half of its hydrogen fuel load already.

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