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There's perpetual hydrogen bomb exploding at the center of our solar system, with megaton explosions erupting every second. It's our closest star: the sun. The sun has burned bright for at least four and a half billion years, and is the source of practically all of the earth’s energy. All life depends on it. While it may look like a giant ball of fire, the sun is actually an erratic sphere of superheated hydrogen and helium gas, powered by thermonuclear reactions. In a process called fusion, atomic nuclei in the sun’s core continually collide and fuse, releasing enormous amounts of energy. Though its core temperature reaches 27 million degrees Fahrenheit, and it’s big enough to accommodate more than one million earths, as stars go, the sun is only average. There are many that are much larger, and smaller, even in our own Milky Way galaxy. While the sun may be ordinary compared to other stars, to earth it’s one of a kind. Life could never survive without it. The sun’s gravity keeps the earth in a stable orbit, preventing it from hurtling into outer space. It creates earth’s life-sustaining weather and climate. Its light powers the photosynthesis that plants need to grow , which in turn produce the food and oxygen that animals need to eat and breathe. The sun is about 93 million miles from earth. To give you an idea of that incredible distance, it takes eight minutes for the light of the sun to reach our eyes. But even at that distance, the sun has dramatic effects on earth. Take the seasons, for example. A mere 23 and a half degree tilt in the earth’s axis toward or away from the sun means the difference between steamy summers and freezing winters. So even the slightest change in the sun could be devastating to earth. Earth’s magnetic field can usually shield us from most of the sun’s particles, but they can still have a rather spectacular effect here on earth. When strong solar winds strike our magnetic field, particles are deflected down toward the poles. They crash into the atmosphere, and create magnificent light shows called “auroras”. Powerful as they are, the sun’s nuclear reactions will not burn forever. Approximately five billion years from now, the sun will burn up its fuel source, and swell to what’s called a “red giant”. At this point, the sun may engulf the earth. But that’s a long time away, and the sun continues as a source of energy to power life on our planet. We just couldn’t live without it.
Duration: 2 minutes and 54 seconds
Country: United States
Producer: National Geographic
Director: National Geographic
Posted by: greenbo on Apr 24, 2010
A science lesson all about the sun
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