At the center of our solar system, the sun has long been a popular object of curiosity and study throughout human history. Stonehenge may have been built primarily to observe it. The Mayans designed their mathematically sophisticated calendars around it. And, Galileo nearly came to blows with other keen minds in describing its unique features. We know more about the sun now than ever before. We have an accurate notion of its physical properties. We can now explain how spectacular solar eclipsesoccur. We also know that the sun's surface-giving rise to solar winds, flares, and sunspots-can have a dramatic effect on the Earth, from power line surges to the beautiful aurora borealis to influencing cycles of climatic warming and cooling.