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Midway out on the Orion arm of the Milky Way lives our Sun, one of about 200 billion stars in our galaxy, home system for the Earth and eight (maybe nine) other planets. 4.6 billion years old and halfway through its expected life, it sustains a continuous nuclear fusion reaction at its core that converts Hydrogen atoms into Helium and produces electromagnetic radiation (sunlight) and nutrinos. The surface boils with plasma heated to 10,000 times the point at which steel turns to gas, and its changing magnetic fields sweep the surface of the star in 11 year cycles, producing sun spots and solar "prominences" like the one in the upper right of this picture. They spew storms of protons into space, reaching Earth about two hours after they are observed.

This picture was taken by SOHO, the Solar and Heliospheric Observatory, managed by the European Space Agency and NASA. Launched 1995, it operates in a solar orbit postioned permanently between the Earth and the Sun. Orignially planned for a two-year mission, the spacecraft life has been extended twice, its three-axis gyroscopes replaced with software in 1999. It is the size of a small truck and weighs about 1000 lbs. Loaded with 12 instruments developed by 15 countries and supported by 1500 scientists around the world, it measures ionized gas blowing out across the solar system on which all life depends.