The gravitational attraction of this medium-size star, our sun, controls the orbits of the planets. A rotating nuclear furnace, mostly of hydrogen and helium, it constantly emits energy. Periodically magnetic fields emerge from its surface in areas called sunspots, darker because they are less hot. Associated with these disturbances, which may last for weeks, are arching streams of gas called prominences and brilliant regions called flares. Such activity affects Earth's magnetic fields, its atmosphere, and possibly its climate. Maximum sunspot activity occurs during 11-year cycles: the most recent one peaked in 1990.
PERIOD OF ROTATION:25 days at equator.
DIAMETER:1,400,000 km.
MASS:333,000 * that of Earth.
TEMPERATURE:15,000,000 C in core; 5,500 C at surface.
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