The Sun is a yellow dwarf star (G2V), about 4.6 billion years old, and the dominant gravitational force in the Solar System. It has a diameter of roughly 1.4 million kilometers and contains around 99.8% of the Solar System’s mass. Nuclear fusion in its core converts hydrogen into helium, producing energy that warms the planets. Above the core lie the radiative and convective zones, followed by the visible photosphere (~5,500 °C), the chromosphere, and the much hotter corona (~2 million °C).
Source: science.nasa.gov
06/11/2011
The Sun's surface keeps changing. The above movie shows how the Sun's surface oozes during a single hour. The Sun's photosphere has thousands of bumps called granules and usually a few dark depressions called sunspots. The above time-lapse movie centered on Sunspot 875 was taken in 2006 by the Vacuum Tower Telescope in the Canary Islands of Spain using adaptive optics to resolve details below 500 kilometers across. Each of the numerous granules is the size of an Earth continent, but much shorter lived. A granule slowly changes its shape over an hour, and can even completely disappear. Hot hydrogen gas rises in the bright center of a granule, and falls back into the Sun along a dark granule edge. The above movie and similar movies allows students and solar scientists to study how granules and sunspots evolve as well as how magnetic sunspot regions produce powerful solar flares. A few days ago, the largest sunspot group in recent years rotated into view.