The Sun
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
APODs including "The Sun"
Large Eruptive Prominence Imaged by STEREO
18/04/2010
What's happened to our Sun? Last week, it produced one of the largest eruptive prominences ever seen. Pictured above, the prominence erupted in only a few hours and was captured in movie form by NASA's twin Sun-orbiting STEREO satellites. A quiescent solar prominence is a cloud of hot solar gas held above the Sun's surface by the Sun's magnetic field. Unpredictably, however, prominences may erupt, expelling hot gas into the Solar System via a Coronal Mass Ejection (CME). As pictured above, many Earths would easily fit under the expanding ribbon of hot gas. Although somehow related to the Sun's changing magnetic field, the energy mechanism that creates and sustains a Solar prominence is still a topic of research.