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"
The Sun Unleashed
10/06/2011
On June 7, the Sun unleashed only a medium sized solar flare as rotation carried active regions of sunpots toward the solar limb. But that flare was followed by an astounding gush of magnetized plasma seen erupting at the Sun's edge in this extreme ultraviolet image from the Solar Dynamics Observatory. Spectacular movies of the event follow the darker, cooler plasma over a period of hours as it rains down across a broad area of the Sun's surface, arcing along otherwise invisible magnetic field lines. An associated coronal mass ejection, a massive cloud of high energy particles, was blasted in the general direction of the Earth and may have already triggered auroral activity after a glancing blow to Earth's magnetosphere.