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"
A Yukon Aurora
08/10/2001
Last week was another good week for auroras. The story began about two weeks ago when two large Coronal Mass Ejections exploded off the Sun. Waves of elementary particles and ions swept out past the Earth on September 28 and 29, causing many auroras. A week ago, a flapping sheet that divides north and south regions of the Sun's magnetic field passed the Earth, again causing auroras. Pictured above is a particularly good image of one of the October 1 northern lights. Taken in Canada's Yukon, the city lights of Whitehorse are seen below dark clouds and a twisting green aurora.