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 Giant and the Glory
06/08/2004
On a flight from Vienna to Brussels, astronomer Franz Kerschbaum looked out the window and photographed this beautiful atmospheric phenomenon, the glory, shining in the direction directly opposite the Sun. Before airplanes, the glory, known to some as the heiligenschein or the Specter of the Brocken, was occasionally seen from mountaintops. There, when conditions were right, one could look away from the Sun and see what appeared to be the shadow of a giant surrounded by a bright halo. Of course, the giant turns out to be the observer, and in the modern version a silhouette of a plane frequently occupies the glory's center. The cause of the glory is relatively complex. Briefly, small droplets of water reflect, refract, and diffract sunlight backwards towards the Sun. The phenomenon has a counterpart in astronomy, where looking out from planet Earth in the direction opposite the Sun yields a bright spot called the gegenschein.