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"
Sigmoids Predict Solar Eruptions
16/03/1999
On the Sun, S marks the spot. Solar explosions have been discovered to explode preferentially from regions marked with this letter. The surface of the quiet Sun is a maze of hot gas and flowing magnetic fields. When two regions of high magnetic field strength approach each other, they typically pass uneventfully. If the two regions pass close enough and in just the right way, however, an X-ray bright S-shaped region called a sigmoid forms and quickly explodes in a Coronal Mass Ejection (CME). Astronomers conjecture that in the center of the sigmoid, a circuit closes that somehow drives the explosion. The above picture shows the Sun in X-ray light. A pre-CME sigmoid is shown on the left inset image, while a post-CME arc is shown in the right inset.