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"
Solstice Celebration
20/06/2004
Season's greetings! Today or tomorrow, depending on your time zone, the Sun reaches its northernmost point in planet Earth's sky marking a season change and the first solstice of the year 2004. In celebration, consider this delightfully detailed, brightly colored image of the active Sun. From the EIT instrument onboard the space-based SOHO observatory, the tantalizing picture is a false-color composite of three images all made in extreme ultraviolet light. Each individual image highlights a different temperature regime in the upper solar atmosphere and was assigned a specific color; red at 2 million, green at 1.5 million, and blue at 1 million degrees C. The combined image shows bright active regions strewn across the solar disk, which would otherwise appear as dark groups of sunspots in visible light images, along with some magnificent plasma loops and an immense prominence at the right hand solar limb.