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 Equal Night
22/09/1996
Today the Sun crosses the celestial equator heading south -- marking the Autumnal Equinox, the first day of Autumn. Equinox means equal night and with the Sun on the celestial equator, Earthlings will experience 12 hours of daylight and 12 hours of darkness. Then, for those in the northern hemisphere, the days will begin to grow shorter with the Sun marching lower in the sky as winter approaches. A few weeks after the Autumnal Equinox of 1994, the Crew of the Shuttle Endeavor recorded this image of the Sun poised above the Earth's limb. The glare illuminates Endeavor's vertical tail (pointing toward the Earth) along with radar equipment in the payload bay. Information: Thursday, September 26 - A Total Lunar Eclipse