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"
Sunset at the Portara
20/03/2009
Today, the Sun crosses the celestial equator heading north at 11:44 UT. Known as an equinox, this astronomical event marks the first day of spring in the northern hemisphere and autumn in the south. It also marks the beginning of Norouz, the Persian (Iranian) new year. Equinox means equal night. With the Sun on the celestial equator, Earth dwellers will experience nearly 12 hours of daylight and 12 hours of darkness. Of course, in the north the days will grow longer, the Sun marching higher in the sky as summer approaches. To celebrate the equinox, consider this scenic view of the setting Sun from the island of Naxos in the Aegean Sea. Recorded last June, the well-planned image captures the Portara (big door) in a dramatic silhouette. Measuring about 6 by 3.5 meters, the Portara is the large entrance to the Greek island's ancient, unfinished Temple of Apollo.