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"
Second Millennium, Last Eclipse
05/01/2001
Christmas Day 2000 featured the final eclipse of the Second Millennium -- a partial solar eclipse visible from much of North America. Astrophotographer Phil Rau recorded the entire event on a single image as the Sun and Moon arced through winter skies above Cary, North Carolina, USA. Using a well positioned, tripod mounted camera and a solar filter, Rau made a short exposure every 10 minutes from 11:00 am to 1:30 pm EST, covering the local duration of the eclipse. The resulting image beautifully illustrates the steady progress of the dark new Moon as it appears to take a bite out of the golden solar disk. From his location, at eclipse maximum (near picture center) just less than 50 percent of the Sun's diameter was covered by the Moon.