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"
Perihelion Sun
11/01/1999
The Earth's orbit is not a perfect, sun-centered circle. At aphelion, the most distant point in Earth's orbit, the Sun is 150 million kilometers away and at perihelion, the closest point, Earth approaches the Sun to within about 147 million kilometers. While aphelion occurs in July, perihelion for planet Earth comes in January. In fact, inhabitants of the Northern Hemisphere, particularly those wearily weathering winter storms, may be surprised to learn that Earth reached its closest point to the Sun on January 3rd this year. This false-color picture recorded near perihelion is from the earth-orbiting Yohkoh Solar Observatory. It shows an increasingly active Sun in the light of X-rays. A negative color scheme is used, darker colors representing more intense X-ray light.