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"
A Fading Moonset Over Hong Kong
15/12/2009
Do stars appear dimmer when nearer the horizon? Yes -- atmospheric air absorbs and reradiates light, so that the greater the airmass through which one peers, the fainter an object will appear. Pictured above in a multi-frame image, stars, the planet Jupiter, and even the Moon show the horizon-dimming effects of Earth's nearly-transparent atmosphere. The image was taken in the evening about three weeks ago over Hong Kong, China. The brightest streak near the center is the setting Moon, while intermittent thin clouds sometimes dispersed moonlight into a larger halo. Jupiter sets just to the Moon's right. The dim steaks cutting across the image horizontally were caused by passing airplanes. The bright strange multi-pronged streak over the house is a helicopter taking off. An astute observer will also notice faint rays emanating from near the horizon. Their cause is unknown, but may be crepuscular rays caused by the Sun shining through gaps in thick clouds. New Mirror: APOD now available in Romanian from Romania